Method for operating a gas sensor device and gas sensor device for determining information about air quality

Abstract

Method for operating a gas sensor device (10) for determining information about air quality, comprising the steps:-providing (S1) a gas sensor device (10) with at least one gas-sensitive electrical sensor resistor (W), with a heating medium (H) for controlled heating of the sensor resistor (W), with a detection device (EF) for detecting the resistance value of the sensor resistor (W) and with a signal processing device (S) for the sensor signal;-Heating (S2) the sensor resistor (W) with the heating medium (H) alternating in at least one first heating mode (HDC) in a first operating phase and at least one second heating mode (LDC) in a second operating phase, wherein each heating mode comprises a sequence of heating pulses, so that the sensor resistor (W) is heated to a predetermined operating temperature at predetermined time intervals for a predetermined duration, wherein the same operating temperature is selected for the at least two different heating modes;and-acquisition (S3) of the resistance value of the sensor resistor (W) and generation of a sensor signal based on this resistance value during the first and second operating phases, wherein the acquisition (S3) takes place during the heating pulses, and only when the gas-sensitive electrical sensor resistor (W) has been heated to the operating temperature, and wherein in each operating phase at least one reference value is determined based on the sensor signal and the reference values ​​of two successive operating phases are compared with each other, wherein a comparison value is determined from the reference values ​​based on the sensor signal at the end of each operating phase, and information about air quality is obtained by means of the comparison value.;

Description

[0001] The present invention relates to a method for operating a gas sensor device and a gas sensor device for determining information about air quality. State of the art

[0002] Conventional gas sensors can be used to determine air quality, for example, indoor air quality (IAQ). These gas sensors typically have a sensitive layer or paste whose electrical resistance changes depending on the concentration of chemically oxidizing or reducing gases. One family of gases commonly found indoors are the so-called VOCs (Volatile Organic Compounds). The sensor signal, particularly the resistance value of the gas-sensitive material, can exhibit unstable behavior over extended periods (greater than a day), and the cause of the resistance change over such long periods is often difficult to reproduce or determine, especially if the gas sensor remains switched off for an extended time (greater than a day).This often makes it difficult to determine whether the observed change in resistance was caused by an actual change in gas concentrations in the ambient air or by intrinsic sensor effects.

[0003] US patent 2016 / 0216227 A1 describes a gas sensor with a layer of metal oxide which can be heated with heating pulses of varying durations. Disclosure of the invention

[0004] The present invention provides a method for operating a gas sensor device according to claim 1 and a gas sensor device for determining information about air quality according to claim 11.

[0005] Preferred further training courses are the subject of the subclaims. Advantages of the invention

[0006] The idea underlying the present invention is to provide a gas sensor device which can be operated in different heating modes of an electrical resistor, advantageously its gas-sensitive material, and which can enable an improved manner and higher significance regarding the inference of resistance changes to the external influences (gas content) on the resistor, in order to better determine and more accurately identify a cause for the resistance change.

[0007] According to the invention, in the method for operating a gas sensor device for determining information about air quality, a gas sensor device is provided with at least one gas-sensitive electrical sensor resistor, with a heating medium for controlled heating of the sensor resistor, with a detection device for detecting the resistance value of the sensor resistor and with a signal processing device for the sensor signal;Heating the sensor resistor with the heating medium alternately in at least one first heating mode in a first operating phase and at least one second heating mode in a second operating phase, each heating mode comprising a sequence of heating pulses such that the sensor resistor is heated to a predetermined operating temperature at predetermined time intervals for a predetermined duration, wherein a substantially similar operating temperature is selected for the at least two different heating modes; and sensing the resistance value of the sensor resistor and generating a sensor signal based on this resistance value during the first and second operating phases.

[0008] The sampling signal is advantageously necessary to enable the gas sensor, i.e., the electrical sensor resistance, to measure at all. The sampling signal can be provided by a power source, such as a battery or a power grid, and, for example, by a control device.

[0009] The detection of the resistance value and the generation of the sensor signal are advantageously performed by the detection device. The sensor signal can advantageously be processed by the signal processing device.

[0010] The resistor advantageously comprises a gas-sensitive material, preferably a layer that is accessible to the ambient air. The gas sensor device, including the heating elements, the resistor, the detection device, and the signal processing device, can advantageously be arranged in a portable housing. The operating phases, advantageously their duration, as well as the duration of the heating pulses and the setting of the operating temperature, can be determined by a control device for the gas sensor device, which can include such a control device. The sensor signal can advantageously be output / generated as a digital signal, as a voltage, or as a current.

[0011] As a reference value, a resistance value known from the resistor's design or from previous calibration measurements can be advantageously defined, along with a known and prevailing air quality at that time, i.e., with the prevailing concentration of oxidizing or reducing gases in the ambient air at the time of the calibration measurement. For example, at the time of the calibration measurement, it can be assumed that the ambient air has average purity. The resistance values ​​determined at later times can then be identified and stored as better or worse air quality values, depending on the deviation of the resistance value, with the concentration of a specific oxidizing or reducing gas serving as the basis for assuming the air quality to be good or bad.

[0012] The measured resistance advantageously provides a conclusion about the concentration of a gas in the ambient air, and the measurement advantageously also depends on the temperature of the sensor and the air, as well as on the relative humidity in the air.

[0013] The first and second heating modes can alternate once or several times in succession. The first operating phase is advantageously designed to operate the heating medium in a specific pulsed mode (duration and / or time interval), and the second operating phase is advantageously designed to operate the heating medium in a different pulsed mode (duration and / or time interval).

[0014] Dependencies on the measurement can be observed, including: the individual behavior of the resistance value for each gas sensor; continuous contamination of the gas-sensitive material, which can cause a drift in sensitivity (impairment) over time; and changes in relative humidity. Operating the gas sensor device with alternating heating modes allows for a more accurate assessment of the actual air conditions, as local and / or short-term effects can be identified and disregarded (filtered out) by comparing values ​​from the different heating phases, a process further enhanced by the signal processing unit.

[0015] It is also possible that the heating devices can operate a third or further heating mode, which may differ in duration, pulse operation, or operating temperature.

[0016] According to a preferred embodiment of the method, after detection the sensor signal is processed by the signal processing device, whereby the air quality of an ambient air relative to an air reference value for the resistance is inferred from the sensor signal.

[0017] According to a preferred embodiment of the method, the time interval between the heating pulses of the first and / or the second heating mode is constant.

[0018] According to a preferred embodiment of the method, the duration of the heating pulses of the first and / or the second heating mode is constant in each case.

[0019] According to a preferred embodiment of the method, the first and second heating modes differ in terms of the time intervals between the heating pulses.

[0020] This refers advantageously to the intervals between the heating pulses of a respective heating mode.

[0021] According to a preferred embodiment of the method, the first and second heating modes differ in the duration of the heating pulses.

[0022] This refers advantageously to the duration of the heating pulses of a respective heating mode.

[0023] According to a preferred embodiment of the method, the detection takes place during the heating pulses, and only when the gas-sensitive electrical resistance has been heated to the operating temperature.

[0024] According to a preferred embodiment of the method, the detection takes place at the end of the heating pulses of the respective heating mode.

[0025] The actual measurement of the resistance value is advantageously only carried out at the end of a heating mode.

[0026] According to a preferred embodiment of the method, at least one reference value is determined in each operating phase based on the sensor signal, and the reference values ​​of two successive operating phases are compared with each other, whereby a comparison value is determined from the reference values, and information about air quality is obtained by means of the comparison value.

[0027] A reference value corresponds, for example, to a resistance value and can be used as a comparison for other measured resistance values ​​at other times and conditions.

[0028] According to a preferred embodiment of the method, the comparison values ​​are determined on the basis of the sensor signal at the end of an operating phase.

[0029] The comparison value advantageously corresponds to the resistance value at the end of a heating mode and serves advantageously as a comparison value for further and subsequent determinations (recording) of the resistance value of subsequent heating modes.

[0030] According to a preferred embodiment of the method, a difference and / or a quotient is formed from the comparison values ​​of successive operating phases.

[0031] According to the invention, the gas sensor device for determining information about air quality comprises at least one gas-sensitive electrical sensor resistor; a heating medium for alternately heating the sensor resistor in at least a first heating mode in a first operating phase and at least a second heating mode in a second operating phase; a detection device configured to detect a resistance value of the sensor resistor and to generate a sensor signal during the first and second operating phases; and a signal processing device by which the sensor signal can be processed.and a control device configured to control the heating medium for heating the gas-sensitive electrical sensor resistor such that the sensor resistor is heated alternately at least in the first heating mode and at least in the second heating mode, so that each operating phase in a first heating mode is followed by an operating phase in another, second heating mode, wherein each heating mode comprises a sequence of heating pulses which heat the sensor resistor to a predetermined operating temperature at predetermined time intervals and for a predetermined duration, wherein the operating temperature of the at least two different heating modes is essentially the same.

[0032] According to a preferred embodiment of the gas sensor device, the signal processing device is configured to infer from the sensor signal the air quality of an ambient air relative to an air reference value for resistance.

[0033] According to a preferred embodiment of the gas sensor device, the signal processing device includes a memory with stored air reference values ​​for the resistance value and the air quality values ​​associated with them.

[0034] In addition to reference values, comparison values ​​from the heating modes can also be stored. The reference values ​​for a specific air quality (air reference value), for example, to determine whether air quality is good or bad at a measured gas concentration, can be re-stored for a specific reference value following subsequent operation of the gas sensor device. This means, for example, that the previously stored value for the best measured air quality can be corrected.

[0035] The gas sensor device continues to be characterized by the features and advantages already mentioned in connection with the process, and vice versa.

[0036] Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings. List of characters

[0037] The present invention will be explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawing.

[0038] They show: Fig. 1 a schematic representation of the gas sensor device according to an embodiment of the present invention; Fig. 2 a schematic block diagram of a signal processing sequence according to an embodiment of the present invention; Fig. 3 a temporal sequence of heating pulses in an embodiment of the method according to the present invention; Fig. 4 a temporal sequence of resistance values ​​in an embodiment of the method according to the present invention, and Fig. 5 a sequence of process steps according to an embodiment of the present invention.

[0039] In the figures, identical reference symbols denote identical or functionally equivalent elements.

[0040] Fig. Figure 1 shows a schematic representation of the gas sensor device according to an embodiment of the present invention.

[0041] The gas sensor device 10for determining information about air quality, comprising at least one gas-sensitive electrical sensor resistor W; a heating medium H for alternately heating the sensor resistor W in at least one first heating mode HDC in a first operating phase and at least one second heating mode LDC in a second operating phase; a detection device EF, which is configured to detect a resistance value of the sensor resistor W and to generate a sensor signal during the first and second operating phases; a signal processing device S by which the sensor signal can be processed;and a control device SE, which is configured to control the heating medium H for heating the gas-sensitive electrical resistance W such that the heating of the sensor resistance occurs alternately at least in the first heating mode HDC and at least in the second heating mode LDC, so that an operating phase in a first heating mode is followed by an operating phase in another, second heating mode, wherein each heating mode comprises a sequence of heating pulses which heat the sensor resistance (W) to a predetermined operating temperature at predetermined time intervals and for a predetermined duration, wherein the operating temperature of the at least two different heating modes is essentially the same.

[0042] The electrical resistor advantageously comprises a gas-sensitive layer or paste, for example a VOC (Volatile Organic Compound). The gas-sensitive material can, for example, comprise SnO2 or ZnO, i.e., tin oxide or zinc oxide.

[0043] The gas sensor device 10 can be connected to a control unit SE, which can control the operating phases and heating modes, the detection unit and the signal processing unit, as well as the management of the reference values ​​stored in the memory S.

[0044] The electrical resistance W can be measured on the outside of a housing of the gas sensor device. 10 The arrangement should be advantageous such that the gas-sensitive layer or paste can be in contact with the ambient air.

[0045] Fig. Figure 2 shows a schematic block diagram of a signal processing sequence according to an embodiment of the present invention.

[0046] Advantageously, a flowchart of preprocessing (in the control unit or the signal processing unit) at the gas sensor unit is shown here, for example, on the left for data (measured values) from the first heating mode and on the right for data (measured values) from the second heating mode. In one step A1 and A2 A resistance value can be measured from the resistor during heating mode. In one step B1 and B2 Can a filter step be performed to filter out a noise signal in one step? C1 and C2 The last measurement point in a heating phase can be extracted as a reference value (a reference value for the resistance value can be determined based on the sensor signal).

[0047] In this process, at least one reference value can be determined in each operating phase based on the sensor signal, and the reference values ​​of two consecutive operating phases can be compared with each other, whereby a comparison value is determined from the reference values, and information about air quality is obtained using the comparison value.

[0048] Taking into account both comparative values ​​from the two (consecutive) heating modes, a difference and / or a quotient can be calculated from the comparative values ​​of successive operating phases in step D. In step E, this difference and / or the quotient can be sent to a device for investigating the baseline measurement (evaluation relative to a stored air reference value), for example, within the signal processing unit, and evaluated. Here, an actually measured resistance can also be evaluated by the device for investigating the baseline measurement against an air reference value, or a new air reference value can be set as a new guideline for good or poor air quality, specifically for this gas sensor device. For example, the highest value from previous periods can always be stored, since the resistance value can be equated with the air purity.The signal processing unit can then evaluate each measured resistance value relative to this air reference value regarding its air quality.

[0049] Fig. Figure 3 shows a temporal sequence of heating pulses in an embodiment of the method according to the present invention.

[0050] The Fig. Figure 3 shows the sequence of heating pulses in the two methods according to Fig. 4. The figure above shows a heating time curve for the first heating mode (left) and for the second heating mode (right) with a duration (period of the heating mode) and individual heating pulses, which may differ in duration for the first and second heating modes.

[0051] The figure below shows a heating time curve for the first heating mode (left) and for the second heating mode (right) with a duration (period of the heating mode) and individual heating pulses, which can be the same in duration for the first and second heating modes.

[0052] The heating medium is advantageously so powerful that the operating temperature is reached in only a fraction of a pulse length (even the shortest). By measuring the resistance, or of other semiconductor materials, at an operating temperature, unwanted temperature-related effects on the measurement during signal processing can be filtered out or prevented altogether. Any slow signal changes, such as those occurring in a constant gas environment, may be due to slow chemical reactions and can appear both during and outside of heating modes.In the first heating mode, where a high rate of heating pulses is possible, chemical processes occurring at operating temperature may dominate. In the second heating mode, where a low rate of heating pulses is possible, chemical processes (and thermal drift, such as changes in sensor properties or resistance with temperature) occurring at room temperature may dominate. Comparing both heating modes can be advantageous for accounting for chemical processes occurring only at operating temperature.

[0053] Fig. Figure 4 shows a temporal sequence of resistance values ​​in an embodiment of the method according to the present invention.

[0054] The figure above shows a time-dependent behavior of the resistance values ​​according to a second method, where the first heating mode (HDC) is operated with a duration (heating mode period) of advantageously 60 s and the second heating mode is also operated with a duration of advantageously 60 s. According to the second method, the operation of the heating medium in a pulsed heating mode advantageously has a heating time relative to the duration of a heating mode period (first and second), which can be the same for both the first and second heating modes.

[0055] For example, the sampling time for the gas sensor is 1 second in the first heating mode and 10 seconds in the second heating mode. The heating time in the first heating mode is 90% of the time of one period in the first heating mode, and the heating time in the second heating mode is 9% of the time of one period in the second heating mode (relative to the period duration). Due to the different sampling times, an actual heating time of, for example, 900 ms (relative heating time * sampling time) can be achieved in one period of the first heating mode, and an actual heating time of 900 ms can also be achieved in one period of the second heating mode.

[0056] The figure below shows a time-dependent behavior of the resistance values ​​according to a first method, where the first heating mode (HDC) is operated with a duration (heating mode period) of advantageously 60 s and the second heating mode is also operated with a duration of advantageously 60 s. According to the first method, the operation of the heating medium in a pulsed heating mode advantageously has a heating time relative to the duration of a heating mode period (first and second), which can differ for the first and second heating modes.

[0057] For example, the sampling time for the gas sensor is 1s and is used in the method 1The same applies to both heating modes. For example, the heating time in the first heating mode is 90% of the time of one period of the first heating mode, and the heating time in the second heating mode is 9% of the time of one period of the second heating mode. By using the same sampling time, an actual heating time of, for example, 900 ms (relative heating time * sampling time) in one period of the first heating mode and an actual heating time of 90 ms in one period of the second heating mode can be achieved.

[0058] In both heating modes, the resistor is advantageously heated to the same operating temperature, for example 360 ​​°C.

[0059] The heating modes advantageously create a periodic behavior of the gas sensor device with marked changes in the signal at transition points between the heating modes.

[0060] Signal processing across heating modes, i.e., a comparison of both heating modes for similarities, yields results in the signal curve that can be advantageously independent of individual behavior of electrical resistance in different gas sensors, dependence of the signal on drifts (changes) in sensitivity over time, and variations in relative humidity and temperature.

[0061] Fig. Figure 5 shows a sequence of process steps according to an embodiment of the present invention.

[0062] In the procedure for operating a gas sensor device to determine information about air quality, a provision is made S1a gas sensor device with at least one gas-sensitive electrical sensor resistor, with a heating medium for controlled heating of the sensor resistor, with a detection device for detecting the resistance value of the sensor resistor and with a signal processing device for the sensor signal; a heating S2 of the sensor resistance alternating with the heating medium in at least a first heating mode in a first operating phase and at least a second heating mode in a second operating phase, wherein each heating mode comprises a sequence of heating pulses, such that the sensor resistance is heated to a predetermined operating temperature at predetermined time intervals for a predetermined duration, wherein an substantially identical operating temperature is selected for the at least two different heating modes; and a detection S3of the resistance value of the sensor resistance and generating a sensor signal based on this resistance value during the first and second operating phases.

[0063] Although the present invention has been fully described above with reference to the preferred embodiment, it is not limited to this embodiment but can be modified in many different ways. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2016 / 0216227 A1

[0003]

Claims

[1] Method for operating a gas sensor device (10) for determining information about air quality, comprising the steps: -Providing (S1) a gas sensor device (10) with at least one gas-sensitive electrical sensor resistor (W), with a heating medium (H) for controlled heating of the sensor resistor (W), with a detection device (EF) for detecting the resistance value of the sensor resistor (W) and with a signal processing device (S) for the sensor signal; -Heating (S2) the sensor resistor (W) with the heating medium (H) alternating in at least one first heating mode (HDC) in a first operating phase and at least one second heating mode (LDC) in a second operating phase, wherein each heating mode comprises a sequence of heating pulses, so that the sensor resistor (W) is heated to a predetermined operating temperature at predetermined time intervals for a predetermined duration, wherein a substantially same operating temperature is selected for the at least two different heating modes; and -Detection (S3) of the resistance value of the sensor resistor (W) and generation of a sensor signal based on this resistance value during the first and second operating phases. [2] Method according to claim 1, wherein after detection the sensor signal is processed (S4) by the signal processing device (S), wherein the air quality of an ambient air relative to an air reference value for resistance is inferred from the sensor signal. [3] Method according to claim 1 or 2, wherein the time interval between the heating pulses of the first and / or the second heating mode is constant. [4] Method according to any one of claims 1 to 3, wherein the duration of the heating pulses of the first and / or the second heating mode is constant. [5] Method according to any one of claims 1 to 4, wherein the first and second heating modes differ by time intervals between the heating pulses. [6] Method according to any one of claims 1 to 5, wherein the first and second heating modes differ in the duration of the heating pulses. [7] Method according to any one of claims 1 to 6, wherein the detection (S3) takes place during the heating pulses, and only when the gas-sensitive electrical resistance has been heated to the operating temperature. [8] Method according to claim 7, wherein the detection (S3) takes place at the end of the heating pulses of the respective heating mode. [9] Method according to any one of claims 1 to 8, wherein in each operating phase at least one reference value is determined based on the sensor signal and the reference values ​​of two successive operating phases are compared with each other, wherein a comparison value is determined from the reference values, and information about air quality is obtained by means of the comparison value. [10] Method according to claim 9, wherein the comparison values ​​are determined on the basis of the sensor signal at the end of an operating phase. [11] Method according to claim 9, wherein a difference and / or a quotient is formed from the comparison values ​​of successive operating phases (S5). [12] Gas sensor device (10) for determining information about air quality, comprising - at least one gas-sensitive electrical sensor resistor (W); - a heating medium (H) for alternating heating of the sensor resistance (W) in at least a first heating mode (HDC) in a first operating phase and at least a second heating mode (LDC) in a second operating phase; - a detection device (EF) which is configured to detect a resistance value of the sensor resistance (W) (S3) and to generate a sensor signal during the first and second operating phases; - a signal processing device (S) by which the sensor signal can be processed; and - a control device (SE) which is configured to control the heating medium (H) for heating (S2) the gas-sensitive electrical resistance (W) such that heating (S2) of the sensor resistance (W) occurs alternately at least in the first heating mode (HDC) and at least in the second heating mode (LDC), so that an operating phase in a first heating mode is followed by an operating phase in another, second heating mode, wherein each heating mode comprises a sequence of heating pulses which heat the sensor resistance (W) to a predetermined operating temperature at predetermined time intervals for a predetermined duration, wherein the operating temperature of the at least two different heating modes is essentially the same. [13] Gas sensor device (10) according to claim 12, wherein the signal processing device (S) is configured to infer from the sensor signal an air quality of an ambient air relative to an air reference value for the resistance. [14] Gas sensor device (10) according to claim 13, wherein the signal processing device (S) comprises a memory (SP) with stored air reference values ​​for the resistance value and the air quality values ​​associated therewith.

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