Gas detector including sensor component and oxidation component, and gas detection method

Abstract

To provide a gas detection device and process for monitoring an area for a combustible target gas.SOLUTION: A gas sample (G) reaches a measuring chamber from the area. A semiconductor sensor (1) includes an electrically conductive sensor component (10). The electrically conductive sensor component (10) has an electrical detection variable. With decreasing concentration of the combustible target gas in the measuring chamber (9), the electrical detection variable increases in some embodiments and decreases in other embodiments. An oxidation component (2) can oxidize the combustible target gas in the measuring chamber. The detection variable is measured at a detection time, and the oxidation component (2) is in a switched-on state or is switched on. The oxidation component (2) oxidizes at least a part of the combustible target gas in the measuring chamber (9) up to a reference time. The detection variable is measured again at the reference time. The difference between the measured value at the reference time and the measured value at the detection time is an indicator for the concentration of the combustible target gas in the measuring chamber (9).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a gas detection apparatus and method for monitoring a spatial region for a combustible target gas.

[0002] In one application, the present invention is directed to a method for producing a combustible target gas, such as methane (CH 4 ) is used to detect the presence of the target gas even when its concentration is low, e.g., below 10 ppm.

[0003] The present invention is based on the object of providing a gas detection device and a gas detection method that are capable of reliably detecting a combustible target gas even when the target gas is present in a relatively low concentration and / or when changes in environmental conditions can significantly affect the measurement.

[0004] This problem is solved by a gas detection device having the features of claim 1 and by a gas detection method having the features of claim 13. Advantageous configurations of the gas detection device according to the invention are, in so far as this is reasonable, also advantageous configurations of the gas detection method according to the invention and vice versa.

[0005] The gas detection device according to the present invention and the gas detection method according to the present invention are adapted to detect at least one combustible target gas, such as methane (CH 4 It is possible to monitor a spatial area for a gas detection device according to the invention. The method according to the invention is carried out with the gas detection device according to the invention. The spatial area is, for example, the area of ​​a production plant or a mine, or the interior of a building or a vehicle or an aircraft.

[0006] In the following, reference is made to a "flammable target gas". The gas sample in the measurement chamber may contain multiple flammable target gases at the same time. The term "flammable target gas" is also intended to indicate the situation where different flammable target gases are present in the measurement chamber. The term "detection of target gas" as used below includes the step of detecting the presence of at least one target gas. In one configuration, it is predefined which flammable target gas is detected. In another application, all flammable target gases in the spatial region are detected.

[0007] The gas sensing device includes a measurement chamber, and the gas sensing device is configured, and the method includes, for continuously or at least temporarily flowing a gas sample from a monitored region into the measurement chamber, e.g., by suction and / or diffusion.

[0008] A conductive sensor component and an oxidation component are arranged in or adjacent to the measurement chamber. The sensor component has a measurable electrical sensing variable and is in surface contact with the gas sample in the measurement chamber. This contact influences the measurable electrical sensing variable of the sensor component, in particular the electrical resistance, in the following way: in a first realization, the lower the concentration of the combustible target gas in the gas sample in the measurement chamber, the higher the value of the sensing variable of the sensor component. In a second realization, the lower the concentration of the combustible target gas in the gas sample in the measurement chamber, the lower the value of this sensing variable. In both realizations, the sensing variable correlates with the target gas concentration in the gas sample. Of course, there may also be cases where the gas sample does not contain any target gas, and therefore the sensing variable is not significantly affected or does not change compared to a reference condition without target gas.

[0009] The oxidation component can be switched on for use and can optionally be switched on and off during use. When switched on, the oxidation component is capable of oxidizing combustible gas in the measurement chamber, provided, of course, that combustible gas is present in the measurement chamber.

[0010] NOTE: The terms "switched on" and "switched off" as used above and below can refer to either an abrupt or gradual transition from the switched off state to the fully switched on state.

[0011] The gas detection device further comprises a detection sensor capable of measuring the magnitude of a sensed variable of the sensor component, for example the actual electrical resistance or voltage across the sensor component, or the intensity of the current flowing through the sensor component, or the total charge.

[0012] The gas detection device further comprises a signal processing and evaluation unit capable of receiving and processing the signal from the detection sensor. In one configuration, the gas detection device comprises a housing, and the other components just mentioned are inside this housing. In another configuration, the evaluation unit is arranged outside the housing, and the signal of the detection sensor is transmitted, preferably wirelessly, to this spatially separated evaluation unit.

[0013] The gas detection device is configured to perform the following steps, and the method according to the invention comprises the following steps: - the oxidation component is switched on or the oxidation component is switched on. During the oxidation period, the switched-on oxidation component completely or at least partially oxidizes the combustible target gas or all combustible target gases in the measurement chamber. The process of oxidizing the combustible target gas by the oxidation component reduces the amount of combustible target gas in the measurement chamber and possibly, but not necessarily, eliminates all combustible target gas in the measurement chamber. Of course, it is possible that there was no combustible target gas in the measurement chamber already at the beginning of the oxidation period, especially if there is currently no combustible target gas in the monitored area. At a sensing time and a reference time, the sensing sensor measures the sensing variable of the sensor component, more precisely the magnitude of the sensing variable at each time. The sensing time is before or even after the reference time. By measuring the magnitude at two different times, there are two measurements of the sensing variable (or more precisely, two measurements of the magnitude of the sensing variable), where both measurements relate to two different times. - the gas detection device is operated such that the following conditions arise: if combustible target gas is present in the monitored area, then at the time of detection, combustible target gas is also present in the measurement chamber; the target gas concentration in the measurement chamber can be just the same as in the monitored area or lower; at the reference time, due to oxidation by the oxidizing component, there is less combustible target gas in the measurement chamber than at the time of detection, or even no combustible target gas is present even if combustible target gas is present in the area; if combustible target gas is present in the monitored area, due to oxidation, at the reference time, there is a lower concentration of combustible target gas in the measurement chamber than in the monitored area and than in the measurement chamber at the time of detection, or even no combustible target gas is present even if combustible target gas is present in the monitored area. - at least during the oxidation period, the oxidation component is switched on and is capable of oxidizing the combustible target gas in the measurement chamber. In a first alternative, the detection time is at or before the start of the oxidation period and the reference time is at or after the end of the oxidation period. In a second alternative, conversely, the reference time is at or before the start of the oxidation period and the detection time is at or after the end of the oxidation period. If the oxidation component is switched on continuously, the period from the earlier of both time points to the later is used as the oxidation period. - the evaluation unit calculates the difference between the measured value of the detection variable of the sensor element measured by the detection sensor at the detection time and the measured value of the detection variable measured by the detection sensor at the reference time. If a combustible target gas occurs in the monitored area, then at the detection time, there is combustible target gas in the measuring chamber. At the reference time, there is less or no combustible target gas at all. - in a first alternative, the evaluation unit automatically determines whether or not a combustible target gas is present in the gas sample as a function of this difference in the measured values. This determination further depends on whether the detection variable becomes larger or smaller with increasing concentration of the target gas and / or on the absolute value of the difference, i.e. |dist|. In a second alternative, the evaluation unit automatically determines, at least approximately, the concentration of the combustible target gas in the gas sample as a function of the difference in the measured values. Preferably, the evaluation unit in the second alternative applies a stored relationship between the difference in the measured values ​​and the target gas concentration to the calculated difference. At least in the second alternative, preferably the oxidation component is switched off at the time of detection. - Both of these alternative forms of detecting the combustible target gas and determining its concentration can be combined.

[0014] According to the first realization, the lower the concentration of the target gas in the measurement chamber, the greater the detected variable of the sensor element. Therefore, the measurement value of the detected variable at the reference time point is greater than the measurement value of the detected variable at the detection time point, which presupposes that combustible target gas is present in the monitored area and therefore also in the measurement chamber. Therefore, according to the second realization, the measurement value of the detected variable at the reference time point is smaller than the measurement value of the detected variable at the detection time point.

[0015] If there is no combustible target gas in the monitored area and therefore in the measuring chamber, the two measured values ​​of the sensed variable measured at both times are ideally equal. In practice, if there is no combustible target gas in the monitored area and therefore also in the measuring chamber at the time of detection, the difference may not be zero due to different environmental conditions. However, in the absence of target gas, this difference between the two measured values ​​is usually smaller in absolute value |dist| than the difference that would result from the presence of combustible target gas in the measuring chamber at the time of detection and the oxidation component oxidizing at least a portion of the combustible target gas in this measuring chamber during the oxidation period. Even if the oxidation component oxidizes only a portion of the combustible gas in the measuring chamber and not all of it, the difference is usually larger than if there was no combustible target gas in the area and therefore also in the measuring chamber. A non-zero difference or being outside a preset tolerance range is therefore a relatively reliable indicator that combustible target gas is present in the monitored area and therefore also in the measuring chamber at the time of detection.

[0016] Upon contact with the combustible target gas, the sensed variable of the sensor element often changes in a measurable manner, even if the combustible target gas is present in the measurement chamber only in low concentrations. However, the sensed variable usually depends not only on the concentration of the combustible target gas, but also on the environmental conditions, in particular the environmental temperature and humidity, and optionally also on the environmental pressure. The value that the sensed variable takes in the absence of combustible target gas in the measurement chamber is often also referred to as the zero value (reference value). Gas detection devices known from the prior art with a sensor element having a sensed variable that responds to the concentration of the combustible target gas often have the following disadvantages: the zero point is highly dependent on the environmental conditions and is usually unknown; or a sensor for the relevant environmental conditions is required, i.e. an additional sensor is required.

[0017] The present invention solves this problem by having the oxidation component oxidize the combustible target gas in the measurement chamber during the oxidation period, and thus measure approximately the actual zero point of the sensing variable of the sensor component at the reference time point. The designation "actual zero point" indicates that the zero point generally depends on changes in environmental conditions and may therefore vary. The time interval between both times is usually very short, so that the environmental conditions do not change significantly during this time interval, and therefore, despite the time interval, the measurement value at the reference time point can be used as the zero point for the measurement at the sensing time point. The difference calculated by the present invention corresponds sufficiently accurately to the difference between the measurement value at the sensing time point and the (actual) zero point at the sensing time point.

[0018] The present invention avoids the need to recalibrate the gas detection device before each use to find the actual zero point. As just described, the zero point is at least approximately obtained automatically by measurements at a reference point in time. In many cases, the present invention also eliminates the need for the gas detection device to include sensors for environmental conditions.

[0019] The present invention also eliminates the need to calibrate the gas detection device during use in order to adapt it to possible zero point changes. In the case of relatively rapid changes in environmental conditions or rapid changes in the target gas concentration, the gas detection device will also provide erroneous results, since the result of the calibration, i.e. the change in the zero point, may already be out of date again. On the other hand, the gas detection device according to the present invention will often provide reliable results even in the case of rapid changes in environmental conditions or rapid changes in the target gas concentration, since the interval between the two points in time can be selected to be sufficiently short, and the measurement and evaluation results do not depend on the predetermined zero point, but only on its difference. The interval between the two points in time can be set, on the one hand, as large as necessary, i.e. such that at least a portion of the combustible target gas is oxidized at the reference point, and, on the other hand, as small as possible. Since the presence of the target gas is determined based on the difference between the two actual measured values, even very low concentrations of the target gas can often be detected reliably and false alarms are often avoided. In many cases, detection that relies on accurate knowledge of the correct zero point would only be unreliable.

[0020] According to the invention, the sensor component has an electrical sensing variable which in a first embodiment is greater and in a second embodiment is smaller for lower target gas concentrations. This sensing variable is in particular an electrical resistance in one embodiment, an electrical capacitance in another embodiment and an electric potential in a third embodiment. The sensor component may, for example, comprise: - a semiconductor whose electrical resistance depends on the concentration of the target gas, or - Heat flow sensors, whose temperature depends on the target gas concentration, or - a photoelectric sensor which generates an electric signal according to the intensity of the electromagnetic radiation incident thereon, the electromagnetic radiation being attenuated by the target gas; - a photoionization detector which generates an electrical signal in response to ionization; - a photoacoustic sensor that generates an electrical signal in response to an acoustic effect that depends on the concentration of the target gas, or - An electrochemical sensor that generates a current whose strength and / or voltage depends on the concentration of the target gas.

[0021] According to the invention, the oxidation component oxidizes at least a portion of the combustible target gas in the measurement chamber during the oxidation period. This oxidized portion is preferably at least 30%, particularly preferably at least 50%, in particular at least 80% of the amount of combustible target gas present in the measurement chamber at the beginning of the oxidation period. In one configuration, the oxidation component oxidizes all of the combustible target gas in the measurement chamber during the oxidation period.

[0022] In one configuration, the gas detection device further comprises a heating element, which is capable of heating the gas sample in the measurement chamber. The heating element can be switched on and off again and is therefore selectively operable in a switched-on and switched-off state. According to this configuration, the oxidation part can also be switched on and off and is therefore selectively operable in a switched-on or switched-off state. According to a configuration in which a heating element is used, the method further comprises the following steps, the gas detection device being configured to carry out the following additional steps: At the beginning of the heating period the heating element is switched on. At the end of the heating period the heating element is switched off again. - The heating element is switched on and heats up. During a heating period, the heating element, which is switched on, heats the gas in the measuring chamber. During the heating period, the oxidation part is in the switched-off state. Conversely, the heating element is in the switched-off state at least during the oxidation period. Preferably, at any one time, either the oxidation part or the heating element is in its respective switched-on state, but not both parts at the same time in their respective switched-on states.

[0023] According to the invention, the target gas concentration to be determined influences the sensing variable of the sensor component. The sensing variable usually further depends on the temperature of the sensor component. This temperature is influenced by the switched-on oxidizing component and the process of switching the oxidizing component on and off. In configurations in which a heating element is used, the heating element inputs more heat energy in the switched-on state than in the switched-off state, thereby reducing the influence of the oxidizing component on the sensor component. Reducing this influence increases the reliability of the sensing result. Ideally, the switched-on heating element and the switched-on oxidizing component cause the same amount of heat energy input per unit time into or on the sensor component.

[0024] According to the presently described configuration, the heating element is switched on during the heating period and switched off during the oxidation period, preferably for the entire oxidation period. The oxidation part is switched on during the oxidation period and switched off for at least part of the heating period, preferably for the entire heating period. Thus, preferably, the oxidation period and the heating period do not overlap at all or only at a certain point. It is also possible that neither the oxidation part nor the heating element is switched on during a further period.

[0025] In one implementation, the end of the heating period coincides with the start of the oxidation period. Alternatively, the end of the oxidation period coincides with the start of the heating period. Both of these configurations reduce the influence of the temperature of the oxidation component on the sensor component compared to configurations where the heating element is switched off and then the oxidation component is switched on only after a time interval or vice versa. Compared to configurations where both the heating element and the oxidation component are switched on at one time, this implementation saves electrical energy. Furthermore, it is easier to keep the amount of thermal energy input per unit time to the sensor component constant.

[0026] Preferably, the gas detection apparatus is in exactly one of the following states at all times during use: - The oxidation part is switched on and the heating element is switched off. - The heating element is switched on and the oxidation element is switched off. The measurement chamber is purged or a gas sample is flowed into the measurement chamber. Preferably, both the heating element and the oxidation part are switched off.

[0027] When not in use, the gas detection device may be switched off, ie, idle.

[0028] As already explained, both the switched-on oxidation component and the switched-on heating element exert thermal energy on the sensor component. Preferably, the amount of thermal energy input per unit time caused by the switched-on heating element is exactly the same as the amount of thermal energy input per unit time by the switched-on oxidation component. This statement applies in the absence of combustible target gas in the measurement chamber.

[0029] The amount of thermal energy input per unit time caused by the oxidation component depends on the geometry, especially the surface, and the temperature of the oxidation component, as well as on the distance between the oxidation component and the sensor component. If the amount of thermal energy input per unit time is the same and no combustible target gas is present in the measurement chamber, ideally the value of the detected variable is also the same, more precisely, when the oxidation component is switched on and the heating element is switched off, the detected variable ideally has the same value as when the oxidation component is switched off and the heating element is switched on. This is optionally the case only after a transient phase that occurs when the oxidation component or the heating element is switched on or off.

[0030] The implementation of the heating element just described eliminates in many cases the need to control the temperature of the detection sensors, oxidizing parts or heating elements, especially to a constant value.

[0031] According to the invention, the oxidation component is switched on at least during the oxidation period. In one embodiment, the oxidation component is switched off at least during the intake period. Thus, the oxidation component is switched on and / or off during continuous operation.

[0032] At least during the intake period, a fluid communication is established between the measurement chamber and the environment, and the gas sample flows from the monitored spatial region into the measurement chamber, for example by diffusion or suction. This intake period is before the oxidation period and ideally does not overlap with the oxidation period or only overlaps with it at a certain point. The detection time point is outside the oxidation period, preferably within the intake period, particularly preferably at the beginning of the intake period. During the intake period, the oxidation component is continuously or at least predominantly switched off, so that the oxidation component does not oxidize the combustible target gas during the intake period or oxidizes it only negligibly little. Thus, assuming that the monitored region contains combustible target gas, combustible target gas accumulates in the measurement chamber during the intake period.

[0033] A configuration in which the oxidation component is switched on and / or off during continuous operation often allows the measurement chamber to be in continuous fluid communication with the monitored area. There is no need to open or close the closure for the intake into the measurement chamber during continuous operation. In particular, in the case of a relatively low concentration of combustible target gas, the switched-on oxidation component oxidizes the combustible target gas in the measurement chamber so rapidly that the fluid communication does not lead to any notable falsification of the measurement result.

[0034] In one embodiment, the detection time point is at the beginning of the oxidation period. In a preferred embodiment, a time interval occurs between the inhalation period and the oxidation period. Within this time interval, a heating period occurs. Preferably, any heating element is switched on at the end of the inhalation period and switched off again at the end of the inhalation period, i.e. before or at the beginning of the oxidation period.

[0035] According to the invention, the oxidation component is switched on at least during the oxidation period and oxidizes the combustible target gas in the measurement chamber. The configurations described below can be combined with an oxidation component that can be switched on and off. However, the configurations described below eliminate the need to switch the oxidation component on and / or off during continuous operation. The oxidation component may be switched on continuously during continuous use. According to this alternative configuration, the measurement chamber can be operated selectively in an open or closed state. When the measurement chamber is in an open state, the gas sample can flow into the measurement chamber from the monitored area. Thus, in the open state, a fluid communication is established between the measurement chamber and the monitored area. In the closed state, the measurement chamber is sealed fluid-tight with respect to said area. "Fluid-tight" means excluding unavoidable gaps and gaps. Preferably, in the idle state, the gas detection device is switched off and fluid-tightly separated from the environment.

[0036] In this configuration, the gas sensing device comprises a closable opening, for example a valve or a slot with a flap or aperture for the opening. When this opening is open, the gas sample can flow from the environment into the measurement chamber. When the opening is closed, the gas sample cannot flow into the measurement chamber, since the measurement chamber is sealed against the environment. Preferably, the opening is closed during the oxidation period and is at least temporarily open before and / or after the oxidation period. However, it is also possible for gas to flow into the measurement chamber during the oxidation period. Usually, the amount of target gas flowing into the measurement chamber when the closure is open during the oxidation period will be less than the amount oxidized by the oxidation part during the oxidation period.

[0037] During the inhalation period, the measurement chamber is in an open state. Preferably, this inhalation period includes the detection time point or the inhalation period occurs before the detection time point. At the reference time point, the measurement chamber is preferably in a closed state.

[0038] During at least the oxidation period, the measuring chamber is in a closed state, and the oxidation component oxidizes the combustible target gas in the measuring chamber, ideally all of the combustible target gas. Since the measuring chamber is in a closed state, the combustible target gas cannot flow into the measuring chamber from the region. During the already mentioned intake period, the measuring chamber is in an open state. During this intake period, the combustible target gas accumulates in the measuring chamber, provided that the combustible target gas is present in the monitored region.

[0039] Both of these configurations can be combined, for example: during the oxidation period, the oxidation part is switched on and the measurement chamber is closed. During the suction period, the oxidation part is switched off and the measurement chamber is open. The combination of both of these configurations often makes it possible to detect the target gas more reliably, even if the target gas is only present in relatively low concentrations in the monitored area. Optionally, there is a heating period between the suction and oxidation periods.

[0040] In a first alternative form of the invention, the detection time is before the reference time. The gas sample has flowed into the measurement chamber at the latest by the detection time. The oxidation period starts at or after the detection time and ends before or at the reference time. Preferably, between the detection time and the reference time, the oxidation component is switched on and / or the measurement chamber is fluid-tightly separated from the monitored area.

[0041] Conversely, in a second alternative embodiment of the invention, the reference time is before the detection time. The oxidation period starts at or after the reference time and ends before or at the detection time. In one embodiment, the measurement chamber is fluid-tightly separated from the region at least during the oxidation period. By the reference time, the oxidation component oxidizes the combustible target gas in the measurement chamber. After the reference time and at least by the detection time, and optionally also thereafter, the gas sample flows into the measurement chamber. Preferably, between the reference time and the detection time, the oxidation component is switched off and / or a fluid communication is established between the measurement chamber and the region.

[0042] It is possible to operate the gas detection device such that a number of successive oxidation periods occur, with a gap between two successive oxidation periods, and the oxidation component oxidizes the target gas in the measurement chamber at least during each oxidation period. For each oxidation period, the magnitude of the detection variable is measured at the detection time and the reference time, respectively, and the evaluation according to the invention is performed again for each oxidation period. This often allows a relatively rapid detection of a combustible target gas.

[0043] In the configurations described below, it is preferably possible to switch the oxidation component on and off. In a first configuration, the time interval of the oxidation is preset constant. The duration of the oxidation period or each oxidation period is equal to this time interval of the oxidation. The time interval of the oxidation, and thus each oxidation period, is made as long as necessary on the one hand and as short as possible on the other hand. "As long as necessary" has the following meaning: even in the case of the highest expected concentration of combustible target gas in the measurement chamber, the oxidation component oxidizes the combustible target gas in the measurement chamber during the oxidation period so that at the end of the oxidation period the measurement chamber does not contain combustible target gas.

[0044] In a second configuration, the duration of the oxidation period or of at least one oxidation period, i.e. the time during which the oxidation component is switched on, depends on the concentration of the combustible target gas in the measurement chamber. This second configuration eliminates the need to pre-set the time interval of the oxidation constant. According to the second configuration, the gas detection device is further configured to perform the following steps, and the method further comprises the following steps: Perform at least one gradient calculation sequence, where one or all gradient calculation sequences include the following steps: The magnitude of the detected variable is measured at least at two time points, which are separated from one another in time, both of which are within the oxidation period. Preferably, the magnitude of the detected variable is measured at a detection time point and at least one further time point which is located after the detection time point in time. Preferably, a sampling rate for the measurement of the detected variable is preset, which sampling rate determines the time interval between two immediately successive measurement time points. - The course of the sensed variable over time during oxidation is approximately determined by the measurements. In the presence of combustible target gas in the measurement chamber, according to a first realization of the sensor component, the sensed variable increases with time until all the target gas is oxidized. The slope of the course of the sensed variable over time is therefore positive until all the target gas is oxidized. According to a second realization, the sensed variable decreases and the slope is negative until all the target gas is oxidized. In the absence of combustible target gas in the measurement chamber, the sensed variable remains approximately constant during the oxidation period in both realizations. - Depending on the measured values ​​of the detected variable, the magnitude of the slope of the detected variable, i.e. the magnitude for derivation of the time course of the detected variable over time, is calculated, preferably by the evaluation unit. In the simplest case, this magnitude of the slope is the difference between two measured values ​​of the detected variable measured at the two latest points in time. The calculated slope can vary over time.

[0045] If the slope of the time course of the detected variable falls below a preset limit value in terms of absolute value, the measurement of the detected variable is terminated. The latest point in time is used as the reference point in time. The measured value at the latest point in time is used as the measured value at the reference point in time. The limit value can be zero or greater. If the slope falls below the preset limit value, substantially all of the target gas in the measurement chamber is oxidized.

[0046] In the second configuration, the higher the concentration of combustible target gas in the measurement chamber, the longer the oxidation period. This second configuration often leads to a particularly fast detection result if no combustible target gas is present in the monitored area and thus in the measurement chamber. In this case, the slope is only influenced by the environmental conditions and usually remains below the pre-set limit value. On the other hand, this second configuration leads to reliable measurement results even in the presence of very high concentrations of combustible target gas. Since in this case too all combustible target gas in the measurement chamber is usually oxidized, the measured value at the second point in time (latest point in time) also serves reliably as a zero value in this case.

[0047] In a third configuration, a functional correlation is provided that describes the time course of the sensed variable during the oxidation period. The functional correlation includes at least one model parameter. Often, the functional correlation has the form of an exponential function, i.e., f(t)=AC*exp(-α*t), or f(t)=A*[1-C*exp(-α*t)] where A, C and α are model parameters.

[0048] During the oxidation period, the sensed variable (or, more precisely, the magnitude of the sensed variable) is measured multiple times and random samples are taken. Using these random samples, values ​​for the model parameters are automatically calculated. By extrapolation, it is often possible to predict the measured value at the second time point with sufficient confidence. The third configuration often provides fast and reliable measurement results for both low and high target gas concentrations.

[0049] In addition, in the third configuration, it is not necessary to preset a fixed oxidation time interval, but it is possible to preset a fixed number N>1 for the number of random sample measurements, i.e., random sample elements, and end the oxidation period when N random sample measurements are complete.

[0050] The second and third configurations can be combined with each other.

[0051] In one implementation, the oxidation component comprises a conductive sensor component. When the oxidation component is switched on, a current flows through the sensor component. When the oxidation component is switched off, no current flows through the sensor component. For example, the oxidation component is configured as a so-called pellistor and comprises a heating element, which acts as the sensor component. The oxidation component further comprises a ceramic coating arranged around the heating element and a catalytic coating on the ceramic coating or a catalytic admixture arranged in the ceramic coating. The heating element acts as the sensor component. A sensing sensor measures a sensing variable of the heating element.

[0052] In another implementation, the oxidation component and the sensor component are separated from each other. A voltage can be applied to the sensor component, so that a current flows through it, regardless of whether the oxidation component is switched on or off. According to this alternative implementation, the oxidation component is only used to oxidize a combustible target gas that may be present in the measurement chamber, but is not also used to detect this target gas. The detection sensor preferably does not measure the size of the oxidation component. In this alternative implementation, the oxidation component may also be configured as a pellistor.

[0053] In one application, the monitored spatial region is directly adjacent to the gas detection device, and the gas sample can flow into the measurement chamber through the inlet. In another application, a gap is created between the monitored spatial region and the gas detection device. The gas sample can only flow from the spatial region through the inlet into the measurement chamber through the fluid guiding unit, and cannot bypass this fluid guiding unit. Due to the spatial gap, the gas detection device is largely protected from environmental influences of the monitored region. The fluid guiding unit can in particular have the shape of a tube or pipe. Preferably, the gas detection device draws the gas sample from the monitored region through the fluid guiding unit.

[0054] In one configuration, the fluid transport unit is fluid-tightly connected to an adapter that can be attached to the gas detection device and removed again from the gas detection device, such that when the adapter is attached, the gas sample can only flow through the fluid guide unit to the measurement chamber, and when the adapter is removed, the gas sample can flow directly from the spatial region to the measurement chamber.

[0055] The gas detection device according to the present invention may be configured as a portable device, and the user may carry the portable device. Preferably, the portable device is provided with a dedicated power supply unit. The gas detection device according to the present invention may be configured as a stationary device, and may be at least temporarily connected to a stationary power supply network. The gas detection device according to the present invention may be provided with an output unit, and the alarm or the determined concentration is output to the output unit.

[0056] The present invention will now be described with reference to exemplary embodiments. [Brief description of the drawings]

[0057] [Figure 1] 1 is a diagram illustrating a schematic diagram of a first embodiment of a gas detection device according to the present invention; [Diagram 2] FIG. 2 is a schematic diagram of a second embodiment of a gas detection device according to the present invention; [Diagram 3] FIG. 2 is a diagram showing an example of a sequence including measurement of a gas detection device. [Figure 4] FIG. 2 is a diagram showing an example of an oxidized part. [Diagram 5] FIG. 1 shows an exemplary flow chart for use of a gas detection device.

[0058] FIG. 1 illustrates generally a first embodiment of a gas sensing device 100 in accordance with the present invention, and FIG. 2 illustrates a second embodiment.

[0059] Gas detection device 100 is used in applications to monitor a spatial region for the presence of and / or determine the concentration of a combustible gas, hereinafter referred to as a "target gas." The spatial region may be, for example, a refinery or other production plant, the interior of a building, a mine, a vehicle, or an aircraft. The combustible gas may be, for example, methane (CH4), methane (CH5), methane (CH6), methane (CH7), methane (CH8), methane (CH9), methane (CH10), methane (CH4), methane (CH11), methane (CH4), methane (CH5), methane (CH6), methane (CH7), methane (CH8), methane (CH9), methane (CH10), methane (CH11), methane (CH12), methane (CH13), methane (CH14), methane (CH15), methane (CH16), methane (CH17), methane (CH18), methane (CH19), methane (CH2), methane (CH2), methane (CH3), methane (CH4), methane (CH4), methane (CH4), methane (CH5), methane (CH5), methane (CH5), methane (CH6), methane (CH2), methane (CH3 ...5), methane (CH5), methane (CH5), methane (CH6), methane (CH5), methane (CH5), methane (CH5), methane (CH5), methane (CH6), methane (CH5), methane (CH5), methane (CH5), methane (CH5), methane (CH5), methane (CH5), methane (CH6), methane (CH5), methane (CH5), methane (CH5), methane (CH5), methane (CH5), methane (CH5), methane 4 ).

[0060] In another application, gas detection device 100 is used to perform an alcohol test on a subject. As is well known, if a subject consumes alcohol such that alcohol is still present in the subject's blood and / or mouth, the subject's breath will contain breath alcohol. In this application, gas detection device 100 includes a mouthpiece into which the subject blows, and at least a portion of the transmitted breath sample reaches the interior of gas detection device 100. Thus, in this application, gaseous breath alcohol is the combustible target gas.

[0061] In one implementation, the gas detection device 100 is a portable device that can be held by a person in one hand or attached to clothing or protective equipment and has a dedicated power supply unit. For example, a user carries such a gas detection device 100 while in an area where at least one combustible target gas may be present. Alternatively, a subject holds the gas detection device 100 in one hand and delivers a breath sample to the mouthpiece. The gas detection device 100 may be configured as a stationary device that can be connected to a stationary power supply grid and does not necessarily have to have a dedicated power supply unit.

[0062] Gas detection apparatus 100 comprises a housing 5 which fluid-tightly encloses a measuring chamber 9 - except for openings described below and except for unavoidable gaps and slits.

[0063] In a first embodiment, an inlet E of the housing 5 leads from the environment to the measurement chamber 9, and an outlet A of the housing 5 leads from the measurement chamber 9 to the environment. A controllable valve 6 is capable of selectively opening and closing the inlet E. A controllable valve 7 is capable of selectively opening and closing the outlet A. When the valve 6 is open, a gas sample G can flow from the environment, i.e. the monitored area, through the inlet E into the measurement chamber 9. When the valve 7 is open, a gas sample G can flow from the measurement chamber 9 to the environment. A signal processing and control unit 12 with a system clock 14 can automatically control the valves 6 and 7 as well as other components described below.

[0064] Optionally, control unit 12 can control pump 13, which when controlled and actuated draws gas sample G into the interior of gas detection device 100 through open inlet E. When outlet A is open, gas simultaneously flows out of measurement chamber 9. It is also possible for gas sample G to diffuse into the interior of gas detection device 100 through inlet E.

[0065] Also possible is a realization in which the pump 13, the inlet E and the outlet A are present but the valves 6 and 7 are not. The inlet E and the outlet A can be continuously open. It is also possible that the valve 6 is replaced by another form of closure, for example an orifice aperture with an orifice pattern, the orifice pattern having at least one orifice, the orifice aperture being movable relative to the housing 5. Depending on the position of the orifice aperture relative to the housing 5, the orifice of the orifice pattern overlaps with the inlet E, which is open, or the orifice aperture closes the inlet E.

[0066] Pump 13 may be driven continuously during operation of gas detection apparatus 100, or it may be alternately switched on and off. An arrangement in which pump 13 is switched on continuously may be combined with a movable orifice aperture. An arrangement in which pump 13 is switched on and off avoids the need to provide an orifice aperture or other closure.

[0067] In the second embodiment (FIG. 2), a gas-permeable membrane 8 separates the measurement chamber 9 from the environment, so that the gas sample G can flow from the environment through the membrane 8 into the measurement chamber 9 and out again through the membrane 8. In the illustrated second embodiment, the membrane 8 replaces the inlet E and outlet A of the first embodiment (FIG. 1). Also in the second embodiment, a pump 13 (not shown in FIG. 2) can now suck the gas sample G through the membrane 8. Preferably, a flame guard, e.g. a metal grid, not shown, prevents the spread of flame from the measurement chamber 9 through the membrane 8 to the environment.

[0068] Also in the second embodiment, an orifice aperture (not shown) can be movable relative to the housing 5 and, depending on its position, can either fluid-tightly separate or open the measurement chamber 9 from the environment.

[0069] Unless otherwise stated, the following description relates to both embodiments.

[0070] Inside the measuring chamber 9, a semiconductor sensor 1 is arranged. The semiconductor sensor 1 comprises a semiconductor component 10 and a heating element 11. The semiconductor component 10 serves as a sensor component within the meaning of the claims. The semiconductor component 10 is electrically conductive and preferably made of a metal oxide, particularly preferably a semiconductor, such as tin dioxide (SnO 21 and 2, semiconductor component 10 is shown as a wire, but this should be understood as a symbol in an equivalent circuit diagram and is only one of several possible implementations. Electrical contacts are shown for semiconductor component 10 and for further components of gas detection apparatus 100, which are described below.

[0071] The gas sample G in the measurement chamber 9 reaches the semiconductor component 10. The gas sample G acts on the semiconductor component 10, affecting its electrical resistance R. In this embodiment, it is this electrical resistance R that is the sensed variable that is affected and can be measured. In this embodiment, the chemical effect is that the higher the concentration of the combustible target gas in the gas sample G and thus in the measurement chamber 9, the lower the electrical resistance R of the semiconductor component 10. One reason is that combustible target gases often have a higher thermal conductivity value than exhaled air, and therefore the combustible target gas in the measurement chamber 9 cools the semiconductor component 10.

[0072] Hereinafter, tin dioxide (SnO 2 ) will be taken as an example to explain the preferred functioning of the semiconductor component 10: the electrical conductivity, and therefore the electrical resistance R, depends on the number of free electrons (charge carriers) in the semiconductor component 10. 2 The surface of the crystal is O 2 Due to the vacancies, the electrons provided by the neighboring Sn atoms have no counterpart. These electrons are free to move. The number of free moving electrons affects the electrical conductivity and thus the electrical resistance R of the semiconductor component 10. The semiconductor component 10 adsorbs oxygen from the environment on its surface. As a result, O 2At least some of the vacancies are occupied by adsorbed oxygen from the environment, binding the previously free electrons. The semiconductor component 10 is heated, for example by means of a heating element 11. The combustible target gas is oxidized on the surface of the semiconductor component 10, whereby the adsorbed oxygen is again desorbed as just described. The density of charge carriers in the form of free electrons therefore increases again. The higher the proportion of oxygen in the environment of the semiconductor component 10, the more free electrons are combined with oxygen and the higher the electrical resistance R. The oxidation of the combustible target gas therefore reduces the amount of oxygen that the semiconductor component 10 can adsorb. Thus, under otherwise identical environmental conditions, the higher the concentration of combustible target gas in the measurement chamber 9, the lower the electrical resistance R of the semiconductor component 10. According to the invention, this property is exploited.

[0073] At each sampling instant of the preset sequence of sampling instants, the magnitude of the actual electrical resistance R of the semiconductor component 10 is again measured. For example, a voltage sensor 25 measures the voltage U applied to the semiconductor component 10. A current intensity sensor 24 measures the current intensity I flowing through the semiconductor component 10. From the voltage U and the current intensity I, the electrical resistance R=U / I is derived. As has just been explained, this electrical resistance R is correlated to the concentration of the target gas in the measurement chamber 9 and further depends on the environmental conditions, in particular the temperature in the measurement chamber 9.

[0074] In the example embodiment, the heating element 11 takes the form of an electrical resistor and is in thermal contact with the semiconductor component 10 such that the temperature of the heating element 11 closely matches the temperature of the semiconductor component 10. As described above, heating of the semiconductor component 10 oxidizes the combustible target gas and desorbs oxygen.

[0075] Fluctuations in environmental conditions, particularly temperature, humidity and air pressure, also affect the electrical conductivity of the semiconductor component 10. One possible reason for this is that the surface temperature of the semiconductor component 10, for example the outer surface temperature of the semiconductor sensor 1, may change depending on the environmental conditions.

[0076] In the following, we will describe how to compensate, to some extent, for the effect of these environmental conditions on the electrical resistance R. With this effect compensated for, the measured electrical resistance R - the sensing variable in general - can be used to determine the desired target gas concentration.

[0077] In a preferred embodiment of the present invention, the temperature of the semiconductor component 10 is kept constant above any possible environmental temperature during use, thereby reducing the effect of the environmental temperature on the electrical resistance R of the semiconductor component 10.

[0078] Preferably, the control unit 12 controls the temperature of the heating element 11 with the control objective that the temperature of the heating element 11 remains constant even with changing environmental conditions, and thus the thermal energy input per unit time that the heating element 11 exerts on the semiconductor component 10 remains constant even with changing environmental temperatures. In one configuration, the control unit 12 varies the voltage U applied to the heating element 11 in order to vary the thermal energy emitted by the heating element 11 as required. In another configuration, the control unit 12 varies the current intensity I through the heating element 11. Both configurations can be combined with each other. Since it is desired that the temperature of the semiconductor component 10 exceeds the temperature of the environment, this one-sided temperature control with the heating element 11 as the actuator is sufficient. Controlled cooling of the heating element 11 is possible, but is usually not necessary.

[0079] The electrical resistance of the semiconductor component 10, even at an approximately constant temperature, depends on the environmental conditions, in particular on the oxygen content in the environment, and sometimes also on the humidity. The electrical resistance R of the semiconductor component 10 is therefore measured at least at a first sampling time t1 and at a subsequent second sampling time t2. At the first sampling time t1 a measurement period Z3 starts and at the second sampling time t2 this measurement period Z3 ends, see FIG. 3. Furthermore, it is possible to measure the electrical resistance R at least once at a sampling time t_x between these two sampling times t1 and t2. In the present embodiment, this measurement period Z3 coincides with an oxidation period, which will be described later. The measurement period as well as the oxidation period start at the first time t1 and end at the second time t2. The reference Z3 is therefore also used for the oxidation period. In the embodiment, the first time t1 serves as the sensing time and the second time t2 serves as the reference time.

[0080] In the diagram of Fig. 3, time t is plotted on the x-axis and the measured resistance R of semiconductor component 10 is plotted on the y-axis. At a first sampling time (detection time) t1, the concentration of combustible target gas in gas sample G and thus in measurement chamber 9 matches sufficiently accurately the target gas concentration in the environment of gas detection device 100, i.e., the monitored area. At a second sampling time (reference time) t2, substantially no combustible target gas is present in measurement chamber 9, due to oxidation of the existing target gas during time period Z3. Thus, the measurement at second sampling time t2 serves as a reference or zero-point measurement.

[0081] In order to be able to perform such a reference measurement at the second sampling time t2, the combustible target gas in the measuring chamber 9 is purged during an oxidation period Z3, so that no combustible target gas is present in the measuring chamber 9 at the second time t2. This purging is achieved by the oxidation part 2 oxidizing the combustible target gas present as a component of the gas sample G in the measuring chamber 9. Of course, it may also be the case that no combustible target gas is present in the monitored area, and thus the measuring chamber 9 is already free of combustible target gas at the first time t1.

[0082] Preferably, a concentration limit is preset as an upper limit of the expected concentration of the target gas in the monitored area. This concentration limit and the volume of the measuring chamber 9 relative to the structure define the maximum possible amount of combustible target gas in the measuring chamber 9. This maximum possible amount of target gas is so small that there is enough oxygen in the measuring chamber 9 to oxidize the entire target gas in the measuring chamber 9.

[0083] The oxidation period Z3 is, on the one hand, long enough that - provided that the concentration of the target gas is below the concentration limit - all the combustible target gas in the measuring chamber 9 is oxidized in the course of the oxidation period Z3. On the other hand, the oxidation period Z3 is preferably as short as possible so that the steps of oxidizing the combustible target gas and measuring the electrical resistance R of the semiconductor component 10 twice can be repeated as frequently as possible.

[0084] In the deviation, the concentration limit value is not necessarily preset. The measurement period and the oxidation period Z3 are ended when the measurement results in an unchanged electrical resistance R, or more precisely, when the slope of the course of the electrical resistance R over time remains below the preset limit value. This indicates that all the combustible target gas in the measurement chamber 9 or at least a preset proportion of the target gas is oxidized.

[0085] The combustible target gas in the measurement chamber 9 is oxidized by the oxidation component 2. FIG. 4 shows a preferred configuration of the oxidation component 2. In this example, the combustible target gas is methane (CH 4 ) The oxidation part 2 causes a chemical reaction [ka] This occurs.

[0086] This chemical reaction is shown in Figure 4. Indeed, oxygen is combined during the oxidation of the target gas. However, the O 2An arbitrary concentration limit is preset so that the decrease in the molecular content is so slight that it causes a negligible change in the electrical resistance R of the semiconductor component 10 .

[0087] In a preferred configuration shown in FIG. 4, the oxidation element 2 is configured as a pellistor and comprises: - a spiral heating segment 20, a preferably spherical covering 21 provided around the heating segment 20; - two electrical contacts 22, and - Plate 23.

[0088] A voltage is applied to the heating segment 20. This heats the heating segment 20 to an operating temperature of 300° C. to 700° C., preferably 400° C. to 550° C. Since the heating segment 20 is in thermal contact with the coating 21, the coating 21 is also heated.

[0089] However, this temperature alone would still not be sufficient to oxidize the combustible target gas to a sufficient extent. A higher temperature would consume more electrical energy and increase the risk of the target gas in the measurement chamber 9 suddenly burning or even exploding. In order to oxidize all the combustible target gas in the measurement chamber 9 even when the temperature is preferably below 550° C., a catalytic material, for example platinum or platinum oxide, is embedded in the cladding 21. Preferably, the cladding 21 is porous, so that the thermally effective surface area of ​​the cladding 21 is larger than if the surface were smooth.

[0090] Between the semiconductor sensor 1 and the oxidation part 2, a thermal barrier 4 is arranged, as shown diagrammatically in Fig. 1 and Fig. 2. This thermal barrier 4 reduces the thermal influence of the oxidation part 2 on the semiconductor sensor 1 and therefore the risk that the electrical resistance R of the semiconductor part 10 may be significantly changed by the heated oxidation part 2 and / or by switching it on and off, which may lead to erroneous measurements. However, at least one opening, preferably a peripheral opening, occurs between the housing 5 and the thermal barrier 4 so that the gas sample G can flow through the entire measurement chamber 9. This is desirable in order that the oxidation part 2 can oxidize all the target gases in the measurement chamber 9, including the target gas behind the thermal barrier 4, and so that the measured electrical resistance R of the semiconductor part 10 can be used as an indication of the desired target gas concentration.

[0091] The control unit 12 can switch the oxidation part 2 on and off. In the first configuration of the invention, the oxidation part 2 is switched on during each oxidation period Z3 by the control unit 12 and switched off outside the oxidation period Z3. The oxidation part 2 has a relatively low thermal mass, so that it quickly reaches the operating temperature of 300°C to 700°C after switching on and quickly cools down to the temperature of the measurement chamber 9 after switching off. This intentionally significant and usually fluctuating temperature change usually inevitably leads to a fluctuation in the amount of thermal energy input per unit time to the outer surface of the semiconductor sensor 1 through the oxidation part 2. This temperature fluctuation usually changes the electrical resistance R of the semiconductor part 10 and can therefore lead to erroneous measurements.

[0092] The oxidized part 2, whose temperature fluctuates in the first configuration, can cause undesirable thermal effects on the semiconductor component 10. In order to reduce these thermal effects in the measurement chamber 9, a controllable heating element 3 is additionally arranged in the measurement chamber 9, in particular on the same side of the thermal barrier 4 as the oxidized part 2.

[0093] According to a first configuration variant, the control unit 12 is able to switch on and off not only the oxidation component 2 but also the heating element 3. Ideally, a switched-on heating element 3 will cause the same input amount of thermal energy per unit time into the semiconductor component 10 as a switched-on oxidation component 2. Effect: the oxidation component 2 has a similar thermal effect on the semiconductor component 10 as the heating element 3. The risk that the actual temperature of the oxidation component 2 will falsify the measurement result of the semiconductor sensor 1 is reduced.

[0094] In one configuration, the heating element 3 comprises a spiral heating segment 20, a coating 21 and electrical contacts 22, similar to the oxidation part 2, but the coating 21 is devoid of catalytic material. Therefore, the switched-on heating element 3 cannot oxidize the combustible target gas in the measurement chamber 9, even if the heating segment 20 is heated.

[0095] Before or after the oxidation period (=measurement period) Z3 there is also an intake period Z1. At least during this intake period Z1 the gas sample G can flow from the region into the measurement chamber 9, in particular by the gas sample G being sucked in by the pump 13 and / or diffusing into the measurement chamber 9. In a first configuration, a heating period Z2 is arranged between the intake period Z1 and the oxidation period Z3, see FIG. 3.

[0096] During each oxidation period Z3, the oxidation part 2 is switched on and the heating element 3 is switched off. During the heating period Z2, the heating element 3 is switched on and the oxidation part 2 is switched off. The heating element 3 heats the gas sample G in the measurement chamber 9 so that no sudden temperature changes occur in the measurement chamber 9 during the transition from the heating period Z2 to the oxidation period (= measurement period Z3). Due to the heating element 3, the amount of thermal energy input per unit time to the semiconductor part 10 during the heating period Z2 is approximately equal to the amount input during the measurement period Z3. In particular, the amount of thermal energy input to the semiconductor sensor 1 changes less over time compared to the case without the heating element 3. During the inhalation period Z1, preferably both the oxidation part 2 and the heating element 3 are switched off.

[0097] In one embodiment, the adjustment is carried out in advance to determine the set operating temperature Temp_Soll(3) of the heating element 3. The heating element 3 reaches this set operating temperature Temp_Soll(3) after switching on. The aim of the adjustment is to equalize the amount of thermal energy input per unit time to the semiconductor sensor 1 by the switched-on heating element 3 and the amount of thermal energy input per unit time by the switched-on oxidation part 2. In addition to the set operating temperature Temp_Soll(3), the distance dist(3) between the heating element 3 and the semiconductor sensor 1 and the distance dist(2) between the oxidation part 2 and the semiconductor sensor 1 can also be changed. For the adjustment, a state in which no combustible target gas is present in the measuring chamber 9 is established. The set operating temperature Temp_Soll(3) and the distance are adjusted in such a way that the sensing variable of the semiconductor part 10, and thus the electrical resistance R here, is the same when the oxidation part 2 is switched on and the heating element 3 is switched off and when the oxidation part 2 is switched off and the heating element 3 is switched on.

[0098] 3 shows an exemplary time course during operation of the gas detection device 100. On the x-axis the time t is plotted and on the y-axis the electrical resistance R of the semiconductor component 10 is plotted. The following description relates to the first embodiment according to FIG.

[0099] A sequence consisting of an inhalation period Z1, a subsequent heating period Z2, and a subsequent measurement period (=oxidation period Z3) is performed at least once. This sequence, preferably having three periods Z1, Z2, Z3, is repeatedly performed using gas detection device 100. Figure 5 shows an exemplary flow chart of such a sequence during operation of gas detection device 100.

[0100] The intake period Z1 starts at the time ta. During the intake period Z1, the valves 6 and 7 are open and the optional pump 13 is switched on. The measurement chamber 9 is flushed and filled with a new gas sample G, i.e. the gas sample G already present in the measurement chamber 9 leaves the measurement chamber 9 through the outlet A and the gas sample G to be examined now leaves the area to be monitored through the inlet E into the measurement chamber 9. In one configuration, the optional pump 13 is switched on and transports the gas sample G from the environment into the measurement chamber 9. It is also possible that the gas sample G to be examined diffuses from this area into the measurement chamber 9.

[0101] 5, ta:S1 denotes the step of opening the valves 6 and 7, switching on the pump 13 and flushing the measuring chamber 9 at the time ta. The heating element 3 and the oxidation part 2 are switched off.

[0102] The intake period Z1 is of such a length that after the end of the intake period Z1 the concentration of the combustible target gas in the measurement chamber 9 is approximately equal to the concentration of the target gas in the environment, and thus in the monitored area. In particular, the intake period Z1 is of such a length that if no combustible target gas is detected in the measurement chamber 9, it is certain that no combustible target gas above the detection limit is also present in the environment. In one configuration, the duration of the intake period Z1 is preset constant.

[0103] During the inhalation period Z1, the oxidation component 2 is switched off. In one implementation, the heating element 3 is also switched off during the inhalation period Z1, thereby saving electrical energy. In another implementation, the heating element is switched on or is switched on during the inhalation period Z1, which often allows the heating period Z2 to be shorter, thereby saving time.

[0104] At time t0, the intake period Z1 ends and the subsequent heating period Z2 begins. During the heating period Z2, the oxidation part 2 remains switched off. The control unit 12 triggers the following events at time t0: - Valves 6 and 7 are closed to isolate the measurement chamber 9 from the environment. - Switch off any pumps 13. - Heating element 3 is switched on.

[0105] In figure 5 t0:S2 means the step of closing valves 6 and 7 and switching off pump 13 at time t0. t0:S3 means the step of switching on heating element 3 at time t0. The oxidation part 2 remains switched off.

[0106] The heating period Z2 during which the heating element 3 is switched on is such that during the heating period Z2 the heating element 3 is heated up to the set operating temperature Temp_Soll(3), which was determined in a previous adjustment as described above and which results in the same amount of thermal energy input per unit time as the oxidizing part 2 which is switched on later.

[0107] In one configuration, a set operating temperature Temp_Soll(3) of the heating element 3 is preset. The actual temperature Temp(3) of the heating element 3 is measured. For example, the actual electrical resistance of the heating element 3 is measured. As is well known, the electrical resistance of a metal is correlated with its temperature, so that the resistance is an indication of the temperature.

[0108] In FIG. 5, E1? indicates the determination as to whether the heating period Z2 has already elapsed, ie whether the heating element 3 has reached the set operating temperature Temp_Soll(3).

[0109] At time t1 (detection time), the heating period Z2 ends and the measurement period Z3 begins. The control unit 12 triggers the following events at time t1: - Measure the electrical resistance R of the semiconductor component 10. The electrical resistance value measured at time t1 is denoted as r1. - Heating element 3 is switched off. - Switch on oxidation part 2.

[0110] During the measurement period Z3, the heating element 3 remains switched off. The valves 6 and 7 remain closed and the pump 13 remains switched off. The oxidation part 2, which is switched on during the oxidation period (= measurement period) Z3, oxidizes the or each combustible target gas in the measurement chamber 9. Of course, it can happen that no combustible target gas is present in the monitored area and thus also in the measurement chamber 9, and therefore the heated oxidation part 2 does not carry out any oxidation.

[0111] In an example embodiment, the first time point t1 is the end of the heating period Z2 and also the start of the measurement period (=oxidation period) Z3. In Fig. 5 t1:S4 means the step of switching off the heating element 3 and switching on the oxidation part 2 at time t1. S5(t) means that the electrical resistance R of the semiconductor part 10 is measured at time t. Initially, the time t is set to t1. The measurement S5(t1) at the first time point t1 gives the resistance value r1.

[0112] At time t2 (reference time point), the measurement period Z3, and therefore the sequence consisting of periods Z1, Z2, and Z3, has ended.

[0113] The control unit 12 triggers the following events at time t2: - The electrical resistance R of the semiconductor component 10 is measured again. A measurement S5(t2) at a second point in time t2 results in a value of the electrical resistance R, which is denoted r2. - Switch off oxidation part 2.

[0114] In the exemplary flow chart, the oxidation period Z3 between t1 and t2 is not preset as a constant. The electrical resistance R is measured at time instants t1, t1+Δt, t1+2*Δt, ..., where Δt is a preset constant interval. As the oxidized part 2 burns the combustible target gas in the measurement chamber 9, the electrical resistance R becomes larger and larger. The resistance value at time instant t is denoted as r(t). The difference between the resistance values ​​at two immediately successive time instants t-Δt and t, i.e. the difference r(t)-r(t-Δt), is calculated.

[0115] In the shown example, no combustible target gas can reach the measuring chamber 9 from the outside during the measuring period Z3. If the difference r(t)-r(t-Δt) is smaller than a predefined limit value ΔR_min, then substantially all of the combustible target gas in the measuring chamber 9 has been oxidized. The time t at which this is determined is used as the time t2 at which the measuring period Z3 ends. The last measured resistance value r(t) is used as the value r2=r(t2).

[0116] In the example shown, the difference r(t)-r(t-Δt) between the two most recent resistance values ​​is used. Overall, the slope of the electrical resistance R as a function of time is calculated, for which the time series r(t1), r(t1+Δt), r(t1+2*Δt), ... is used. If this slope falls below a predefined limit value, the time of the most recent measurement is used as the second time point t2.

[0117] In FIG. 5, t2:S6 means that at time t2, the oxidation part 2 is switched off.

[0118] The subsequent sequence is started. The suction period Z1 of the subsequent sequence is shown in Figure 3. Optionally, at a second time t2, the valves 6 and 7 are opened again and the pump 13 is switched on again.

[0119] In the first configuration just described, the oxidation component 2 is switched on only during the oxidation period Z3 and switched off otherwise. In the following, an alternative second configuration is described. In this second configuration, the oxidation component 2 is switched on not only during the oxidation period Z3 but also at least during the intake period Z1. Optionally, the oxidation component 2 remains switched on during the entire operation of the gas detection device 100 and is switched off only in the idle state of the gas detection device 100. In many cases, configurations in which the oxidation component 2 remains switched on dispense with the heating element 3. The intake period Z1 can be followed directly by the oxidation period Z3, making the heating period Z2 unnecessary. However, the second configuration can also be used in combination with the heating element 3, which compensates to some extent for possible fluctuations in the amount of thermal energy input caused by the oxidation component 2 to the semiconductor component 10.

[0120] In the second configuration, during the intake period Z1, the measuring chamber 9 is open so that the gas sample G can flow from the monitored region into the measuring chamber 9. During the oxidation period Z3, the measuring chamber 9 is closed and thus fluid-tightly closed to the monitored region so that combustible target gas cannot flow into the measuring chamber 9 during the oxidation period Z3, even if the target gas is present in the region.

[0121] The step of opening and closing the measurement chamber 9 and thereby selectively operating in an open or closed state can for example be realised in any of the following ways: Switching the pump 13 on and off. In particular, the pump 13 is switched on during the suction period Z1 and switched off during the oxidation period Z3. Opening and closing the valve 6 at the inlet E. The valve 6 is open during the intake period Z1 and closed during the oxidation period Z3. - moving the above-mentioned orifice aperture or even the flap relative to the housing 5 so that the orifice aperture 5 or the flap opens the inlet E during the intake period Z1 and closes it during the oxidation period Z3.

[0122] Both of these configurations can be combined with each other, which often increases the reliability of gas detection device 100. According to this combination, during the inhalation period Z1, inlet E is open and oxidation part 2 and optional heating element 3 are switched off. During the oxidation period Z3, inlet E is closed, oxidation part 2 is switched on and optional heating element 3 is switched off. During the optional heating period Z2, inlet E is preferably closed.

[0123] The following description relates to both the configuration according to FIG. 1 and to two configurations, namely one in which the oxidation part 2 is switched on and off and one in which the measuring chamber 9 is opened and closed.

[0124] The two measured values ​​r1 and r2 for the electrical resistance R, and optionally further measured values, are transmitted to a signal processing and evaluation unit 15, which in the implementation shown is a component of the control unit 12. As already explained, in the present embodiment, the greater the proportion (concentration) of combustible target gas in the measurement chamber 9, the smaller the electrical resistance R of the semiconductor component 10. The electrical resistance R also depends on the environmental conditions. According to the invention, the difference Δr=r2-r1 is calculated and evaluated by the evaluation unit 15. This difference Δr depends essentially only on the determined concentration of combustible target gas in the measurement chamber 9, the environmental conditions having approximately the same effect on the electrical resistance R at the two measurement times t1 and t2. "Substantially" means that the influence of the environmental conditions on the difference Δr is negligibly small. In this way, the influence of the environmental conditions is compensated for by the calculation.

[0125] In one configuration, gas detection device 100 is used to determine whether at least one combustible target gas is present in a monitored area. During use, the sequence Z1, Z2, Z3 is repeated. If, after completion of the sequence, the measured difference Δr is above the difference limit value, the combustible target gas has been detected. If not, it is certain that no combustible target gas is actually present, but of course this assumes that gas detection device 100 is not damaged. In internal tests with a particular combustible target gas, the inventors have found that gas detection device 100 according to the present invention can reliably detect this target gas at concentrations below 10 ppm, and often even below 2 ppm.

[0126] Preferably, gas detection device 100 is pre-calibrated. In this calibration, various concentrations con(1), con(2), ... of the target gas to be detected are successively established in the environment of gas detection device 100. For each concentration con(i), the difference Δr(i) is measured at least once each. Preferably, multiple sequences Z1, Z2, Z3 are performed and the measured differences are averaged. This calibration results in an empirically determined functional relationship Con=f(ΔR). This empirically determined functional relationship is stored in a data memory of evaluation unit 15 in a computer-evaluable form. Note: Con represents a quantity and con represents a specific measurement value of this quantity.

[0127] Preferably, during this adjustment, the heating element 3 is also set as described above, such that the input per unit time of thermal energy by the heating element 3 is equal to the input per unit time by the oxidizing part 2 .

[0128] When gas detection device 100 is used, the sequence Z1, Z2, Z3 is performed repeatedly. The stored functional relationship f is applied to the measured difference Δr to obtain the determined actual target gas concentration con=f(Δr).

[0129] According to the invention, the electrical resistance R of the semiconductor component 10 is measured at least at both times t1, t2. In one embodiment, the electrical resistance R is additionally measured at at least one intermediate time t_x between the times t1 and t2. In a preferred development, the course of the electrical resistance R over time is measured during a measurement period Z3. Outliers and other measurement errors are to a certain extent compensated for by calculation, for example by suitable numerical processing by smoothing.

[0130] In a second embodiment according to FIG. 2, the gas detection device 100 does not have an inlet E and an outlet A. In one configuration, a movable aperture or another suitable closure can selectively open or close the fluid communication between the measurement chamber 9 and the environment. In this configuration, at least one sequence with an intake period Z1, a heating period Z2 and a measurement period Z3 is also implemented, in which the fluid communication between the measurement chamber 9 and the environment is open during the intake period Z1 and is blocked during the heating period Z2 and the measurement period Z3. The configuration according to FIG. 2 with the movable closure can be combined with a realization in which the oxidation part 2 is continuously switched on and the heating element 3 may be present but is not required.

[0131] On the other hand, if fluid communication is continuously established between the measurement chamber 9 and the environment through the membrane 8, then a sequence consisting only of a heating period Z2 and a subsequent measurement period Z3 is preferably performed at least once, the control unit 12 triggering the steps described above for both periods Z2 and Z3. In this configuration, the heating period Z2 simultaneously serves as the inhalation period Z1. [Explanation of symbols]

[0132] 1 Semiconductor sensor with semiconductor component 10 and heating element 11 2. A controllable oxidation component 2 comprising a heating wire 20, a ceramic and catalytic coating 21, electrical contacts 22 and a plate 23, configured as a catalytic pellistor. 3. Controllable heating element in the measurement chamber 9 4. Thermal barrier between the oxidized part 2 and the heating element 3 on the one hand and the semiconductor sensor 1 on the other hand 5 Housing of gas detection device 100 surrounding measurement chamber 9 6 Inlet E valve 7. Valve for outlet A 8 Gas-permeable membrane connecting the measurement chamber 9 with the environment 9. A measurement chamber of the gas detection device 100, surrounded by a housing 5 and containing the semiconductor sensor 1, the oxidation component 2, the heating element 3, and the thermal barrier 4. 10 Semiconductor component of semiconductor sensor 1, functioning as a sensor component, whose electrical resistance R is to be measured 11 Heating element of semiconductor sensor 1 for heating semiconductor component 10 12 a signal processing and control unit for controlling the heating element 11 of the semiconductor sensor 1, the oxidation part 2, the heating element 3, the optional valves 6 and 7 and the optional pump 13 and having an evaluation unit 15 13 A controllable pump that draws a gas sample G from the environment and delivers it through the inlet E into the measurement chamber 9 14 System clock of control unit 12 15 a signal processing and evaluation unit for determining the concentration of the combustible target gas and which is a component of the control unit 12 20 Heating wire of oxidation part 2 21 Ceramic and catalytic coating of oxidation component 2 22 Electrical contact of oxidized part 2 23 Oxidized Part 2 Plate 24 Current intensity sensor for measuring the current intensity I flowing through the semiconductor component 10 25 Voltage sensor for measuring voltage U applied to semiconductor component 10 100 Gas sensing device comprising a measuring chamber 9 in a housing 5, a semiconductor sensor 1, an oxidation part 2, a heating element 3, a thermal barrier 4, an inlet E with an optional valve 6 and an outlet A with a valve 7, an optional membrane 8 and an optional pump 13. A outlet from the measuring chamber 9, equipped with a valve 7 dist(2) Distance between the oxide part 2 and the semiconductor sensor 1 dist(3) Distance between heating element 3 and semiconductor sensor 1 E. Inlet to the measuring chamber 9, equipped with a valve 6 E1? Judgment: Has heating period Z2 passed? G. A gas sample from the monitored area flows through the inlet E or membrane 8 into the measurement chamber 9 and is analyzed there. R is the electrical resistance of the semiconductor component 10, as determined based on measurements from sensors 24 and 25 r1 Measured value of electrical resistance R at time t1 r2 Measured value of electrical resistance R at time t2 r(t) is the measured electrical resistance R at time t ΔR_min Predefined limit value for change in electrical resistance R Step S1: At time ta, valves 6 and 7 are opened, pump 13 is switched on, and measuring chamber 9 is flushed. Step S2: At time t0, valves 6 and 7 are closed and pump 13 is switched on. Step S3: Switch on heating element 3 at time t0 Step S4: At time t1, the heating element 3 is switched off and the oxidation part 2 is switched on. t0 Start of heating period Z2 t1: a first time point at which the detection variable is measured and serves as a detection time point - at this first time point, there may be combustible target gas present in the measurement chamber 9 t2: A second time point at which the sensed variable is measured and serves as a reference time point - at this second time point, there is no combustible target gas present in the measurement chamber 9 due to oxidation. ta Start of inhalation period Z1 Z1: the inhalation period during which the gas sample G flows into the measurement chamber 9 and the heating element 3 is switched off Z2: heating period starting at time t0, during which the heating element 3 is switched on and the oxidation part 2 is switched off Z3: the oxidation period from the first time t1 to the second time t2, during which the oxidation part 2 is switched on and the heating element 3 is switched off

Claims

1. A gas detection device (100) for monitoring a spatial region for a combustible target gas, wherein the gas detection device (100) - a measurement chamber (9), - a conductive sensor component (10, 20), - an oxidation component (2), - a detection sensor (24, 25), - a signal processing and evaluation unit (15) and is provided with, wherein the gas detection device (100) - at least temporarily, a gas sample (G) flows from the spatial region into the measurement chamber (9), - the conductive sensor component (10, 20) is configured to contact the gas sample (G) in the measurement chamber (9), is configured as, the conductive sensor component (10, 20) has a measurable electrical detection variable (R) whose value becomes larger or smaller as the concentration of the combustible target gas in the gas sample (G) in the measurement chamber (9) is lower, the detection sensor (24, 25) is configured to measure the magnitude of the electrical detection variable (R) of the conductive sensor component (10, 20), the oxidation component (2) is configured to oxidize the combustible target gas contained in the gas sample (G) in the measurement chamber (9), wherein the gas detection device (100) the oxidation component (2) completely or at least partially oxidizes the combustible target gas in the gas sample (G) in the measurement chamber (9) during an oxidation period (Z3), the detection sensor (24, 25) measures the magnitude of the electrical detection variable (R) of the conductive sensor component (10, 20) not only at a detection time point (t1) but also at a reference time point (t2), is configured as, the oxidation period (Z3) starts at the detection time point (t1) or after the detection time point (t1), and ends before the reference time point (t2) or at the reference time point (t2), the gas detection device (100) further when there is a combustible target gas in the spatial region to be monitored, - there is a combustible target gas in the measurement chamber (9) also at the detection time point (t1), - at the reference time point (t2), due to the oxidation during the oxidation period (Z3), the combustible target gas present in the measurement chamber (9) is less than at the detection time point (t1), is configured as, the signal processing and evaluation unit (15) For the electrical detection variable (R), a difference (Δr) between the measured value (r2) at the reference time point (t2) and the measured value (r1) at the detection time point (t1) is calculated, depending on the difference (Δr), - automatically determine whether a combustible target gas is present in the gas sample (G), and / or - automatically determine the concentration of the combustible target gas in the gas sample (G) A gas detection device (100) configured as described above. **Claim 2** The oxidation component (2) can be switched on and off, The gas detection device (100) further includes a heating element (3) that can be switched on and off, The heating element (3) is configured to heat the gas sample (G) in the measurement chamber (9) in the switched-on state, The gas detection device (100), - During the heating period (Z2), the heating element (3) is in the switched-on state and the oxidation component (2) is in the switched-off state, - During the oxidation period (Z3), the oxidation component (2) is in the switched-on state and the heating element (3) is in the switched-off state The gas detection device (100) according to claim 1, configured as described above. **Claim 3** The oxidation component (2) generates an amount of thermal energy input to the conductive sensor component (10, 20) in the switched-on state, The heating element (3) generates an amount of thermal energy input to the conductive sensor component (10, 20) in the switched-on state, The amount of thermal energy input per unit time by the switched-on heating element (3) is the same as the amount of thermal energy input per unit time by the switched-on oxidation component (2). The gas detection device (100) according to claim 2. **Claim 4** The gas detection device (100), If the gas sample (G) in the measurement chamber (9) does not contain a combustible target gas under the same environmental conditions, The electrical detection variable (R) of the conductive sensor component (10, 20) is When the oxidation component (2) is switched on and the heating element (3) is switched off, When the oxidation component (2) is switched off and the heating element (3) is switched on Takes the same value The gas detection device (100) according to claim 2 or 3, configured as described above. **Claim 5** The gas detection device (100), The heating period (Z2) is temporally prior to the oxidation period (Z3). The gas detection device (100) according to claim 2 or 3, which is configured as such.

6. The oxidation component (2) is - capable of being switched on and off, - switched on during the oxidation period (Z3) and switched off outside the oxidation period (Z3), the gas detection device (100) according to any one of claims 1 to 3.

7. The gas detection device (100) is configured to perform at least one inclination calculation sequence, At least one of the inclination calculation sequences is - the detection sensors (24, 25) measure the magnitude of the electrical detection variable (R) of the conductive sensor component (10, 20) at least at the detection time point (t1) and the intermediate time point (t_x), wherein the intermediate time point (t_x) is during the oxidation period (Z3) and is temporally separated from the detection time point (t1), - the signal processing and evaluation unit (15) calculates the magnitude of the inclination of the electrical detection variable (R) over time according to at least two measured values of the electrical detection variable (R), including the step of The signal processing and evaluation unit (15) is if the inclination calculated in the inclination calculation sequence is below a preset limit value (ΔR_min), - uses the most recent time point at which the magnitude of the electrical detection variable (R) was measured as the reference time point (t2), - uses the measured value at the most recent time point as the measured value (r2) at the reference time point (t2), The gas detection device (100) according to any one of claims 1 to 3, which is configured as such.

8. The oxidation component (2) is - capable of being switched on and off, - switched on during the oxidation period (Z3) and switched off during at least the inhalation period (Z1), The gas detection device (100) is configured such that the gas sample (G) flows from the space region into the measurement chamber (9) during at least the inhalation period (Z1), the gas detection device (100) according to any one of claims 1 to 3.

9. The gas detection device (100) is configured such that the gas sample (G) also flows from the space region into the measurement chamber (9) during the oxidation period (Z3). The gas detection device (100) according to claim 8, which is configured as such.

10. The measurement chamber (9) is operable in a selectively open state and a closed state, The gas detection device (100) - In the open state, the gas sample (G) flows into the measurement chamber (9), - In the closed state, the measurement chamber (9) is fluid-tightly sealed with respect to the space region is configured as such, The gas detection device (100) the measurement chamber (9) - is in an open state during an inhalation period (Z1) that includes the detection time point (t1) or is before the detection time point (t1), - is in a closed state at the reference time point (t2) The gas detection device (100) according to any one of claims 1 to 3, which is configured as such.

11. The gas detection device (100) the oxidation component (2) is switched on during the inhalation period (Z1) as well The gas detection device (100) according to claim 10, which is configured as such.

12. A current flows through the conductive sensor components (10, 20) at least when the oxidation component (2) is switched on. The gas detection device (100) according to any one of claims 1 to 3.

13. A method for monitoring a space region for a combustible target gas using a gas detection device (100), wherein the gas detection device (100) - a measurement chamber (9), - conductive sensor components (10, 20), - detection sensors (24, 25), - an oxidation component (2) is provided with, The method at least temporarily, a gas sample (G) flows from the space region into the measurement chamber (9), the conductive sensor components (10, 20) come into contact with the gas sample (G) in the measurement chamber (9), the contact affects the conductive sensor components (10, 20), and the effect is such that the value of the measurable electrical detection variable (R) of the conductive sensor components (10, 20) becomes larger or smaller as the concentration of the combustible target gas in the gas sample (G) in the measurement chamber (9) is lower, the oxidation component (2) oxidizes the combustible target gas contained in the gas sample (G) in the measurement chamber (9) at least during an oxidation period (Z3), In addition to the detection time point (t1), the detection sensors (24, 25) also measure the magnitude of the electrical detection variable (R) of the conductive sensor components (10, 20) at a reference time point (t2), the oxidation period (Z3) starts at the detection time point (t1) or after the detection time point (t1), and ends before the reference time point (t2) or at the reference time point (t2), when there is a combustible target gas in the spatial region to be monitored, - there is a combustible target gas in the measurement chamber (9) also at the detection time point (t1), - at the reference time point (t2), due to the oxidation during the oxidation period (Z3), the combustible target gas present in the measurement chamber (9) is less than at the detection time point (t1), calculate the difference (Δr) between the measured value (r2) at the reference time point (t2) and the measured value (r1) at the detection time point (t1), depending on the difference (Δr), - automatically determine whether there is a combustible target gas in the gas sample (G) and / or - automatically determine the concentration of the combustible target gas in the gas sample (G) A method comprising the steps of causing this.

14. The gas detection device (100) further comprises a heating element (3) that can be switched on and switched off again, the oxidation component (2) can also be switched on and switched off again, The method is, - switch on the oxidation component (2) at the start of the oxidation period (Z3) and switch it off at the end of the oxidation period (Z3), - switch on the heating element (3) at the start of a heating period (Z2) outside the oxidation period (Z3) and switch it off again at the end of the heating period (Z2), - the switched-on heating element (3) heats the gas sample (G) in the measurement chamber (9) The method according to claim 13, comprising the steps of.

15. Perform the slope calculation sequence at least once, at least one of the slope calculation sequences is, - the detection sensors (24, 25) measure the magnitude of the electrical detection variable (R) of the conductive sensor components (10, 20) at least at the detection time point (t1) and an intermediate time point (t_x), wherein the intermediate time point (t_x) is during the oxidation period (Z3) and is temporally distant from the detection time point (t1), - calculating the magnitude of the slope of the electrical detection variable (R) over time according to at least two measured values of the electrical detection variable (R); if the calculated slope is below a preset limit value (ΔR_min); - using the most recent time point at which the magnitude of the electrical detection variable (R) was measured as the reference time point (t2); - using the measured value at the most recent time point as the measured value (r2) at the reference time point (t2) The method according to claim 13 or 14, comprising the steps of.

16. Performing the first sequence and / or the second sequence, The first sequence is - the oxidation component (2) is switched off during the inhalation period (Z1); - the gas sample (G) flows into the measurement chamber (9) at least during the inhalation period (Z1); comprising the steps of The second sequence is - operating the measurement chamber (9) in an open state during the inhalation period (Z1), in which open state the gas sample (G) flows from the space region to be monitored into the measurement chamber (9); - operating the measurement chamber (9) in a closed state, in which closed state the measurement chamber (9) is fluid-tightly sealed against the space region; - when the measurement chamber (9) is operated in the closed state, the oxidation component (2) is at least switched on The method according to claim 13 or 14, comprising the steps of.

Images