gas sensor

Abstract

This gas sensor provides a configuration that maintains high detection accuracy over a long period of time, even when the heating temperature of the thermal conductivity sensor is set to a low temperature and a humidity sensor is used. [Solution] The gas sensor 1 comprises thermal conductivity sensors 10 and 20, a temperature sensor 30, and a humidity sensor 40 for measuring the first gas humidity. The thermal conductivity sensors 10 and 20 measure the first and second thermal conductivity, which have different sensitivity characteristics to the humidity of the gas, and determine the difference between the first and second thermal conductivity corresponding to the gas temperature. Next, the second gas humidity is determined from the relationship between the difference value, the first gas humidity, and a predetermined difference value and humidity. Next, the apparent gas concentration is determined from the relationship between the temperature, the second gas humidity, a predetermined humidity and the apparent thermal conductivity. Next, a correction amount for the gas concentration is determined from the relationship between the gas temperature, the second gas humidity, a predetermined humidity and the correction amount for the gas concentration. Finally, the true gas concentration is detected by correcting the apparent gas concentration with the correction amount.

Description

Technical Field

[0001] The present disclosure relates to a gas sensor.

Background Art

[0002] In recent years, fuel cell electric vehicles (FCEVs) equipped with a motor as a driving power source and using hydrogen as a fuel have been sold. A fuel cell vehicle runs by rotating a motor using electrical energy generated by a chemical reaction of hydrogen and oxygen in a fuel cell. Since hydrogen as a fuel is a flammable gas, if a gas sensor for detecting the presence and concentration of hydrogen is arranged near a hydrogen storage tank or a fuel cell to which hydrogen is supplied, leakage of hydrogen from the tank, the fuel cell, etc. can be detected.

[0003] Patent Document 1 discloses a gas sensor capable of detecting the concentration of carbon dioxide gas. The gas sensor is a heat conduction type gas sensor, and two thermal conductivity sensors (thermistors in Patent Document 1) are used as temperature measuring bodies. The gas sensor utilizes the fact that the thermal conductivity of carbon dioxide gas is significantly different from that of air, and takes out the change in the heat dissipation characteristics of the two thermal conductivity sensors due to the concentration of carbon dioxide gas as a gas detection voltage. However, since the thermal conductivity in the measurement atmosphere changes not only depending on the concentration of carbon dioxide gas but also depending on the humidity of the atmosphere, there is a risk that the influence of humidity becomes a measurement error.

[0004] Therefore, the gas sensor disclosed in Patent Document 1 heats one thermal conductivity sensor to, for example, 150°C and the other thermal conductivity sensor to, for example, 300°C. When the heating temperature is 150°C, the heat dissipation characteristics of the thermal conductivity sensors change significantly depending on the concentration of carbon dioxide gas, whereas when the heating temperature is 300°C, the heat dissipation characteristics of the thermal conductivity sensors hardly change depending on the concentration of carbon dioxide gas. Furthermore, since the heat dissipation characteristics of both thermal conductivity sensors change depending on the humidity in both cases, the effect of humidity can be canceled by connecting the two thermal conductivity sensors in series.

[0005] Patent Document 2 discloses a hydrogen sensor that is attached to a pipe through which a gas to be detected flows and detects the hydrogen concentration in the gas. The hydrogen sensor consists of a body, a support arm that extends from the body through a sensor mounting hole in the pipe to the center of the pipe, and a detection head supported at the tip of the support arm. A thermal conductivity sensor (gas detection element in Patent Document 2) is used in the detection head of the hydrogen sensor. Since thermal conductivity is affected by the humidity of the atmosphere, the hydrogen sensor disclosed in Patent Document 2 is configured to determine the accurate thermal conductivity of the target gas by correcting it using a humidity sensor, and then measure the concentration. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-089156 [Patent Document 2] Japanese Patent Publication No. 2007-309908 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in methods that cancel the effect of humidity by changing the heating temperature of a thermal conductivity sensor, such as the gas sensor disclosed in Patent Document 1, durability is poor when the temperature of the thermal conductivity sensor becomes high. Furthermore, in order to obtain durability, rare and expensive metals such as platinum must be used, making the gas sensor costly. Moreover, it is known that the durability of thermal conductivity sensors is insufficient in high humidity atmospheres.

[0008] Therefore, when detecting carbon dioxide gas by heating the thermal conductivity sensor to a low temperature (for example, below 50°C), correction using a humidity sensor, as disclosed in Patent Document 2 for the hydrogen sensor, can be considered. However, for example, when a capacitive humidity sensor is used as the humidity sensor, although the detection accuracy of humidity is high in the initial stages of use, the detection accuracy decreases as the period of use lengthens due to deterioration such as corrosion of the wet / dry film (polymer) (aging deterioration). Therefore, it is difficult to maintain the initial detection accuracy over long periods, such as the lifetime of an automobile. Thus, there was room for further improvement in conventional gas sensors.

[0009] Therefore, there is a need for a gas sensor that can maintain high detection accuracy over a long period of time, even when the heating temperature of the thermal conductivity sensor is set to a low temperature and a humidity sensor is used. [Means for solving the problem]

[0010] One embodiment of the gas sensor according to this disclosure is a gas sensor for detecting the gas concentration of a gas to be detected, comprising: a thermal conductivity sensor for measuring the gas thermal conductivity of the gas; a temperature sensor for measuring the gas temperature of the gas; and a humidity sensor for measuring the first gas humidity of the gas, wherein the thermal conductivity sensor measures a first thermal conductivity and a second thermal conductivity, which have different sensitivity characteristics to the humidity of the gas, as the gas thermal conductivity, determines the difference between the first thermal conductivity and the second thermal conductivity corresponding to the gas temperature, determines the second gas humidity of the gas based on the difference, the first gas humidity, and a predetermined relationship between the difference between the first and second thermal conductivity and the humidity, determines the apparent gas concentration based on the relationship between the gas temperature, the second gas humidity, and a predetermined relationship between the humidity and the apparent gas thermal conductivity, determines the correction amount for the gas concentration based on the relationship between the gas temperature, the second gas humidity, and a predetermined correction amount for the humidity and the gas concentration, and detects the true gas concentration by correcting the apparent gas concentration with the correction amount.

[0011] According to this embodiment, the gas sensor determines the second gas humidity based on the difference between the first and second thermal conductivity, the difference, the first gas humidity, and a predetermined relationship between the difference between the first and second thermal conductivity and the humidity. Therefore, the gas humidity can be obtained with high accuracy over a long period of time without being affected by the decrease in measurement accuracy due to the aging of the humidity sensor. Furthermore, since the correct amount for the gas concentration can be accurately determined based on the relationship between the gas temperature, the second gas humidity, and a predetermined correction amount for the gas concentration, the true gas concentration contained in the gas can be obtained with high accuracy over a long period of time. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram showing the gas sensor and control unit according to this embodiment. [Figure 2] This is a diagram showing the configuration of the first sensor. [Figure 3] This graph shows the relationship between the humidity and thermal conductivity of the detected gas. [Figure 4] This graph shows the relationship between the humidity of the detected gas and the difference between its first and second thermal conductivity values. [Figure 5] This graph shows the relationship between the humidity of the detected gas and the correction amount for hydrogen concentration. [Figure 6] This is a flowchart illustrating a method for detecting the hydrogen concentration in a gas to be detected. [Modes for carrying out the invention]

[0013] The embodiments of the gas sensor according to this disclosure will be described in detail below with reference to the drawings. The embodiments described below are illustrative examples for illustrating the gas sensor, and the gas sensor of this disclosure is not limited to these embodiments. Therefore, the gas sensor according to this disclosure can be implemented in various forms without departing from its essence.

[0014] [Gas sensor configuration] As shown in Figure 1, the gas sensor 1 is configured to include a first sensor 10 (an example of a thermal conductivity sensor), a second sensor 20 (an example of a thermal conductivity sensor), a temperature sensor 30, and a humidity sensor 40. The first sensor 10 and the second sensor 20 in this embodiment can measure the thermal conductivity of a gas (an example of gas thermal conductivity). Based on the measured thermal conductivity, the concentration of hydrogen gas (an example of a gas) in the gas (hereinafter also simply referred to as "hydrogen concentration") can be detected. Hereinafter, the gas whose hydrogen concentration is to be detected will also be referred to as the "detected gas." The detected gas is, for example, air. The hydrogen concentration is defined by the percentage (Vol.%) of the volume of hydrogen gas in a unit volume of the detected gas.

[0015] The gas sensor 1 is controlled by the control unit 50. The first sensor 10 and the second sensor 20 are, for example, MEMS (Micro Electro Mechanical Systems) devices. Because MEMS devices have good heat dissipation, the change in thermal conductivity in response to changes in hydrogen concentration in the gas being detected is large, which allows the gas sensor 1 to be made highly sensitive.

[0016] Since the first sensor 10 and the second sensor 20 have similar configurations, the configuration of the first sensor 10 will be described here as an example. As shown in Figure 2, the first sensor 10 has a pair of detection elements 11 that come into contact with the gas to be detected, and a pair of comparator elements 12 that come into contact with a gas (for example, nitrogen) that does not contain hydrogen, or contains only a very small amount of hydrogen, and has a constant hydrogen concentration. The pair of detection elements 11 and the pair of comparator elements 12 are resistive elements configured to be heated by, for example, a heater. The pair of detection elements 11 and the pair of comparator elements 12 are arranged to face each other, forming a so-called bridge circuit.

[0017] The bridge circuit is a circuit that, when a drive voltage (e.g., pulse voltage) is applied from the power supply 13, produces an output voltage (V in Figure 2) corresponding to the resistance value of the resistive element. In the first sensor 10 of this embodiment, the output voltage value changes according to the hydrogen concentration in the gas to be detected. Specifically, when the hydrogen concentration in the gas to be detected changes, the thermal conductivity of the gas to be detected changes, and the surface temperature of the pair of detection elements 11 changes. When the surface temperature of the pair of detection elements 11 changes, the resistance value changes. On the other hand, the resistance value of the pair of comparison elements 12 does not change. Thus, since the change in the output voltage of the bridge circuit is caused only by the change in the hydrogen concentration in the gas to be detected, it becomes possible to detect the hydrogen concentration in the gas to be detected based on the output voltage value of the bridge circuit corresponding to the thermal conductivity of the gas to be detected. Note that the relationship between the hydrogen concentration and thermal conductivity in the gas to be detected has a positive correlation, where the thermal conductivity increases as the hydrogen concentration increases.

[0018] By the way, if the detected gas contains moisture (water vapor) in addition to hydrogen gas, the thermal conductivity of the detected gas becomes even higher. That is, when the detected gas contains moisture, the hydrogen concentration detected based on the measured thermal conductivity indicates a value higher than the actual hydrogen concentration. Therefore, when the detected gas contains moisture, it is necessary to perform a correction to subtract the hydrogen concentration (an example of the apparent gas concentration) detected based on the thermal conductivity measured by the first sensor 10 and the second sensor 20. However, the amount of correction to be subtracted varies depending on the temperature and moisture content (humidity) of the detected gas. Therefore, the gas sensor 1 has a temperature sensor 30 and a humidity sensor 40 in order to determine the amount of correction for performing a correction to detect the true hydrogen concentration. Note that, as described in the background art, the measurement accuracy of humidity decreases due to aging deterioration. The degree of decrease varies depending on the usage environment, but after 10 years of use, it changes by about 5%RH to 6%RH from the correct humidity value. Therefore, in the gas sensor 1, the humidity sensor 40 is used for reference.

[0019] The control unit 50 controls the operation of the gas sensor 1. The control unit 50 detects the hydrogen concentration corresponding to the thermal conductivity of the detected gas based on the output voltage values of the bridge circuits of the first sensor 10 and the second sensor 20. As shown in FIG. 1, the control unit 50 includes a control unit 52, an arithmetic unit 54, and a storage unit 56.

[0020] 〔Method for Detecting Hydrogen Concentration〕 Next, a method for detecting the hydrogen concentration in the detected gas will be described using FIGS. 3 to 6. As shown in FIG. 3, in the storage unit 56 of the control unit 50, the relationship (map) between the humidity of the detected gas and the thermal conductivity of the detected gas at each of the first sensor 10 and the second sensor 20 when the temperature of the detected gas is 60° C. and 80° C. is stored in advance. In FIG. 3, only the thermal conductivities for 60° C. and 80° C. are shown. Similar to FIG. 5 described later, in the storage unit 56, the same relationship is stored every 10° C. between 10° C. and 100° C. As shown in FIG. 3, the first sensor 10 and the second sensor 20 have different amounts of change in thermal conductivity (sensitivity characteristics) with respect to changes in humidity. In both the case of 60° C. and 80° C., the second sensor 20 has a larger amount of change in thermal conductivity with respect to changes in humidity and is more sensitive. Hereinafter, the cases of 60° C. and 80° C. will be described together as the temperature of the detected gas for detecting the hydrogen concentration.

[0021] Further, as shown in FIG. 5, in the storage unit 56, the relationship (map) between the humidity of the detected gas and the correction amount of the hydrogen concentration at each 10° C. between 10° C. and 100° C. for each of the first sensor 10 and the second sensor 20 is stored in advance. Furthermore, in the storage unit 56, for each of the first sensor 10 and the second sensor 20, the relationship (map) between the thermal conductivity of the detected gas in a state without containing moisture and the hydrogen concentration at each 10° C. between 10° C. and 100° C. is stored (not shown).

[0022] In detecting the hydrogen concentration in the gas to be detected, first, a command from the control unit 50 simultaneously performs the following actions: measuring the temperature of the gas to be detected (an example of gas temperature) using the temperature sensor 30 of the gas sensor 1, measuring the humidity of the gas to be detected (an example of first gas humidity) using the humidity sensor 40, measuring the thermal conductivity of the gas to be detected (hereinafter also referred to as first thermal conductivity) using the first sensor 10, and measuring the thermal conductivity of the gas to be detected (hereinafter also referred to as second thermal conductivity) using the second sensor 20 (step S1). At this time, the detection element 11 and comparison element 12 of the first sensor 10, and the detection element and comparison element of the second sensor 20 are all heated to a low temperature, for example, about 50°C. In the first sensor 10 and the second sensor 20, the comparison element is sealed in a space purged with nitrogen, for example, so as not to come into contact with the gas to be detected. The temperature of the gas to be detected measured by the temperature sensor 30, the humidity of the gas to be detected measured by the humidity sensor 40, the first thermal conductivity, and the second thermal conductivity are output to the control unit 50. Furthermore, the temperature measurement of the detected gas by the temperature sensor 30 of the gas sensor 1, the humidity measurement of the detected gas by the humidity sensor 40, the thermal conductivity measurement of the detected gas by the first sensor 10, and the thermal conductivity measurement of the detected gas by the second sensor 20 do not have to be performed at the same time; the measurement timing of at least one sensor may be different. In this case, the order of measurement is not particularly important, but if the measurement timing of the thermal conductivity measurement of the detected gas by the first sensor 10 and the thermal conductivity measurement of the detected gas by the second sensor 20 are different, i.e., if there is a time difference in the measurement timing, it is preferable that the time difference in the measurement timing be short.

[0023] Next, the calculation unit 54 of the control unit 50 calculates the difference between the input first thermal conductivity and the second thermal conductivity (hereinafter also referred to as the first difference) (step S2), and outputs the calculation result to the control unit 52. The calculation unit 54 also reads from the storage unit 56 the relationship between the humidity of the detected gas at the temperature input from the temperature sensor 30 (60°C or 80°C) and the respective thermal conductivity of the first sensor 10 and the second sensor 20 (map shown in Figure 3), and calculates the difference between the first thermal conductivity and the second thermal conductivity at each humidity (hereinafter also referred to as the second difference). The calculation result is shown in Figure 4. In this embodiment, the second difference is the difference value at each humidity calculated from the first thermal conductivity and the second thermal conductivity at 60°C, as shown in Figure 3, and the difference value at each humidity calculated from the first thermal conductivity and the second thermal conductivity at 80°C. The calculation unit 54 outputs the calculation result to the control unit 52. Furthermore, if the temperature of the gas to be detected is a temperature not included in the map of Figure 3 stored in the memory unit 56, such as 63°C, the calculation unit 54 proportionally distributes the values ​​of the thermal conductivity at 60°C and 70°C and each humidity to calculate the first and second thermal conductivity at 63°C and each humidity.

[0024] The control unit 52 compares the value of the first difference and the value of the second difference input from the calculation unit 54 and determines whether there is only one value for the second difference that is the same as the value of the first difference, or whether there are two such values ​​(step S3). For example, if the value of the first difference is X in Figure 4, and the temperature of the detected gas is 60°C, the humidity of the detected gas for which the second difference is X is uniquely determined to be approximately 53%. However, if the temperature of the detected gas is 80°C, there are two possible humidity values ​​for the detected gas for which the second difference is X: approximately 23% and approximately 64%, and the humidity cannot be uniquely determined.

[0025] Therefore, when the temperature of the detected gas is 80°C, the control unit 52 compares the humidity of the detected gas input from the humidity sensor 40 with two humidity values ​​for the detected gas where the second difference is X, and selects the humidity that is closer to the humidity measured by the humidity sensor 40 as the humidity of the detected gas. That is, when the temperature of the detected gas is 80°C, and there are two humidity values ​​for the detected gas where the second difference is X (Yes in step S3), the control unit 52 selects the humidity that is closer to the humidity measured by the humidity sensor 40 (step S4). Here, for example, suppose the humidity measured by the humidity sensor 40 and input to the control unit 50 is 26%. In that case, the humidity of the detected gas that is close to the humidity measured by the humidity sensor 40 is 23%. Therefore, the control unit 52 selects 23% as the humidity of the detected gas when the temperature of the detected gas is 80°C. On the other hand, when there is only one humidity for the detected gas where the second difference is X, such as when the temperature of the detected gas is 60°C (No. in step S3), the control unit 52 selects that humidity (approximately 53%) (step S5). At this time, the control unit 52 may, for confirmation, refer to the humidity of the detected gas input from the humidity sensor 40. Hereinafter, the humidity selected by the control unit 52 based on the second difference will also be referred to as the second gas humidity.

[0026] Next, the control unit 52 selects the first thermal conductivity of the first sensor 10 and the second thermal conductivity of the second sensor 20 from the relationship (map) shown in Figure 3, based on the selected humidity and the temperature of the gas to be detected, and detects the hydrogen concentration in the gas to be detected based on the relationship (not shown) between the thermal conductivity of the gas to be detected in a moisture-free state, which is read from the storage unit 56 (step S6). Theoretically, the hydrogen concentration detected based on the first thermal conductivity and the hydrogen concentration detected based on the second thermal conductivity will be the same value, but by using the thermal conductivity of a highly sensitive sensor whose thermal conductivity changes significantly with respect to changes in humidity (in this embodiment, the second thermal conductivity of the second sensor 20), a more accurate hydrogen concentration can be obtained.

[0027] As described above, if the detected gas contains moisture, a thermal conductivity higher than the thermal conductivity corresponding to the true hydrogen concentration will be detected. In this embodiment, the values ​​of the first and second thermal conductivity selected by the control unit 52 based on Figure 3 are the values ​​when the detected gas contains moisture, and are higher than the thermal conductivity values ​​when it does not contain moisture. Therefore, the hydrogen concentration in the detected gas detected based on the first and second thermal conductivity shown in Figure 3 is an apparent hydrogen concentration that is higher than the true hydrogen concentration. For this reason, it is necessary to correct the apparent hydrogen concentration in order to detect the true hydrogen concentration.

[0028] Therefore, as shown in Figure 5, the control unit 52 reads from the storage unit 56 a relationship (map) of the correction amount for the hydrogen concentration in the detected gas when the humidity of the detected gas changes in 10°C increments between 10°C and 100°C. Then, it applies the temperature measured by the temperature sensor 30 and the second gas humidity to Figure 5 to determine the correction amount for the hydrogen concentration in the detected gas. Then, by subtracting the determined correction amount from the apparent hydrogen concentration detected by the above method, the true hydrogen concentration in the detected gas is detected (step S7). As described above, if the temperature of the detected gas is a temperature not included in the map of Figure 5 stored in the storage unit 56, such as 63°C, the calculation unit 54 proportionally distributes the numerical values ​​of the correction amounts for hydrogen concentration at 60°C and 70°C humidity to calculate the correction amount for hydrogen concentration at each humidity at 63°C.

[0029] Thus, in the gas sensor 1, the humidity of the detected gas is determined based on the difference between the first thermal conductivity and the second thermal conductivity (first difference) and the relationship (map) between the humidity of each detected gas and the thermal conductivity of the detected gas. Therefore, the humidity of the detected gas can be obtained with high accuracy over a long period of time without being affected by the decrease in measurement accuracy due to the aging of the humidity sensor 40. Furthermore, since the correction amount for the hydrogen concentration can be accurately determined based on the temperature and humidity of the detected gas, the true concentration of hydrogen gas contained in the detected gas can be obtained with high accuracy over a long period of time.

[0030] Furthermore, as described above, in this embodiment, the first sensor 10 and the second sensor 20 are heated to a low temperature of approximately 50°C or less, compared to the heating temperature (300°C) of the gas sensor disclosed in Patent Document 1. Therefore, the first sensor 10 and the second sensor 20 are less susceptible to deterioration due to heat over time, and the initial detection accuracy of thermal conductivity can be maintained over a long period of time. As a result, the humidity obtained based on the difference in thermal conductivity can also be obtained with high accuracy over a long period of time.

[0031] [Other Embodiments] Embodiments of this disclosure may be configured as follows, in addition to the embodiments described above (parts having the same functions as the embodiments described above are given the same numbers and reference numerals as the embodiments described above).

[0032] (1) In the above embodiment, the gas sensor 1 comprises a first sensor 10 and a second sensor 20 having different sensitivity characteristics to changes in humidity, but is not limited to this. For example, the gas sensor 1 may have only the first sensor 10. In this case, the thermal conductivity is measured twice by applying a driving voltage (pulse voltage) twice to a pair of detection elements 11 of the first sensor 10. Specifically, the first thermal conductivity is measured by applying a first driving voltage to the first sensor 10, and then the second thermal conductivity is measured by applying a second driving voltage, which has a different voltage value and / or on-time than the first driving voltage. By making the first driving voltage and the second driving voltage different, the surface temperatures of the pair of detection elements 11 are different, so that even if the hydrogen concentration in the gas to be detected is the same, the sensitivity characteristics of the first sensor 10 can be made different. In this way, since the first thermal conductivity and the second thermal conductivity are measured with only the first sensor 10, the manufacturing cost of the gas sensor 1 can be reduced.

[0033] In this case, it is preferable to increase (lengthen) the voltage value and / or on-time of the second drive voltage relative to the first drive voltage, as this shortens or eliminates the time required to lower the surface temperature of the pair of detection elements 11 after the application of the first drive voltage. This allows for the measurement of the first and second thermal conductivity by shortening the time (interval time) from the application of the first drive voltage to the application of the second drive voltage. If the first sensor 10 is a MEMS device, it has excellent heat dissipation, so the interval time is, for example, about 10 to 30 milliseconds.

[0034] (2) In the above embodiment, the gas sensor 1 detected the concentration of hydrogen gas, but it is not limited to this. The gas sensor 1 can be used to detect the concentration of any gas whose thermal conductivity changes significantly depending on the concentration. Carbon dioxide gas is an example of such a gas.

[0035] (3) In the above embodiment, the difference between the first thermal conductivity and the second thermal conductivity (second difference) at each humidity was calculated by the calculation unit 54. However, the second difference at each humidity may be stored in advance in the storage unit 56 and read by the control unit 52.

[0036] (4) In the above embodiment, the detection element 11 of the first sensor 10 and the detection element of the second sensor 20 were both heated to approximately 50°C, but this is not limited to this. For example, the temperature of the detection element 11 of the first sensor 10 and the detection element of the second sensor 20 do not have to be 50°C. Also, the temperature of the detection element 11 of the first sensor 10 and the temperature of the detection element of the second sensor 20 may be different. This makes it possible to make the sensitivity characteristics different even if the first sensor 10 and the second sensor 20 are the same sensor.

[0037] (5) In the above embodiment, the gas sensor 1 had a temperature sensor 30 and a humidity sensor 40, but a temperature and humidity sensor in which the temperature sensor 30 and the humidity sensor 40 are integrated may be used.

[0038] (6) As described above, the humidity obtained based on the thermal conductivity of the first sensor 10 and the second sensor 20 maintains high accuracy over long periods. Therefore, the humidity sensor 40 may be periodically calibrated based on the humidity obtained from the thermal conductivity of the first sensor 10 and the second sensor 20. By periodically calibrating the humidity sensor 40 in this way, the decrease in measurement accuracy due to the aging of the humidity sensor 40 can be minimized.

[0039] (7) In the above embodiment, the comparison element 12 of the first sensor 10 (and the second sensor 20) is configured to be in contact with nitrogen, but is not limited to this. It may be air or the like. However, even if these gases are used, it is desirable that they do not contain moisture.

[0040] (8) In the above embodiment, the first sensor 10 and the second sensor 20 are configured as MEMS devices, but the embodiment is not limited to this. The first sensor 10 and the second sensor 20 may have configurations other than MEMS devices, as long as the thermal conductivity of the gas to be detected can be measured with high accuracy.

[0041] (9) In the above embodiment, the hydrogen concentration was detected based on the thermal conductivity measured by the highly sensitive second sensor 20, but the hydrogen concentration may also be detected based on the thermal conductivity measured by the relatively less sensitive first sensor 10. Alternatively, the hydrogen concentration may be detected based on the average value of the thermal conductivity measured by the first sensor 10 and the thermal conductivity measured by the second sensor 20.

[0042] In the gas sensor 1 described in the above embodiment, the following configuration can be envisioned.

[0043] <1> One embodiment of the gas sensor (1) is a gas sensor (1) for detecting the gas concentration of a gas to be detected, comprising a thermal conductivity sensor (10, 20) for measuring the gas thermal conductivity of the gas, a temperature sensor (30) for measuring the gas temperature of the gas, and a humidity sensor (40) for measuring the first gas humidity of the gas. The thermal conductivity sensor (10, 20) measures a first thermal conductivity and a second thermal conductivity, which have different sensitivity characteristics to the humidity of the gas, as the gas thermal conductivity, and determines the difference between the first thermal conductivity and the second thermal conductivity corresponding to the gas temperature. Based on the difference, the first gas humidity, and a predetermined relationship between the difference between the first and second thermal conductivity and the humidity, it determines the second gas humidity of the gas. Based on the relationship between the gas temperature, the second gas humidity, and a predetermined humidity and the apparent gas thermal conductivity, it determines a correction amount for the gas concentration based on the relationship between the gas temperature, the second gas humidity, and a predetermined humidity and the correction amount for the gas concentration. The apparent gas concentration is corrected by the correction amount to detect the true gas concentration.

[0044] According to this embodiment, the gas sensor (1) determines the second gas humidity of the gas based on the difference between the first thermal conductivity and the second thermal conductivity, the difference value, the first gas humidity, and a predetermined relationship between the difference between the first and second thermal conductivity and the humidity. Therefore, the humidity of the gas can be obtained with high accuracy over a long period of time without being affected by the decrease in measurement accuracy due to the aging of the humidity sensor (40). Furthermore, since the correct amount of gas concentration can be accurately determined based on the relationship between the gas temperature, the second gas humidity, and a predetermined correction amount for humidity and gas concentration, the true gas concentration contained in the gas can be obtained with high accuracy over a long period of time.

[0045] <2> the above <1> In the gas sensor (1) described above, it is preferable that there be two thermal conductivity sensors, one thermal conductivity sensor (10) measuring the first thermal conductivity and the other thermal conductivity sensor (20) measuring the second thermal conductivity, and that the first and second thermal conductivity are measured simultaneously.

[0046] According to this embodiment, the first thermal conductivity is measured with one thermal conductivity sensor (10), and the second thermal conductivity is measured simultaneously with the other thermal conductivity sensor (20). Therefore, the second gas humidity can be determined by measuring the first and second thermal conductivity at the same gas concentration. This makes it possible to detect the second gas humidity and the true gas concentration with higher accuracy.

[0047] <3> the above <1> In the gas sensor (1) described above, it is preferable to have one thermal conductivity sensor, to detect a first thermal conductivity by applying a first drive voltage to the thermal conductivity sensor (10), and to detect a second thermal conductivity by applying a second drive voltage different from the first drive voltage to the thermal conductivity sensor (10).

[0048] According to this embodiment, since the first thermal conductivity and the second thermal conductivity are measured by a single thermal conductivity sensor (10), the true gas concentration can be detected without using two thermal conductivity sensors. This reduces the manufacturing cost of the gas sensor (1).

[0049] <4> the above <1> from <3> In the gas sensor (1) described in any one of the above, it is preferable to calibrate the humidity sensor (40) based on the second gas humidity.

[0050] According to this embodiment, by periodically calibrating the humidity sensor (40) based on the humidity of the second gas, the decrease in measurement accuracy due to the aging of the humidity sensor (40) can be minimized. [Industrial applicability]

[0051] This disclosure can be used in gas sensors. [Explanation of Symbols]

[0052] 1: Gas sensor, 10: First sensor (thermal conductivity sensor), 20: Second sensor (thermal conductivity sensor), 30: Temperature sensor, 40: Humidity sensor

Claims

1. A gas sensor for detecting the gas concentration of the gas to be detected, A thermal conductivity sensor for measuring the thermal conductivity of the aforementioned gas, A temperature sensor for measuring the gas temperature of the aforementioned gas, The system includes a humidity sensor for measuring the first gas humidity of the aforementioned gas, The thermal conductivity sensor measures a first thermal conductivity and a second thermal conductivity, which have different sensitivity characteristics to the humidity of the gas, as the thermal conductivity of the gas. The difference between the first thermal conductivity and the second thermal conductivity corresponding to the gas temperature is determined. Based on the aforementioned difference value, the first gas humidity, and the relationship between the predetermined difference value between the first and second thermal conductivity and the humidity, the second gas humidity of the gas is determined. The apparent gas concentration is determined based on the gas temperature, the second gas humidity, and the predetermined relationship between the humidity and the apparent gas thermal conductivity. Based on the gas temperature, the second gas humidity, and a predetermined relationship between the humidity and the correction amount for the gas concentration, the correction amount for the gas concentration is determined. A gas sensor that detects the true gas concentration by correcting the apparent gas concentration with the correction amount.

2. The system has two of the aforementioned thermal conductivity sensors, The other thermal conductivity sensor measures the first thermal conductivity, The other thermal conductivity sensor measures the second thermal conductivity, The gas sensor according to claim 1, wherein the first thermal conductivity and the second thermal conductivity are measured simultaneously.

3. The system has one of the aforementioned thermal conductivity sensors, The first thermal conductivity is detected by applying a first drive voltage to the thermal conductivity sensor. The gas sensor according to claim 1, wherein the second thermal conductivity is detected by applying a second drive voltage different from the first drive voltage to the thermal conductivity sensor.

4. A gas sensor according to any one of claims 1 to 3, which performs calibration of the humidity sensor based on the second gas humidity.

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