Gas detector

Abstract

To provide a gas detector capable of obtaining concentration indication value with high accuracy without subjected to environmental variation regardless of power saving.SOLUTION: The gas detector comprises: gas detection means 10 not including compensation element insensitive to detected gas; and control means 30. The control means 30 includes: a drive control part 31 intermittently driving the gas detection means 10 to perform a steady energization mode M1 and an energization stop mode M2 alternately and repeatedly; and a concentration calculation part 35 calculating concentration of the detected gas. The concentration calculation part 35 has functions of: calculating absolute humidity of the detected gas from a first output value at a first detection point TS1 set within a prescribed time range from execution start of the steady energization mode M1; and for calculating concentration of the detected gas from a second output value at a second detection point Ts2 elapsed predetermined times from the first detection point Ts1, performing humidity correction based on the absolute humidity of the detected gas.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a gas detector. [Background technology]

[0002] For example, in combustible gas sensors such as catalytic combustion gas sensors and hot wire semiconductor gas sensors, the electrical resistance value changes when the test gas comes into contact with the surface of the gas sensing part, and the concentration of the test gas can be measured by detecting the amount of change in this electrical resistance value. Conventionally, such a combustible gas sensor is provided with a gas detection element having a gas sensitive portion and a compensation element which is insensitive to the detected gas.

[0003] In a gas detector equipped with such a combustible gas sensor, it is necessary to supply power to the compensating element in the same manner as to the gas detection element, which makes it difficult to reduce the power consumption of the gas detector. Recently, in order to reduce the power consumption of gas detectors, gas detectors have been proposed that include a catalytic combustion type gas sensor that does not have a compensating element as gas detection means (see, for example, Patent Document 1).

[0004] On the other hand, in a combustible gas sensor that does not have a compensating element, the output varies (drifts) depending on the temperature and humidity of the measurement environment. For this reason, a combustible gas sensor has been proposed that is provided with a temperature detection unit and a humidity detection unit and is configured to correct the output variation due to the temperature and humidity of the measurement environment (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2015-224892 A [Patent Document 2] JP 2018-194409 A Summary of the Invention [Problem to be solved by the invention]

[0006] In such a combustible gas sensor, normally, after the power is turned on and the output becomes stable, the gas concentration is obtained by performing temperature correction and humidity correction on the obtained output. However, it has become clear that such a method cannot sufficiently compensate for output fluctuations caused by environmental fluctuations, and it is difficult to obtain a highly reliable concentration indication value. It is difficult to determine whether the cause of the error in the concentration indication value is a deviation in temperature correction or a deviation in humidity characteristics, and it is difficult to obtain a concentration indication value with high accuracy. Furthermore, in order to perform humidity correction, the gas detector must be provided with a humidity detection means, which increases the number of parts.

[0007] The present invention was completed in consideration of the above circumstances, and its object is to provide a gas detector which is power-saving yet capable of obtaining highly accurate concentration indications without being affected by environmental fluctuations. [Means for solving the problem]

[0008] The gas detector of the present invention is a gas detector comprising a gas detection means having no compensation element insensitive to the test gas, and a control means, wherein the control means comprises a drive control section which controls the operation of the gas detection means, and a concentration calculation section which calculates the concentration of the test gas, wherein the drive control section has a function of intermittently driving the gas detection means to alternate between a steady current mode in which a predetermined voltage is applied to the gas detection means and a current stop mode in which current to the gas detection means is stopped, and the concentration calculation section has a function of calculating the absolute humidity of the test gas from a first output value obtained at a first detection time point which is set within a predetermined time range from the start of execution of the steady current mode, and a function of performing humidity correction based on the absolute humidity of the test gas when calculating the concentration of the test gas from a second output value obtained at a second detection time point which is a predetermined time after the first detection time point. This solves the above problem. Effect of the Invention

[0009] Focusing on the fact that there is a correlation between the first output value at the first detection point when zero gas is introduced and absolute humidity, the inventors conducted extensive research and found that there is a correlation between the absolute humidity and the difference between the first output value at the first detection point when the test gas is introduced and the first output value at the first detection point when zero gas is introduced, and that by utilizing this correlation from the first output value at the first detection point when the test gas is introduced, it is possible to obtain the absolute humidity of the measurement environment atmosphere with high reliability based on the first output value at the first detection point, regardless of the type of test gas. Therefore, according to the invention of claim 1, even if the gas detector itself does not have a humidity detection means, humidity information can be obtained from the output of the gas detection means, which makes it possible to reduce the number of parts, and by performing humidity correction based on the obtained humidity information, it is possible to compensate for output fluctuations caused by humidity fluctuations at least in the measurement environment atmosphere.

[0010] According to the invention of claim 2, by performing humidity correction not only on the second output value obtained at the second detection time point but also on the span value of the second output value, a concentration indication value can be obtained with even higher accuracy. According to the invention of claim 3, by using temperature-corrected data based on temperature information acquired by the temperature detection means when calculating the concentration of the test gas, the reliability of the concentration indication value can be further improved. According to the invention as defined in claim 4, humidity information of the measurement environment atmosphere can be acquired with high reliability. According to the invention of claim 5, the concentration of the test gas is calculated based on the output obtained when the output of the gas detection means is stable, so that the concentration indication value can be highly reliable. According to the invention as defined in claim 6 and claim 7, the zero output value can be stably maintained, so that highly reliable gas detection can be obtained for a long period of time. According to the invention of claim 8, it is possible to configure the gas detector without using a compensation element that is usually required to eliminate the effects of environmental fluctuations, thereby making it possible to reduce the power consumption of the gas detector itself. [Brief description of the drawings]

[0011] [Figure 1] 1 is a block diagram showing an outline of the configuration of an example of a gas detector of the present invention; [Diagram 2] FIG. 2 is a circuit diagram showing an outline of the configuration of an example of a gas detection means. [Diagram 3] 5A and 5B are diagrams for explaining drive control of the gas detection means, in which (a) is a graph showing a change over time in applied voltage, and (b) is a graph showing a change over time in a current value that is an output from the gas detection means. [Figure 4] FIG. 4 is an operational flow diagram showing an example of a method for calculating the concentration of a test gas. [Diagram 5] 2 is a graph showing a temperature-humidity program set in an environmental test chamber in Example 1. [Figure 6]4 is a graph showing the change over time in concentration indication value before humidity correction, obtained in Example 1. [Figure 7] 1 is a graph showing the change over time in the concentration indication value when only the primary humidity correction was performed, obtained in Example 1. [Figure 8] 1 is a graph showing the change over time in concentration indication value after secondary humidity correction, obtained in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a block diagram showing an outline of the configuration of one example of a gas detector of the present invention. This gas detector comprises gas detection means 10, temperature detection means 20, control means 30, storage means 40, timer means 50, display means 60, and alarm means 70.

[0013] The gas detection means 10 according to this embodiment is, for example, a catalytic combustion type gas sensor or a hot wire type semiconductor gas sensor, and is configured to achieve power saving by not having a compensating element that is insensitive to the gas to be detected. Note that the gas detection means 10 is not limited to a catalytic combustion type gas sensor or a hot wire type semiconductor gas sensor, and other solid state sensors such as a semiconductor gas sensor or a thermal conduction type gas sensor can be used.

[0014] Specifically, as shown in Fig. 2, the gas detection means 10 includes a measurement circuit 15 including a gas detection element 11, a current detection resistor 16, and a power supply 19. In this measurement circuit 15, the gas detection element 11 and the current detection resistor 16 are connected in series to the power supply 19. In the measurement circuit 15, a voltage detection means 17 is connected in parallel to the gas detection element 11, and a current detection means 18 is connected in parallel to the current detection resistor 16.

[0015] The gas detection element 11 is configured such that a gas sensitive portion 12 is formed around a resistive heating element 13 which generates heat when electricity is applied thereto. The gas sensitive portion 12 in the gas detection element 11 is made of an oxidation catalyst sintered together with, for example, an alumina carrier when the gas detection means 10 is configured as a catalytic combustion type gas sensor, and is made of a sintered metal oxide semiconductor when the gas detection means 10 is configured as a hot wire type semiconductor gas sensor. The resistance heating element 13 in the gas detection element 11 is constituted by a heater having a coil portion in which a metal wire made of, for example, platinum or an alloy thereof is wound in a coil shape.

[0016] When the gas detection means 10 is constituted by a catalytic combustion type gas sensor, a voltage controlled to a constant level is applied from the power source 19 to the resistance heating element 13, thereby heating the gas sensing part 12. At this time, a constant resistance value is maintained in the gas detection element 11. When the test gas comes into contact with the surface of the gas sensing part 12, the temperature of the surface of the gas sensing part 12 rises, and the resistance value of the resistance heating element 13 changes accordingly. The amount of change in resistance value is detected by measuring the value of the current flowing through the current detection resistor 16 by the current detection means 18. Furthermore, when the gas detection means 10 is configured as a hot wire semiconductor gas sensor, a voltage controlled to a constant magnitude is applied from the power source 19 to the resistance heating element 13, thereby heating the gas sensing part 12. At this time, a constant resistance value is maintained in the gas detection element 11. When the gas to be detected comes into contact with the surface of the gas sensing part 12, oxygen adsorbed on the surface of the metal oxide semiconductor constituting the gas sensing part 12 is released, and the resistance value of the metal oxide semiconductor changes accordingly, resulting in a change in the resistance value of the entire gas detection element 11. The amount of change in this resistance value is detected by measuring the value of the current flowing through the current detection resistor 16 with the current detection means 18.

[0017] The temperature detection means 20 is, for example, a thermistor of an electric resistance change type that detects the temperature of the test gas by measuring a resistance change caused by contact with the gas. The temperature detection means 20 may be a thermistor of a capacitance type, and is not particularly limited as long as it can detect the temperature of the test gas.

[0018] The control means 30 includes a drive control section 31 that controls the operation of the gas detection means 10, and a concentration calculation section 35 that calculates the concentration of the gas to be detected.

[0019] As shown in Fig. 3(a), the drive control section 31 has a function of alternately executing a steady current mode M1 in which a predetermined voltage Vs is applied to the gas detection element 11 and a current stop mode M2 ​​in which current to the gas detection element 11 is stopped. By controlling current to the gas detection means 10 in this manner, the control means 30 extracts a change in the electric resistance value of the resistive heating element 13 or a change in the electric resistance value of the entire gas detection element 11 as a current value, as shown in Fig. 3(b). The current value, which is the output value of the gas detection means 10, tends to decrease over time from the start of voltage application during steady current mode M1 and to stabilize after a predetermined time has passed.

[0020] The execution time of each of the steady current application modes M1 is preferably 0.4 to 2.0 seconds, and more preferably 0.7 to 1.2 seconds. When the execution time of each steady current mode M1 is less than 0.4 seconds, the gas detection element 11 does not reach the required temperature, and it may be difficult to measure the concentration of the test gas with high accuracy. On the other hand, when the execution time of each steady current mode M1 exceeds 2.0 seconds, the gas detection element 11 continues to be maintained at a high temperature, and deterioration over time, such as alloying, occurs in the gas detection element 11, which makes it more likely to cause changes in resistance and fluctuations in the zero output value. Moreover, the execution time of each of the power supply cut-off modes M2 is preferably 0.5 seconds or more, and more preferably 0.5 to 4.0 seconds. If the execution time of each of the power supply cut-off modes M2 is less than 0.5 seconds, heat is generated by the steady power supply mode M1 before the gas detection element 11 is sufficiently cooled, and deterioration over time, such as alloying, progresses in the gas detection element 11, which makes it more likely that resistance changes and zero output value fluctuations will occur. In addition, if the execution time of each of the power supply cut-off modes M2 is too long, there is the disadvantage of a slower gas detection response. If the execution time of each of the power-off modes M2 is 4.0 seconds or less, the desired gas detection can be reliably performed. Since power consumption can be reduced by extending the execution time of the power-off mode M2, if the response time satisfies the requirements of each site of use, the longer the execution time, the more power consumption can be reduced.

[0021] The concentration calculation unit 35 calculates the absolute humidity [g / m 3 ] has the function of calculating

[0022] The absolute humidity is calculated by utilizing the correlation between the absolute humidity and the difference ΔIc (=Ic-I0) between the first output value I0 at the time of introducing a zero gas having a reference temperature [°C] previously obtained and the first output value Ic obtained for the test gas. This correlation was found by the present inventors and is previously obtained and recorded in the storage means 40. The reference temperature can be set as appropriate, and is 20°C as an example. The first detection time point Ts1 is preferably set within a time range of 0.02 to 0.2 seconds after the start of execution of the steady current mode M1. If the first detection time point Ts1 is set within a time range of less than 0.02 seconds after the start of execution of the steady current mode M1, the acquired current value will not be stable. On the other hand, if the first detection time point Ts1 is set within a time range of more than 0.2 seconds after the start of execution of the steady current mode M1, the gas detection element 11 will become hot, and the humidity detection accuracy will deteriorate.

[0023] Here, a correlation expressed by a quadratic approximation formula is established between the difference ΔIc of the first output values ​​and the absolute humidity. The coefficients in the quadratic approximation formula are, for example, 3 This correlation has been found by the present inventors and is previously obtained and recorded in the storage means 40. Therefore, even if the gas detector itself does not include a humidity detection means, humidity information of the measurement environment atmosphere can be obtained from the first output value Ic of the gas detection means 10.

[0024] In addition, in this embodiment, when calculating the absolute humidity, the first output value Ic is temperature-corrected based on the temperature information acquired by the temperature detection means 20. This makes it possible to acquire humidity information of the measurement environment atmosphere with even higher reliability. The temperature correction for the first output value Ic is performed by utilizing the correlation between the temperature difference of the test gas with respect to the reference temperature and the first output value at the first detection time point Ts1. This correlation was found by the present inventors and is acquired in advance and recorded in the storage means 40. A correlation expressed by a linear approximation formula is established between the first output value at the first detection time point TS1 for each of a plurality of types of dry air with different temperatures and the temperature difference of the dry air with respect to the reference temperature, and the temperature correction is performed assuming that the first output value Ic acquired for the test gas has the same temperature characteristics as the first output value for dry air.

[0025] In addition, the concentration calculation unit 35 has a function of performing humidity correction based on the absolute humidity of the test gas when calculating the concentration of the test gas from the second output value Id obtained at the second detection time Ts2 a predetermined time after the first detection time Ts1. Specifically, the concentration calculation unit 35 has a function of performing a primary humidity correction on the second output value Id based on the acquired humidity information, and a secondary humidity correction on the span value Sp based on the acquired humidity information. The span value Sp is calculated by multiplying the primary corrected output value Ids1 obtained by performing a primary humidity correction on the second output value Id by a reference environment (reference temperature [°C], reference humidity [g / m 3 The standard humidity can be set appropriately, but an example is 11 g / m 3 It is.

[0026] The second detection time point Ts2 is preferably set within a time range of 0 to 0.2 seconds before the end of execution of the steady current mode M1. If the second detection time point Ts2 is set within a time range of more than 0.2 seconds before the end of execution of the steady current mode M1, the concentration calculation will be performed before the output stabilizes, reducing the reliability of the concentration indication value.

[0027] The primary humidity correction for the second output value Id is performed by correcting the zero output value I0 according to the humidity of the measurement environment atmosphere, thereby correcting the second output value Id acquired for the test gas. Specifically, the primary humidity correction is performed using a correlation between the output value at the second detection time point Ts2 for the zero gas and the absolute humidity, which has been acquired in advance. This correlation has been found by the present inventors, and is acquired in advance and recorded in the storage means 40. Here, a correlation expressed by a primary approximation formula is established between the output value at the second detection time point Ts2 for the zero gas and the absolute humidity.

[0028] In addition, in this embodiment, when performing the primary humidity correction, the second output value Id is temperature-corrected based on the temperature information acquired by the temperature detection means 20. This can further improve the reliability of the concentration indication value. The temperature correction for the second output value Id is performed by utilizing the correlation between the temperature difference of the test gas with respect to the reference temperature and the second output value at the second detection time point Ts2. This correlation was found by the present inventors and is acquired in advance using dry air as zero gas and recorded in the storage means 40. A correlation expressed by a linear approximation formula is established between the second output value at the second detection time point Ts2 for each of a plurality of types of dry air with different temperatures and the temperature difference of the dry air with respect to the reference temperature, and the temperature correction is performed assuming that the second output value Id acquired for the test gas has the same temperature characteristics as the second output value for dry air.

[0029] In this embodiment, the span value is obtained by subtracting the zero output value I0 from the primary corrected output value Ids1 obtained by performing primary humidity correction on the second output value Id, and the secondary humidity correction on the span value is performed by utilizing the correlation shown by a linear approximation equation that exists between the span value and absolute humidity. This correlation was found by the present inventors, and is previously obtained and stored in the storage means 40. Specifically, a correlation shown by a linear approximation formula is established between the span value and absolute humidity for each calibration gas of known concentration (e.g., 50% LEL). Therefore, by using a linear approximation formula using a humidity correction coefficient set so that the concentration indication value for each calibration gas falls within a predetermined range and the error in the concentration indication value due to the error in the calculated absolute humidity matches the error in the concentration indication value when zero gas is introduced, secondary humidity correction can be performed on the span value. Here, if the humidity correction coefficient is set so that the concentration indication value falls within a range of 50±15% LEL for each calibration gas, for example, there is no practical problem and the concentration indication value can be highly reliable. Also, the error in the concentration indication value when zero gas is introduced is within a range of, for example, ±10% LEL.

[0030] In addition, in this embodiment, when performing the secondary humidity correction, the primary corrected output value Ids1 is temperature corrected based on the temperature information acquired by the temperature detection means 20. This can further improve the reliability of the detection result. The temperature correction for the primary corrected output value Ids1 is performed in the same manner as the temperature correction for the second output value Id described above.

[0031] The storage means 40 stores, for example, an individual calibration curve (sensitivity curve) specific to the gas detection means 10, which indicates the relationship between the output value of the gas detection means 10 and the concentration indication value, a zero calibration value (zero output value) and a span calibration value for the gas detection means 10 in a reference environment (reference temperature [°C], reference humidity [mg / L]), a linear approximation formula for temperature correction of the first output value, a quadratic approximation formula for calculating absolute humidity, a linear approximation formula for temperature correction of the second output value, a linear approximation formula for humidity correction of the second output value, a linear approximation formula for temperature correction of the span value, a linear approximation formula for humidity correction of the span value, and an alarm point for an instantaneous value of the gas concentration. Here, a plurality of pieces of information such as the individual calibration curve, the span calibration value, and the alarm point set for each of a plurality of types of detected gas may be stored.

[0032] In this gas detector, gas detection of a target gas in a measurement environment is performed in accordance with the operational flow shown in FIG. That is, after the gas detector is powered on and a predetermined warm-up process is performed, the gas detection means 10 is driven by a drive pulse as shown in Fig. 3 based on time information from the clock means 50, and a first output value and a second output value are obtained at a first detection time point Ts1 and a second detection time point Ts2 in the steady current mode M1 (S1). At the same time, temperature information of the detected gas is obtained by the temperature detection means 20, and a first temperature-corrected output value and a second temperature-corrected output value are calculated by performing temperature correction on the first output value and the second output value (S2). Next, the absolute humidity of the gas to be detected is calculated based on the first temperature-corrected output value (S3), and a primary humidity correction is performed on the second temperature-corrected output value to calculate a primary humidity-corrected output value Ids1 (S4). Then, a span value of the primary humidity-corrected output value Ids1 relative to the zero output value I0 is calculated (S5), and the span value is subjected to temperature correction and secondary humidity correction to calculate a secondary humidity-corrected output value Ids2 (S6). The concentration of the test gas is calculated from the secondary humidity correction output value Ids2 thus obtained using the calibration curve data, and the result is displayed on the display means 60. At this time, if the concentration of the test gas exceeds the alarm point, an alarm is issued by the alarm means 70.

[0033] Thus, according to the above gas detector, even if the gas detector itself does not have a humidity detection means, humidity information can be obtained from the output of the gas detection means 10, making it possible to reduce the number of parts, and by performing temperature correction and humidity correction based on the temperature information from the temperature detection means 20 and the acquired humidity information, it is possible to compensate for output fluctuations caused by environmental fluctuations in the measurement environment, and therefore it is possible to indicate the concentration with high accuracy.

[0034] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications can be made. For example, in the above embodiment, the gas detection means is configured to obtain a current value as an output value, but the gas detection means may be configured to obtain a voltage value as an output value. Furthermore, the reference temperature and reference humidity as the reference environment can be set appropriately, and a plurality of reference temperatures and reference humidities may be set. EXAMPLES

[0035] Specific examples of the gas detector of the present invention will now be described. <Example 1> A gas detector according to the present invention was produced according to the configuration shown in FIGS. A catalytic combustion type gas sensor was used as the gas detection means (10), and was operated with the execution time in the steady current mode (M1) being 1 second and the execution time in the current stop mode (M2) being 4.0 seconds. The first detection time point (Ts1) was set to 0.05 seconds after the start of the steady current mode (M1), and the second detection time point (Ts2) was set to 0.05 seconds before the end of the steady current mode (M1).

[0036] The gas detector was placed in the environmental test chamber. Dry air was circulated in the environmental test chamber at a flow rate of 0.5 L / min, and the environmental test chamber was operated according to the temperature-humidity program shown in Figure 5, while the gas detector was also operated. The curve shown by the dashed line in Figure 5 shows the change in temperature over time in the environmental test chamber, and the curve shown by the solid line shows the change in humidity over time in the environmental test chamber. After the operation of the environmental test chamber and the gas detector was started, methane gas with a concentration of 50% LEL, with dry air as the base gas, was introduced into the environmental test chamber for one minute every hour. The piping was set so that the introduced methane gas was fully adapted to the humidity inside the environmental test chamber before being introduced into the gas detector. The change over time of the concentration indication value before humidity correction, the change over time of the concentration indication value when only the primary humidity correction is performed, and the change over time of the concentration indication value after the secondary humidity correction are shown in Figures 6 to 8, respectively.

[0037] Even if the humidity in the ambient atmosphere fluctuates significantly (within the time ranges indicated by the arrows in Figures 5 to 8), it was confirmed that the zero point indication accuracy is improved by performing primary humidity correction (humidity correction of the zero output value) as can be seen from Figures 6 and 7, and that the accuracy of the concentration indication value is improved by performing secondary humidity correction (humidity correction of the span value) as can be seen from Figures 7 and 8. Here, the measurement error for the methane gas concentration was within the range of ±3%. From the above, it was confirmed that humidity information can be obtained with high reliability from the first output value obtained at the first detection time point, and that the concentration indication value of the detected gas can be obtained with high accuracy by humidity correcting the second output value obtained at the second detection time point based on the obtained humidity information.

[0038] <Examples 2 to 4> In the above Example 1, gas detection was performed in the same manner as in Example 1, except that propane gas, isobutane gas, or hydrogen gas was used instead of methane gas as the test gas, and it was confirmed that the concentration of the test gas could be detected with high accuracy, as in Example 1. When propane gas was used as the test gas, the measurement error for the propane gas concentration was within ±4%, when isobutane gas was used, the measurement error for the isobutane gas concentration was within ±5%, and when hydrogen gas was used, the measurement error for the hydrogen gas concentration was within ±3%.

[0039] From the above, it has been confirmed that the gas concentration calculation method according to the present invention can obtain a concentration indication value with a certain degree of accuracy regardless of the type of gas to be detected.

[0040] <Example 5> In the above Example 1, a hot wire type semiconductor gas sensor was used as the gas detection means instead of the catalytic combustion type gas sensor. Gas detection was performed in the same manner as in Example 1, and it was confirmed that the concentration of the test gas (methane gas) could be detected with high accuracy, as in Example 1. The measurement error for the concentration of methane gas was within the range of ±5%. [Explanation of symbols]

[0041] 10 Gas detection means 11 Gas detection element 12 Gas sensing part 13 Resistance heating element 15...Measuring circuit 16 Current sensing resistor 17 Voltage detection means 18 Current detection means 19... power supply 20 Temperature sensing means 30 Control means 31 Drive control section 35...Concentration calculation section 40 ... storage means 50... Timekeeping means 60...Display means 70... Alarm means M1: Steady current mode M2: Power off mode Ts1: First detection time Ts2: Second detection time

Claims

1. A gas detector comprising a gas detection means having no compensation element insensitive to a gas to be detected, and a control means, the control means includes a drive control unit that controls an operation of the gas detection means, and a concentration calculation unit that calculates a concentration of the test gas; the drive control unit has a function of intermittently driving the gas detection means so as to alternately repeat a steady current mode in which a predetermined voltage is applied to the gas detection means and a current stop mode in which current supply to the gas detection means is stopped, a first output value obtained at a first detection point which is set within a predetermined time range from the start of execution of the steady current mode, and a second output value obtained at a second detection point which is a predetermined time after the start of execution of the steady current mode, the second output value being obtained at a second detection point which is set within a predetermined time range from the start of execution of the steady current mode, the second output value being obtained at a second detection point which is set within a predetermined time range from the start of execution of the steady current mode, the

2. The gas detector according to claim 1, characterized in that the concentration calculation unit performs a primary humidity correction on the second output value, and performs a secondary humidity correction on a span value calculated from the second output value after the primary humidity correction and a zero output value obtained in advance.

3. The gas detection device further includes a temperature detection means for detecting a temperature of the gas to be detected.

2. The gas detector according to claim 1, wherein the concentration calculation section has a function of performing temperature correction based on the temperature of the test gas when calculating the concentration of the test gas and performing humidity correction.

4. 2. The gas detector according to claim 1, wherein the first detection time point is 0.02 to 0.2 seconds after the start of execution of the steady current mode.

5. 2. The gas detector according to claim 1, wherein the second detection time point is 0 to 0.2 seconds before the end of execution of the steady current mode.

6. 2. The gas detector according to claim 1, wherein the steady current mode is performed for a period of time ranging from 0.4 to 2.0 seconds.

7. 2. The gas detector according to claim 1, wherein the power-off mode is performed for a period of time of 0.5 seconds or more.

8. 2. A gas detector according to claim 1, wherein said gas detection means comprises a catalytic combustion type gas sensor or a hot wire type semiconductor gas sensor.

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