EVALUATION ARRANGEMENT FOR A THERMAL GAS SENSOR, METHOD AND COMPUTER PROGRAM

Description

Technical area

[0001] Embodiments according to the invention relate to evaluation arrangements for a thermal gas sensor, methods and computer programs. Background of the invention

[0002] Gases can currently be analyzed for their properties using a wide variety of sensors. Various patient ventilation systems are currently available on the market. These are differentiated according to use in clinical and home care settings (e.g., systems from Heinen+Löwenstein, Dräger, and Stephan Medizintechnik). Only their top-of-the-line systems from these providers include all the necessary measuring devices for determining pressure, respiratory flow, and respiratory gas analysis. This requires a combination of several devices, most of which measure remotely from the patient.

[0003] In view of this, there is a need for a concept that enables a better compromise between reducing the installation space and reducing the system weight of a gas measurement system and provides accurate flow measurement and fast gas analysis.

[0004] This problem is solved by the independent patent claims.

[0005] Further developments according to the invention are defined in the subclaims. Summary of the invention

[0006] One embodiment relates to an evaluation arrangement for a thermal gas sensor with at least one heater (e.g., a heating element) and at least one detector (e.g., a thermocouple structure or "thermopile structure," temperature-variable resistors, or thermistors). The evaluation arrangement is designed, for example, to obtain information about an amplitude of a detector signal from a first detector (e.g., D1.Uss) and information about a first phase difference between a heater signal and the detector signal from the first detector (e.g., (D1-Hz).phi). The evaluation arrangement can further be designed to form a combination signal as an intermediate variable depending on the information about the amplitudes of the detector signal (e.g., D1.Uss and / or D2.Uss) and depending on the information about the first phase difference, which can combine amplitude information and phase information. The evaluation arrangement is further designed, for example, toto determine information about a gas concentration or information about a thermal conductivity of a fluid (e.g. a gas or gas mixture) based on the combination signal (e.g. without separately considering the individual information flowing into the combination signal in the further course of the calculations).

[0007] According to one embodiment, the heater and the at least one detector can be cyclically swapped to minimize possible (synchronization) errors. In other words, at a first point in time, the detector can act as a heater and the heater as a detector, and at a second point in time, the detector can serve as a detector and the heater as a heater.

[0008] According to one embodiment, the evaluation arrangement comprises two detectors, with these two detectors being equidistant from the heater. In this case, the combined signal can include, for example, a sum of the information about the amplitudes of the two detector signals (e.g., D1.Uss and D2.Uss) from the two detectors and a sum of the information about the two phase differences ((D1-Hz).phi and (D2-Hz).phi) of the two detectors.

[0009] One embodiment relates to an evaluation arrangement for a thermal gas sensor with at least one heater (e.g. a heating element) and two detectors arranged at different distances from the heater (e.g. a first thermocouple structure and a second thermocouple structure or temperature-variable resistors or thermistors), wherein the evaluation arrangement is designed to obtain information about an amplitude of a detector signal of a first detector (e.g. D1.Uss), information about an amplitude of a detector signal of a second detector (e.g. D2.Uss), information about a first phase difference between a heater signal and the detector signal of the first detector (e.g. (D1-Hz).phi), and information about a second phase difference between the heater signal and the detector signal of the second detector (e.g. (D2-Hz).phi).The evaluation arrangement can be designed to form a combination signal as an intermediate variable depending on the information about the amplitudes of the detector signals (e.g., D1.Uss of the first detector and D2.Uss of the second detector), depending on the information about the first phase difference, and depending on the information about the second phase difference, which can combine amplitude information and phase information. The evaluation arrangement is further designed to determine information about a gas concentration or information about a thermal conductivity of a fluid (e.g., a gas or gas mixture) based on the combination signal (e.g., without separately considering the individual pieces of information included in the combination signal in the further course of the calculations).

[0010] According to one embodiment, gas can be arranged in the thermal gas sensor between the at least one heater and the detectors arranged at different distances or at equal distances (e.g., symmetrically) from the heater, which gas can be analyzed using the evaluation arrangement in cooperation with the thermal gas sensor. For this purpose, for example, heat is transported from the at least one heater to the first detector and the second detector via the gas or gas mixture located therebetween. A detector signal detected by the first detector or a detector signal detected by the second detector can indicate the heat transported from the heater to the respective detector. If a heating signal amplitude (e.g., heater amplitude) of the at least one heater varies (e.g., periodic excitation of the heater), a varying amplitude corresponding to the heater can also be detected by the two detectors.The detector signal of the first detector or the second detector can be sent to the evaluation device. Thus, the evaluation device can obtain the respective information about the amplitude from the detector signal of the first detector and the detector signal of the second detector, as well as information about the first phase difference between the heater signal and the detector signal of the first detector and information about the second phase difference between the heater signal and the detector signal of the second detector. For this purpose, the evaluation device can, for example, receive the heater signal from the thermal gas sensor in addition to the detector signals of the first detector or the second detector.Alternatively, the evaluation arrangement can, for example, receive directly from the thermal gas sensor the information about the amplitude of the detector signal of the first detector, the information about the amplitude of the detector signal of the second detector, the information about the first phase difference and the information about the second phase difference.

[0011] This embodiment of the evaluation system is based on the finding that the combined signal, based on the information about the amplitudes of the detector signals and dependent on the information about the first phase difference and the information about the second phase difference, represents a very stable signal that can be further processed very quickly by the evaluation system, for example, to determine a gas concentration or information about the thermal conductivity of the fluid. Thus, the evaluation system allows for rapid gas analysis.

[0012] According to one embodiment, the evaluation arrangement can be designed to obtain information about a heater amplitude. The evaluation arrangement can also be designed to form a linear combination of the information about the heater amplitude, the information about amplitudes of the detector signals, the information about the first phase difference, and the information about the second phase difference in order to determine the combination signal (sigX). The information about the heater amplitude can, for example, be information about a heating power. Here, the information about a heater amplitude can also be referred to as Hz.Uss. The evaluation arrangement can, for example, obtain the information about the heater amplitude directly from the thermal gas sensor or, for example, from a heater signal sent from the thermal gas sensor to the evaluation arrangement.The linear combination can, for example, have a first term that has a first linear combination of the information about the heater amplitude and the information about amplitudes of the detector signals, and a second term that has a second linear combination of the information about the first phase difference and the information about the second phase difference. In this case, for example, the first term and the second term can be weighted with different constants in the linear combination in order to determine the combination signal. Because the evaluation arrangement takes the heater amplitude into account when determining the combination signal, the heater signal (e.g. a signal of periodic temperature waves emitted by the heater) can be compared with the detector signal of the first detector or the second detector (e.g.A received signal of periodic temperature waves can be compared, allowing the heat transfer from the heater via the gas being analyzed to the two detectors to be determined very precisely. This enables very precise and rapid gas analysis with the evaluation system.

[0013] According to one embodiment, the evaluation arrangement can be designed to evaluate the combination signal sigX according to sigX = sigUss * Ka + sigPhi * Kp Here, sigUss can be amplitude information or an amplitude signal that can depend on the information about the amplitude of the detector signal from the first detector and on the information about the amplitude of the detector signal from the second detector. The term sigPhi can be phase information or an added phase signal that can depend on the information about the first phase difference and on the information about the second phase difference, and the factors Ka and Kp can be constants. The constants Ka and Kp can separately weight the amplitude information and the phase information, respectively, so that the evaluation arrangement can obtain the combination signal sigX. The amplitude information sigUss can be a linear combination of the information about the amplitude of the detector signal from the first detector and the information about the amplitude of the detector signal from the second detector.The phase information sigPhi can be a linear combination of the information about the first phase difference and the information about the second phase difference. The constants Ka and Kp can, for example, represent conversion factors. According to one embodiment, Ka and Kp are weighting factors for an optimized combination signal, whereby the factors Ka and Kp can represent unitless quantities (for an embedded system such as the one used here, which, for example, provides a CO2 concentration, this is not necessary). According to one embodiment, the embedded system provides, for example, AD digits for the amplitude, and phase information is determined, for example, from the timing unit of the embedded system, which measures, for example, the times until the comparator flips over. A conversion to amplitude and time / angle is therefore specified, for example, by the technical data of a circuit and the embedded system (µController) of the evaluation arrangement.The factors are selected, for example, so that both signal components (amplitude and phase) are included in the combination signal SigX in approximately equal proportions over the measuring range of the CO2 calibration, so that, for example, the greatest measurement resolution is achieved in SigX. The factors Ka and Kp are determined empirically, for example, in order to obtain the best signal for SigX. The constants Ka and Kp can, for example, depend on a concentration, temperature, or pressure of a gas to be analyzed. This means that the amplitude information sigUss can be matched to the phase information sigPhi. This enables the evaluation system to further process both amplitude information and phase information in one go using the combination signal, which allows, for example, the evaluation system to analyze the gas detected by the gas sensor very quickly, efficiently, and precisely.

[0014] According to one embodiment, the evaluation arrangement is designed to obtain the amplitude information sigUss according to sigUss=2*Hz.Uss-(D1.Uss+D2.Uss). The term Hz.Uss can be information about a heater amplitude, the term D1.Uss can be information about the amplitude of the detector signal of the first detector, and D2.Uss can be information about the amplitude of the detector signal of the second detector. Thus, the amplitude information sigUss can represent a relative amplitude signal. In other words, the amplitude information can be a difference between twice the heater amplitude and a sum of the information about the amplitude of the detector signal of the first detector and the information about the amplitude of the detector signal of the second detector.Through this special calculation of the amplitude information sigUss, it can be achieved that the amplitude information sigUss depends essentially on heat transfer through the fluid, and unknown heat transfers, for example, from the at least one heater into the gas to be analyzed and from the gas to be analyzed into the first or second detector, are not or only barely taken into account. Thus, the combination signal sigX, which may depend on the amplitude information sigUss, is not influenced at all or only barely by unknown heat transfers, allowing the evaluation system to very precisely determine properties of the gas to be analyzed, such as information about the gas concentration or information about the thermal diffusivity of the fluid.

[0015] According to one embodiment, the evaluation arrangement can be designed to calculate a polynomial (e.g., first-degree polynomial, e.g., Ay(sigX)) of the combination signal in order to obtain information about the gas concentration or information about the thermal diffusivity of the fluid. The evaluation arrangement's polynomial formation of the combination signal can be used to perform drift correction of the combination signal. For example, concentration drift, pressure drift, and temperature drift can be corrected by the polynomial formation.For example, the evaluation system can calculate three polynomials of the combined signal, where a first polynomial can represent a relationship between the gas concentration and the combined signal, a second polynomial can represent a relationship between pressure and signal shift (pressure drift of the combined signal), and a third polynomial can represent a relationship between temperature and pressure shift. This feature can thus correct potential inaccuracies, and the evaluation system can be designed to analyze the fluid very precisely, reducing potential errors.

[0016] According to one embodiment, the evaluation arrangement can be designed to multiply a polynomial of the combination signal by a correction term in order to obtain information about the gas concentration or information about the thermal diffusivity. The correction term can depend on the combination signal, information about a pressure (p), and information about a temperature (T). Thus, the correction term can, for example, compensate for a pressure and temperature dependence of the combination signal. For example, a polynomial representing a relationship between a gas concentration and the combination signal can be corrected for pressure and temperature drift using the correction term.Thus, by multiplying the correction term by the polynomial of the combined signal, potential error influences on the evaluation system can be reduced, allowing the evaluation system to be configured to obtain very precise information about the gas concentration or thermal diffusivity. This can minimize pressure- and temperature-dependent errors, for example, which may arise during the detection of a detector signal by the first detector or the second detector of the gas sensor.

[0017] According to one embodiment, the evaluation arrangement can be designed to carry out a calculation according to C = pol sigX ⋅ 1 − f p sigX − const 1 ⋅ 1 − f T p − const 2 to obtain information C about the gas concentration. The term sigX can be the combination signal, the term pol(sigX) can be a polynomial of the combination signal sigX, f(p) can be a function of the pressure p (or a measured pressure p in an environment of the thermal gas sensor), const1 can be a first constant, f(T) can be a function of the temperature T (or a measured temperature T in an environment of the thermal gas sensor), and const2 can be a second constant. The function f(p) can, for example, be a polynomial that can represent a relationship between a pressure and a signal shift, and f(T) can be a polynomial that can represent a relationship between a temperature and a signal shift. With this feature, the polynomial of the combination signal can be corrected for pressure- or temperature-dependent errors caused by the gas sensor.can be reduced, which enables very precise gas analysis by the evaluation arrangement.

[0018] According to one embodiment, the evaluation arrangement can be designed to carry out a calculation according to C vol% = A . y sigX ⋅ 1 − B . y p − B . ref sigX − B . ref ⋅ 1 − C . y T − C . ref p − C . ref to obtain the information C about the gas concentration. The term sigX can be the combination signal, Ay(sigX) can be a polynomial (e.g. first order) of the combination signal sigX, By(p) can be a function of the pressure p (or a measured pressure p in an environment of the thermal gas sensor), B.ref can be a constant, Cy(T) can be a function of the temperature T (or a measured temperature T in an environment of the thermal gas sensor) and C.ref can be a second constant. Here, By(p) is, for example, a polynomial function (e.g. second order) that can represent a relationship between the pressure p and a signal shift (e.g. of the combination signal sigX). The function Cy(T) is, for example, a polynomial function (e.g. second order) that can represent, for example, a relationship between the temperature T and a pressure shift.Thus, the evaluation arrangement is designed to determine very precisely, for example, information about the gas concentration of a fluid to be analyzed, since the function By(p) of the pressure p and the function Cy(T) of the temperature T can form a correction term that can correct the combination signal sigX.

[0019] According to one embodiment, the evaluation arrangement can be designed to take into account a pressure and / or a temperature in an environment of the thermal gas sensor when determining the information about the gas concentration. For this purpose, the evaluation arrangement can, for example, receive information about the pressure and / or the temperature in the environment of the thermal gas sensor. The pressure in the environment of the thermal gas sensor is determined, for example, by a pressure sensor, and the temperature in the environment of the thermal gas sensor is determined, for example, by a temperature sensor and transmitted to the evaluation arrangement. The pressure sensor and / or the temperature sensor can be arranged in the environment of the thermal gas sensor.This allows the evaluation system to make corrections depending on the pressure and / or temperature, and thus to analyze the fluid very precisely and thus to obtain very precise information, for example, about the gas concentration or the thermal conductivity of the fluid.

[0020] According to one embodiment, the evaluation arrangement can be designed to use the combination signal, information about the temperature in an environment of the thermal gas sensor, and information about a pressure in an environment of the thermal gas sensor as input variables for a drift correction when determining the information about the gas concentration, and to obtain the information about the gas concentration as a result of the drift correction. Apart from the three input variables mentioned, the drift correction, for example, no longer receives any further variables, but instead uses, for example, only (e.g., additional) previously obtained constants—determined, for example, during calibration. The evaluation arrangement can thus be designed to calculate out possible errors in the calculation of the gas concentration caused by drift and thus perform a drift correction.Drift can occur at different temperatures and pressures and thus distort the determination of the gas concentration, which can be prevented or suppressed with this feature. This allows the evaluation system to determine very precise information about the gas concentration.

[0021] According to one embodiment, the evaluation arrangement is designed to obtain the combination signal, or a further combination signal, based on a quotient between amplitude information, which is dependent on the information about the amplitude of the detector signal of at least the first detector and optionally also on the information about the amplitude of the detector signal of the second detector, and phase information, which is dependent on the information about the first phase difference and optionally on the information about the second phase difference. Furthermore, the evaluation arrangement can be designed to determine information about a concentration of a gas, e.g., a third gas in a gas mixture, depending on the combination signal. In other words, the quotient is a ratio between the information about the amplitude and the phase information.According to one embodiment, the third gas shifts this ratio, whereby the evaluation arrangement can be designed to infer the concentration of the third gas component based on this ratio.

[0022] According to one embodiment, the evaluation arrangement is designed to evaluate the combination signal sigV according to sigV = sigUss * Kav / sigPhi * Kpv to obtain. In the formula, sigUss can be amplitude information that depends on the information about the amplitude of the detector signal of the first detector and optionally on the information about the amplitude of the detector signal of the second detector. Furthermore, sigPhi can be phase information that depends on the information about the first phase difference and optionally on the information about the second phase difference. Furthermore, Kav and Kpv represent constants. The combination signal sigV represents, for example, the ratio between the information about the amplitude and the phase information. In other words, the evaluation arrangement is designed to use the ratio sigV of the amplitude and phase signals to determine a further physical gas parameter, with which the evaluation arrangement can be used, for example by correlation, to draw conclusions about the unknown concentration of a known third gas in the gas mixture to be analyzed.Kav and Kpv are new weighting factors that amplify changes in the ratio of amplitudes and phases.

[0023] According to one embodiment, the evaluation arrangement is designed to obtain information about how much heat is dissipated by the heater during a heating period, and to determine information about a concentration of a gas, e.g. a third gas of a gas mixture, depending on the information about how much energy is dissipated by the heater during the heating period. A heating period can be understood as a time period between a first zero crossing of a heating voltage and a second zero crossing of the heating voltage. Alternatively, the heating period can also be understood as a time period from a first point in time at which the heating voltage changes from zero volts to greater or less than zero volts, to a second point in time at which the heating voltage changes from greater or less than zero volts to zero volts. The heating signal can, for example,a sine signal, a cosine signal, a square wave, a triangular wave, or a sawtooth wave. During the heating period, the heat is dissipated into the gas mixture surrounding the heater. How much heat is dissipated from the heater to the surrounding gas depends, for example, on the thermal conductivity of the surrounding gas or on the thermal conductivity of gas components of the surrounding gas mixture. Thus, the evaluation system can be designed to determine the thermal conductivity of the unknown gas or gas mixture using the heat dissipated by the heater.

[0024] According to one embodiment, the evaluation arrangement is designed to obtain information on how much heat is dissipated by the heater during a heating period, based on a measurement of a current flow through the heater at a predetermined heating voltage. In other words, the heating voltage applied to the heater is fixed during the heating period, and the current flow changes depending on how much heat is dissipated to the gas or gas mixture. The more heat is dissipated, the less the temperature of the heater increases and thus, assuming a positive TKR (temperature coefficient of resistance), the value of the heater resistance increases, whereby the current flow decreases less. Thus, by determining the current flow through the heater using the evaluation arrangement, conclusions can be drawn about the composition of the gas mixture to be analyzed.The current flow can be used as additional information by the evaluation system to further improve the accuracy of the gas analysis.

[0025] According to one embodiment, the evaluation arrangement is designed to obtain the current flow shortly after the predetermined heating voltage is switched on and shortly before the predetermined heating voltage is switched off. From a difference between these two current flow data, the evaluation arrangement can determine a change in the current flow during the heating period. The greater the difference, the lower the thermal conductivity of the gas or gas mixture to be analyzed. The evaluation arrangement is thus designed to use the thermal conductivity of the gas or gas mixture, for example, as an additional parameter in an analysis of the gas or gas mixture. In other words, the evaluation arrangement can be designed to use the measurement of the thermal conductivity as a further physical parameter of the unknown gas mixture, for example by the evaluation arrangementis designed to evaluate the difference in heater current between an initial peak shortly after the heater voltage is switched on and shortly before the heater voltage is switched off (per period). Shortly after the heater voltage is switched on can mean a time within a period of 10 µs to 1 ms, 100 µs to 800 µs, or 300 µs to 500 µs, such as 400 µs, after switching on.

[0026] One embodiment provides a method for evaluating signals from a thermal gas sensor having at least one heater and at least one detector. Heat can, for example, be transferred from the heater to the detector via a gas to be analyzed. The method can comprise obtaining information about an amplitude of a detector signal from a first detector (for example, D1.Uss) and information about a first phase difference between a heater signal and the detector signal from the first detector (for example, (D1-Hz).phi). A combination signal can be formed as an intermediate variable depending on the information about the amplitudes of the detector signal and depending on the information about the first phase difference. The combination signal can, for example, combine amplitude information and phase information.Information about a gas concentration or information about the thermal diffusivity of a fluid (e.g., a gas or gas mixture) can be determined based on the combined signal. This determination can be made, for example, without having to separately consider the individual information included in the combined signal in the subsequent calculations.

[0027] One embodiment provides a method for evaluating signals from a thermal gas sensor having at least one heater and two detectors arranged at different distances or equal distances from the heater. Heat can, for example, be transferred from the heater to the two detectors via a gas to be analyzed. The method can include obtaining information about an amplitude of a detector signal from a first detector (for example, D1.Uss), information about an amplitude of a detector signal from a second detector (for example, D2.Uss), information about a first phase difference between a heater signal and the detector signal from the first detector (for example, (D1-Hz).phi), and information about a second phase difference between the heater signal and the detector signal from the second detector (for example, (D2-Hz).phi).A combination signal can be generated as an intermediate variable, dependent on the information about the amplitudes of the detector signals, dependent on the information about the first phase difference, and dependent on the information about the second phase difference. The combination signal can, for example, combine amplitude information and phase information. Information about a gas concentration or information about the thermal diffusivity of a fluid (e.g., a gas or gas mixture) can be determined based on the combination signal. This determination can, for example, be made without separately considering the individual pieces of information included in the combination signal in the further course of the calculations.

[0028] An embodiment according to the present invention relates to an evaluation arrangement for a thermal gas sensor with at least one heater and two detectors. The two detectors can, for example, but not necessarily, be arranged at different distances from the heater. The evaluation arrangement is designed to regulate a heating power applied to the heater as a function of at least one sensor signal from at least one of the two detectors in order to bring the at least one sensor signal into a predetermined value range. Furthermore, the evaluation arrangement is designed to take into account information about the heating power (for example Hz.Uss) when deriving information about a gas concentration from the sensor signals from the two detectors.

[0029] This exemplary embodiment of the evaluation arrangement is based on the realization that the evaluation arrangement can vary the heating power in order to keep the at least one sensor signal within the predetermined value range for different gases or gas mixtures. By keeping the at least one sensor signal within the predetermined value range, it can be optimally analyzed without having to accept significant information losses. If, for example, the evaluation arrangement receives information that an amplitude of the sensor signal is lower than the predetermined value range, the evaluation arrangement can apply heating power to the heater in order to increase the heating power of the heater and thus raise the amplitude of the sensor signal into the predetermined value range.If, however, the evaluation arrangement receives information that the sensor signal has an amplitude greater than the predetermined value range, the evaluation arrangement can apply heating power to the heater in order to reduce the heating power of the heater and thus lower the amplitude of the sensor signal into the predetermined value range. Thus, the evaluation arrangement can, for example, keep the at least one sensor signal constant within the predetermined value range by the evaluation arrangement applying or adjusting the heating power to the heater depending on the at least one sensor signal. Thus, by combining the information about the heating power and the information about the sensor signals, the evaluation arrangement can derive information about a gas concentration or a thermal conductivity of a gas. Furthermore, the evaluation arrangement can thereby enable precise flow measurement and rapid gas analysis.

[0030] According to one embodiment, the evaluation arrangement can be designed to apply a periodic signal to the heater. The periodic signal defines, for example, a square-wave signal or a pulse with a defined power or a sine signal. Optionally, the evaluation arrangement has a processor that can generate the periodic signal. It should be noted that, due to the timer structures present in the processor, a square-wave signal can be generated with significantly greater temporal precision than a synthetic sine signal, which would be output by the processor on its digital / analog (DA) port. By applying the periodic signal to the heater, the two detectors each detect a periodic sensor signal. The periodic sensor signals thus obtained can differ from one another and also from the periodic signal of the heater in terms of amplitude, offset, and phase position.From the information obtained by the evaluation system, the evaluation system can determine thermal conductivity, thermal diffusivity, and, if the density of a gas (a gas to be analyzed by the thermal gas sensor) is known, also a specific heat capacity. Thus, for example, from the variation in heating power, which can represent information about the heating power, information about a gas concentration or thermal conductivity / thermal diffusivity can be derived. If the heater of the thermal gas sensor has a low thermal mass, the periodic signal applied to the heater can currently be modulated by the evaluation system at frequencies of up to 300 Hz, since heat can be added and removed quickly. Thus, a periodic signal enables accurate, fast, and efficient gas analysis.

[0031] If the periodic signal is, for example, a pulse with a defined power, the electrical crosstalk of the steep edges of the heater signal to the detectors would be clearly distinguishable in time from the thermal wave, which arrives later. With a duty cycle of 50%, it is possible that the switch-off edge at the heater can electrically crosstalk into the sensor signal if the heater receives the heat wave at the same time and at least one detector is measuring. By designing the electronics (RC elements), the heater edges can be slightly rounded and the detector signals shifted outside the crosstalk interference. On a powerful embedded platform, heater operation with a shorter duty cycle could become more important, as a clear temporal separation can be achieved between electrical interference and signal.Of course, the pulse should be wide enough for the heater to deliver enough power / heat so that at least one detector can measure, which can represent a lower limit of the duty cycle of 5%.

[0032] According to one embodiment, the evaluation arrangement can be designed to switch the heating power applied to the heater between two values.

[0033] This allows the heater to be supplied with a heating output in the form of a periodic square-wave signal, for example. The two values ​​(e.g., in the form of heater voltages) can be specified by a digital-to-analog converter. An analog switch can be used to alternately apply one of two voltages to a heater amplifier. This feature makes it possible to determine very precisely at any time which heating output and phase position is applied to the heater. This allows at least one sensor signal to be compared very precisely with the heater signal, allowing the evaluation device to perform a very accurate gas analysis.

[0034] According to one embodiment, the evaluation arrangement can be designed to regulate an amplitude of the heating power such that both a minimum value of the at least one sensor signal and a maximum value of the at least one sensor signal lie within the predetermined value range. This ensures that, for example, an amplitude of the at least one sensor signal for the entire at least one sensor signal (for example, for the entire time in which the thermal gas sensor has detected the at least one sensor signal via at least one of the two detectors) lies within the predetermined value range. The minimum value can, for example, represent a minimum amplitude of the at least one sensor signal and the maximum value a maximum amplitude. Thus, the amplitude of the heating power can be measured at least twice, e.g.when checking whether the minimum value of the at least one sensor signal lies within the predetermined value range, and when checking whether the maximum value of the at least one sensor signal lies within the predetermined value range. Thus, the accuracy of the evaluation arrangement can be improved, since this feature determines at least two values ​​(a minimum value and the maximum value) of the at least one sensor signal, and based on these, the amplitude of the heating power can be regulated. The evaluation arrangement can be designed accordingly to carry out a very precise gas analysis.

[0035] Optionally, the predetermined value range can have a minimum value range and a maximum value range. For example, the evaluation arrangement can be designed to regulate the amplitude of the heating power such that the minimum value of the at least one sensor signal lies within the minimum value range of the predetermined value range and the maximum value of the at least one sensor signal lies within the maximum value range of the predetermined value range. This enables the at least one sensor signal to cover, for example, almost the entire value range, thus ensuring that little to no information is lost.

[0036] According to one embodiment, the minimum value or the maximum value of the at least one sensor signal can define a phase position or an offset of the at least one sensor signal.

[0037] The predetermined value range can, for example, represent an operating range of an analog-to-digital converter. If the minimum value of the at least one sensor signal and / or a maximum value of the at least one sensor signal lies outside the predetermined value range, the analog-to-digital converter cannot convert the at least one sensor signal correctly, which may cause the evaluation system to derive erroneous information about the gas concentration or thermal conductivity from the at least one sensor signal. This can be prevented or reduced by the feature described herein.

[0038] According to one embodiment, the evaluation arrangement can be designed to adjust or regulate an amplitude of the heating power such that an amplitude of the at least one sensor signal lies within a predetermined amplitude range. The predetermined amplitude range (can, for example, be determined / defined by the predetermined value range) can, for example, represent an operating range of an analog-to-digital converter. The amplitude of the at least one sensor signal should utilize at least 50%, at least 65%, or at least 75% of the predetermined amplitude range so that a meaningful analysis of the at least one sensor signal can be carried out by the evaluation arrangement. Optionally, the predetermined amplitude range can also define that the amplitude of the at least one sensor signal utilizes at least 50%, at least 65%, or at least 75% of the value range of the analog-to-digital converter.If the amplitude of at least one sensor signal is outside the specified amplitude range, information may be lost and, for example, only an incorrect derivation of information about the gas concentration or thermal conductivity may be obtained from the sensor signal.

[0039] Likewise, problems can arise if the amplitude of the at least one sensor signal only utilizes a very small portion of the specified amplitude range. In this case, for example, the analog-to-digital converter cannot be fully utilized, thereby reducing the quality of the analysis by the evaluation system. The feature described herein can ensure high accuracy when analyzing the at least one sensor signal by the evaluation system. This enables the analog-to-digital converter to operate under optimized conditions, thus ensuring very precise gas analysis by the evaluation system.

[0040] According to one embodiment, the evaluation arrangement can be designed to set or regulate sampling times at which a sensor signal is sampled. The sensor signal can, for example, be a preprocessed sensor signal and / or one with a DC offset. This allows, for example, the evaluation arrangement to set sampling times at which the evaluation arrangement expects the sensor signal to be within the predetermined value range. If the sensor signal is not within the predetermined value range, the evaluation arrangement can apply heating power to the heater in order to bring the sensor signal into the predetermined value range at the sampling time. The evaluation arrangement is thus designed to set or regulate optimized sampling times at which the evaluation arrangement can perform a very fast and accurate gas analysis of the gas detected by the thermal gas sensor.

[0041] According to one embodiment, the evaluation arrangement is designed to set the sampling times such that sampling occurs at a time (e.g., a first sampling time) at which the sensor signal reaches a maximum value, and such that sampling occurs at a time (e.g., a second sampling time) at which the sensor signal reaches a minimum value. Sampling can occur, for example, with a maximum phase difference of + / - 0.5%, + / - 1%, + / - 2%, or + / - 5%. According to one embodiment, sampling can occur at that time with a deviation of + / - 15 µs, + / - 100 µs, + / - 2.1 ms, + / - 4.2 ms, + / - 6.3 ms, or + / - 10 ms. The fact that the evaluation device can set the sampling times so precisely enables the evaluation device to check whether the minimum value and / or the maximum value thus recorded lies within the predetermined value range.Furthermore, the maximum value and the minimum value of the sensor signal can be compared very precisely with maximum values ​​and minimum values ​​of the sensor signals of other gas types, whereby the evaluation arrangement is designed to carry out a very precise and efficient gas analysis by means of the sampling times set in this way.

[0042] According to one embodiment, the evaluation device can be designed to combine a sensor signal from at least one of the detectors with an offset signal generated by a digital-to-analog converter in order to obtain an input signal for the analog-to-digital converter. Furthermore, the evaluation device can be designed to adjust the offset signal in order to ensure that the input signal of the analog-to-digital converter remains within a predetermined range (e.g., the predetermined value range) during an entire period of the sensor signal. The offset signal can, for example, be generated in response to a detection that an input value of the analog-to-digital converter exceeds a predetermined upper threshold value (e.g., 95%, 90%, or 85% of a maximum processable input value of the analog-to-digital converter), or in response to a detection that an input value of the analog-to-digital converter exceeds a predetermined lower threshold value (e.g.,5%, 10% or 15% of a maximum processable input value of the analog-to-digital converter).

[0043] The offset signal can thus, for example, change an offset of the sensor signal in order to bring the sensor signal into the specified range. It should be noted here that the offset signal can, for example, be used by the evaluation device to generate the input signal, which can represent an offset-shifted sensor signal. The evaluation arrangement can thus shift the sensor signal into the specified range by combining the at least one sensor signal with the offset signal during the entire period. If, for example, the input signal nevertheless exceeds the specified range, the evaluation device can apply heating power to the heater in order to bring the at least one sensor signal within the specified range during the entire period. The specified range can, for example, represent an operating range of an analog-to-digital converter.Thus, the feature described herein makes it possible for the at least one sensor signal to be used by the evaluation device, which may comprise the analog-digital converter, to derive very precise information about the gas concentration or the thermal conductivity.

[0044] According to one embodiment, the evaluation device can be designed to regulate the heating power only when a setting or adjustment of the sampling times is in a steady state and when an adjustment of the offset signal is in a steady state. A steady state is understood, for example, to mean that the evaluation device has determined the sampling times within possible tolerances and thus the sampling times do not need to be further adjusted or adjusted. In the steady state, the sampling times are adjusted, for example, such that both a maximum value (within tolerances) and a minimum value (within tolerances) of the at least one sensor signal are sampled.In addition, a steady state can be defined as the offset signal adjusted by the evaluation device, when combined with the at least one sensor signal, generating an input signal that remains within a predetermined range throughout the entire period of the sensor signal. Thus, a steady state can mean that the evaluation device has precisely determined all of the necessary output parameters (such as the sampling times (and from these, for example, the maximum and minimum values ​​of the sensor signals) or the offset signal) in order to very precisely analyze the at least one sensor signal and derive information about the gas concentration or thermal conductivity. From information about the heating power adjusted by the evaluation device and the information derived from the at least one sensor signal by means of the evaluation device, the evaluation device can very precisely obtain information about the gas concentration or thermal conductivity.Determine the thermal conductivity of the gas detected by the gas sensor.

[0045] According to one embodiment, the evaluation device can be configured to pause the control of the heating power while the sampling times are being adjusted or adjusted and / or while the offset signal is being adjusted. This feature can reduce errors during the adjustment or adjustment of the sampling times and / or during the adjustment of the offset signal, or enable very fast and efficient adjustment, whereby the evaluation device can be configured to very quickly and very accurately determine information about the gas concentration and the thermal diffusivity of a gas.

[0046] According to one embodiment, the evaluation arrangement can be designed to regulate both an average heating power or a maximum heating power as well as an amplitude of the heating power. Since, for example, a periodic excitation signal can be applied to the heater, the average heating power can be, for example, a power averaged over a time in which the excitation signal is applied to the heater. In a periodically excited heater, the amplitude of the heating power can vary. Thus, the maximum heating power can, for example, correspond to a maximum amplitude of the heating power of the heater within a time period. Alternatively, the amplitude of the heating power can also be almost constant. Accordingly, for example, an amplitude of the heating power can be regulated to vary over time.

[0047] An embodiment according to the present invention provides a method for operating an evaluation arrangement for a thermal gas sensor with at least one heater and two detectors, which are arranged, for example, at different distances from the heater or at the same distance from the heater. The method comprises regulating a heating power applied to the heater as a function of at least one sensor signal from at least one of the two detectors in order to bring the at least one sensor signal into a predetermined value range. Furthermore, the method comprises taking into account information about the heating power (for example Hz.Uss) when deriving information about a gas concentration from the sensor signals from the two detectors.

[0048] An embodiment according to the present invention relates to a computer program with a program code for carrying out a method when the program runs on a computer.

[0049] One embodiment relates to an evaluation arrangement for a thermal gas sensor with at least one heater and at least one detector, or two detectors arranged at different distances from the heater, or two detectors arranged at the same distance from the heater. The evaluation arrangement can be designed to apply a periodic signal with a predetermined period to the heater. Furthermore, the evaluation arrangement can be designed to sample at least one sensor signal from one of the detectors at three points in time, wherein a second sampling time is offset by 90° relative to the period from a first sampling time, and wherein a third sampling time is offset by 180° relative to the period from the first sampling time.The evaluation arrangement can also be designed to detect, based on three sample values ​​based on a sample of the sensor signal at the first sample time, at the second sample time, and at the third sample time, whether a first sample value and a third sample value represent a maximum value and a minimum value of the sensor signal. The sample times (e.g., the first sample time, the second sample time, and / or the third sample time) can have a deviation from the sample time specified by the evaluation arrangement of + / - 0.5°, + / - 1°, + / - 2°, or + / - 5°. Thus, the second sample time can be offset from the first sample time, for example, by 1 / 4 period, 5 / 4 period, or 9 / 4 period, and the third sample time can be offset from the first sample time, for example, by 1 / 2 period, 3 / 2 period, or 5 / 2 period.

[0050] This exemplary embodiment of the evaluation arrangement is based on the finding that an amplitude of the at least one sensor signal, detected by one of the at least two detectors of the thermal gas sensor arranged at different distances from the heater, can be measured very precisely if an analog / digital conversion of the at least one sensor signal occurs at the correct times. This is, for example, the time at which the at least one sensor signal has the maximum or minimum value. The evaluation arrangement can be designed to detect that the first sampling time and the third sampling time are incorrectly selected by sampling the at least one sensor signal at the second sampling time, at which a "zero crossing" of the at least one sensor signal is assumed.If the first sampling time, the second sampling time, and the third sampling time are correct, the evaluation system can determine whether the first sample value and the third sample value represent a maximum and a minimum value of the sensor signal. The second sampling time can thus ensure this check for the evaluation system.

[0051] Furthermore, this makes it possible to determine a value range (e.g., from the minimum value to the maximum value) of the sensor signals and to check whether this range lies within the operating range of the analog / digital converter, so that the sensor signals can be analyzed in an optimized manner with little to no loss of information. If the evaluation device determines that the determined minimum and maximum values ​​are not within the value range, the evaluation arrangement can be designed to adjust the periodic signal applied to the heater to bring the sensor signals detected by the detectors into the value range.

[0052] Furthermore, the sampling times in the form of the minimum and / or maximum values ​​represent very well-defined positions of the sensor signals, whereby phase differences and / or amplitude differences between the periodic signal of the heater and the at least one sensor signal from at least one of the detectors can be determined very precisely, simply, and efficiently by the evaluation device. From the phase differences and amplitude differences thus determined, the evaluation device can, for example, perform a very precise gas analysis.

[0053] It can therefore be stated that the evaluation arrangement can carry out a very accurate, fast and efficient gas analysis of the gas detected by the thermal gas sensor by very precisely determining, for example, amplitudes (e.g. minimum value, maximum value) of the sensor signal (a signal detected by at least one of the two detectors, transmitted from the heater via the gas) by precisely determining the first sampling time, the second sampling time and the third sampling time.

[0054] According to one embodiment, the evaluation arrangement can be designed to change sampling times depending on the detection of whether the first sample value and the third sample value represent a maximum value and a minimum value of the sensor signal. For this purpose, the evaluation arrangement can detect whether the sampling times have been incorrectly selected. The first sample value and the third sample value represent a maximum value or a minimum value of the sensor signal and if, for example, there is a deviation of the sampling time of less than ±0.5°, ±0.7° or ±1° or less than ±10 µs, ±15 µs or ±20 µs, the evaluation device decides, for example, that no change to the sampling values ​​will be made. This makes it possible to correct the sampling times and to set them so precisely by the evaluation arrangement that the evaluation arrangement can perform a very accurate, fast and efficient gas analysis.

[0055] According to one embodiment, the evaluation arrangement can be designed to set or regulate the sampling times such that the first sample value represents a first extreme value of the sensor signal, for example a maximum value or a minimum value, and the third sample value represents a second extreme value, for example the minimum value or the maximum value, of the sensor signal. The second sample value can, for example, represent a mean value or DC component of the sensor signal (e.g., a zero crossing of the sensor signal). Thus, the evaluation arrangement can be designed to sample the at least one sensor signal and check whether the first sample value and the third sample value represent a maximum value or a minimum value of the sensor signal until the first sample value represents the first extreme value of the sensor signal and the third sample value represents the second extreme value of the sensor signal.This ensures that the evaluation system is adjusted in such a way that the amplitude of the sensor signal can be determined very precisely. The evaluation system thus performs, for example, a very precise gas analysis of the gas detected by the thermal gas sensor.

[0056] According to one embodiment, the evaluation arrangement can be designed to take into account information about a time at which the sensor signal passes through a predetermined threshold value when setting or adjusting the sampling times. The predetermined threshold value can, for example, correspond to a DC component or an average value of the sensor signal. The time at which the sensor signal passes through the predetermined threshold value can, for example, correspond to the second sampling time. The predetermined threshold value can, for example, define a "zero crossing" of the sensor signal, wherein the "zero crossing" can be provided with an offset. If the evaluation arrangement combines, for example, the information about the time at which the sensor signal passes through the predetermined threshold value with the remaining two sampling times (e.g.B. the first sampling time and the third sampling time), the evaluation system can very quickly and easily check or detect whether the first sampling value and the third sampling value correspond to the maximum and minimum values ​​of the sensor signal. Thus, the sampling times can be determined very precisely and accurately by the evaluation system, which also enables very accurate gas analysis by the evaluation system.

[0057] According to one embodiment, the evaluation arrangement can be designed to check whether a second sample value at the second sampling time is equal to an average value of the first sample value at the first sampling time and the third sample value at the third sampling time, and to detect, depending on the check, whether the first sample value and the third sample value represent a maximum value and / or a minimum value of the sensor signal. According to one embodiment, the second sample value can deviate from the average value with a tolerance of at most ±0.5%, ±1%, or ±5% of a difference between the first sample value and the third sample value. This feature enables the evaluation arrangement to detect, with the aid of the second sampling time, whether the first sample value and the third sample value correspond to the maximum value or the minimum value of the sensor signal.Thus, possible errors in the evaluation system when determining the first sample value, the second sample value and the third sample value can be reduced and a very precise gas analysis can be carried out.

[0058] According to one embodiment, the evaluation arrangement can be designed to apply a periodic square-wave signal or a pulse with a defined power with a duty cycle of preferably 50% to the heater. Alternatively, the duty cycle can also be in a range from 5 to 50%. For example, a duty cycle tolerance of ±1%, ±2%, or ±5% is possible. According to one embodiment, the evaluation arrangement can be designed to change the duty cycle at a fixed operating voltage of the heater in order to adjust the heating power of the heater.This enables the evaluation arrangement to determine a very precise heater signal via the duty cycle and to analyze a gas very precisely by determining the sampling times of the at least one sensor signal that corresponds to the heater signal (the heater signal is transported via the gas to the detectors and detected by the detectors, for example, as a sensor signal).

[0059] According to one embodiment, the evaluation arrangement can be designed to combine a sensor signal from at least one of the detectors with an offset signal generated by a digital-to-analog converter, to obtain an input signal for an analog-to-digital converter, and to adjust the offset signal to ensure that the input signal of the analog-to-digital converter remains within a predetermined range (e.g., a value range) throughout an entire period of the sensor signal. Furthermore, the evaluation arrangement can be designed to adjust the sampling times after adjusting the offset signal and, after changing the sampling times, to perform a new check to determine whether the sample values ​​obtained with the changed setting of the sampling times still lie within the predetermined range.The analog-to-digital converter, for example, digitizes signal values ​​present at the sampling times and thus samples the sensor signal. The evaluation device can adjust the offset signal, for example, in response to a detection that an input value of the analog-to-digital converter exceeds a predetermined upper threshold (e.g., 95%, 90%, or 85% of a maximum processable input value of the analog-to-digital converter) or in response to a detection that an input value of the analog-to-digital converter falls below a predetermined lower threshold (e.g., 5%, 10%, or 15% of a maximum processable input value of the analog-to-digital converter). The sampling times can be adjusted, for example, as part of a tracking of the sampling times after an adjustment of the offset signal.The offset signal can, for example, be used to ensure that the input signal, consisting of the combined sensor signal and the offset signal, remains within the specified range. The specified range can be defined, for example, as the detectable limit of the analog-to-digital converter (e.g., an operating range of the analog-to-digital converter). The offset signal can, for example, amplify or reduce the sensor signal and thus continuously (e.g., during the entire period) keep it within an optimal operating range or operating window (e.g., the specified range) of the analog-to-digital converter.

[0060] The specified range within which the input signal of the analog-to-digital converter should remain throughout the entire period of the sensor signal can be defined both by a specified range for the amplitude of the sensor signal and by a specified range for the offset of the sensor signal. For example, the offset signal can not only offset the sensor signal within the specified range of the analog-to-digital converter, but also regulate the amplitude of the sensor signal such that the input signal has an amplitude that occupies a large part of the specified range in terms of amplitude. If the evaluation system has changed the sampling times, the sampling times are checked again using the obtained sampling values ​​(or input values ​​of the analog-to-digital converter). The specified range within which the obtained sampling values ​​should lie can, for example, be between the specified lower threshold value and the specified upper threshold value.Optionally, the evaluation system can be designed to readjust the offset signal and / or the heater's heating power if necessary after re-checking the obtained sample values. Thus, the evaluation system enables the sensor signal to be analyzed very precisely by an analog-to-digital converter, since the sensor signal is converted with an offset signal, for example, into an input signal that can occupy an optimal operating range of the analog-to-digital converter (the specified range). This enables the evaluation system to perform a very precise gas analysis using the characteristic.

[0061] According to one embodiment, the evaluation arrangement can be designed to regulate a heating power applied to the heater depending on at least one sensor signal from at least one of the detectors in order to bring the at least one sensor signal within a predetermined value range. Furthermore, the evaluation arrangement can be designed to take into account information about the heating power (for example Hz.Uss) when deriving information about a gas concentration from the sensor signals. The evaluation arrangement can, for example, be designed to regulate a heating power such that an amplitude of the sensor signal can be brought within the predetermined value range. The amplitude can be the minimum value and / or the maximum value of the sensor signal or a difference between the maximum value and the minimum value.If, for example, the sensor signal has a very low amplitude, the evaluation arrangement can apply a heating power to the heater so that the sensor signal detected by a detector has an amplitude that covers at least almost the entire predetermined value range. The predetermined value range can, for example, represent an operating range of an analog-to-digital converter with which the sensor signal can be processed by the evaluation arrangement. Accordingly, the evaluation arrangement can, for example, apply a heating power to the heater so that the at least one sensor signal occupies at least 70%, 75%, or 80% of the operating range of the analog-to-digital converter. The evaluation arrangement can be designed to determine information about the gas concentration or the thermal conductivity of the sensor signal depending on information about the heating power and depending on information about the sensor signal.The information about the heating power can, for example, define a heating power amplitude, a heating power phase, and / or a heating power offset. The information about the sensor signal can, for example, define a sensor signal amplitude, a sensor signal phase, and / or a sensor signal offset. Thus, the evaluation system can be used to analyze a gas very precisely.

[0062] One embodiment provides a method for operating a thermal gas sensor with at least one heater and two detectors arranged at different distances from the heater. The method can comprise applying a periodic signal with a predetermined period to the heater. At least one sensor signal can be sampled by one of the detectors at three points in time, wherein a second sampling time can be offset from a first sampling time by 90°, relative to the period (for example, + / - 2% or + / - 2°) (i.e., for example, by 1 / 4 period, 5 / 4 period, or 9 / 4 period), and wherein a third sampling time can be offset from the first sampling time by 180°, relative to the period (for example, + / - 2% or + / - 2°) (i.e., for example, by 1 / 2 period, 3 / 2 period, or 5 / 2 period).Based on three sample values, which are based on a sample of the sensor signal at the first sampling time, at the second sampling time, and at the third sampling time, it can be detected (for example by an evaluation arrangement) whether a first sample value and a third sample value represent a maximum value and a minimum value of the sensor signal (for example, up to a DC offset). The fact that the first sample value and the third sample value represent a maximum value and a minimum value of the sensor signal can mean, for example, that the first sample value represents a maximum value and the third sample value a minimum value, or that the first sample value represents a minimum value and the third sample value a maximum value (this applies to all embodiments listed herein).

[0063] One embodiment relates to a computer program having a program code for carrying out a method when the program runs on a computer. Short character description

[0064] Embodiments are explained in more detail below with reference to the accompanying figures. With regard to the schematic figures shown, it should be noted that the illustrated functional blocks are to be understood both as elements or features of the disclosed device and as corresponding method steps of the disclosed method, and corresponding method steps of the disclosed method can also be derived therefrom. They show: Fig. 1a shows a schematic representation of a gas sensor; Fig. 1b shows a schematic representation of an evaluation arrangement for a thermal gas sensor; Fig. 1c shows a schematic representation of an evaluation arrangement for a thermal gas sensor with a control of a heating power, according to an embodiment of the present invention; Fig. 1d shows a schematic representation of an evaluation arrangement for a thermal gas sensor with a sampling of a sensor signal at three points in time; Fig. 2a shows a schematic representation of a gas sensor on the light microscope; Fig. 2b shows a schematic representation of a gas sensor in the scanning electron microscope; Fig. 3 shows a schematic representation of a section of a scanning electron microscopy image of a micro-bridge for a gas sensor; Fig.4 shows a schematic representation of a gas sensor with a first interruption with an extension perpendicular to a heater, different from an extension perpendicular to a heater of a second interruption; Fig. 5 shows a schematic representation of a gas sensor with a first interruption region and a second interruption region, with a plurality of interruptions; Fig. 6a shows a schematic representation of a gas sensor with the same number of interruptions in both a first interruption region and a second interruption region; Fig. 6b shows a schematic representation of a gas sensor with a plurality of interruptions in a first interruption region and a single interruption in a second interruption region; Fig.6c shows a schematic representation of a gas sensor, wherein a plurality of interruptions in a first interruption region have a different extent perpendicular to a heater than a plurality of interruptions in a second interruption region; Fig. 7 shows a schematic representation of a principle of a gas sensor; Fig. 8 shows a schematic representation of heat transport at a gas sensor; Fig. 9 shows a diagram of a heater signal, a first sensor signal, and a second sensor signal; Fig. 10 shows a schematic representation of a heater control for a gas sensor; Fig. 11 shows a schematic representation of a circuit for evaluating a sensor signal from a gas sensor; Fig. 12 shows a schematic representation of a control system for a gas sensor; Fig. 13a shows a block diagram of a method for analyzing a sensor signal from a gas sensor;13b shows a block diagram of a method for evaluating a sensor signal from a gas sensor with tracking of sampling times; Fig. 14 shows a diagram of a phase shift between a heater signal and two sensor signals from a gas sensor; Fig. 15 shows a diagram of amplitudes of at least one sensor signal from a gas sensor; Fig. 16 shows a diagram of phase shifts between a first sensor signal and a second sensor signal from a gas sensor as a function of pressure; Fig. 17a shows a diagram of a phase shift of a sensor signal from a gas sensor as a function of frequency; Fig. 17b shows a diagram of an amplitude of a sensor signal from a gas sensor as a function of frequency; Fig. 18 shows a diagram of phase shifts of a first sensor signal, a second sensor signal, and a heater signal from a gas sensor as a function of nitrogen concentration;19 a diagram of an amplitude of a first sensor signal and a second sensor signal of a gas sensor as a function of a nitrogen concentration; Fig. 20 a diagram of a combination signal of a gas sensor for different gas mixtures; Fig. 21 a diagram of a combination signal of a gas sensor as a function of a CO2 concentration; Fig. 22 a diagram of a combination signal of a gas sensor as a function of a pressure; Fig. 23 a diagram of a relationship between a gas pressure and a gas temperature for a gas sensor; Fig. 24 a block diagram of a method for generating a combination signal of a gas sensor; Fig. 25 a diagram of a thermal conductivity as a function of a combination signal; Fig. 26 a diagram of a current flow in a heater during a heating period for a first gas mixture; Fig. 27 a diagram of a current flow in a heater during a heating period for a second gas mixture;Fig. 28 shows a diagram of a current flow in a heater during a heating period for a third gas mixture; Fig. 29 shows a diagram of different phase information for different gas mixtures; Fig. 30 shows a diagram of different amplitude information for different gas mixtures; and Fig. 31 shows a diagram of a combination signal for different gas mixtures. Detailed description of the embodiments according to the figures

[0065] Before exemplary embodiments are explained in more detail below with reference to the drawings, it is pointed out that identical, functionally identical or equivalent elements, objects and / or structures in the different figures are provided with the same or similar reference numerals, so that the description of these elements shown in different exemplary embodiments is interchangeable or can be applied to one another.

[0066] Fig. 1ashows a schematic representation of a gas sensor 100. The gas sensor 100 can have a membrane 110 (e.g., a thin-film membrane), a heating element 120, a first thermocouple structure 130, and a second thermocouple structure 140. Optionally, the gas sensor can also have only the first thermocouple structure 130 or the second thermocouple structure 140. The membrane 110 can be spanned by a frame 150 and have a first interruption region 160 and a second interruption region 170. The first interruption region 160 of the membrane 110 can have at least one interruption 162, and the second interruption region 170 of the membrane 110 can also have at least one interruption 172. The heating element 120 can, for example, be arranged as a self-supporting bridge structure on the membrane 110 between the first interruption region 160 and the second interruption region 170 of the membrane 110.The first thermocouple structure 130 may have a hot end 132 and a cold end 134. The hot end 132 of the first thermocouple structure 130 may be disposed on the membrane 110 on a side of the first break region 160 opposite the heating element 120. The second thermocouple structure 140 may also have a hot end 142 and a cold end 144. The hot end 142 may be disposed on the membrane 110 on a side of the second break region 170 opposite the heating element 120.

[0067] The membrane 110 can be a thin-film membrane with a thickness between 200 nm and 4000 nm, 300 nm and 3000 nm, 400 nm and 2000 nm, or between 1 µm and 10 µm. According to one embodiment, the thickness of the entire membrane is approximately 2 µm (it consists, for example, of several membrane, sensor, and passivation layers). The membrane layer can comprise, for example, Si oxide and / or Si nitride. The thickness can be defined as an extension of the membrane 110 into the plane of the sheet, i.e., for example, perpendicular to a surface of the membrane 110 on which the heating element 120, the first thermocouple structure 130, and the second thermocouple structure 140 are arranged. The membrane 110 may comprise conductive material, insulating material or semiconductor material, wherein the material may have a very low thermal conductivity, for example, below 5 W / (m*K), below 100 mW / (m*K) or below 50 mW / (m*K).For example, a semiconductor with adapted basic doping can serve as a cost-effective substrate for the production of the membrane 110 in a simple five-mask MEMS process.

[0068] According to one embodiment, the heating element 120 (the heating element 120 may also be referred to as a heater below) may form a cantilevered bridge structure and / or comprise a wire. According to one embodiment, the heating element 120 may be spanned from one side of the frame 150 to an opposite side of the frame 150. For example, a voltage may be applied to the heating element 120, whereby the heating element 120 can transfer heating power to a gas to be analyzed, located, for example, in the first interruption region 162 and / or in the second interruption region 172. The voltage applied to the heating element 120 may, for example, be a periodic voltage signal, such as a sine signal or a periodic square wave signal. Thus, the heating element 120 can, for example, provide a periodic heater signal (for example, the heating power).The heater signal may be transmitted, for example, via the membrane 110 and / or via a gas located, for example, in the first interruption 162 or the second interruption 172, to the first thermocouple structure 130 and / or the second thermocouple structure 140.

[0069] The first thermocouple structure 130 and / or the second thermocouple structure 140 are, for example, formed in a meandering shape, which can correspond, for example, to series-connected thermocouples forming a thermocouple chain. The first thermocouple structure 130 and / or the second thermocouple structure 140 can thus serve as a detector, wherein the first thermocouple structure 130 and / or the second thermocouple structure 140 can detect, for example, the heater signal.

[0070] According to one embodiment, the first thermocouple structure 130 and / or the second thermocouple structure 140 can be arranged entirely on the membrane 110, or at least partially on the membrane 110 and at least partially on the frame 150. For example, a temperature of the frame 150 can serve as a comparison temperature (here, for example, the cold ends 134 of the first thermocouple structure 130 and / or the cold ends 144 of the second thermocouple structure 140 can be arranged), and the part of the thermocouple structure arranged on the membrane 110 (e.g., the hot ends 132, 142) can detect a measurement temperature (e.g., the heater signal). The hot ends 132, 142 and the cold ends 134, 144 are connected, for example, to a conductor.For example, a conductor comprising a first material can connect a first cold end to a first hot end, and a second conductor comprising a second material can connect the first hot end to a second cold end. This connection of a first conductor and a second conductor can represent a thermocouple, which can be connected in series to form a thermocouple chain, for example, and can thus represent, for example, the first thermocouple structure 130 or the second thermocouple structure 140. A temperature difference (e.g., between the reference temperature and the measurement temperature) can thus occur along these conductors, for example, which can induce an electrical voltage at the ends (e.g., the hot ends and / or the cold ends) of the metallic conductors.Thus, the first thermocouple structure 130 and / or the second thermocouple structure 140 can be configured, for example, to convert heat into electrical energy. According to one embodiment, the first thermocouple structure 130 and / or the second thermocouple structure 140 can be a wire or a cantilevered bridge structure.

[0071] According to one embodiment, the membrane 110 can be spanned by the frame 150 made of carrier material, which is designed such that the thermal expansion coefficient and / or thermal conductivity of the membrane material differs from the thermal expansion coefficient and / or thermal conductivity of the carrier material. The frame 150 can comprise carrier material or substrate material with which the membrane 110 can be supported, for example. Thus, a comparison temperature can be set on the frame 150, for example. According to one embodiment, the frame 150 and the membrane 110 can also have the same thermal expansion coefficient.

[0072] According to one embodiment, the membrane 110 may have a lower thermal conductivity than the frame 150. In this case, the membrane 110 in particular should, for example, have a very low thermal conductivity so that, for example, the heater signal from the heating element 120 is transmitted mainly via the gas to be analyzed (arranged, for example, in the first interruption 162 and / or in the second interruption 172) to the first thermocouple structure 130 and / or the second thermocouple structure 140, instead of via the membrane 110. Thus, for example, heat transport via the membrane 110 can be suppressed, reduced, or slowed down.

[0073] The membrane 110 can thus be configured to suppress parasitic heat conduction from the heating element 120 to the first thermocouple structure 130 or to the second thermocouple structure 140. For example, the thermal conductivity of the membrane 110 can be selected such that little to no heat is conducted from the heating element 120 via the membrane 110 to the first thermocouple structure 130 or the second thermocouple structure 140, and a large part of the heat, or all of the heat, is conducted via the gas to be analyzed.

[0074] In contrast, the thermal conductivity of the carrier material of the frame 150, which holds the membrane 110, can be very high. For example, silicon with a thermal conductivity of 150 W / (m*K) can be used as the carrier material. The carrier material can thus serve as a heat sink. For example, the first thermocouple structure 130 or the second thermocouple structure 140 is arranged at least partially, e.g., with the hot ends 132, 142, on the membrane and at least partially, e.g., with the cold ends 134, 144, on the carrier material, whereby a temperature difference can occur within the first thermocouple structure 130 or the second thermocouple structure 140, which can be used to detect the heat transport from the heating element 120 to the respective thermocouple structure 130, 140.

[0075] According to one embodiment, the cold ends of the first thermocouple structure 130 and the cold ends of the second thermocouple structure 140 can thus be arranged on the carrier material of the frame 150. They are located, for example, where the membrane 110 is supported by the carrier material.

[0076] According to one embodiment, the first interruption region 160 of the membrane 110 can have a continuous interruption 162 whose longitudinal extent 164 is large enough to completely cover the area between the first thermocouple structure 130 and the heating element 120. The second interruption region 170 of the membrane 110 can have a continuous interruption 172 whose longitudinal extent 174 is large enough to completely cover the area between the second thermocouple structure 140 and the heating element 120. Thus, the longitudinal extent 164, 174 is, for example, as large as the entire length of the heating element 120 and / or at least as long as the entire length of the first thermocouple structure 130 and / or the second thermocouple structure 140.This allows as little heat as possible to be transferred from the heating element 120 to the first thermocouple structure 130 or the second thermocouple structure 140 via the membrane 110, but rather a large part via a gas in the first interruption 162 in the first interruption region 160 and / or in the second interruption 172 in the second interruption region 170.

[0077] According to one embodiment, the transverse extent 166 of the at least one interruption 162 of the first interruption region 160 may be different from the transverse extent 176 of the at least one interruption 172 of the second interruption region 170. The transverse extent 166, 176 of the first interruption 162 or the second interruption 172 may, for example, be oriented in a direction perpendicular to a direction of maximum extension of the heating element 120 or in a direction from the heating element 120 to the respective thermocouple structures (e.g., the first thermocouple structure 130 and / or the second thermocouple structure 140). Fig. 1a For example, the first interruption 162 and the second interruption 172 have the same transverse extent 166, 176.

[0078] According to one embodiment, the first interruption 162 can have a longitudinal extent 164 and a transverse extent 166, such that the first interruption 162 corresponds to the extents of the first interruption region 160. Likewise, the second interruption 172 can, for example, have a longitudinal extent 174 and a transverse extent 176, such that the second interruption 172 corresponds to the extents of the second interruption region 170. Thus, for example, the entire first interruption region 160 can represent the first interruption 162, and the entire interruption region 170 can represent the interruption 172.

[0079] Optionally, the membrane 110 can have a third and / or a fourth interruption region on the side of the cold ends 134, 144 of the first thermocouple structure 130 and / or the second thermocouple structure 140. Thus, for example, the first thermocouple structure 130 can be arranged in the form of a wire or a self-supporting bridge structure between the first interruption region 160 and a third interruption region, or the second thermocouple structure 140 can be arranged, for example, as a wire or as a self-supporting bridge structure between the second interruption region 170 and the fourth interruption region. Thus, the first thermocouple structure 130 and / or the second thermocouple structure 140 can be surrounded, for example, on two sides by the gas to be analyzed.

[0080] According to one embodiment, the first thermocouple structure 130 may have a different distance from the heating element 120 than the second thermocouple structure 140. In Fig. 1aFor example, the first thermocouple structure 130 has the same distance from the heating element 120 as the second thermocouple structure 140. During the transmission of the heater signal from the heating element 120 via the first interruption 162 to the first thermocouple structure 130 or from the heating element 120 via the second interruption 172 to the second thermocouple structure 140, unknown heat transfers can occur from the heating element into the gas to be analyzed, arranged in the first interruption 162 and / or the second interruption 172, and from the gas to the first thermocouple structure 130 and / or the second thermocouple structure 140. The heater signal from the heating element 120 detected by the first thermocouple structure 130 may, for example, be referred to as a first sensor signal, and the heater signal from the heating element 120 detected by the second thermocouple structure 140 may, for example, be referred to as a second sensor signal.

[0081] The first sensor signal and / or the second sensor signal can, for example, comprise the two unknown heat transitions (e.g.: heating element -> gas, gas -> thermocouple structure) and a heat transfer via the gas to be analyzed. If the first thermocouple structure 130 is at a different distance from the heating element 120 than the second thermocouple structure 140, a difference signal from the gas sensor can be created from the first sensor signal and the second sensor signal, for example by subtracting the unknown heat transitions (the first sensor signal can have the same heat transitions as the second sensor signal), and thus the difference signal only comprises, or to a large extent, the heat transfer via the gas to be analyzed from the heating element 120 to the respective thermocouple structure 130, 140, but does not comprise, or comprises to a very small extent, the unknown heat transitions.

[0082] According to one embodiment, the first interruption region 160 and the second interruption region 170 can have a plurality of interruptions (e.g., the interruption 162 and the interruption 162 1 or the interruption 172 and the interruption 172 1 ), which can be arranged such that (e.g., due to the remaining membrane material 110) a lattice structure is created (e.g., in the first interruption region 160 or the second interruption region 170), in which the interruptions are arranged in rows parallel to the heating element 120 and the rows are offset from one another. The interruptions in an interruption region 160, 170 can differ from one another both in the longitudinal extent 164, 174 and in the transverse extent 166, 176. According to Fig. 1aFor example, the interruption 162 1 of the first interruption region 160 has a smaller longitudinal extent than the longitudinal extent 164 of the interruption 162. Likewise, the interruption 172 1 of the second interruption region 170 can have a smaller longitudinal extent than the longitudinal extent 174 of the interruption 172.

[0083] According to one embodiment, the first interruption region 160 and the second interruption region 170 can have a plurality of interruptions, which can be arranged to create a lattice structure in which a path of heat conduction through the membrane 110 is longer than a direct path 122a, 122b. The direct path 122a, 122b can, for example, be a straight path perpendicular to the heating element 120, from the heating element 120 to the thermocouple structure 130, 140. The direct path 122a, 122b can run through the interruptions 162 and 1621 or through the interruptions 172 and 1721, respectively, whereby heat conduction through the gas to be analyzed can be detected by the first thermocouple structure 130 and / or the second thermocouple structure 140. However, if the direct path 122a, 122b were to occur only via the membrane 110 and not via the gas to be analyzed, the gas sensor 100 cannot ensure a meaningful analysis of the gas.

[0084] According to one embodiment, the at least one interruption 162, 172 in the first interruption region 160 and in the second interruption region 170 can form rectangular cutouts with optionally rounded corners. This is, for example, an elongated hole. These can also be oval holes, for example. Even if in Fig. 1aWhile the interruption 162 of the first interruption region 160 and the interruption 172 of the second interruption region 170 are depicted as rectangular interruptions (holes), the interruptions can have any shape (such as triangular, circular, square, polygonal, etc.). The shape of the interruptions 162, 172 can be adapted so that a heat path from the heating element to the first thermocouple structure 130 and / or to the second thermocouple structure 140 via the membrane 110 is as long as possible and a path via the gas to be analyzed represents a very short path. This makes it possible to transport as much heat as possible via the gas to be analyzed and not via the membrane 110, whereby the gas sensor 100 can analyze the gas very precisely.

[0085] According to one embodiment, the at least one interruption 162, 172 can be at least three times longer than its width. Thus, for example, the longitudinal extent 164 of the interruption 162 can be three times longer than the transverse extent 166, or the longitudinal extent 174 of the interruption 172 can be three times longer than the transverse extent 176. Thus, the length represents, for example, the longitudinal extent 164, 174, and the width represents, for example, the transverse extent 166, 176. The length can be defined, for example, as a direction parallel to the heating element 120 (or to a direction of maximum extent of the heating element 120), and the width can be defined as a direction perpendicular to the heating element 120 (or to a direction of maximum extent of the heating element 120).

[0086] According to one embodiment, a distance 168 between a plurality of interruptions 162, 162 in the first interruption region 160 and a distance 178 between a plurality of interruptions 172, 172 in the second interruption region 170 can correspond to the smallest structure width that can be realized and results in a mechanically durable lattice structure. The distance 168, 178 can define a width of webs between two interruptions consisting of membrane material of the membrane 110. The smaller the distance 168, 178, the less heat is transferred via the membrane 110 from the heating element 120 to the first thermocouple structure 130 and / or the second thermocouple structure 140, and the more heat is transferred via the gas to be analyzed.

[0087] According to one embodiment, the first thermocouple structure 130 and the second thermocouple structure 140 can be passivated with a protective layer. The protective layer can protect the first thermocouple structure 130 and the second thermocouple structure 140 from damage caused by the gas to be analyzed and thus prevent possible inaccuracies of the gas sensor during gas analysis due to damage to the first thermocouple structure 130 or the second thermocouple structure 140.

[0088] According to one embodiment, the hot end 132 of the first thermocouple structure can extend to an edge of the first interruption region 160 of the membrane 110, and the hot end 142 of the second thermocouple structure 140 can extend to an edge of the second interruption region 170 of the membrane 110. The distance between the hot end 132 and the first interruption region 160, or the distance between the hot end 142 and the second interruption region 170, should, for example, not be greater than 0.5 mm, 100 nm, or 10 µm. If, for example, the interruption 162 or the interruption 142 extends to this edge, the membrane 110 has only a very small distance between the respective hot ends and the respective interruption. This can enable the membrane material of the membrane 110 to enable detection of the heater signal by the first thermocouple structure 130 ornot or only slightly affected by the second thermocouple structure 140, whereby the gas sensor 100 can analyze the gas very precisely.

[0089] Fig. 1bshows a schematic representation of an evaluation arrangement 200, which can also be referred to herein as an evaluation device, for a thermal gas sensor 100 with at least one heater 120 and two detectors arranged at different distances 180 1 , 180 2 from the heater 120 (a first detector 130 and a second detector 140). The first detector 130 can be spaced from the heater 120 by the distance 180 1 , and the second detector 140 can be spaced from the heater 120 by the distance 180 2 .The evaluation arrangement 200 can be designed to obtain information 210 about an amplitude of a detector signal of a first detector 130, information 220 about an amplitude of a detector signal of a second detector 140, information 210 about a first phase difference between a heater signal and the detector signal of the first detector 130 and information 220 about a second phase difference between the heater signal and the detector signal of the second detector 140.

[0090] According to one embodiment, the information 210 can include both the amplitude of the detector signal of the first detector 130 and the first phase difference between the heater signal and the detector signal of the first detector 130, just as the information 220 can include both the amplitude of the detector signal of the second detector 140 and the second phase difference between the heater signal and the detector signal of the second detector 140. However, it is also possible for the amplitude of the detector signal of the respective detector (the first detector 130 or the second detector 140) to be sent from the thermal gas sensor to the evaluation arrangement separately from the first phase difference or the second phase difference.According to one embodiment, it is also possible that the information 210 and the information 220 are not transmitted to the evaluation arrangement 200 via separate lines, but for example via a common line or wirelessly.

[0091] According to one embodiment, the evaluation arrangement 200 can be designed to form a combination signal 230 as an intermediate variable depending on the information 210, 220 about the amplitudes of the detector signals and depending on the information 210, 220 about the first phase difference and the second phase difference. The combination signal 230 can combine amplitude information and phase information of the detector signal of the first detector 130 and the detector signal of the second detector 140. The evaluation arrangement 200 can be designed to determine information 240 about a gas concentration or a thermal conductivity of a fluid, for example a gas or gas mixture, based on the combination signal 230. The evaluation arrangement 200 can perform this determination, for example, without separately considering the individual pieces of information 210, 220 flowing into the combination signal 230 again in the further course of the calculations.

[0092] The amplitude of the detector signal can, for example, be provided directly as information 210, 220 from the respective detector 130, 140. The information 210, 220 about the first phase difference and second phase difference between the heater signal 122 and the detector signal of the respective detector 130, 140 can, for example, be determined by the thermal gas sensor 100 and transmitted to the evaluation arrangement 200.

[0093] Alternatively, the detector signal of the first detector 130 or the detector signal of the second detector 140 can be transmitted to the evaluation arrangement 200 via the information 210 or the information 220, respectively, and the heater signal 122 can additionally be transmitted directly to the evaluation arrangement 200. The evaluation arrangement can be configured to determine the respective amplitude from the detector signal of the first detector 130 and from the detector signal of the second detector 140 and to determine the first phase difference and the second phase difference in order to form the combination signal 230 depending on the information thus determined.

[0094] Because the evaluation arrangement 200 forms the combination signal 230, the evaluation arrangement 200 can correct possible errors of the thermal gas sensor 100 very easily and much more quickly to obtain the information 240 about the gas concentration and thermal conductivity than if the evaluation arrangement 200 separately corrected the information 210 about the amplitude of the detector signal of the first detector 130 and the first phase difference, as well as the information 220 about the amplitude of the detector signal of the second detector 140 and the second phase difference. The combination signal 230 can thus facilitate the determination of the information 240 about the gas concentration and the thermal conductivity of the gas to be analyzed and enable the suppression or reduction of errors generated by the thermal gas sensor 100.

[0095] According to one embodiment, the evaluation arrangement 200 can be designed to obtain information about a heater amplitude, for example information about a heating power from the heater signal 122, and to form a linear combination of the information about the heater amplitude, the information 210 and the information 220 in order to determine the combination signal 230.

[0096] Alternatively, the evaluation arrangement 200 can not only obtain the information about the heater amplitude from the heater signal 122, but also, as already described above, calculate information about the first phase difference and about the second phase difference if the information 210 comprises, for example, the detector signal of the first detector 130 and the information 220 comprises the detector signal of the second detector 140.

[0097] Thus, the combination signal 230 includes not only the phase of the heater signal in the form of the first phase difference and the second phase difference, but also the heater amplitude, which enables the evaluation arrangement 200 to determine the information 240 about the gas concentration and the thermal conductivity of the gas to be analyzed as a function of the first distance 180 1 and the second distance 180 2 of the two detectors from the heater 120. For example, the detector signal of the first detector 130 has a greater amplitude than the detector signal of the second detector 140 because the distance 180 2 of the second detector 140 from the heater 120 is greater than the distance 180 1 of the first detector 130 from the heater 120. With increasing distance from the heater 120, the heater amplitude detected by the respective detector 130, 140 may decrease.With the additional information about the heater amplitude, the evaluation arrangement 200 can thus determine the information 240 about the gas concentration and the thermal conductivity even more accurately, since the heater amplitude of the heater signal 122 can be considered as a reference, and thus the combination signal 230 can have a relative amplitude signal. A relative amplitude signal, for example, is less error-prone than an absolute amplitude signal.

[0098] According to one embodiment, the evaluation arrangement 200 can be configured to obtain the combination signal sigX 230 according to sigX=sigUss*Ka+sigPhi*Kp. The term sigUss can be an amplitude information or an amplitude signal that can depend on the information 210 about the amplitude of the detector signal of the first detector 130 and on the information 220 about the amplitude of the detector signal of the second detector 140. For example, sigUss can be a linear combination of the information 210 about the amplitude of the detector signal of the first detector 130 and the information 220 about the amplitude of the detector signal of the second detector 140. sigPhi may be phase information or an added phase signal that may depend on the information 210 about a first phase difference and on the information 220 about the second phase difference.For example, sigPhi can be an addition of the information 210 about the first phase difference and the information 220 about the second phase difference. Ka and Kp can be constants. The combination signal 230 determined in this way can include amplitude information sigUss and phase information sigPhi, whereby four pieces of information (e.g., the information 210 about the amplitude of the detector signal of the first detector 130, the information 220 about the amplitude of the detector signal of the second detector 140, the information 210 about a first phase difference between the heater signal and the detector signal of the first detector 130, and the information 220 about the second phase difference between the heater signal and the detector signal of the second detector 140) are combined in the combination signal 230, whereby the evaluation arrangement 200 can use less power to process the information 210, 220.Thus, the evaluation arrangement 200 can be designed to determine information 240 about the gas concentration and thermal conductivity very efficiently, quickly and accurately.

[0099] According to one embodiment, the evaluation arrangement 200 can be configured to obtain the amplitude information sigUss according to sigUss=2*Hz.Uss-(D1.Uss+D2.Uss). Hz.Uss can be information about the heater amplitude, which can be obtained from the heater signal 122. D1.Uss can be information 210 about the amplitude of the detector signal of the first detector 130, and D2.Uss can be information 220 about the amplitude of the detector signal of the second detector 140. Thus, the amplitude information sigUss can represent a relative amplitude signal, since the information 210 about the amplitude of the detector signal of the first detector 130, the information 220 about the amplitude of the detector signal of the second detector 140 and the heater amplitude Hz.Uss can be offset against each other so that the information 210 about the amplitude of the detector signal of the first detector 130 and the information 220 about the amplitude of the detector signal of the second detector 140 can be viewed relative to the heater amplitude. By viewing the amplitudes relative to each other, possible errors in absolute amplitude values ​​can be avoided, whereby the evaluation arrangement 200 can very precisely determine the information 240 about the gas concentration and thermal conductivity.

[0100] According to one embodiment, the evaluation arrangement 200 can be configured to calculate a polynomial, for example, of the first degree, of the combination signal 230 in order to obtain the information 240 about the gas concentration or the thermal diffusivity. The polynomial (e.g., polynomial y) can be obtained, for example, according to y=A0+A1*sigX+A2*sigX 2<. By forming the polynomial of the combination signal 230 by the evaluation arrangement 200, the combination signal 230 can be very easily and efficiently corrected for possible pressure drift or temperature drift errors.

[0101] According to one embodiment, the evaluation arrangement 200 can be configured to multiply the polynomial of the combination signal 230 by a correction term to obtain the information 240 about the gas concentration and / or the thermal diffusivity. The correction term of the combination signal 230 can be dependent on information about a pressure and on information about a temperature and, for example, compensate for a pressure and temperature dependence. In other words, the correction term of the combination signal 230 can compensate for a pressure drift and / or a temperature drift. Thus, a possible misinterpretation by the evaluation arrangement 200 of the signals detected by the thermal gas sensor 100 is reduced.

[0102] According to one embodiment, the evaluation arrangement 200 can be designed to perform a calculation according to C = pol sigX ⋅ 1 − f p sigX − const 1 ⋅ 1 − f T p − const 2 to obtain the information C 240 about the gas concentration. sigX can be the combination signal 230, pol(sigX) can be a polynomial of the combination signal sigX 230, f(p) can be a function of a pressure p, const1 can be a constant, f(T) can be a function of the temperature T, and const2 can be a second constant. f(p) can be a function of a measured pressure p in an environment of the thermal gas sensor 100, and f(T) can be a function of a measured temperature T in an environment of the thermal gas sensor 100. The second term of the multiplication 1 − f p sigX − const 1 ⋅ 1 − f T p − const 2 can also be understood as a correction term of the combination signal 230. The correction term can depend on the measurement conditions of the gas sensor 100 (such as an ambient pressure / measurement pressure or an ambient temperature / measurement temperature). The correction term can thus correct possible influences of an ambient pressure or an ambient temperature of the thermal gas sensor 100 on the determination of the information 240 about the gas concentration. Thus, possible pressure drift or temperature drift can be suppressed.

[0103] According to one embodiment, the evaluation arrangement 200 can be designed to perform a calculation according to C vol% = A . y sigX ⋅ 1 − B . y p − B . ref sigX − B . ref ⋅ 1 − C . y T − C . ref p − C . ref to obtain the information C 240 about the gas concentration. In the formula, sigX can be the combination signal 230, Ay(sigX) can be a polynomial of the combination signal sigX 230 (e.g., first order), By(p) can be a function of the pressure p (e.g., a polynomial function, e.g., second order), B.ref can be a constant, Cy(T) can be a function of the temperature T (e.g., a polynomial function, e.g., second order), and C.ref can be a second constant. The function By(p) can, for example, be a function of a measured pressure p in an environment of the thermal gas sensor 100, and the function Cy(T) can be a function of a measured temperature T in an environment of the thermal gas sensor 100. The second term 1 − B . y p − B . ref sigX − B . ref ⋅ 1 − C . y T − C . ref p − C . ref The multiplication for calculating the information C 240 about the gas concentration can define a correction term. The correction term can depend, for example, on the pressure p and the temperature T. For example, By(p) can be a polynomial function dependent on the pressure p, whereby, for example, a correction for possible pressure influences on the calculation of the information 240 about the gas concentration can be taken into account. Likewise, by forming the polynomial function Cy(T) as a function of the temperature T, a possible influence of the temperature T on the calculation of the information 240 about the gas concentration can be taken into account very precisely. By forming the polynomial functions, both as a function of the pressure p and as a function of the temperature T, error corrections can be very well approximated, whereby the evaluation arrangement 200 can be designed to determine the information 240 about the gas concentration very effectively and very precisely.

[0104] According to one embodiment, the evaluation arrangement 200 can be designed to consider a pressure and / or a temperature in an environment of the thermal gas sensor 100 when determining the information 240 about the gas concentration and / or the thermal conductivity. For this purpose, the thermal gas sensor 100 can, for example, have pressure and temperature sensors with which it can detect the pressure and / or the temperature in the environment and transmit it to the evaluation arrangement 200. Thus, the evaluation arrangement 200 can, for example, consider and correct possible miscalculations of the information 240 about the gas concentration and / or the thermal conductivity due to different pressure and / or temperature conditions in the environment of the thermal gas sensor 100.Thus, the evaluation arrangement 200 can react to the pressure and / or the temperature in the environment of the thermal gas sensor 100 and accordingly determine the information 240 about the gas concentration and / or the thermal conductivity very precisely.

[0105] According to one embodiment, the evaluation arrangement 200 can be configured to use the combination signal 230, information about the temperature in an environment of the thermal gas sensor 100, and information about a pressure in an environment of the thermal gas sensor 100 as input variables for a drift correction when determining the information 240 about the gas concentration and / or the thermal conductivity in order to obtain the information about the gas concentration and / or the thermal conductivity as a result of the drift correction. Thus, for example, the drift correction can be applied to the combination signal depending on the information about the temperature and the pressure in order to obtain the information 240 about the gas concentration and / or the thermal conductivity.For example, the drift correction may not receive any further variables besides the three aforementioned input variables (the combination signal, the temperature information, and the pressure information), but may instead use only previously obtained constants, for example, determined during calibration. The constants may be specific to the thermal gas sensor 100 used. Thus, the evaluation arrangement 200 may be designed to account for small differences between thermal gas sensors 100 in the calculation of the information 240 about the gas concentration and / or thermal conductivity in order to obtain a very accurate result (information 240). The drift correction may, for example, correct a temperature drift and / or a pressure drift.

[0106] Fig. 1cshows a schematic representation of an evaluation arrangement 200 according to the invention for a thermal gas sensor 100 with at least one heater 120 and two detectors (a first detector 130 and a second detector 140). The first detector 130 can have a first distance 180 1 from the heater 120, and the second detector 140 can have a second distance 180 2 from the heater 120. According to Fig. 1cThe first detector 130 and the second detector 140 have the same distance 180 1 , 180 2 from the heater 120. However, it is also possible for the first distance 180 1 to differ from the second distance 180 2 . For example, the first detector 130 can be arranged at a different distance from the heater 120 than the second detector 140. The evaluation arrangement 200 according to the invention is designed to regulate a heating power with which the heater 120 can be acted upon, depending on at least one sensor signal (e.g. a first sensor signal 210 and / or a second sensor signal 220) from at least one of the detectors (e.g. the first detector 130 and / or the second detector 140) (for example with a control unit 250 for controlling a heating power), in order to bring the at least one sensor signal 210, 220 into a predetermined value range.

[0107] In order to analyze or further process the at least one sensor signal 210, 220 by the evaluation arrangement, for example, it is advantageous if the at least one sensor signal 210, 220 is brought into the predetermined value range by the evaluation arrangement 200. If the heating power is increased, for example, an amplitude or a frequency of the at least one sensor signal 210, 220 can also be increased. This can be done, for example, by the evaluation arrangement 200 if the at least one sensor signal 210, 220 is too small and the predetermined value range is very large. Thus, after the heating power has been regulated by the control unit 250, the new sensor signal 210, 220 can fill the predetermined value range or lie within it. The predetermined value range can, for example, depend on the components used in the evaluation arrangement 200, such as an analog-to-digital converter (ADC).For example, the ADC can further process the at least one sensor signal 210, 220 very well if the at least one sensor signal 210, 220 is adapted in the predetermined value range adapted to the ADC (e.g. ADC working range).

[0108] The evaluation arrangement 200 can also be designed to regulate the heating power of the heater 120 with the control unit 250 such that the heating power of the heater 120 is reduced. As a result, the at least one sensor signal 210, 220 can also be reduced. This can be advantageous, for example, if the at least one sensor signal 210, 220 exceeds the predetermined value range, i.e., is too large. The fact that the evaluation arrangement 200 is designed to regulate the heating power of the heater 120 with the control unit 250 makes it possible for no or very little information from the at least one sensor signal 210, 220 to be lost during further processing of the at least one sensor signal 210, 220, for example, by components of the evaluation arrangement 200, such as the ADC.

[0109] According to one embodiment, the control unit 250 of the evaluation arrangement 200 can transmit a control signal 252 to the heater 120 for controlling the heating power of the heater 120. In addition, the control unit 250 can provide information 122 about the controlled heating power of the heater 120 to the evaluation arrangement 200.

[0110] The evaluation arrangement 200 according to the invention is designed to take into account information 122 about the heating power when deriving information 240 about a gas concentration and / or a thermal conductivity from the at least one sensor signal 210, 220. This makes it possible for the control unit 250 to bring the sensor signal 210, 220 into the predetermined value range and additionally to take into account the information 122 about the heating power in the analysis, since the at least one sensor signal 210, 220 is dependent on the heating power. In addition, this evaluation arrangement 200 makes it possible for one sensor signal, e.g., the first sensor signal 210 or the second sensor signal 220, to be sufficient to derive the information 240 about the gas concentration and / or the thermal conductivity of a gas or fluid (e.g., a gas or gas mixture) with a certain degree of accuracy.If both the first sensor signal 210 and the second sensor signal 220 and the heating power 122 are used to derive the information 240, the determination of the information 240 is overdetermined, whereby the information 240 can be determined very precisely by the evaluation arrangement 200. If the first distance 180 1 of the first detector 130 differs from the second distance 180 2 of the second detector 140 from the heater 120, the information 240 about the gas concentration and / or the thermal conductivity of a gas can, for example, also be derived only from the first sensor signal 210 and the second sensor signal 220, without the information 122 about the heating power of the heater 120.

[0111] According to one embodiment, the evaluation arrangement 200 can also receive the information 122 about the heating power from the thermal gas sensor 100 instead of from the control unit 250.

[0112] According to one embodiment, the evaluation arrangement 200 can be designed to apply a periodic signal (e.g., the control signal 252) to the heater 120. The periodic signal can be, for example, a periodic square-wave signal or sinusoidal signal. If the control signal 252, and thus the heat emitted by the heater 120 to the gas to be analyzed, is a periodic signal, the first sensor signal 210 detected by the first detector 130 and the second sensor signal 220 detected by the second detector 140 can also be periodic. However, due to the first distance 180 1 and the second distance 180 2 , the first sensor signal 210 and / or the second sensor signal 220 can differ in phase from the periodic signal of the heater 120 and also in amplitude from the periodic signal of the heater 120.These differences can, for example, be used by the evaluation arrangement 200 to determine the information 240 about the gas concentration and / or the thermal conductivity very precisely.

[0113] According to one embodiment, the evaluation arrangement 200 can be configured to switch the heating power applied to the heater 120 (for example, via the control signal 252) between two values. Thus, for example, a periodic square-wave signal can be applied to the heater 120. Thus, the heater 120 can, for example, alternately transmit a first heating power and a second heating power to the gas to be analyzed.

[0114] According to one embodiment, the evaluation arrangement 200 can be designed to regulate an amplitude of the heating power (for example, with the control unit 250) such that both a minimum value of the at least one sensor signal 210, 220 and a maximum value of the at least one sensor signal 210, 220 lie within the predetermined value range. If the amplitude of the heating power of the heater 120 is increased, for example, by the control signal 252, the minimum value of the at least one sensor signal 210, 220 can be reduced and the maximum value of the at least one sensor signal 210, 220 can be increased, for example. If the amplitude of the heating power is reduced, for example, by the control signal 252, the minimum value of the at least one sensor signal 210, 220 can be increased and the maximum value of the at least one sensor signal 210, 220 can be reduced.

[0115] According to one embodiment, the predetermined value range can be dependent on a value range of a component, such as an ADC, of ​​the evaluation arrangement 200. Thus, for example, the predetermined value range can be determined depending on a component value range (for example, a component of the evaluation arrangement 200). For example, the predetermined value range can specify that the minimum value of the at least one sensor signal 210, 220 should be in a range from 0% to 30%, 1% to 25%, or 2% to 20% of the component value range, and that the maximum value of the at least one sensor signal 210, 220 should be in a range from 70% to 100%, 75% to 99%, or 80% to 98% of the component value range. Thus, the predetermined value range can, for example, have a lower value range in which the minimum value should lie and an upper value range in which the maximum value should lie.

[0116] According to one embodiment, the evaluation arrangement 200 can be designed to adjust or regulate an amplitude of the heating power (for example, with the control unit 250) such that an amplitude of the at least one sensor signal 210, 220 lies within a predetermined amplitude range. If the at least one sensor signal 210, 220 comprises, for example, a periodic sinusoidal signal, the amplitude should lie within the predetermined amplitude range at any time of the sensor signal. The amplitude of the at least one sensor signal should utilize the entire predetermined amplitude range. The predetermined amplitude range can, for example, comprise / be divided into an upper, middle, and lower amplitude range.To ensure that the specified amplitude range is utilized by the amplitude of the at least one sensor signal, a maximum amplitude of the at least one sensor signal should, for example, lie in the upper range and a minimum amplitude should lie in the lower range. The specified amplitude range can, for example, depend on the component range. For example, the specified amplitude range can be determined such that the amplitude of the at least one sensor signal utilizes at least 50%, at least 65%, or at least 75% of a component value range of, for example, an analog-to-digital converter.

[0117] According to one embodiment, the evaluation arrangement 200 can be designed to set or adjust sampling times at which a sensor signal 210, 220 can be sampled. The sensor signal 210, 220 can optionally be preprocessed, for example, by the evaluation arrangement 200 or the thermal gas sensor 100 and / or subjected to a DC offset. According to one embodiment, it can be advantageous if the sensor signal 210, 220 is sampled at a time of maximum amplitude and at a time of minimum amplitude. These two sampling times can, for example, be set or adjusted by the evaluation arrangement 200 if the evaluation arrangement 200 determines that the sampling times have been incorrectly selected.By precisely adjusting the sampling times, it is possible for the evaluation arrangement to very easily determine, for example, a phase difference or amplitude difference between the first sensor signal 210 and a heater signal (e.g., emitted by the heater 120 and controlled by the control signal 252) or between the second sensor signal 220 and the heater signal. Using the very precise phase difference and / or amplitude differences, the evaluation arrangement 200 can very precisely determine or derive the information 240 about the gas concentration and / or thermal conductivity of the gas to be analyzed.

[0118] According to one embodiment, the evaluation arrangement 200 can be configured to adjust the sampling times such that sampling occurs, for example, with a phase difference of a maximum of + / - 2°, at a time at which the sensor signal 210, 220 reaches a maximum value, and such that sampling occurs, for example, with a phase difference of a maximum of + / - 2°, at a time at which the sensor signal 210, 220 reaches a minimum value. The maximum value can, for example, define a maximum amplitude of the sensor signal 210, 220, and the minimum value can define a minimum amplitude of the sensor signal 210, 220, as already explained above.

[0119] According to one embodiment, the evaluation device 200 can be designed to combine a sensor signal 210, 220 from at least one of the detectors 130, 140 with an offset signal generated by a digital-to-analog converter to obtain an input signal for the analog-to-digital converter. The evaluation device 200 can be designed to adjust the offset signal to ensure that the input signal of the analog-to-digital converter remains within a predetermined range throughout an entire period of the sensor signal 210, 220. Thus, the offset signal can be designed, for example, to adapt the sensor signal 210, 220 such that the input signal is generated that lies within a component value range of the analog-to-digital converter. Thus, the offset signal can be adjusted / adjusted, for example, to be able to react to different sensor signals 210, 220 from different gases to be analyzed.For example, the offset signal can be configured to reduce a sensor signal 210, 220 that is too large so that the resulting input signal lies within the specified range. Furthermore, the offset signal can be configured to increase the sensor signal 210, 220 if the sensor signal 210, 220 is too small so that an input signal is created that lies within the specified range.

[0120] Thus, the evaluation arrangement 200 can be designed, on the one hand, to bring the amplitude of the sensor signal 210, 220 into the predetermined value range by regulating the heating power and, by combining the sensor signal 210, 220 with the offset signal, to change an offset of the sensor signal 210, 220 such that the sensor signal 210, 220 lies within the predetermined value range. This enables the sensor signal 210, 220 to be analyzed very precisely, and thus very precise information 240 about the gas concentration and / or thermal conductivity of the gas to be analyzed can be determined by the evaluation arrangement 200.

[0121] According to one embodiment, the evaluation device 200 can be configured to regulate the heating power only when a setting or adjustment of the sampling times is in a steady state and when an adjustment of the offset signal is in a steady state. A steady state can be understood to mean that the sampling times have been determined by the evaluation device 200 such that the sensor signal 210, 220 can be sampled at predefined events (such as a maximum amplitude (maximum value), a zero crossing, or a minimum amplitude (minimum value)).Likewise, the steady state can mean that the offset signal has been adjusted in such a way that the sensor signal 210, 220, when the offset signal is combined with the sensor signal 210, 220, generates an input signal that lies within the predetermined range, in order to thus analyze the sensor signal 210, 220 very precisely, with no or only minimal loss of information, by means of the evaluation arrangement. Thus, for example, presets (such as the sampling times in the steady state or the offset signal in the steady state) can be determined by the evaluation device 200, so that when the heating power is regulated by the control unit 250, the new sensor signal 210, 220 can be analyzed very precisely with the presets and, under certain circumstances, no new regulation of the sampling times orof the offset signal is no longer necessary to derive the information 240 about the gas concentration and / or the thermal conductivity from the sensor signal 210, 220.

[0122] According to one embodiment, the evaluation arrangement 200 can be configured to pause the control of the heating power (for example, by the control unit 250) while the sampling times are being adjusted or adjusted and / or while the offset signal is being adjusted. This can ensure, for example, that no changes are made to the sensor signal 210, 220 while the sampling times and the offset signal are not yet in a steady state. This can ensure that the sensor signal 210, 220 can be analyzed very precisely, since the sampling times and the offset signal can be determined very precisely with very little or no susceptibility to error.

[0123] According to one embodiment, the evaluation arrangement 200 can be configured to regulate both an average heating power or a maximum heating power as well as an amplitude of the heating power. Thus, the control unit 250 can transmit, for example, as a control signal 252, a new heater signal for the heater 120 to the thermal gas sensor 100, wherein the control signal has, for example, a changed average heating power, maximum heating power, or amplitude of the heating power. However, it is also possible for the control signal 152 to include information indicating how the average heating power, the maximum heating power, or the amplitude of the heating power should be changed by the thermal gas sensor for the heater 120.

[0124] Fig. 1dshows a schematic representation of an evaluation arrangement 200 for a thermal gas sensor 100 with at least one heater 120 and two detectors (e.g. a first detector 130 and a second detector 140) arranged at different distances (e.g. a first distance 180 1 and a second distance 180 2 ) from the heater 120. The first detector 130 can, for example, have the first distance 180 from the heater 120 and the second detector 140 can have the second distance 180 2 from the heater 120. The evaluation arrangement 200 can be designed to apply a periodic signal 260 with a predetermined period to the heater 120. The periodic signal can be, for example, a square-wave signal, a pulse signal with known power, or a sine-wave signal. Optionally, it can also be a sine-wave signal with harmonics or a triangular signal.The periodic signal can also be referred to as a heater signal and can be transferred from the heater 120 in the form of heat via a gas to be analyzed to the first detector 130 and / or to the second detector 140. The transferred heat can be detected by the first detector 130 as a first sensor signal 210 and by the second detector 140 as a second sensor signal 220. The first sensor signal 210 and the second sensor signal 220 can have a first periodic signal and a second periodic signal, respectively, each with the predetermined period duration. This enables the gas to be analyzed to be analyzed very precisely with regard to its gas concentration and / or thermal conductivity by the thermal gas sensor 100 or the evaluation arrangement 200. The evaluation arrangement 200 can be designed to receive at least one sensor signal (e.g.the first sensor signal 210 and / or the second sensor signal 220) from one of the detectors 130, 140 at three points in time (for example, by a sampling device 270). A second sampling time can, for example, be offset in time by 90° relative to a first sampling time, based on the period duration (for example, by + / - 2°). Thus, for example, the second sampling time can be offset in time by 1 / 4 of a period duration, 5 / 4 of a period duration, or 9 / 4 of a period duration from the first sampling time. A third sampling time can be offset in time by 180° relative to the first sampling time or by 90° relative to the second sampling time, based on the period duration. The first sampling time, the second sampling time, and the third sampling time can have a tolerance of + / - 2%.The third sampling time can therefore be offset in time by, for example, 1 / 2 a period, 3 / 2 a period, or 5 / 2 a period compared to the first sampling time. Thus, the sensor signal 210, 220 can be sampled at precisely defined locations, whereby information 240 about a gas concentration and / or a thermal conductivity can be determined very precisely from the sensor signal 210, 220. The evaluation arrangement 200 can be designed to detect, based on three samples based on a sample of the sensor signal at the first sampling time, at the second sampling time, and at the third sampling time (for example, performed by the sampling device 270), whether a first sample and a third sample represent a maximum value and a minimum value of the sensor signal 210, 220. This can be done, for example, by the checking device 280.The checking device 280 can, for example, ignore a DC offset and thus check, except for a DC offset, whether the first sample value represents, for example, a maximum value and the third sample value represents, for example, a minimum value of the sensor signal 210, 220. The second sampling time can thus, for example, be a "zero crossing" of the sensor signal 210, 220 and be taken into account by the checking device 280.

[0125] The first sampling time, the second sampling time, and / or the third sampling time, as well as the first sensor signal 210 and the second sensor signal 220, can be used to determine the information 240 about the gas concentration and / or the thermal conductivity of a gas detected by the thermal gas sensor 100. Optionally, the heater signal 122 can also be included in the determination of the information 240. Thus, for example, a phase difference between the first sensor signal 210 and the second sensor signal 220, as well as an amplitude difference between the first sensor signal 210 and the second sensor signal 220, can be determined, for example, based on the sampling times / sampling values. Optionally, a phase difference and / or an amplitude difference between the first sensor signal 210 and the heater signal 122, or between the second sensor signal 220 and the heater signal 122, can also be determined.From the phase differences and amplitude differences thus determined, the information 240 about the gas concentration and / or thermal diffusivity can be determined.

[0126] According to one embodiment, the evaluation arrangement 200 can be designed to change the sampling times depending on a detection of whether the first sample value and the third sample value represent a maximum value and / or a minimum value of the sensor signal 210, 220. This can be done, for example, by means of a sampling control device 290. Thus, for example, new sampling times can be determined if the first sample value and the third sample value do not correspond to a maximum value and / or a minimum value of the sensor signal 210, 220. By controlling the sampling times, it can be ensured that the sampling values ​​correspond to predetermined values. If the checking device 280 determines, for example, that deviations outside a tolerance occur (for example, + / - 2°), the sampling times can be changed / adjusted by the sampling control device 290.

[0127] According to one embodiment, the evaluation arrangement 200 can be configured to adjust or regulate the sampling times such that the first sample represents a first extreme value of the sensor signal 210, 220, for example, a maximum value or minimum value, and the third sample represents a second extreme value, for example, the minimum value or the maximum value of the sensor signal 210, 220. The second sample can, for example, represent an average value or DC component of the sensor signal 210, 220, such as a "zero crossing."

[0128] According to one embodiment, the evaluation arrangement 200 can be designed to take into account information about a time at which the sensor signal 210, 220 passes through a predetermined threshold value when setting or adjusting the sampling times. This time can be, for example, the second time, which can represent, for example, a DC component or an average value of the sensor signal 210, 220. For example, the checking device 280 can use the second sampling time to check the first sampling time and / or the second sampling time.Thus, if the checking device 280 determines, based on the second sampling time, that the first sample does not correspond to a maximum or minimum value of the sensor signal 210, 220 and / or the third sample does not correspond to the minimum or maximum value of the sensor signal 210, 220, the sampling control device 290 can readjust or adjust the sampling times. The predetermined threshold value can, for example, define a "zero crossing" (e.g., up to a DC offset).

[0129] According to one embodiment, the evaluation arrangement 200 can be designed to check whether a second sample value at the second sampling time is equal to an average value of the sample value at the first sampling time and the third sample value at the third sampling time, and to detect, depending on the check, whether the first sample value and the third sample value represent a maximum value and a minimum value of the sensor signal. The second sample value should, for example, be equal to a mean value of the sample value and the second sample value with a tolerance of at most ±1% of a difference between the first sample value and the third sample value. If this is not the case, the checking device 280 can detect that the sampling times have been incorrectly selected.Since the first sample represents a first extreme value and the third sample represents a second extreme value of the sensor signal 210, 220, offset by 180° relative to the period, the second sample can be exactly halfway between the first sampling time and the second sampling time. Thus, the second sample can correspond to the mean of the other two samples. This can thus represent an efficient and accurate method for verifying the samples using the verification device 280.

[0130] According to one embodiment, the evaluation arrangement 200 can be designed to apply a periodic square-wave signal 260 with a duty cycle of preferably 50% to the heater 120. However, it is also possible for the periodic square-wave signal to have a duty cycle in the range of 5% to 50%, 8% to 48%, or 10% to 45%. The periodic square-wave signal 260 applied to the heater 120 can have a tolerance of + / - 2%. According to one embodiment, the duty cycle for a periodic sequence of pulses indicates a ratio of a pulse duration to a period duration.

[0131] According to one embodiment, the evaluation arrangement 200 can be configured to combine a sensor signal 210, 220 with an offset signal generated by a digital-to-analog converter to obtain an input signal for an analog-to-digital converter. The analog-to-digital converter can, for example, digitize the signal values ​​present at the sampling times (e.g., the first sample value, the second sample value, and / or the third sample value) and thus sample the sensor signal 210, 220. The sampling device 270 can, for example, comprise the analog-to-digital converter.

[0132] According to one embodiment, the evaluation arrangement 200 can be designed to adjust the offset signal to ensure that the input signal of the analog-to-digital converter remains within a predetermined range throughout an entire period of the sensor signal 210, 220. For example, the offset signal can change an offset of the sensor signal 210, 220 such that an input signal is created that lies within a working range (e.g., the predetermined range) of the analog-to-digital converter, so that no information from the sensor signal 210, 220 is lost during digitization or so that information loss is reduced. For example, the sampling device 270 can check whether an input value of the analog-to-digital converter exceeds a predetermined upper threshold value, for example, of the predetermined range, or falls below a predetermined lower threshold value, for example, of the predetermined range.Accordingly, the sampling device 270 can generate the offset signal, which can be combined with the sensor signal 210, 220 so that the input value, for example, a value of the input signal, remains within the specified range. The evaluation arrangement 200 can be designed to adjust the sampling times after adjusting the offset signal and, after changing the sampling times, to perform a further check to determine whether the sample values ​​obtained with the changed setting of the sampling times still lie within the specified range. Thus, for example, the offset signal can first be generated for the sensor signal 210, 220 using the evaluation arrangement 200, and then sampling times can be determined, checked, and, if necessary, adjusted using the sampling device 270 (this can, for example, represent a tracking of the sampling times).This tracking can result in new sample values, which can result in a renewed adjustment of the offset signal by the evaluation arrangement 200. Thus, for example, the offset signal and the sampling times can always be adjusted or tracked alternately until, for example, the analog-to-digital converter can further process the sensor signal 210, 220. Thus, at this point in time, the offset signal and the sampling times can be in a steady state.

[0133] The sampling time settings changed by the sampling control device 290 generate, for example, new sampling values ​​that can be considered input values ​​of the analog-to-digital converter. To ensure that the input signal of the analog-to-digital converter remains within the specified range, both the offset signal and the heating power of the heater 120 can be adjusted. The offset signal can, for example, adjust an offset of the sensor signal 210, 220, and the change in the heating power can adjust an amplitude of the sensor signal 210, 220, resulting in an input signal that lies within the specified range.

[0134] According to one embodiment, the evaluation arrangement 200 can be configured to regulate a heating power applied to the heater 120 depending on at least one sensor signal 210, 220 from at least one of the detectors 130, 140 in order to bring the at least one sensor signal 210, 220 into a predetermined value range. The evaluation arrangement 200 can be configured to take into account information about the heating power (e.g., the heater signal 122) when deriving information 240 about a gas concentration and / or thermal conductivity from the sensor signals 210, 220. For example, if the heating power of the heater 120 is increased, the sensor signal 210, 220 can experience an increase in an amplitude of the sensor signal 210, 220, or if the heating power is reduced, the at least one sensor signal 210, 220 can experience a reduction in an amplitude of the sensor signal 210, 220.Thus, for example, the sensor signal 210, 220 can be brought into the predetermined value range by regulating the heating power of the heater 120.

[0135] In the following, embodiments of the thermal gas sensor and the evaluation arrangement are described with reference to further figures. 1.1 Technology variants for a thermal gas sensor

[0136] Fig. 2a and Fig. 2beach show a schematic representation of a gas sensor 100 for measuring physical gas properties. The thermal gas sensor 100 can have a thin-film membrane 110 and a heating element 120, which can be arranged, for example, as a self-supporting bridge structure on the membrane 110 between a first interruption region 160 of the membrane 110 and a second interruption region 170 of the membrane 110. In this case, a thickness of the thin-film membrane 110 (it consists, for example, of several base, sensor, and passivation layers) in the case of a wire sensor (an example of the temperature sensor structures 130, 140; see Fig. 2 and Fig. 3 ) e.g. between 1-10µm. The heating element 120 can also be referred to as a heater. According to Fig. 2a and Fig. 2bThe entire first interruption region 160 can have an interruption 162 in the membrane 110, and the entire second interruption region 170 can have an interruption 172 in the membrane. Thus, the heating element 120 can be arranged in a cantilevered manner between the first interruption 162 and the second interruption 172. The first interruption 162 can be delimited by the heating element 120 and a first temperature sensor structure 130, in the form of a cantilevered bridge structure. The second interruption 172 can be delimited by the heating element 120 and a second temperature sensor structure 140, for example in the form of a cantilevered bridge structure. The first temperature sensor structure 130 and / or the second temperature sensor structure can be a wire sensor, thermopiles, temperature-variable resistors, or thermistors.

[0137] Optionally, the gas sensor 100 may include a first external break 192 and a second external break 194. Thus, for example, the first thermocouple structure 130 may be a cantilevered bridge structure between the first break 160 and the second external break 194, and the second thermocouple structure 140 may be a cantilevered bridge structure between the second break 172 and the first external break 192. The first thermocouple structure 130 may also be referred to as a first detector or first sensor, and the second thermocouple structure 140 may also be referred to as a second sensor or second detector.

[0138] Above Fig. 2aA cross-section of the gas sensor 100 can be seen. The gas sensor 100 comprises, for example, a frame 150 made of carrier material. The frame 150 made of carrier material can, for example, span the membrane 110. According to one embodiment, the membrane 110 can have a thickness 111 (for example, an extension perpendicular to a surface of the membrane 110 on which the first thermocouple structure 130, the second thermocouple structure 140, and the heating element 120 are arranged) in a range from 1 µm to 50 µm, 2 µm to 25 µm, or 3 µm to 10 µm, such as 8 µm. According to one embodiment, the membrane 110 can be realized by a recess 190 in the frame 150. For example, the recess 190 can be selected so that a membrane 110 with the desired thickness 111 can be realized.

[0139] According to the embodiment in Fig. 2a and 2bFor example, the recess 190 can be designed such that only the heating element 120, the first thermocouple structure 130, and the second thermocouple structure 140 remain spanned between the frame 150. According to one embodiment, a surface of the membrane 110 on which the first thermocouple structure 130, the second thermocouple structure 140, and the heating element 120 are arranged can have an extension in a range from 200x200 µm 2< to 5x5 mm 2<, 500x500 µm 2< to 2000x2000 µm 2<, or 800x800 µm 2< to 1200x1200 µm 2<, wherein the extension can be square or rectangular. The gas sensor 100 may have a thickness 101 (for example, parallel to the thickness 111 of the membrane 110) in a range from 500 nm to 5 mm, 1 µm to 1 mm, or from 200 µm to 600 µm, such as 400 µm.An extension of the gas sensor 100, parallel to the surface of the membrane 110 on which the heating element 120 is arranged, can be in a range from 1x1 mm 2< to 1x1 cm 2< , 1.5x1.5 mm 2< to 9x9 mm 2< or from 2x2 mm 2< to 8x8 mm 2< , such as 6.5x2.5 mm 2< .

[0140] According to one embodiment, the first thermocouple structure 130, the second thermocouple structure 140 and / or the heating element 120 may be part of the membrane 110.

[0141] To measure heat transfer dependent on the gas type or gas mixture, a microchip (example of the thermal gas sensor 100) with three filigree bridge structures (e.g., the heating element 120, the first thermocouple structure 130, and the second thermocouple structure 140) can be used, which can be self-supporting between a frame and surrounded by the gas to be analyzed as microwires. The gas to be analyzed can, for example, be arranged in the first interruption 162, the second interruption 172, the first outer interruption 192, and / or the second outer interruption 194. A central bridge structure can be designed as the heater 120, and two detector structures (e.g., the first thermocouple structure 130 and the second thermocouple structure 140) located on either side at different distances from the heater 120 can be used as temperature sensors for measuring a transfer response from the gas mixture.

[0142] The middle wire (the heating element 120) is subjected to a periodic heating signal, for example, whereby heat is radiated from the heating element. Heat transfer can occur via unknown heat transfers from the heater 120 into the gas to be analyzed and from the gas into the sensor wire (e.g., into the first thermocouple structure 130 and / or the second thermocouple structure 140). The heat transfer thus detected by the first thermocouple structure 130 and / or the second thermocouple structure 140 can be understood as a transfer response or as a sensor signal (e.g., a first sensor signal detected by the first thermocouple structure 130 and a second sensor signal detected by the second thermocouple structure 140). By measuring a temperature response (e.g., the transfer response) with, for example, two identical sensors (e.g.,By placing the first thermocouple structure 130 and / or the second thermocouple structure 140 at different distances from the heater 120, the unknown heat transfers in the measuring arrangement can be eliminated. The phase and amplitude of the two sensor signals can essentially depend on the heat transfer through the gas. 1.1.1 The gas sensor 100, for example, as a MEMS wire sensor (evaluation of a TCR (temperature coefficient of a resistance) on detector resistors (e.g., a resistor of the first thermocouple structure 130 and / or the second thermocouple structure 140)) (Alternative embodiment, optionally usable in combination with the signal generation and evaluation according to Section 1.2 and the evaluation algorithm according to Section 1.3)

[0143] A first variant of the thermal gas sensor 100 can be constructed on the basis of a silicon-on-insulator (SOI) wafer substrate. It consists, for example, of a microchip with self-supporting, filigree bridge structures made of silicon microwires (e.g., the first temperature sensor structure 130 and the second temperature sensor structure 140) that are spanned in the gas space to be analyzed. A central wire can be designed as a heater 120, and two detector wires (e.g., the first temperature sensor structure 130 and the second temperature sensor structure 140) can serve as temperature sensors on either side of the heater at different distances from it (see Fig. 2a , Fig. 2b ).

[0144] Fig. 2a shows, for example, a photo of the MEMS wire sensor chip (the gas sensor 100) on a light microscope (left) and Fig. 2b For example, shows a close-up of structures in a scanning electron microscope (right).

[0145] Fig. 3 shows a schematic representation of a silicon bridge 120 / 130 / 140, which can be used, for example, for a heating element, a first thermocouple structure and / or a second thermocouple structure of a gas sensor. In other words, Fig. 3A detail of a micro-bridge (SEM, scanning electron microscope) of a thermal MEMS wire sensor (e.g., a gas sensor). The illustrated silicon bridge 120 / 130 / 140 can be manufactured, for example, using SOI technology. For example, a substrate or carrier material of a frame 150 can comprise oxide material 152, silicon material 154, and aluminum material 156. To create the silicon bridge, silicon material 154 can be at least partially removed, for example, to create incisions 158 (e.g., trenches) in the carrier material of the frame 150 and thereby create the silicon bridge 120 / 130 / 140. The silicon bridge 120 / 130 / 140 can be arranged on the membrane 110 (e.g., consisting of oxide material 152).

[0146] The membrane 110 can, for example, have a first interruption region 160 / 162 and a second interruption region 170 / 172. Both the first interruption region 160 / 162 and the second interruption region 170 / 172 have, for example, an interruption, which can be, for example, a cavity. Thus, the membrane 110 can have a first interruption 162 and a second interruption 172, in which the gas to be analyzed can be arranged and, for example, receives heat from the silicon bridge 120 / 130 / 140 if the silicon bridge represents a heating element 120 or can transfer heat to the silicon bridge 120 / 130 / 140 if the silicon bridge 120 / 130 / 140 represents the first thermocouple structure 130 and / or the second thermocouple structure 140. The silicon bridge 120 / 130 / 140 can be contacted by the aluminum material 156, whereby the aluminum material 156 can serve, for example, as a bond pad.For example, the bond pad can be used to apply an exciting heater signal to the heating element 120 or to read the first thermocouple structure 130 and / or the second thermocouple structure 140 (for example, a first or second sensor signal). Advantages of SOI technology:

[0147] crystalline resistance tracks, the temperature coefficient of resistance (TKR) for the detectors (e.g. for the first thermocouple structure 130 and the second thermocouple structure 140) can depend solely on the basic doping of the wafer material (in the active layer) similarly high TKR as with platinum with high basic resistance of the resistors of the temperature detectors (e.g. the first thermocouple structure 130 and the second thermocouple structure 140) enables miniaturized sensor dimensions (e.g. dimensions of the first thermocouple structure 130 and the second thermocouple structure 140) due to short (e.g. from one frame side of the frame 150 to an opposite frame side of the frame 150) resistance tracks of the bridge structures 120, 130, 140 (less than 1 mm) as well as for the area of ​​the resistance temperature detectors (RTD) (e.g.the first thermocouple structure 130 and the second thermocouple structure 140) comparably low temperature measurement errors due to self-heating, since, for example, basic resistance values ​​greater than 8 kOhm can be used, which can require less than 360 µW of power consumption during measurement. Heater resistor (e.g. of heater 120) can be adapted to a low operating voltage by implantation (preferably 3.3V) very homogeneous distribution of the ohmic sensor resistors, e.g. the resistance of the first thermocouple structure 130 and / or the second thermocouple structure 140, over the wafer (e.g. the frame 150) in a narrow process field, in particular the tolerances of the detector resistors (e.g. sensor resistors) are, for example, B. by tolerances of the SOI material in an active layer (active layer, basic doping and material thickness) as well as by the lateral structural accuracy of the dry etching (Deep-RIE). Disadvantages of SOI technology:

[0148] Comparably expensive SOl substrate material when purchasing wafers Availability usually not in stock in the desired specifications (wafer diameter, material thickness of handle and active layer, doping of the active layer) Currently no passivation of the structures, passivation may lead to bimetallic effects due to the different material expansion of the layers upon heat input, change in the characteristic curve of the TKR 1.1.2 The gas sensor 100, for example, as a MEMS thermopile sensor on a thin-film membrane (embodiment according to aspect 1, optionally usable in combination with the signal generation and evaluation according to section 1.2 and the evaluation algorithm according to section 1.3)

[0149] Fig. 4 shows a schematic representation of a gas sensor 100 on the left side and a detailed view of the gas sensor 100 on the right side.

[0150] According to one embodiment, the gas sensor 100 may include a membrane 110 and a heating element 120 that may be disposed on the membrane 110 between a first discontinuity region 160 of the membrane 110 and a second discontinuity region 170 of the membrane 110. The first discontinuity region 160 may include a discontinuity 162, and the second discontinuity region 170 may include a discontinuity 172.

[0151] The first interruption 162 and / or the second interruption 172 may have a longitudinal extension parallel to a direction of maximum extension of the heating element 120 (which may be referred to as a heater, for example) and a transverse extension, for example in a direction perpendicular to a direction of maximum extension of the heating element 120. According to Fig. 4Thus, the first interruption 162 can have a greater transverse extent than the second interruption 172. Furthermore, the first interruption 162 and the second interruption 172 can be arranged according to Fig. 4have the same longitudinal extent. The first interruption 162 and the second interruption 172, for example, have a longitudinal extent that is large enough that the first interruption 162 and the second interruption 172 completely cover the area between the first thermocouple structure 130 and the second thermocouple structure 140, respectively, and the heating element 120. For example, the longitudinal extent of both the first interruption 162 and the second interruption 172 is along the entire length of the heating element 120. This prevents a large portion of the heat radiated by the heating element 120 from being transported via the membrane 110. Thus, it is possible to ensure that a large portion of the heat is transferred to the respective thermocouple structure 130, 140 via the gas arranged in the first interruption 162 and the second interruption 172.

[0152] The first thermocouple structure 130 may, for example, have a different distance from the heating element 120 than the second thermocouple structure 140. Thus, according to Fig. 4For example, the first thermocouple structure 130 is at a greater distance from the heating element 120 than the second thermocouple structure 140. The first thermocouple structure 130 can, for example, detect a first heat transfer 210 from the heating element 120 to the gas in the first interruption 162 and from the gas to the first thermocouple structure 130 and record it as a first sensor signal. The second thermocouple structure 140 can, for example, detect a second heat transfer 220 from the heating element 120 to the gas in the second interruption 172 and from the gas to the second thermocouple structure 140 and provide it as a second sensor signal. Due to the different distances between the first thermocouple structure 130 and the second thermocouple structure 140 and the heating element 120, a difference signal can be formed from the first sensor signal and the second sensor signal, whereby unknown transitions (such asB a transition from the heating element to the gas or from the gas to the respective thermocouple structure) can be calculated out and thus, for example, mainly or only the heat transfer via the gas in the first interruption 162 or the second interruption 172 by the gas sensor 100 is considered.

[0153] According to one embodiment, the gas sensor 100 may further comprise a frame 150 that can span the membrane 110. The first thermocouple structure 130 and the second thermocouple structure 140 may be arranged at least partially on the membrane 110 and at least partially on the frame 150. The first thermocouple structure 130 and the second thermocouple structure 140 may have hot ends 132, 142 arranged facing the heating element 120. In addition, the first thermocouple structure 130 and the second thermocouple structure 140 may have cold ends 134, 144, which may be arranged on a side of the first thermocouple structure 130 or the second thermocouple structure 140 opposite the side with the hot ends 132, 142 and are thus arranged facing away from the heating element 120. For example, the hot ends 132, 142 may be arranged on the membrane 110 and the cold ends 134, 144 may be arranged on the frame 150.For example, the frame 150 may comprise a different material than the membrane 110. This allows, for example, the cold ends 134, 144 to be subjected to a reference temperature through the frame material of the frame 150, relative to a temperature measured by the hot ends 130, 142, transmitted by the heating element 120.

[0154] In other words, the left side of the gas sensor 100 can be a layout and the right side of the Fig. 4 a photo of the gas sensor 100 (e.g., a MEMS membrane sensor) for measuring, for example, a gas-type-dependent heat transfer (embodiment according to aspect 1). In Fig. 4For example, a variant of the gas sensor 100 with a constant interruption (e.g., a first interruption 162 and a second interruption 172) of a membrane 110 can be seen. The constant interruption 162, 172 causes, for example, that a major portion of heat transport between a heater 120 and the detectors (e.g., the first thermocouple structure 130 and the second thermocouple structure 140) necessarily occurs via the measurement gas volume enclosed between the two elements, for example, via the measurement gas arranged in the first interruption 162 and in the second interruption 172.

[0155] To reduce the process complexity in the technological production of, for example, the gas sensor 100 and to increase the sensitivity in measuring the gas-type-dependent heat transport 210, 220, a microchip based on a thin-film membrane 110 with heater 120 and thermopile structures 130, 140 (detectors) can be realized, in which the thin-film membrane 110 can be etched out in a lateral region between heater 120 and detectors 130, 140.

[0156] Compared to a wire sensor (as described in Section 1.1.1), the membrane sensor (e.g., gas sensor 100) requires only one-third of the heating energy while maintaining identical sensitivity to the gas concentration of a binary mixture. As with the wire sensor, the heater structure (e.g., heating element 120) is positioned centrally as a self-supporting, filigree bridge structure in a measuring chamber containing the gas to be detected. The two detector wires arranged on both sides of the heater 120 (for example) at different distances can be replaced by "thermopile" (thermocouple) structures (e.g., the first thermocouple structure 130 and / or the second thermocouple structure 140), which can lie on the laterally spanned membrane surfaces (of the membrane 110) and which can, for example, extend to the pit edge (e.g., an edge of the first interruption 162 or the second interruption 172).

[0157] For example, the cold ends 134, 144 of the thermopiles 130, 140 should directly contact the carrier material (e.g., the frame 150), which can have a high thermal conductivity (e.g., silicon approx. 150 W / (m*K)) and can serve as a heat sink (heat sink near room temperature). Between the cold ends 134, 144 of the thermopiles and the silicon, for example, lies the base membrane material (material of membrane 110), which electrically insulates the contacts from the silicon. However, since this layer is very thin, the heat from the thermopiles can be easily transferred to the silicon. Thus, the excess temperature (e.g., measured using the hot ends 132, 142) can be measured as a direct difference to the room temperature (e.g., measured using the cold ends 134, 144). For example, a measuring point for temperature compensation is mechanically connected directly to or with the silicon chip (e.g., the frame 150).

[0158] To reduce a parasitic effect of heat transport 210, 220 between heater 120 and detector structures 130, 140 due to heat conduction in the membrane material of membrane 110, membrane 110 can be consistently interrupted, so that heat transport 210, 220 from heater 120 to detectors 130, 140 can occur primarily over a shortest lateral distance and thus, for example, travels a distance across an intermediate volume of the measurement gas (e.g., arranged in the first interruption 162 and the second interruption 172). This can significantly increase the gas-type-dependent transmission response (e.g., the first sensor signal and the second sensor signal) of sensor 130, 140 to periodic heat pulses from heater 120.

[0159] According to one embodiment, Fig. 5on the left side a schematic representation of the gas sensor 100 and on the right side an enlarged detailed view of the gas sensor 100. The gas sensor 100 from Fig. 5 can provide the same features and functionalities as the gas sensor 100 from Fig. 4 wherein the gas sensor 100 consists of Fig. 5 from the gas sensor 100 to Fig. 4 in one embodiment of the first interruption region 160 or the second interruption region 170. For example, the first interruption region 160 of the gas sensor 100 can be Fig. 5 a plurality of interruptions 162 i and the second interruption region 170 may also have a plurality of interruptions 172 i. For example, the index i of the interruptions 162 i of the first interruption region 160 of the gas sensor 100 may range from 1 to 23, since the first interruption region 160 according to the embodiment in Fig. 5 23interruptions. The index i of the interruptions 172 i of the second interruption region 170 of the gas sensor 100 can, for example, range from 1 to 14, since the second interruption region 170 according to an embodiment of the Fig. 5 14 interruptions. Optionally, the index i of both the interruptions 162 i and the interruptions 172 i can define a natural number, where the index i specifies, for example, how many interruptions 162 i , 172 i are present in an interruption range 160, 170.

[0160] The interruptions 162i, 172i can be arranged in the first interruption region 160 and the second interruption region 170, respectively, in rows parallel to a direction of maximum extension of the heating element 120, and the rows can also be offset from one another. This means, for example, that transverse webs 112 formed by membrane material (extending, for example, in a direction perpendicular to a direction of maximum extension of the heating element 120, from the heating element 120 to the respective thermocouple structure 130, 140) of successive rows are offset from one another. This has the effect, for example, that a parasitic heat conduction 114a, 114b in the membrane 110 travels the longest possible path.

[0161] The interruptions 162 i , 172 i are arranged, for example, such that a lattice structure is created in the membrane 110, in which a path of a parasitic heat conduction 114a, 114b through the membrane 110 is longer than a direct path 210, 220. A direct path 210, 220 can, for example, be a straight path perpendicular to the heating element 120, from the heating element 120 to the respective thermocouple structure 130, 140, wherein the direct path 210, 220 can be passed through by a gas to be analyzed, arranged in the interruptions 162 i , 172 i . The path of the parasitic heat conduction 114a, 114b through the membrane 110 should, for example, not run in a straight line, but rather a winding path, as shown in Fig. 5, form. For example, there should be no direct heat path purely via the membrane 110. This allows the first thermocouple structure 130 and the second thermocouple structure 140 to detect heat transfer from the heating element 120 via the direct path 210 and 220, respectively, and minimizes the influence of parasitic heat conduction 114a, 114b during detection, allowing the gas to be analyzed very accurately.

[0162] The interruptions 162 i , 172 i can, for example, be elongated interruptions which can be located perpendicular to a main direction of heat conduction (for example the direct path 210, 220 from the heating element 120 to the thermocouple structures 130, 140) with a tolerance of + / - 20°.

[0163] According to one embodiment, the interruptions 162i, 172i can be rectangular cutouts with rounded corners. These can also be referred to as elongated holes, for example, and they can also be oval holes, for example. The interruptions 162i, 172i can be at least three times longer than they are wide. The length can be defined, for example, as a direction parallel to a maximum extent of the heating element 120 and the width as a direction perpendicular to the maximum extent of the heating element 120. This feature allows the path of the parasitic heat conduction 114a, 114b to be realized as very long, whereby the quality of the gas analysis by the gas sensor 100 can be increased.

[0164] According to one embodiment, the interruptions 162i, 172i in the first interruption region 160 and the second interruption region 170, respectively, can be arranged such that a distance 116a, 116b between the interruptions 162i, 172i corresponds to a smallest structural width that can be realized and results in a mechanically durable lattice structure. The distance 116a, 116b is, for example, a width of webs made of membrane material of the membrane 110. The smaller the distance 116a, 116b is realized, the lower the parasitic heat conduction 114a, 114b can be, whereby the quality of an analysis of a gas by the gas sensor 100 can be increased. The distance 116a, 116b should be selected such that the grid structure in the membrane 110 created by the interruptions 162i, 172i is mechanically durable in order to ensure a high quality of the gas analysis by the gas sensor 100.

[0165] In other words, Fig. 5a layout of a MEMS membrane sensor (e.g., the gas sensor 100), for example, for measuring the gas-type-dependent heat transport (e.g., via the direct path 210, 220) (embodiment according to aspect 1). Thus, the gas sensor 100 can be made of Fig. 5 a variant with a grid structure made of the membrane material of the membrane 110 to increase the mechanical stability of the gas sensor 100. The geometric shape of the grid can be selected such that the parasitic heat conduction 114a, 114b in the membrane material has to travel the longest possible path.

[0166] Fig. 5shows a further embodiment of the gas sensor 100, which features a grid structure between the heater 120 and detector elements (e.g., the first thermocouple structure 130 or the second thermocouple structure 140), which is intended to improve the mechanical stability of the gas sensor 100 during long-term operation. Such an arrangement can reduce the gas-type-dependent sensitivity of the thermal gas sensor 100, since heat conduction can now also occur parasitically 114a, 114b via the grid webs of the membrane material. Thus, a portion of the heat energy periodically introduced into the heater 120 can reach the detector structures (e.g., the first thermocouple structure 130 or the second thermocouple structure 140) earlier in time than the portion of the heat energy that is transported through the measurement gas over the laterally shortest distance 210, 220. Due to the thermal mass of the detectors (e.g. the first thermocouple structure 130 orthe second thermocouple structure 140), which can respond to a periodic excitation as a low-pass filter, both heat wave propagation times (e.g. the parasitic heat conduction 114a with the heat transfer via the direct path 210 or the parasitic heat conduction 114b with the heat transfer via the direct path 220) are blended into a single sinusoidal detector signal (e.g. a first sensor signal or a second sensor signal).

[0167] The geometric shape of the grid is selected, for example, so that the parasitic heat conduction 114a, 114b in the membrane material must travel the longest possible path. The oval holes (e.g., the interruptions 162i, 172i) are arranged perpendicular to the main direction of heat conduction. The aspect ratio of the oval holes is, for example, at least three times longer than they are wide, and the web width (e.g., the spacing 116a, 116b) corresponds, for example, to the smallest achievable structure width that results in a mechanically durable grid structure with the available layer technology.

[0168] Fig. 6a , Fig. 6b and Fig. 6c show schematic representations of further embodiments of a gas sensor 100. The gas sensor 100 can be made of Fig. 6a , Fig. 6b and Fig. 6c the same features and functionalities as the Gas Sensor 100 from Fig. 4 and / or Fig. 5Differences between the gas sensors 100 may occur in the first interruption region 160 and the second interruption region 170 of the gas sensor 100.

[0169] The gas sensor 100 can be Fig. 6a For example, eight interruptions 162 i in the first interruption region 160 and eight interruptions 172 i in the second interruption region 170. For example, the interruptions 162 i can have a greater transverse extent than the interruptions 172 i. In addition, the interruptions 162 i , 172 i can have different longitudinal extents within their respective interruption regions 160 and 170, respectively.

[0170] The gas sensor 100 from Fig. 6b For example, has a first interruption area 160 with eight interruptions 162 i and a second interruption area 170 with a continuous interruption 172. Thus, in the variant of Fig. 6bFor example, in the interruption areas 160, 170 the variants from Fig. 6a or Fig. 5 and from Fig. 4 combined with each other.

[0171] The gas sensor 100 from Fig. 6c For example, it has a first interruption region 160 and a second interruption region 170 with a plurality of interruptions 162 i , 172 i , wherein the first interruption region 160 can have, for example, 23 interruptions 162 i and the second interruption region 170 can have, for example, 14 interruptions 172 i . For example, the interruptions 162 i , 172 i of an interruption region 160 or 170 can have the same transverse extent and / or the same longitudinal extent. Optionally, it is also possible for the interruptions 162 i , 172 i to have the same longitudinal extent and / or transverse extent only in rows.

[0172] In other words, Fig. 6a , Fig. 6b and 6crepresent further layout variants of the MEMS membrane sensor (for example the gas sensor 100), which differ in the number and size of the perforations of the membrane (e.g. the interruptions 162 i , 172 i ) (embodiments according to aspect 1).

[0173] Advantages of thermopile structures (e.g., the first thermocouple structure 130 or the second thermocouple structure 140) on membrane technology (examples): A simple 5-mask MEMS process on inexpensive substrates is possible because the properties of the wafer material, e.g., only need to be specified in terms of thickness, surface quality, and for the structuring of the pit in an adapted basic doping. In contrast to the gas sensor on SOI, structuring of a pit (e.g., for the membrane 110) must be specified in an adapted basic doping. The structures (e.g., the heating element 120, the membrane 110, the first thermocouple structure 130, the second thermocouple structure 140) are passivated with protective layers, for example, and offer better resistance to free radicals that may be present in the measurement gas and can etch the active sensor structures (e.g., the first thermocouple structure 130 and / or the second thermocouple structure 140), thereby mechanically weakening or thermally altering them.For example, the gas sensor 100 on a thin-film membrane 110 requires only a third of the heating power to achieve the same gas sensitivity; the power consumption is approximately 12 mW compared to 36 mW with SOI technology. Thermopiles (thermocouples) 130, 140 can be implemented as detectors of a heat distribution field in the measurement space instead of temperature-variable resistor structures (RTDs): The electronic signal evaluation of the thermopiles 130, 140 is almost powerless at 0.6 µW, for example, while the detectors (e.g., the first thermocouple structure 130, the second thermocouple structure 140 made of . Fig. 2a , Fig. 2b or Fig. 3) based on resistance structures of SOI technology require a current flow for stable signal generation, due to which a heating power is introduced into the detector, which is low at approx. 140 µW, but is 200 times greater than that of thermopile technology and contributes to the self-heating of the RTD detectors and can thus parasitically reduce the gas selectivity. Disadvantages of membrane technology:

[0174] filigree perforated membranes 110 can break during production as well as during continuous operation, an optimized design (see e.g. Fig. 4 , Fig. 5 , Fig. 6a , Fig. 6b or Fig. 6c ) is recommended. 1.1.3 Sensor principle (details optional)

[0175] Fig. 7schematically illustrates a basic principle of the thermal sensor 100 (the gas sensor can also be referred to herein as a thermal sensor): Clearly visible is the spatial separation between heater 120 and sensor structures 130, 140 (the first temperature sensor structure and the second temperature sensor structure can also be referred to herein as sensor structures, detector structures, sensors, temperature sensors or detectors) with thermal coupling through the gas mixture to be analyzed; as well as the measurement with sensor structures 130, 140. The sensor structures 130, 140 can be arranged at different distances from the heater 120 or at the same distance.

[0176] In other words, Fig. 1 a schematic representation of a basic sensor principle for a path 122a, 122b of heat transport through the gas to be measured between heater 120 and detectors 130, 140. Heater 120 and sensors 130, 140 separated by medium

[0177] Heater 120 and sensor(s) 130, 140 are arranged separately in the medium and surrounded by the gas to be analyzed. The heat flow 122a, 122b from heater 120 to temperature sensors 130, 140, for example, occurs solely via the gas itself. Measurement at multiple intervals

[0178] The heat transport 122a, 122b also occurs, for example, via unknown heat transfers 122a 1 , 122b 1 from the heater 120 into the gas to be analyzed and via unknown heat transfers 122a 2 , 122b 2 from the gas into the sensor structure 130, 140. When measuring at two distances 180 1 , 180 2 , the heat transfers 122a 1 , 122b 1 , 122a 2 , 122b 2 are almost the same. The difference between the two sensor signals depends essentially on the heat transfer through the medium itself. Measurement at equal intervals

[0179] Analogous to the measurement with multiple distances, unknown heat transitions 122a 1 , 122b 1 , 122a 2 , 122b 2 also occur here. By evaluating a sum of the two sensor signals, a very precise gas analysis can also be carried out and, under certain circumstances, the unknown heat transitions 122a 1 , 122b 1 , 122a 2 , 122b 2 can also be taken into account in the analysis.

[0180] It should be noted that when measuring with multiple distances, an evaluation of a sum signal can also be carried out as an alternative.

[0181] Furthermore, it should be noted that an evaluation of a sum signal is preferred over an evaluation of a difference signal, since the signal-to-noise ratio of the difference signal is smaller than that of the sum signal.

[0182] Optionally, a quotient of the difference signal and the sum signal (this is a common standardization) can be used for evaluation. This emphasizes the measurement effect more than if only the sum signal or only the difference signal is evaluated. Electrical analogy

[0183] To identify and estimate the heat flows, an electrical analogy was created (see e.g. Fig. 8 ). Optimizing heat loss is an essential factor in increasing the sensitivity of the sensor 130, 140 without having to supply excessive heating power, e.g., via the heating element 120.

[0184] According to one embodiment, Fig. 8 Features and functionalities of the gas sensor 100 from Fig. 7 In other words, Fig. 8a schematic representation of the heat transport at the gas sensor 100. The heat transport from the heater 120 (temperature TH ) to the sensor 130, 140 (temperature TS ) takes place essentially through the gas to be measured. 1.2 Example of the gas sensor in operation: Signal generation and evaluation on an embedded system 1.2.1 Operating principle (details optional)

[0185] With a sinusoidal heating power 122, the sensor signals 210, 220 have a sinusoidal curve (see e.g. Fig. 9 ), which is highly dependent on the thermal properties of the gas surrounding the sensor structures. By measuring the temperature of the heater 120 with two identical sensors 130, 140 at different distances 180 1 , 180 2 from the heater 120, the unknown heat transfers in the measuring arrangement can be eliminated or reduced.

[0186] For evaluation, transmitted and received periodic temperature waves are compared (see Fig. 9). By calibrating the signal 210, 220 via the phase shift 212, 222 between the heater and the sensors, the CO2 content in air can be resolved to 0.2 vol%, e.g., using the gas sensor. Since gases are compressible and their density changes due to pressure and temperature, the corresponding drifts should be compensated.

[0187] Fig. 2 shows a comparison of signals 210, 220 when excited with sinusoidal heating power 122 for CO2 and N2. With the same heating power 122, the received sensor signals 210, 220 differ in amplitude, offset, and phase. According to one embodiment, the signals 210, 220 are differential signals from a signal of a first thermocouple structure and a second thermocouple structure of the gas sensor.

[0188] By evaluating additional measured values ​​provided by the sensor, thermal conductivity, thermal diffusivity and, if the density of the gas is known, also the specific heat capacity can be determined - a possible way to analyze even unknown gas mixtures.

[0189] The structural difference between self-supporting bridge structures and closed thin-film membranes largely achieves parasitic thermal decoupling between the heater and detector elements, significantly improving signal quality. Due to the heater's low thermal mass, it is possible to modulate the heater at frequencies up to 300 Hertz, as heat can be rapidly added and removed. 1.2.2 Theoretical considerations for determining thermal diffusivity (details optional)

[0190] To determine the thermal diffusivity at sinusoidal heating power 122, a model according to [ Baehr 2008 ] can be used.

[0191] The following equation describes the time-dependent (time t) temperature propagation along the length axis x in a rod which is subjected to a sinusoidal temperature at one end (mean value T m , amplitude TA , angular frequency ω): T x t = T m + T A ⋅ η ⋅ e − k 1 ⋅ x ⋅ sin 2 πf ⋅ t − k 1 ⋅ x + ϵ

[0192] When entering the gaseous medium from the heater, the temperature field experiences the phase shift ε 0 and the damping n 0 . ϵ 0 = arctan k 1 + k und 1 η 0 = 1 + 2 k + 2 k 2

[0193] The temperature field experiences the phase shift depending on the distance x travelled through the medium ε (x) = k 1 x and the damping n (x) = e -k 1·< x< . The essential factor for the change in the path-dependent quantities, k 1 , depends on [ Baehr 2008 ] of the thermal diffusivity a, the angular frequency ω and thus from the excitation frequency f away: k 1 = ω 2 ⋅ a = π ⋅ f a

[0194] The factor for taking into account the influences on heat transfer between solid and gas is derived from the factor k 1 , the heat transfer coefficient α and thermal conductivity λ : k = k 1 ⋅ λ α = b α ⋅ π ⋅ f mit dem Wärmeeindringkoeffizienten b : b = λ ⋅ c p ⋅ ρ = λ α

[0195] To determine the thermal diffusivity according to the above-mentioned model, the evaluation of the phase shift is sufficient. The total phase shift in Equation (1) amounts: Δ φ = k 1 ⋅ x + ϵ 0

[0196] If two temperature measurements are compared at two different distances, the constant heat transfer effects cancel each other out: Δ φ x 2 − Δ φ x 1 = k 1 ⋅ x 2 + ϵ − k 1 ⋅ x 1 + ϵ

[0197] Simplified with the differences Δ φ 12 = Δφ( x 2 ) - Δφ( x 1 ) and Δx 12 = x 2 - x 1 Δ φ 12 = k 1 ⋅ Δ x 12 and with (3) we get: Δ φ 12 = π ⋅ f a ⋅ Δ x 12

[0198] For the thermal conductivity α (with angles in radians) the following applies: a = π ⋅ f ⋅ Δ x 12 2 Δ φ 12 2

[0199] If the phase shifts are in degrees, the thermal diffusivity is α : a = 180 ° 2 ⋅ f π ⋅ Δ x 12 2 Δ φ 12 2

[0200] The temperature wave oscillates harmonically at the same angular frequency as its excitation and decays rapidly with increasing penetration depth in the medium, strongly damped, while the phase shift increases. Penetration depth and wavelength increase with increasing oscillation period and thermal diffusivity of the medium. When considering the wavelength L From the temperature oscillation, which results from the distance between two measuring points x 1 and x 2 where the phase angle differs by 2π, the penetration depth of the temperature wave can be derived at which the temperature amplitude has decreased to the nth part of its value at the entry point into the medium x=0. The following applies: aus e − 2 π x n / Λ = 1 / n ergibt sich : x n = Λ 2 π ⋅ ln n = a π ⋅ f ln n

[0201] The attenuation of the amplitude is therefore also a measure of the thermal conductivity of the medium. 1.2.3 Theoretical considerations for determining thermal conductivity (details optional)

[0202] The thermal conductivity λ of the medium is represented by the average temperature distribution in the measuring chamber. Depending on the average heater temperature and the gas type or mixture concentration in the volume of the measuring chamber, an average temperature is established at the temperature detectors, which is proportional to the heat flow through the gaseous medium from the heater via the detectors to the housing wall. To determine the thermal conductivity, the temperatures of the heater and the detectors must be known. With appropriate calibration, for example, it is sufficient to regulate one detector (preferably the one closest to the heater) to a constant (excess) temperature, if the required average heating energy is determined as a measure of the thermal conductivity.

[0203] After [Simon 2002] and [Baar 2001]The basic principle for measuring the thermal conductivity of gases is that a temperature rise above the ambient temperature is generated in a flow-free measuring chamber using a heating element (e.g., a hot wire or a hot plate) suspended in the gas. The heating power required to achieve this temperature rise ΔT to maintain, is the direct measure of thermal conductivity λ and can be described with the following relationship: P = λ ⋅ ΔT ⋅ G where G is the geometric constant of the arrangement. A condition for correct measurement is a static gas in the measuring space, e.g., in a dead volume or behind a diffusion barrier, since convective heat flow leads to a measurement error. [Baar 2001]. In the literature, these measurement errors are discussed, as well as methods that can measure thermal conductivity in the presence of convective heat flow [IST AG 2011, 2013, 2015].Furthermore, methods with periodic excitation of the heater are known, which can determine not only the concentration of binary gas mixtures, but also multi-component mixtures using Fourier analysis [Grien 2012]. 1.2.4 Embedded µController (Embedded Microcontroller) Electronics and software of the gas sensor according to the invention (details optional)

[0204] The task of the electronics and signal evaluation is to generate, for example, a reliable measurement result directly dependent on the gas concentration using a miniaturized system that is as cost-effective as possible. Furthermore, the gas sensor according to the invention should be usable in a respiratory gas monitor in which the carbon concentration in the air mixture can change with high dynamics. The gas sensor should be able to resolve changes in the gas composition during the inspiration and expiration cycle up to a rate of 60 breaths per minute. Rapid evaluation of the sensor signals is therefore desirable. 1.2.4.1 Hardware 1.2.4.1.1 Heater control, e.g., of the gas sensor according to the invention (embodiments according to aspect 3, details optional)

[0205] Fig. 10shows an electrical circuit diagram of a heater control for a thermal gas sensor according to an embodiment of the present invention. A CPU specifies, for example, a lower and upper heater voltage and switches between these two values ​​in a timer-controlled manner. A CPU can measure the current heater current at specific times to calculate the heater power. In other words, Fig. 10 a heater supply with voltage setting and current measurement.

[0206] In contrast to the theoretical analogy discussed above, which applies the laws governing a damped oscillation to a heat transfer phenomenon using the example of a sinusoidal heater excitation, the developed µController electronics generates a square wave signal (for example). Due to the timer structures present in the processor, this signal can be generated with significantly greater temporal precision than a synthetic sinusoidal signal that would be output by the processor on its digital / analog (DA) port.

[0207] For example, two heater voltages are specified via a DA converter. This is due to the fact that the DA converter is controlled via SPI, and the point in time at which a new DA value is adopted cannot be precisely determined by the selected processor chip (CPU). However, this is a prerequisite for determining the phase position of the sensor response. Therefore, one of the two voltages is alternately applied to the heater amplifier via an analog switch, for example. To reduce the propagation of the steep switching edges in the system, they are smoothed, for example, by a downstream low-pass filter. The operational amplifier (OP) circuit raises the voltage to the voltage level required by the heater. Another OP compensates, for example, for the voltage drop occurring across the current measuring resistor. Since the current is measured and the heater voltage is known, the heater power can be calculated.This is important because the heater resistance can change with temperature.

[0208] For example, a heater duty cycle of 50% can be used (where, for example, a periodic square wave signal with a duty cycle of, for example, 50% + / -2% is applied to the heater).

[0209] Alternatively, shorter duty cycles can also be used, for example in the range 5..50%.

[0210] To achieve the same power between a sine wave (offset at Upp / 2, both half-waves in the positive range) and a square wave, a duty cycle of 42% is required, for example, for the equivalent square wave or for an "equivalent" or square wave signal with the same power.

[0211] In some embodiments, the adjustment of the heater power by controlling the duty cycle is not realized - this is more difficult on the MSP430, but interesting when using more powerful µControllers: You can work with a fixed operating voltage and only change the duty cycle (a type of PWM control).

[0212] In other words, it is optionally possible to adjust the (average) heater power by changing the duty cycle. Alternatively, the heater power can be adjusted by changing the voltage level (the voltage applied to the heater) or the current level (the current flowing through the heater or heating element). The two options can also be combined. 1.2.4.1.2 Detector signal evaluation, e.g., of the gas sensor (details optional)

[0213] Fig. 11shows an electrical circuit diagram of a detector signal evaluation of a thermal gas sensor according to an embodiment of the present invention. Both a first thermocouple structure and a second thermocouple structure of the gas sensor can be Fig. 11 illustrated detector signal evaluation to evaluate heat transferred from a heating element of the gas sensor to the first thermocouple structure and the second thermocouple structure via a gas to be analyzed in a respective detector signal (e.g. detected by means of the first thermocouple structure or the second thermocouple structure and can also be referred to herein as a sensor signal). According to one embodiment, in Fig. 11The detector signal evaluation of sensor 1 (first thermocouple structure) is shown. The detector signal evaluation is configured, for example, to receive a first input signal, e.g., a DAC signal CO2_S1_Win from a CPU (magnifying glass function), and a second input signal, e.g., a detector signal CO2_Sensor1, and to provide a first output signal, such as an amplified detector signal CO2_S1_an, and a second output signal, such as a comparator signal for a phase evaluation CO2_S1_dig.

[0214] According to one embodiment, a CPU controls a heater so that the amplitude of the sensor signal remains within an ADC range. A magnifying glass function, for example, keeps the sensor signal within the ADC limits. Phase evaluation is performed, for example, via the comparator using the MSP430 timer structures.

[0215] The resistance change of the sensor wire (e.g., the thermocouple structure) is very small. For this reason, an amplifier with a high gain is preferred or required. Since the absolute value of an input voltage (e.g., the sensor signals) depends on many factors, it is recommended to compensate for this value.

[0216] One possibility would be to use an alternating current (AC) amplifier. The disadvantage is that this causes an unknown phase shift.

[0217] For this reason, a direct current (DC) amplifier was used, which has no phase shift. To compensate for the DC component of the signal, in one embodiment, the negative input terminal at the differential input of the operational amplifier (OP) is raised to the average value of the detector signal and actively tracked using a software controller. The processor's digital-to-analog converter (DAC) outputs this voltage directly. Due to the differential operation of the differential input on the OP, the DC components of the input voltages are subtracted from one another and only the AC component of the signal is amplified. According to one aspect, the analog-to-digital converter (ADC) signal is measured and checked to see whether it lies within reasonable limits that can be detected by the ADC. If the signal reaches the upper or lower voltage limit of the OP, the DAC value is adjusted accordingly.This creates an amplifier in which the amplified signal is continuously maintained within the optimal operating range or window. The gain factor at the amplifier can be increased by removing the DC component, a kind of "magnifying glass function." The DAC value required for compensation can serve as an additional parameter for evaluation, allowing the absolute mean detector temperature to be determined. Using the relationship in equation (5), the thermal conductivity of the gas mixture can be determined.

[0218] To determine the phase position of the sensor signal, a Schmitt trigger, for example, was used. It is set to switch just above or below the zero crossing of the sensor signal. This is where the signal is steepest and thus causes the least phase noise. The DC component is removed, for example, using a capacitor. This allows the phase of the sensor response to be determined.

[0219] By using the processor's internal timer structures (MSP430, Texas Instruments), a theoretical phase resolution of 0.009° is possible. However, this is not achieved due to circuit noise. 1.2.4.2 Software (details optional; functionalities according to aspects 3 and 4 are described together here, but can be used separately) e.g. for the gas sensor

[0220] The software has various tasks, for example: Setting the starting values ​​for the heater voltage, the sampling times of the sensor signals, and the starting value for the DC operating point (magnifying glass function). First, an attempt is made to find the DC operating point. To do this, the DAC values ​​of the two sensors are adjusted so that the sensor signal is, for example, in the middle of the ADC range. Measuring the sensor voltage at specific times. To determine the amplitude, the voltage is recorded at the presumed maximum and minimum. To detect if the sampling time is incorrect, a further measurement is taken at the presumed "zero crossing." If the sampling times are correct, the following applies, for example: Umax + Umin 2 = U 0 If the sampling times are incorrect, the above formula is no longer correct. This allows the software to recognize, for example, that the sampling times need to be adjusted. The readjustment can be deactivated via software, for example. It only occurs when the signal is within the ADC limits. If the amplitude controller is active, an attempt is made, for example, to keep the amplitude of the Sensor1 signal at a certain setpoint. The heater energy is regulated, for example, so that the S1 amplitude fills the ADC range by at least 3 / 4. The controller can optionally be deactivated via software. Furthermore, it is only active, for example, if no sampling times or DC offsets have been changed. This optionally ensures that this control loop is only active in the steady state. Determination of the phase position of the sensor signal using the Schmitt trigger circuit (optional).Depending on the settings, the three sampling times of the sensor signal for the next sampling period are also calculated. Ambient pressure and temperature are recorded via additional sensors (optional). 1.2.4.3 Software controller (details optional) e.g. for the gas sensor

[0221] Fig. 12 shows a schematic representation of nested controllers of the software for a thermal gas sensor according to an embodiment of the present invention.

[0222] The software contains several nested controllers. The innermost is the DC operating point controller. The sampling times are only adjusted when the DC operating point has stabilized (no adjustment of the DC offset was necessary). In the amplitude control loop, for example, the amplitude of S1 is kept constant—but only when no adjustment of the DC offset and sampling time was necessary. In the outer control loop, the heating energy required to regulate the S1 amplitude can (optionally) be adjusted in such a way that the thermal system can dynamically adapt to a wide range of different gas mixtures.

[0223] For example, amplitude determination requires three A / D samples per sensor wire: minimum at the lower peak, zero crossing, and maximum at the upper peak. The procedure is as follows: For example, all AD values ​​are initially measured using the current setting. A check is then made to see whether the min / max A / D values ​​for S1 and S2 are within the valid range. If not, the amplifier's DC operating point is adjusted (via DAC) and all other controls are temporarily disabled. The other controls are only enabled again when both sensor channels are within the permissible operating range (A / D max < 3900 or A / D min > 200, i.e., within 5% to 95% of the A / D range of 4096 digits). To ensure the amplitude is measured correctly, the A / D conversion should occur at the correct time (upper / lower peak and, for verification purposes, the zero crossing). There are currently two ways to do this: ∘ Via the A / D conversion itself: The time of the zero crossing is expected to be half the time between the two measured times for the minimum and maximum peaks of the A / D values, ie, (Min+Max) / 2 should be equal to the A / D value at zero crossing. In the event of deviations, the sampling time for the next measurement is adjusted. A deviation of, for example, around 0.625° (degrees) or 14.47 µs is tolerated. ∘ Via the comparator signal: Since the comparator switches at the time of the zero crossing of the sensor signal, the time at which the A / D measurements should take place can be determined, for example: 90° (or 2.0833 ms for the upper peak), 180° (4.1666 ms for the zero crossing of the negative edge) and 270° (6.2499 ms for the lower peak) are added to the measured value of the switching time of the positive edge. A deviation of 0.625° is also tolerated here. For example, only when both controllers (DC operating point and phase) did not require a change in the control value, and were therefore in a steady state, does the amplitude controller intervene.This adjusts the heater value so that the desired amplitude of S1 is achieved.

[0224] In Fig. 11 a shows a block diagram illustrating the control and tracking of the DC operating points of the two detector amplifiers according to an embodiment of the present invention.

[0225] In Fig. 13b A block diagram is shown illustrating the tracking of the sampling times for the amplitude measurement of the detector signals and the S1 amplitude controller. Once all controllers are adjusted, the gas mixture is evaluated using the measured values ​​for amplitude and phase of the detectors.

[0226] According to one embodiment, the Figures 13a and 13b be viewed as a block diagram, where Fig. 13b with Fig. 13a is connected via the "Tracking of the sampling times" block. 1.2.4.4 Timing table (details optional) e.g. for the gas sensor

[0227] The ADC measurement times at which the μController's analog-to-digital converter measures the heater current consumption and the detector voltages (an example of the sensor signals) are defined, for example, in a software timing table that extends over two heater pulse periods. According to one embodiment, these two periods are required because, for example, the processor used only has one timer available for variable ADC control. When the heater is operated at 120 Hz, all measured values ​​relevant for gas mixture analysis are obtained after two periods, i.e., at a frequency of 60 Hz. Since the heater pulse shape is stable over the period, the consumed heater current can be measured at fixed times: at 45° for the peak value and at 170° for the lowest heater current value (generally zero).The 3 ADC measurements per detector (upper and lower peaks as well as the zero crossing) are expected as variable measurements in time windows defined in the timing table: . ADC_SENSOR1: ∘ CO2-S1-min: 33.6° .. 123.6° (778 µs .. 2861 µs) ∘ CO2-S1-zero: 123.6° .. 213.6° (2861 µs .. 4944 µs) ∘ CO2-S1-max: 213.6° .. 303.6° (4944 µs .. 7028 µs) ADC_SENSOR2: ∘ CO2-S2-min: 68.6°-141.4° (1588 µs .. 3273 µs) ∘ CO2-S2-zero: 158.6°-231.4° (3671 µs .. 5356 µs) ∘ CO2-S2-max: 248.6° .. 321.4° (5755 µs .. 7440 µs) 1.3 Evaluation algorithm for calibration to a gas mixture with drift correction against gas pressure and gas temperature (for example according to aspect 2; details optional), e.g. of a gas sensor 1.3.1 Measurements in gas mixtures 1.3.1.1 Binary mixture

[0228] In Fig. 14As an example, a CO 2 dependence of the sensor in the phase signal at constant temperature and constant pressure is shown. Three phase shifts are shown: A phase difference D1-Hz.dPhi (red) between heater and detector 1, with a 200 µm distance, a phase difference D2-Hz.dPhi (blue) between heater and detector 2, with a 300 µm distance and a phase difference D2-D1.dPhi (green, right y-axis) between detector 2 and detector 1. According to one embodiment, Fig. 14 Phase shifts of heater detectors for (0...5)vol% CO2 in air at a pressure of p=1010 mbar, a temperature of T amp =24°C and a heating power of P=(15±12.5) mW at a frequency of f=120 Hz.

[0229] In Fig. 15As an example, measured amplitudes at detectors D1 and D2 as well as a sum signal of the amplitudes formed relative to the heater amplitude are shown over the CO2 dependence of the sensor. For example, the amplitude D1.Uss (red) at detector 1 and the amplitude D2.Uss (blue) at detector 2 are shown. Both amplitude signals decrease, e.g., when the CO2 concentration increases, i.e., when the thermal diffusivity in the gas mixture increases. By forming the difference between the heater amplitude and the sum of the detector amplitudes, the relative amplitude signal sigUss=2*Hz.Uss-(D1.Uss+D2.Uss) (green, right y-axis) will increase with an increase in the CO2 content in the gas mixture, for example. According to one embodiment, Fig. 15 the amplitudes of the detectors for (0...5) vol% CO 2 in air at a pressure of p=1010 mbar, a temperature of T amp =24°C and a heating power of P=(15±12.5) mW at a frequency of f=120 Hz. 1.3.1.2 Pressure dependence

[0230] A sensor signal can be highly dependent on pressure and temperature. To correctly determine gas properties, the cross-effects should be known and corrected by the algorithms. Fig. 16 For example, the cross-sensitivity of the sensor signal in air to absolute pressure and for different temperatures is shown. For example, the cross-sensitivity of a phase shift D2-D1 between the detectors D2-D1 (e.g., between the first thermocouple structure D1 and the second thermocouple structure D2) for air is shown to pressure p=(910...1110) mbar over different temperatures T amp =(18...28)°C in air at a heating power of P=(15±12.5) mW and a frequency of f=120 Hz.

[0231] The pressure influence shows a linear relationship, while the temperature influence shows a quadratic relationship, as theoretically calculated. Both cross-sensitivities are in the order of magnitude of the signal for the gas concentration itself. 1.3.1.3 Heating power and frequency dependence

[0232] Fig. 17a shows a plot of a sensor signal for phase versus frequency when measured in CO 2 . In other words, Fig. 17a A diagram of a phase shift in 100% CO2 as a function of frequency. The phase goes into saturation.

[0233] Fig. 17b shows a plot of a sensor signal for amplitude versus frequency when measured in CO 2 . In other words, Fig. 17b A graph of the amplitude in 100% CO2 as a function of frequency. The amplitude decreases towards zero.

[0234] Compared to air, the heating power should be reduced somewhat when measuring in combustible gases to prevent the system from exceeding its A / D range. When varying the heating power, it has been found that in practice it is more sensible to operate the system with the largest possible sensor amplitudes and thus obtain more stable signals than setting the heating power to a minimum, which, although less thermally influenced, also reduces the signal-to-noise ratio. The heating energy periodically introduced into the sensor must be able to leave the sample volume within this period to prevent it from heating up continuously. For example, a peak heating power of approximately 26 mW at 120 Hz was set up for three measuring systems.

[0235] The sensor behavior represents an ideal first-order low-pass filter; there are no harmonic spectral components in the sensor signal. For this reason, actively sweeping through a frequency spectrum does not provide any additional information. Therefore, it was decided to operate the sensor at a fixed frequency. The electronics complexity of the system could be reduced, and the measurement time required to obtain a reliable value is significantly shorter. (All optional) The higher the excitation frequency at the heater, the less energy can be transferred between the heater and detector through the gas, because the thermal mass of the sensor itself limits the transfer speeds between the solid and the gas. The amplitude decreases with increasing frequency, leading to a vanishing signal approaching zero (see Fig. 17b ), the phase shift saturates to a maximum (see Fig. 17a ).

[0236] Optimizing phase resolution, phase difference, and amplitude for different gas mixtures resulted in the best phase response at a frequency of, for example, 120 Hz with a heating power of 26 mW for the microwire sensor and 160 Hz with approximately 8 mW for the MEMS thermopile sensor on a thin-film membrane. (Details optional) 1.3.1.4 Fuel gas mixtures

[0237] Different gas compositions were examined at a measuring station. Fig. 18shows a change in the phase signal of a methane sensor with increasing nitrogen admixture as an almost linear behavior. For example, the phase signal is shown as a function of the nitrogen concentration in methane as a phase difference D1-Hz.dPhi (red) between heater and detector 1, with a 200µm separation, a phase difference D2-Hz.dPhi (blue) between heater and detector 2, with a 300µm separation, and a phase difference D2-D1.dPhi (green, right y-axis) between detector 2 and detector 1. The phase shift of the heater-detectors is shown according to an embodiment for (0...30) vol% N 2 in methane at a pressure of p=990 mbar, a temperature T amp =21°C and a heating power of P=(13±12.5)mW with a frequency of f=120 Hz in Fig. 18 shown.

[0238] Fig. 19shows a diagram of the amplitude D1.Uss (red), detected by the first detector, and the amplitude D2.Uss (blue), detected by the second detector. The amplitudes of the detectors are plotted according to an embodiment for (0...30) vol% N 2 in methane at a pressure of p=990 mbar, a temperature T amp =21°C and a heating power of P=(13±12.5)mW with a frequency of f=120 Hz in Fig. 19 Both amplitude signals D1.Uss and D2.Uss decrease, for example, when the N 2 concentration in methane increases, i.e., when the thermal diffusivity in the gas mixture decreases. By calculating the difference between the heater amplitude and the sum of the detector amplitudes, the relative amplitude signal sigUss = 2*Hz.Uss-(D1.Uss+D2.Uss) (green, right y-axis) increases with increasing N 2 concentration.

[0239] Fig. 20shows a diagram of a calculated sensor signal sigX (an example of a combination signal of the gas sensor) consisting of phase and amplitude for different fuel gas mixtures. Fig. 20 shows the sensor signal (an example of a combination signal from the gas sensor) for various fuel gases and their mixtures: methane, ethane, and propane, as well as the mixtures: methane95-ethane05, methane93-ethane05-CO202, methane91-ethane05-CO204, methane91-ethane05-CO202-propane02, methane90-ethane10, and natural gas-L (the two-digit numbers indicate the proportion of the gas components in volume percent). Methane, ethane, and propane show significant differences, but the methane mixtures with proportions of 2 vol% to 10 vol% of other gases also differ from each other. The sensor signal is in Fig. 20 according to an embodiment for different fuel gases at a pressure of p=1001 mbar, a temperature T amp =26°C and a heating power of P=(13±12.5)mW with a frequency of f=120 Hz in Fig. 20 shown. 1.3.1.5 Findings from measurements in gas mixtures

[0240] The sensor signal exhibits strong pressure and temperature dependencies. To accurately determine the gas properties of a known mixture with traceability to standard conditions and comparison from tables, the cross-effects, for example, must be known and corrected. The pressure influence exhibits a linear relationship, while the temperature influence exhibits a quadratic relationship. Both cross-sensitivities are of the order of magnitude of the signal for the gas concentration itself. 1.3.2 Method for calibration to a gas mixture with drift correction against gas pressure and gas temperature (for example according to aspect 2; details optional) for e.g. a gas sensor 1.3.2.1 Sum signal from phase and amplitude (example)

[0241] A combination of phase and amplitude measurements (combined signal) has proven to produce a particularly stable sensor signal. Both signals are weighted using separate constants and added together, for example, to form a single sensor signal: sigX = sigUss * Ka + sigPhi * Kp where sigX the calculated sum signal, sigUss the relative amplitude signal and sigPhi represents the added phase signal of both detectors. The factors Ka and Kp are constants by which both partial signals are multiplied. When converting the amplitude signal to mV, for example, Ka = 1 / 3500 and when converting the phase signal to degrees, for example, Kp = 1 / 276 for CO 2 -air mixtures up to 30 vol% CO 2 .

[0242] The added phase signal sigPhiFor example, it is calculated from the sum of the two phase differences for the propagation times between the rising edge of the heater pulse and the rising edges at the detectors. For example, the following applies: sigPhi = D 1 − Hz . phi + D 2 − Hz . phi where (D1-Hz).phi and (D2-Hz).phi represent the phase differences between the heater and the detectors.

[0243] As in Fig. 14 As can be seen, the phase difference between heater and detectors increases with increasing CO 2 concentration, ie with increasing thermal conductivity, but the two amplitudes at the detectors decrease with increasing thermal conductivity ( Fig. 15 ).

[0244] For example, by calculating the difference between the heater amplitude and the sum of the detector amplitudes, the relative amplitude signal increases with increasing CO2 content in the gas mixture: sigUss = 2 * Hz . Uss − D 1 . Uss + D 2 . Uss

[0245] The signal calculated from phase and amplitude sigXFor example, it ranges between (1.7..2.0) for (0..6) vol% CO 2 . The device (e.g. the gas sensor) was measured in a temperature range between (16..28)°C and in the barometric pressure field between (900..1200) mbar. 1.3.2.2 Drift correction via polynomial compensation (details optional)

[0246] When calibrating the sensor to a known gas mixture, the strong pressure and temperature dependence of the sensor signal should be compensated in order to be able to infer a gas concentration from the measured value.

[0247] This results, for example, in a 4-dimensional vector field (matrix) consisting of gas concentration (CO2 [vol%]), the sensor signal sigX (sum signal of phase and amplitude), the pressure drift and the temperature drift. It is noticeable that the individual graphs in the diagram consist of Fig. 21the relationship between the gas concentration and the sensor signal, which each represent a constant ambient pressure or a constant temperature, are shifted parallel to each other. If one now forms a mean graph from all parallel shifted characteristic curves, one obtains a normalized relationship of the signal for a mean temperature and a mean pressure (see red line 230a in Fig. 21 ).

[0248] Fig. 21shows the matrix of measurement data for a variation in the gas concentration of (0..5) vol% CO2 in nitrogen in the pressure range (900..1200) mbar and in a temperature range of (16..28)°C. Using a pressure-dependent polynomial function, the green line 230b of the calibration curve can be shifted to a current working pressure. The red line 230a corresponds to the mean of all blue lines 2301 to 23016 and is a characteristic curve of the sensor signal relative to the gas concentration, normalized to an average temperature and an average pressure.

[0249] If the characteristics of the sensor signal sigX from the measured variation for each temperature and a mean gas concentration plotted against pressure (see Fig. 22), you also get a set of curves consisting of straight lines that are shifted parallel to each other. Higher pressures and cold gas, i.e. gas molecules that are closer to each other, lead to a higher sensor signal, while low pressures and warm gas result in a lower signal. sigX.

[0250] Fig. 22 This shows a pressure dependence of the sensor signal sigX for a fixed average gas concentration, a set of curves from different temperatures. The lowest line 230 1 describes the relationship at the highest temperature of 28°C in the variation, and the top line 230 7 represents the pressure dependence of the signal at 16°C.

[0251] If you place in the parallel family of lines in Fig. 22 for a fixed mean sensor signal sigX a horizontal straight line that intersects all lines of the family of curves, the relationship is obtained in Fig. 23 between gas pressure and gas temperature.

[0252] Fig. 23shows a slightly quadratic relationship between gas pressure and gas temperature (for an average gas concentration and an average sensor signal sigX). 1.3.2.3 Determination of a regression constant (details optional)

[0253] When calibrating the gas sensor to a specific gas mixture, regressions are successively created from the variation matrix using the relationships described above. Regression level A describes the relationship between the gas concentration of the calibration reference and the sensor signal. sigX. The individual curves per pressure and temperature are each plotted in a quadratic regression according to the form: y = A.c0 + A.c1*sigX + A.c2*sigX^2 Since the slope of all curves is almost constant and the quadratic coefficient c2 approaches zero, the mean value of all values ​​for the coefficients A.c0, A.c1 and A.c2 is calculated, resulting in Fig. 21Red shows the mean characteristic curve 230a over the entire measured value variation 230 1 to 230 16 . This must be shifted on the x-axis according to the drift influence of the pressure. Due to the pressure-dependent sigX 0 = f(p) the corresponding offset A.c0, which is included in the equation of the regression level A is used.

[0254] The regression level B describes the pressure drift of the sensor signal sigX. The offset A.c0 is recalculated depending on the pressure drift: A.c0 = sigX. y0 - B . c1 *Pressure. x 0 - B.c2* Pressure. x 0 ^2 . Can sigX. y0 = 0, the equation simplifies to: A.c0 = - (B.c1 *Pressure. x0 + B.c2* Pressure .x 0 ^2). The (now) pressure-dependent polynomial coefficient A.c0=f(p) is replaced (substituted) in the regression equation of plane A, for example.

[0255] The determined pressure-dependent offset for the polynomial of the regression level A is calculated, for example, from the cosine relationship of the angle relationship between offset and slope with: A.c1 = A.c0 / sigX 0 ; sigX 0 = f(p) and A.c0 = (-1)* sigX * A.c1. For higher-order polynomials, the first derivative of the curve should be formed and the slope at the reference point calculated from this. Regression level Polynomial coefficients Coefficient of determination Reference to the previous level (Middle of the variation range) c0 c1 c2 A Signal to CO2 -266,153759 144,315423 0 0,999258 0 B Pressure to signal shift 0,94394 0,001017 -1,50E-07 0,999929 1,843335 C Temperature to pressure shift 884,519093 7,844777 -0,023415 0,9983 1050 Table 1: Polynomial coefficients of the three regression levels (examples) 1.3.2.4 Conversion of the signal to a CO2 value (example; details optional)

[0256] The calculated value for the gas concentration from the polynomial of the regression level A For example, it is corrected for pressure and temperature drift: CO 2 vol% = A . y sigX ⋅ 1 − B . y p − B . ref sigX − B . ref ⋅ 1 − C . y T − C . ref p − C . ref where Ay(sigX), By(p) and Cy(T) correspond to the complete polynomials for the measurement signal, the gas pressure and the gas temperature.

[0257] If the fixed references, which represent the geometric center of the variation range, are inserted into the formula and the polynomials are solved accordingly, the following equations result. B.ref = By( c.ref) follows: CO 2 vol% = A . y sigX ⋅ 1 − B . c 1 ⋅ p − C . ref + B . c 2 ⋅ p 2 − C ⋅ ref 2 sigX − B . y C . ref ⋅ 1 − C . y T − C . ref p − C . ref

[0258] For C.ref = 1050 mbar used results in: CO 2 vol % = A . y sigX ⋅ 1 − B . c 1 ⋅ p − 1050 + B . c 2 ⋅ p 2 − 1050 2 sigX − B . y 1050 ⋅ 1 − C . y T − 1050 p − 1050

[0259] Fig. 24 shows a block diagram of a schematic procedure for determining a gas concentration taking into account the influences of pressure and temperature from the generated sensor signal sigX. In other words, Fig. 24 a schematic representation of the formation of the sensor signal sigX from amplitudes and phases as well as the determination of a gas concentration from sigX taking into account the influence of pressure and temperature (example).

[0260] In addition to calibrating the sensor signal to the concentration of a known gas mixture, it is also possible to measure the thermal conductivity a of the gas mixture directly. In Fig. 25 The theoretically calculated thermal diffusivity was plotted against the sensor signal sigX. In other words, Fig. 25 the thermal diffusivity versus the sensor signal sigX at constant pressure and constant temperature in a mixture of carbon dioxide CO 2 in nitrogen N 2 . The thermal diffusivity 240 1 (red line) decreases with increasing CO 2 concentration 240 2 (green line).

[0261] Thus, a design and evaluation of a thermal gas sensor for measuring physical gas properties is described herein. This invention proposes the following (aspects can be used independently and in combination): Sensor design based on two technology variants: MEMS wire sensor on SOI substrate and thermopile sensor on thin-film membrane Operation of the gas sensor: Signal generation and evaluation on an embedded system Evaluation algorithm for calibration to a gas mixture with drift correction against gas pressure and temperature 1.4 Market - Possible Application Areas (Optional) In medical technology for ventilation In natural gas analysis - determination of the calorific value

[0262] There are various systems for patient ventilation on the market today. These are differentiated according to use in the clinical and home care sector (e.g. systems from the companies Heinen+Löwenstein, Dräger and Stephan Medical Technology). Only their top-of-the-line systems from these providers include all the necessary measuring devices for determining pressure, respiratory flow, and respiratory gas analysis. This requires combining several devices, which primarily measure remotely from the patient. This suggests that cost-effective near-patient measurement of respiratory flow and CO2 levels has not yet been implemented, thus confirming the innovative nature of the project with the development of a multi-sensor system with hybrid filters.

[0263] We believe that the successful development of the new MEMS-based gas measurement system represents a significant advance in sensor technology for ventilation technology. The integration of both sensors (CO2 and flow) into a single sensor system leads to a significant reduction in installation space and system weight (a key criterion for intubated patients). Only the patient-proximal measurement location directly on the mask or tube—as close as possible to the airways—enables sufficiently accurate measurements to avoid influences from tubes, movement, or other sources of interference. The thermal measurement principle is also expected to enable more precise flow measurements and rapid gas analysis.

[0264] Fig. 26 , Fig. 27 and Fig. 28show a diagram in which a heating voltage 300 applied to a heater of a gas sensor, a current flow 310 during a heating period 302, measurement times 320 for an optional ADC (analog-to-digital converter) of an evaluation arrangement according to the invention, and a comparator signal for a detector (e.g., for a first detector or for a second detector) are shown. The evaluation arrangement according to the invention is designed, for example, to obtain the information on how much heat is dissipated by the heater during the heating period 302 based on a measurement of the current flow 310 through the heater at a predetermined heating voltage 300. According to one embodiment, the evaluation arrangement is designed to obtain the current flow 310 shortly after the predetermined heating voltage 300 is switched on and shortly before the predetermined heating voltage is switched off. This means, for example,that a start peak 312 of the heating current 310 and a heating current end value 314 of the current flow 310 can be processed by the evaluation arrangement.

[0265] According to one embodiment, the start peak 312 always has the same value for one and the same gas sensor (small fluctuations of less than 1%, 0.5%, or 0.1% may occur). According to the Figures 26 to 28 In the illustrated embodiments, the start peak 312 is always at 2.93V and approximately 400µs after switching on. This value of the start peak 312 is for a gas sensor in the Figures 26 to 28 For other gas sensors, the value of the start peak 312 may differ from that shown in the Figures 26 to 28 It should be noted that the value of the start peak 312 can vary not only between different gas sensors, but also between identical gas sensors.

[0266] The heater heats up during heating period 302, causing the heater resistance to rise according to a positive TCR (temperature coefficient), and the heater to reach a final temperature at the switch-off moment (I Hz = U / R Hz → I Hz ≈ 1 / R Hz ). The smaller the final heating current value 314, the hotter the heater, the less heat is transferred to the gas or gas mixture surrounding the heater being analyzed, and the lower the thermal conductivity of the gas or gas mixture.

[0267] In the embodiments according to the Figures 26 to 28 A gas or gas mixture is analyzed by a gas sensor according to the invention and / or an evaluation arrangement according to the invention. According to the embodiment of Fig. 26 a gas mixture with 10% CO 2 and 90% N 2 (nitrogen) was analyzed, according to the embodiment from Fig. 27 the gas nitrogen (100% N 2 ) is analyzed and according to the embodiment from Fig. 28The gas oxygen (100% O 2 ) is analyzed. These components have different thermal conductivities, such as oxygen with a thermal conductivity λ of 0.0263 W / (m*K), nitrogen with a thermal conductivity λ of 0.0260 W / (m*K), and CO 2 with a thermal conductivity λ of 0.0168 W / (m*K).

[0268] According to the embodiment from Fig. 26 the heating current final value 314 reaches 2.7 V, resulting in a difference between the switch-on (start peak 312) and switch-off current (heating current final value 314) of 220 mV (deltaU=220 mV). According to the embodiment of Fig. 27 the heating current final value 314 reaches 2.71 V, resulting in a difference between the switch-on (start peak 312) and switch-off current (heating current final value 314) of 214 mV (deltaU=220 mV). According to the embodiment of Fig. 28The final heating current value 314 reaches 2.72 V, resulting in a difference between the switch-on current (start peak 312) and the switch-off current (heating current final value 314) of 210 mV (deltaU=220 mV). In other words, the evaluation system processes (examines) the difference in the heating current (current flow 310) between the switch-on and switch-off moments, i.e., between the cold and hot heater.

[0269] The CO 2 mixture of Fig. 26 Compared with the examples shown Fig. 27 and Fig. 28 The highest heater temperature is reached and therefore the lowest heating current (e.g. the lowest heating current final value 314) is achieved here, since CO 2 has only half the thermal conductivity compared to N 2 and O 2. In comparison, the heater according to Fig. 27 in 100 vol.% N 2 does not reach the final temperature (e.g. the heating current final value 314) as in the 10%CO 2 -90%N 2 mixture of Fig. 26 . Likewise, the heater reaches Fig. 28in 100 vol.% O 2 does not reach the final temperature (e.g. the heating current final value 314) as in the 10%CO 2 -90%N 2 mixture of Fig. 26 . The difference between inrush and cut-off current in Fig. 28 is the lowest at 210 mV and accordingly the gas analyzed here also has the highest thermal conductivity compared to the 10%CO 2 -90%N 2 mixture (see Fig. 26 ) and the 100 vol.% N 2 (see Fig. 27 ) on.

[0270] According to one embodiment, a measurement effect is minimal because the heater according to the invention is highly doped, for example, to enable heating with 3 V. Furthermore, the TCR (temperature coefficient) of the heater can be low (e.g., ≤ 6*10 -3 < 1 / K, ≤ 4.1*10 -3 < 1 / K, ≤ 3.9*10 -3 < 1 / K).

[0271] Thus, with the present gas sensor and / or the present evaluation arrangement, for example, a sensor signal (e.g. the current flow 310) is used to differentiate the concentration of a third gas. In emergency ventilation, increased oxygen concentrations are used. For example, it is usual to use a mixture of 50 vol.% O 2 in N 2. Without correction of the sensor signal at a higher oxygen concentration compared to the fresh gas during calibration, the gas sensor (e.g. a CO 2 sensor, such as the gas sensor according to the invention) shows a concentration of -5% CO 2 at 50 vol.% O 2 in the N 2 -O 2 gas mixture, for example. This means that the change in the third gas component, a change in the concentration of oxygen, in the mixture may lead to an error signal in the CO 2 sensor. A concentration mixture of approximately 56% oxygen and 5% CO 2 in nitrogen N 2 also shows the same value on the sensor, for example. B. a CO2 concentration of 0 vol.% as in the fresh gas calibration with 21 vol.% O 2 and approx. 78 vol.% N 2 .

[0272] If there is no technical possibility to communicate the oxygen concentration of the inhalation gas to the sensor so that a concentration display of the gas sensor according to the invention can be corrected accordingly, the sensor would, for example, display incorrect values.

[0273] As in the Figures 26 to 28 To recognize, information about the thermal conductivity is contained in the final temperature the heater reaches before it shuts down. If one now compares the temperature difference (deltaU) between the current peak 312 at the beginning of heating and the final value 314 shortly before shutdown, one could conclude that different deltaU values ​​indicate different thermal conductivities in the gas mixture.

[0274] According to one embodiment, the heater is operated with a constant voltage (which is determined according to the Figures 26 to 28corresponds to a value of 3000 digits at a D / A output, but is only an example here and can be freely selected). With the current measurement via, for example, a shunt resistor and a CURRENT SHUNT MONITOR, e.g., the INA199A, component U402, as in Fig.10 , a voltage signal is obtained that is proportional to the heating current. Figures 26 to 28 Screenshots of the signals recorded on the oscilloscope are shown, with the heater current curve (current flow 310) greatly enlarged (noise can be reduced by shielding the test leads). A product of heater voltage 300 and measured heater current 310, for example, allows a statement to be made about the heater power. The heater current 310 decreases slightly over time because the heater heats up and, due to its temperature gradient of the resistor (TKR), its internal resistance increases. Due to the higher internal resistance, less current can flow at the same heater voltage (I Hz ≈ 1 / R Hz ).

[0275] How much energy the heater can release into the surrounding gas depends, among other things, on the thermal conductivity of the gas. With 10% CO2 in N2, for example, the heater cannot release as much heat because CO2 has a thermal conductivity of λ=0.0168 W / (m*K). The heater therefore reaches a higher final temperature before switching off than with a 100% N2 gas. The measurement determined a difference of deltaU = 220mV. Nitrogen N2 has a thermal conductivity of λ=0.0260 W / (m*K). The heater could release almost twice as much heat as with a 100% CO2 gas. The measurement determined a deltaU of 214mV. The difference in thermal conductivity between nitrogen and oxygen O2 is not very large. Nevertheless, with the gas sensor and / or the evaluation arrangement described here, a deltaU of 210 mV can be determined, which is somewhat smaller than when measuring in N 2 .

[0276] In Fig. 29Four different phase signals are shown, which can represent the phase information sigPhi for the evaluation arrangement according to one embodiment. For example, the information 210 about the first phase difference, the information 220 about the second phase difference, a phase sum 400 (information 210 + information 220), and a phase difference 410 (information 220 - information 210) are shown. According to one embodiment, a temperature of T=24°C and a pressure of p=1013 mbar are present when measuring the phase information 210, 220, 400, and 410. However, this is only an example, and the phase information 210, 220, 400, and 410 can also be acquired with other environmental parameter settings (different temperature, different pressure).

[0277] According to the Fig. 29In the exemplary embodiment shown, a first section (e.g., measuring points 4520 to 4620) represents the respective phase information 210, 220, 400, and 410 for a 10 vol.% CO2 in N2 gas mixture, a second section (e.g., measuring points 4670 to 4780) represents the respective phase information 210, 220, 400, and 410 for a 100 vol.% N2 gas, and a third section (e.g., measuring points 4960 to 5070) represents the respective phase information 210, 220, 400, and 410 for a 100 vol.% O2 gas. Times between the individual sections are, for example, waiting times until the respective mixture is adjusted.

[0278] The phase sum 400 represents, for example, a stable sum signal D1+D2 (D1 corresponds to detector 1 and D2 corresponds to detector 2) of the phase positions. A distinction between 100 vol.% O 2 and 100 vol.% N 2 is present for all phase information, for example. According to the exemplary embodiment, the largest signal difference occurs between 10 vol.% CO 2 and 0 vol.% CO 2 in N 2. Since the phase difference signal 410 is currently very noisy, the phase sum 400 is preferred as phase information.

[0279] In Fig. 30Information 210 about an amplitude of a detector signal from a first detector and information 220 about an amplitude of a detector signal from a second detector are displayed. According to one embodiment, a temperature of T=24°C and a pressure of p=1013 mbar are present when measuring the amplitude information 210 and 220. However, this is only an example, and the amplitude information 210 and 220 can also be acquired with other environmental parameter settings (different temperature, different pressure).

[0280] According to the Fig. 30In the illustrated embodiment, a first section (e.g., measuring points 4520 to 4650) represents the respective amplitude information 210, 220 for a 10 vol.% CO 2 in N 2 gas mixture, a second section (e.g., measuring points 4670 to 4810) represents the respective amplitude information 210, 220 for a 100 vol.% N 2 gas, and a third section (e.g., measuring points 4960 to 5120) represents the respective amplitude information 210, 220 for a 100 vol.% O 2 gas. Times between the individual sections are, for example, waiting times until the respective mixture is adjusted.

[0281] The information 210 about the amplitude of the detector signal of the first detector and the information 220 about the amplitude of the detector signal of the second detector represent, for example, stable amplitude signals, with D2 (the second detector) according to this embodiment having greater noise because its amplitude is lower than the amplitude at D1 (the first detector) (approximately 5 mV compared to 1.8 mV in air). For both amplitude information 210, 220, a clearer distinction between 100 vol.% O 2 and 100 vol.% N 2 occurs than for the phase signals (see 210, 220, 400, and 410 in Fig. 29 ). Thus, a comparison of the relationships between phase and amplitude may be useful in order to determine the concentration of the third gas O 2 using the evaluation system (e.g., if the system has drifted too far from the fresh air calibration).

[0282] Fig. 31shows a combination signal sigX 230 (with the right y-axis) and a CO2 reference signal 500 (with the left y-axis). According to one embodiment, the temperature of the combination signal sigX 230 is measured at T=24°C and a pressure of p=1013 mbar. However, this is only an example, and the combination signal sigX 230 can also be recorded with other environmental parameter settings (different temperature, different pressure).

[0283] According to the Fig. 31In the illustrated embodiment, a first section (e.g. measuring points 4610 to 4650) represents the combination signal sigX 230 for a 10 vol.% CO 2 in N 2 gas mixture, a second section (e.g. measuring points 4700 to 4810) represents the combination signal sigX 230 for a 100 vol.% N 2 gas and a third section (e.g. measuring points 4960 to 5100) represents the combination signal sigX 230 for a 100 vol.% O 2 gas. Times between the individual sections are, for example, waiting times until the respective mixture is adjusted. An NDIR reference detector (see reference signal 500), for example, only detects a CO 2 concentration and cannot distinguish between N 2 and O 2.

[0284] All three gas mixtures are clearly distinguishable from each other with the combination signal 230. Therefore, it is proposed to compare the phase-amplitude ratios to determine the concentration of the third gas, O2.

[0285] While the difference between 100% N 2 and 100% O 2 has only a small effect on the phase signal ( Fig. 29 ), the difference in the amplitude signals between a 10%CO2-90%N2 and a 100%N2 mixture is almost as large as the difference between 100%N2 and 100%O2 ( Fig. 30 ). The combination signal sigX ( Fig. 31 ) blurs this behavior somewhat.

[0286] Further examples of implementation are presented below.

[0287] According to one embodiment, the gas sensor is a membrane sensor. The thermal gas sensor based on membrane and thermopile technology with a perforated membrane can be designed to minimize parasitic heat transfer via the membrane or the suspensions of the structures in order to obtain a higher gas-sensitive signal.

[0288] According to one embodiment, the gas sensor can comprise electronics, wherein the electronics can comprise one or more of the following aspects, individually or in combination. The electronics can comprise a DC sensor amplifier with an operating point tracked via software. Furthermore, the electronics can be designed to measure the phase position via the internal timer structure of the μController (MSP430), for example by using the precise generation of the heater excitation signal via the analog switch via the internal timer structure of the μController (MSP430). Furthermore, the electronics can be designed to measure the phase position of the sensor signals via a Schmitt trigger, which measures the sensor signals freed from the DC offset at the zero point crossing, since this is where the signals are steepest and thus the phase noise is minimized.Optionally, the electronics include control of the heating power via S1 amplitude controller and / or control of sampling timing.

[0289] According to one embodiment, the gas sensor may have a calibration. The calibration may be configured to generate a pseudo-signal from phase and amplitude, with the focus on a pseudo-signal in the signal generation and formula.

[0290] According to a first aspect, an evaluation arrangement 200 for a thermal gas sensor 100 with at least one heater 120 and at least one detector 130, 140 is designed to obtain information 210 about an amplitude of a detector signal of a first detector 130 and information 210 about a first phase difference between a heater signal and the detector signal of the first detector 130; and to form a combination signal 230 as an intermediate variable depending on the information 210, 220 about the amplitudes of the detector signal and depending on the information 210, 220 about the first phase difference, and to determine information 240 about a gas concentration or information 240 about a thermal conductivity of a fluid based on the combination signal 230.

[0291] According to a second aspect, an evaluation arrangement 200 for a thermal gas sensor 100 with at least one heater 120 and two detectors 130, 140 arranged at different distances from the heater 120 is designed to obtain information 210 about an amplitude of a detector signal of a first detector 130, information 220 about an amplitude of a detector signal of a second detector 140, information 210 about a first phase difference between a heater signal and the detector signal of the first detector 130, and information 220 about a second phase difference between the heater signal and the detector signal of the second detector 140;and to form a combination signal 230 as an intermediate variable depending on the information 210, 220 about the amplitudes of the detector signals and depending on the information 210, 220 about the first phase difference and depending on the information about the second phase difference, and to determine information 240 about a gas concentration or information 240 about a thermal conductivity of a fluid based on the combination signal 230;

[0292] According to a third aspect with reference to at least one of the first to second aspects, the evaluation arrangement 200 is designed to obtain information 122 about a heater amplitude and to form a linear combination of the information 122 about the heater amplitude, the information 210, 220 about amplitudes of the detector signals, the information 210 about the first phase difference and the information 220 about the second phase difference in order to determine the combination signal 230.

[0293] According to a fourth aspect with reference to at least one of the first to third aspects, the evaluation arrangement 200 is designed to evaluate the combination signal sigX 230 according to sigX = sigUss * Ka + sigPhi * Kp to obtain, where sigUss is amplitude information that depends on the information 210 about the amplitude of the detector signal of the first detector 130 and on the information 220 about the amplitude of the detector signal of the second detector 140; and where sigPhi is phase information that depends on the information 210 about the first phase difference and on the information 220 about the second phase difference; and where Ka and Kp are constants.

[0294] According to a fifth aspect with reference to the fourth aspect, the evaluation arrangement 200 is designed to receive the amplitude information sigUss according to sigUss = 2 * Hz . Uss − D 1 . Uss + D 2 . Uss where Hz.Uss is information 122 about a heater amplitude, where D1.Uss is information 210 about the amplitude of the detector signal of the first detector 130, and where D2.Uss is information 210 about the amplitude of the detector signal of the second detector 140.

[0295] According to a sixth aspect with reference to at least one of the first to fifth aspects, the evaluation arrangement 200 is designed to calculate a polynomial of the combination signal 230 in order to obtain the information 240 about the gas concentration.

[0296] According to a seventh aspect with reference to at least one of the first to sixth aspects, the evaluation arrangement 200 is designed to multiply a polynomial of the combination signal 230 by a correction term in order to obtain the information 240 about the gas concentration, wherein the correction term is dependent on the combination signal 230, information about a pressure and information about a temperature.

[0297] According to an eighth aspect with reference to at least one of the first to seventh aspects, the evaluation arrangement 200 is designed to perform a calculation according to C = pol sigX ⋅ 1 − f p sigX − const 1 ⋅ 1 − f T p − const 2 to obtain the information C 240 about the gas concentration, where sigX is the combination signal 230, where pol(sigX) is a polynomial of the combination signal sigX 230; where f(p) is a function of the pressure p; where const1 is a first constant; where f(T) is a function of the temperature T; and where const2 is a second constant.

[0298] According to a ninth aspect with reference to at least one of the first to eighth aspects, the evaluation arrangement 200 is designed to perform a calculation according to C vol% = A . y sigX ⋅ 1 − B . y p − B . ref sigX − B . ref ⋅ 1 − C . y T − C . ref p − C . ref to obtain the gas concentration information C 240, where sigX is the combination signal 230, where Ay(sigX) is a polynomial of the combination signal sigX 230; where By(p) is a function of the pressure p; where B.ref is a constant; where Cy(T) is a function of the temperature T; and where C.ref is a second constant.

[0299] According to a tenth aspect with reference to at least one of the first to ninth aspects, the evaluation arrangement 200 is designed to take into account a pressure and / or a temperature in an environment of the thermal gas sensor 100 when determining the information 240 about the gas concentration.

[0300] According to an eleventh aspect with reference to at least one of the first to tenth aspects, the evaluation arrangement 200 is designed to use the combination signal 230, information about the temperature in an environment of the thermal gas sensor 100 and information about a pressure in an environment of the thermal gas sensor 100 as input variables of a drift correction when determining the information 240 about the gas concentration, and to obtain the information 240 about the gas concentration as a result of the drift correction.

[0301] According to a twelfth aspect with reference to at least one of the first to eleventh aspects, the evaluation arrangement 200 is designed to obtain the combination signal 230 based on a quotient between amplitude information 210, 220, which is dependent on the information 210 about the amplitude of the detector signal of at least the first detector 130; and phase information 210, 220, 400, 410, which is dependent on the information 210 about the first phase difference; and wherein the evaluation arrangement 200 is designed to determine the information 240 about a concentration of a gas depending on the combination signal 230.

[0302] According to a thirteenth aspect with reference to at least one of the first to twelfth aspects, the evaluation arrangement 200 is designed to evaluate the combination signal sigV 230 according to sigV = sigUss * Kav / sigPhi * Kpv to obtain, where sigUss is amplitude information 210, 220 that depends on the information 210 about the amplitude of the detector signal of the first detector 130; and where sigPhi is phase information 210, 220, 400, 410 that depends on the information 210 about the first phase difference; and where Kav and Kpv are constants.

[0303] According to a fourteenth aspect with reference to at least one of the first to thirteenth aspects, the evaluation arrangement 200 is designed to obtain information about how much heat is dissipated by the heater during a heating period 302 and to determine the information 240 about a concentration of a gas depending on the information about how much energy is dissipated by the heater during the heating period 302.

[0304] According to a fifteenth aspect with reference to the fourteenth aspect, the evaluation arrangement 200 is designed to obtain the information on how much heat is dissipated by the heater during a heating period 302 based on a measurement of a current flow 310 through the heater at a predetermined heating voltage 300.

[0305] According to a sixteenth aspect with reference to the fifteenth aspect, the evaluation arrangement 200 is designed to obtain the current flow 310 shortly after the predetermined heating voltage 300 is switched on and shortly before the predetermined heating voltage 300 is switched off.

[0306] According to a seventeenth aspect, a method for evaluating signals from a thermal gas sensor having at least one heater and at least one detector comprises the following step: obtaining information about an amplitude of a detector signal from a first detector and information about a first phase difference between a heater signal and the detector signal from the first detector; and wherein a combination signal is formed as an intermediate variable depending on the information about the amplitudes of the detector signal and depending on the information about the first phase difference, and wherein information about a gas concentration or information about a thermal conductivity of a fluid is determined based on the combination signal.

[0307] According to an eighteenth aspect, a method for evaluating signals from a thermal gas sensor having at least one heater and two detectors arranged at different distances from the heater comprises the following step: obtaining information about an amplitude of a detector signal from a first detector, information about an amplitude of a detector signal from a second detector, information about a first phase difference between a heater signal and the detector signal from the first detector, and information about a second phase difference between the heater signal and the detector signal from the second detector;and wherein a combination signal is formed as an intermediate variable depending on the information about the amplitudes of the detector signals and depending on the information about the first phase difference and depending on the information about the second phase difference, and wherein information about a gas concentration or information about a thermal conductivity of a fluid is determined based on the combination signal;

[0308] A nineteenth aspect relates to a computer program comprising program code for carrying out the method according to aspect 17 or aspect 18 when the program runs on a computer.

[0309] According to a twentieth aspect, an evaluation arrangement 200 for a thermal gas sensor 100 having at least one heater 120 and at least one detector 130, 140 is designed to regulate 250, 252 a heating power applied to the heater 120 as a function of at least one sensor signal from at least one detector 130, 140, in order to bring the at least one sensor signal into a predetermined value range; and to take into account information 122 about the heating power when deriving information 240 about a gas concentration from the sensor signals.

[0310] According to a twenty-first aspect with reference to the twentieth aspect, the evaluation arrangement 200 is designed to apply a periodic signal 260 to the heater 120.

[0311] According to a twenty-second aspect with reference to at least one of the twentieth to twenty-first aspects, the evaluation arrangement 200 is designed to switch the heating power applied to the heater 120 between two values.

[0312] According to a twenty-third aspect with reference to at least one of the twentieth to twenty-second aspects, the evaluation arrangement 200 is designed to regulate 250, 252 an amplitude of the heating power such that both a minimum value of the at least one sensor signal and a maximum value of the at least one sensor signal lie within the predetermined value range.

[0313] According to a twenty-fourth aspect with reference to at least one of the twentieth to twenty-third aspects, the evaluation arrangement 200 is designed to adjust or regulate 250, 252 an amplitude of the heating power such that an amplitude of the at least one sensor signal lies in a predetermined amplitude range.

[0314] According to a twenty-fifth aspect with reference to at least one of the twentieth to twenty-fourth aspects, the evaluation arrangement 200 is designed to set or regulate sampling times at which a sensor signal is sampled 270, 280, 290.

[0315] According to a twenty-sixth aspect with reference to the twenty-fifth aspect, the evaluation arrangement 200 is designed to set the sampling times 270, 280, 290 such that sampling occurs at a time at which the sensor signal reaches a maximum value and such that sampling occurs at a time at which the sensor signal reaches a minimum value.

[0316] According to a twenty-seventh aspect with reference to at least one of the first to twenty-sixth aspects, the evaluation arrangement 200 is designed to combine a sensor signal from at least one detector 130, 140 with an offset signal generated by a digital-to-analog converter in order to obtain an input signal for the analog-to-digital converter in order to adjust the offset signal in order to ensure that the input signal of the analog-to-digital converter remains within a predetermined range during an entire period of the sensor signal.

[0317] According to a twenty-eighth aspect with reference to at least one of the twenty-fifth to twenty-seventh aspects, the evaluation arrangement 200 is designed to regulate 250, 252 the heating power only when an adjustment or regulation 270, 280, 290 of the sampling times is in a steady state and when an adjustment of the offset signal is in a steady state.

[0318] According to a twenty-ninth aspect with reference to at least one of the twenty-fifth to twenty-eighth aspects, the evaluation arrangement 200 is designed to stop the control 250, 252 of the heating power while an adjustment or regulation 270, 280, 290 of the sampling times takes place and / or while an adjustment of the offset signal takes place.

[0319] According to a thirtieth aspect with reference to at least one of the twentieth to twenty-ninth aspects, the evaluation arrangement 200 is designed to regulate both an average heating power or a maximum heating power and an amplitude of the heating power 250, 252.

[0320] According to a thirty-first aspect, a method for operating an evaluation arrangement for a thermal gas sensor having at least one heater and at least one detector comprises regulating a heating power applied to the heater as a function of at least one sensor signal from at least one detector in order to bring the at least one sensor signal into a predetermined value range; and taking into account information about the heating power when deriving information about a gas concentration from the at least one sensor signal.

[0321] A thirty-second aspect relates to a computer program for carrying out the method according to aspect 31 when the computer program is executed on a computer.

[0322] According to a thirty-third aspect, an evaluation arrangement 200 for a thermal gas sensor 100 with at least one heater 120 and at least one detector 130, 140 is designed to apply a periodic signal 260 with a predetermined period to the heater 120, and to sample 270 at least one sensor signal from a detector 130, 140 at three points in time, wherein a second sampling time is offset by 90 degrees with respect to the period from a first sampling time, and wherein a third sampling time is offset by 180 degrees with respect to the period from the first sampling time, and to detect 280, based on three sampling values ​​based on a sampling of the sensor signal at the first sampling time, at the second sampling time, and at the third sampling time, whether a first sampling value and a third sampling value represent a maximum value and a minimum value of the sensor signal.

[0323] According to a thirty-fourth aspect with reference to the thirty-third aspect, the evaluation arrangement 200 is designed to change 290 sampling times depending on the detection 280 of whether the first sample value and the third sample value represent a maximum value and a minimum value of the sensor signal.

[0324] According to a thirty-fifth aspect with reference to the thirty-fourth aspect, the evaluation arrangement 200 is designed to set or adjust 270, 280, 290 the sampling times such that the first sample value represents a first extreme value of the sensor signal and the third sample value represents a second extreme value of the sensor signal.

[0325] According to a thirty-sixth aspect with reference to at least one of the thirty-fourth to thirty-fifth aspects, the evaluation arrangement 200 is designed to take into account information about a time of passage of the sensor signal through a predetermined threshold value when setting or adjusting 270, 280, 290 the sampling times.

[0326] According to a thirty-seventh aspect with reference to at least one of the thirty-third to thirty-sixth aspects, the evaluation arrangement 200 is designed to check 280 whether a second sample value at the second sampling time is equal to an average value of the first sample value at the first sampling time and the third sample value at the third sampling time, and to detect, depending on the check 280, whether the first sample value and the third sample value represent a maximum value and a minimum value of the sensor signal.

[0327] According to a thirty-eighth aspect with reference to at least one of the thirty-third to thirty-seventh aspects, the evaluation arrangement 200 is designed to apply a periodic square-wave signal with a duty cycle of preferably 50% to the heater 120.

[0328] According to a thirty-ninth aspect with reference to at least one of the thirty-third to thirty-eighth aspects, the evaluation arrangement 200 is designed to combine a sensor signal from at least one detector 130, 140 with an offset signal generated by a digital-to-analog converter in order to obtain an input signal for an analog-to-digital converter, and to adjust the offset signal in order to ensure that the input signal of the analog-to-digital converter remains within a predetermined range throughout an entire period of the sensor signal, and to adjust the sampling times 270, 280, 290 after adjusting the offset signal; and to perform a renewed check 280 after changing the sampling times 290 to determine whether sample values ​​obtained with the changed setting of the sampling times continue to lie within the predetermined range.

[0329] According to a fortieth aspect, with reference to at least one of the thirty-third to thirty-ninth aspects, the evaluation arrangement 200 is designed to regulate a heating power applied to the heater 120 as a function of at least one sensor signal from at least one detector 130, 140, in order to bring the at least one sensor signal into a predetermined value range; and to take into account information 122 about the heating power when deriving information 240 about a gas concentration from the sensor signals.

[0330] According to a forty-first aspect, a method for operating a thermal gas sensor having at least one heater and at least one detector comprises applying a periodic signal having a predetermined period to the heater, and wherein at least one sensor signal is sampled by a detector at three points in time 270, wherein a second sampling time is offset by 90 degrees relative to a first sampling time, with respect to the period, and wherein a third sampling time is offset by 180 degrees relative to the first sampling time, and wherein, based on three sampling values ​​based on a sampling of the sensor signal at the first sampling time, at the second sampling time, and at the third sampling time, it is detected 280 whether a first sampling value and a third sampling value represent a maximum value and a minimum value of the sensor signal.

[0331] Although some aspects have been described in connection with a device, it should be understood that these aspects also represent a description of the corresponding method, so that a block or component of a device can also be understood as a corresponding method step or as a feature of a method step. Analogously, aspects described in connection with or as a method step also represent a description of a corresponding block, detail, or feature of a corresponding device. Some or all of the method steps can be carried out by (or using) a hardware apparatus, such as a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, some or more of the key method steps can be carried out by such an apparatus.

[0332] Depending on specific implementation requirements, embodiments of the invention may be implemented in hardware or software. The implementation may be performed using a digital storage medium, such as a floppy disk, a DVD, a Blu-ray Disc, a CD, a ROM, a PROM, an EPROM, an EEPROM, or a FLASH memory, a hard disk, or other magnetic or optical storage device storing electronically readable control signals that can interact or cooperate with a programmable computer system to perform the respective method. Therefore, the digital storage medium may be computer-readable.

[0333] Some embodiments according to the invention thus comprise a data carrier having electronically readable control signals capable of interacting with a programmable computer system such that one of the methods described herein is carried out.

[0334] In general, embodiments of the present invention may be implemented as a computer program product having program code, wherein the program code is operable to perform one of the methods when the computer program product is run on a computer.

[0335] The program code can, for example, also be stored on a machine-readable medium.

[0336] Other embodiments include the computer program for performing one of the methods described herein, wherein the computer program is stored on a machine-readable carrier.

[0337] In other words, an embodiment of the method according to the invention is thus a computer program which has a program code for carrying out one of the methods described herein when the computer program runs on a computer.

[0338] A further embodiment of the method according to the invention is thus a data carrier (or a digital storage medium or a computer-readable medium) on which the computer program for performing one of the methods described herein is recorded. The data carrier, the digital storage medium, or the computer-readable medium are typically physical and / or non-perishable or non-transitory.

[0339] A further embodiment of the method according to the invention is thus a data stream or a sequence of signals that represents the computer program for carrying out one of the methods described herein. The data stream or the sequence of signals can be configured, for example, to be transferred via a data communication connection, for example via the Internet.

[0340] A further embodiment comprises a processing device, for example a computer or a programmable logic device, which is configured or adapted to carry out one of the methods described herein.

[0341] A further embodiment comprises a computer on which the computer program for performing one of the methods described herein is installed.

[0342] A further embodiment according to the invention comprises a device or a system designed to transmit a computer program for performing at least one of the methods described herein to a recipient. The transmission can be electronic or optical, for example. The recipient can be, for example, a computer, a mobile device, a storage device, or a similar device. The device or system can, for example, comprise a file server for transmitting the computer program to the recipient.

[0343] In some embodiments, a programmable logic device (e.g., a field-programmable gate array, an FPGA) may be used to perform some or all of the functionality of the methods described herein. In some embodiments, a field-programmable gate array may interact with a microprocessor to perform any of the methods described herein. In general, in some embodiments, the methods are performed by any hardware device. This may be general-purpose hardware, such as a computer processor (CPU), or method-specific hardware, such as an ASIC.

[0344] The devices described herein may be implemented, for example, using a hardware apparatus, or using a computer, or using a combination of a hardware apparatus and a computer.

[0345] The devices described herein, or any components of the devices described herein, may be implemented at least partially in hardware and / or in software (computer program).

[0346] The methods described herein may be implemented, for example, using a hardware apparatus, or using a computer, or using a combination of a hardware apparatus and a computer.

[0347] The methods described herein, or any components of the methods described herein, may be implemented at least in part by hardware and / or by software.

[0348] The above-described embodiments are merely illustrative of the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be apparent to others skilled in the art. Therefore, it is intended that the invention be limited only by the scope of the following claims and not by the specific details presented in the description and explanation of the embodiments herein. 1.5 Literatur

[0349] [Baehr 2008] HD Baehr and K. Stephan, Heat and Mass Transfer, 6th revised edition ed Springer-Verlag, 2008. [Simon 2002] I. Simon and M. Arndt. Thermal and gas-sensing properties of a micromachined thermal conductivity sensor for the detection of hydrogen in automotive applications. Sensors and Actuators A: Physical, 97-98, pp. 104-108, April 2002. doi: 10.1016 / S0924-4247(01)00825-1. [Baar 2001] JJ van Baar, RJ Wiegerink, TSJ Lammerink, GJM Krijnen, and M. Elwenspoek. Micromachined structures for thermal measurements of fluid and flow parameters. Journal of Micromechanics and Microengineering, 11(4), pp. 311-318, July 2001. doi: 10.1088 / 0960-1317 / 11 / 4 / 304. [IST AG 2011] DE 10 2011 075519 A1; Filing date: May 9, 2011; Disclosure date: November 15, 2012; Title: Method and device for thermally determining the mass flow rate of a medium in a line; Applicant: Innovative Sensor Technology IST AG [CH]; Inventor: Christoph Hepp.Florian Krogmann, Mirko Lehmann, Jiri Polak. [IST AG 2013] DE 10 2013 102398 A1; Filing date: March 11, 2013; Disclosure date: September 11, 2014; Title: Thermal flow sensor for determining a gas or the composition of a gas mixture, as well as its flow velocity; Applicant: Innovative Sensor Technology IST AG [CH]; Inventors: Christoph Hepp, Florian Krogmann. [IST AG 2015] DE 10 2015 107584 A1; Filing date: May 13, 2015; Disclosure date: November 17, 2016; Title: Method for determining a product of heat capacity and density: Applicant: Innovative Sensor Technology IST AG [CH]; Inventors: Christoph Hepp, Florian Krogmann, Diego Reyes. [Grien 2012] H. Grienauer - AMS GmbH, Dielheim: Gas analysis with thermally modulated thermal conductivity sensors with Fourier analysis of the measurement signal; 16th GMA / ITG Conference on Sensors and Measurement Systems 2012; May 22-23, 2012; Nuremberg, Germany; Chapter 1.2 Chemical Sensors; pp. 54-61; DOI: 10.5162 / sensoren2012 / 1.2.2; ISBN: 978-3-9813484-0-8

[2003] A. Al-Salaymeh, M. Alhusein, F. Durst, (2003) "Development of a two-wire thermal flow sensor for industrial applications", Journal of Quality in Maintenance Engineering, Vol. 9 Issue: 2, pp. 113-131, https: / / doi.org / 10.1108 / 13552510310482370

[2009] DE 10 2008 047511 A1; Filing date: September 11, 2008; Disclosure date: March 19, 2009; Title: Device and method for respiratory gas analysis; Applicant: Weinmann Geräte für Medizin GmbH + Co. KG; Inventor: Florian Dietz.

[2011] Kliche, Billat, Messner, Zengerle: Sensor system for thermal gas analysis of gas mixtures, conference paper in Proc. of Microsystems Technology Congress 2011, Darmstadt, Germany, (Poster), 10.Oktober 2011, Seite 875-878, ISBN: 978-3-8007-3367-5 (2011)

[2011] Sensor for gas analysis based on thermal conductivity, specific heat capacity and thermal diffusivity; K Kliche, S Billat, F Hedrich, C Ziegler, R Zengerle; Micro Electro Mechanical Systems (MEMS), 2011 IEEE 24th International Conference on Micro Electro Mechanical Systems.

[2013] Sensor for thermal gas analysis based on micromachined siliconmicrowires; K Kliche, G Kattinger, S Billat, L Shen, S Messner, R Zengerle, IEEE Sensors Journal 13 (7), 2626-2635; 2013.

Claims

1. An evaluation arrangement (200) for a thermal gas sensor (100) with at least one heater (120) and two detectors (130, 140), wherein the evaluation arrangement (200) is configured to control (250, 252) a heating power applied to the heater (120) dependent on at least one sensor signal (210, 220) from at least one of the two detectors (130, 140) in order to bring the at least one sensor signal (210, 220) into a predetermined value range; and wherein the evaluation arrangement (200) is configured to consider information (122) about the heating power when deriving information (240) about a gas concentration from the sensor signals of the two detectors (130, 140).

2. The evaluation arrangement (200) according to claim 2, wherein the evaluation arrangement (200) is configured to apply a periodic signal (260) to the heater (120).

3. The evaluation arrangement (200) according to claim 1 or 2, wherein the evaluation arrangement (200) is configured to switch the heating power applied to the heater (120) between two values.

4. The evaluation arrangement (200) according to any of claims 1 to 3, wherein the evaluation arrangement (200) is configured to control (250, 252) an amplitude of the heater power such that a minimum value of the at least one sensor signal (210, 220) and a maximum value of the at least one sensor signal (210, 220) are in the predetermined value range.

5. The evaluation arrangement (200) according to any of claims 1 to 4, wherein the evaluation arrangement (200) is configured to set or adjust (250, 252) an amplitude of heating power such that an amplitude of the at least one sensor signal (210, 220) is in a specified amplitude range.

6. The evaluation arrangement (200) according to any of claims 1 to 5, wherein the evaluation arrangement (200) is configured to set or adjust (270, 280, 290) sampling times at which the sensor signal (210, 220) is sampled.

7. The evaluation arrangement (200) according to claim 6, wherein the evaluation arrangement (200) is configured to set (270, 280, 290) the sampling times such that sampling is carried out at a point in time at which the sensor signal (210, 220) reaches a maximum value, and such that the sampling is carried out at a point in time at which the sensor signal reaches a minimum value.

8. The evaluation arrangement (200) according to any of claims 1 to 7, wherein the evaluation arrangement (200) is configured to combine a sensor signal (210, 220) from at least one detector (130, 140) with an offset signal generated by a digital-analog converter in order to obtain an input signal for the analog-digital converter, wherein the evaluation arrangement (200) is configured to adjust the offset signal in order to achieve that the input signal of the analog-digital converter remains within a predetermined range during an entire period of the sensor signal (210, 220).

9. The evaluation arrangement (200) according to any of claims 6 to 8, wherein the evaluation arrangement (200) is configured to control (250, 252) the heating power only when the sampling times are set or adjusted (270, 280, 290) in a steady state, and when the offset signal is adjusted in a steady state.

10. The evaluation arrangement (200) according to any of claims 6 to 9, wherein the evaluation arrangement (200) is configured to stop controlling (250, 252) the heating power while the sampling times are being set or adjusted (270, 280, 290) and / or while the offset signal is being adjusted.

11. The evaluation arrangement (200) according to any of claims 1 to 10, wherein the evaluation arrangement (200) is configured to control (250, 252) a mean heating power or a maximum heating power as well as an amplitude of the heating power.

12. A method for operating an evaluation arrangement (200) for a thermal gas sensor (100) with at least one heater (120) and two detectors (130, 140), wherein the method includes controlling a heating power applied to the heater (120) dependent on at least one sensor signal (210, 220) from at least one of the two detectors (130, 140) in order to bring the at least one sensor signal (210, 220) into a predetermined value range; and wherein the method includes considering information about the heating power when deriving information about a gas concentration from the sensor signals (210, 220) of the two detectors (130, 140).

13. A computer program for performing the method according to claim 12 when the computer program runs on a computer.