JPH10282031A - Device and method for gas detection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a detection accuracy by providing, for example, an alter nate voltage output circuit for applying a voltage for detection consisting of an alternate voltage to a series circuit of a gas-sensing body and a load resistor. SOLUTION: A gas sensor S uses a metal oxide semiconductor as a gas- sensing body 24 and has a heater 25 for heating the gas-sending body 24. An alternate voltage output circuit 1 applies a voltage for detection consisting of an alternate voltage to a series circuit of the gas-sensing body 24 and a load resistor RL. A detection circuit 4 consisting of a microcomputer detects a gas due to the change in a voltage across the load resistor RL. Then, the alternate voltage output circuit 1 converts a DC square wave voltage being outputted from the detection circuit 4 to a DC, triangular wave voltage by an integration circuit 2. The triangular wave voltage becomes an AC, square wave voltage by a differential circuit 3 and is applied to a series circuit of the gas-sensing body 24 and the load resistor RL, thus improving a sensitivity as compared with a case when a DC voltage is used as a detection voltage and at the same time reducing the temperature dependency of sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detection device and a gas detection method.

[0002]

2. Description of the Related Art Conventionally, a gas detecting device using a gas sensor using a metal oxide semiconductor as a gas-sensitive body has been provided.

[0003]

By the way, in the above-mentioned conventional gas detection device, a detection voltage consisting of a DC voltage is applied between both ends of a series circuit of a gas-sensitive body and a load resistor.
The gas is detected by the change in the voltage across the load resistance due to the change in the resistance value of the gas-sensitive body caused by the contact of the gas with the surface of the gas-sensitive body. There is a problem that the detection accuracy is deteriorated due to the influence of the humidity in the atmosphere. In order to solve this kind of problem, research on gas-sensitive material has been conducted in various places, but the problem has not been solved yet. Also,
It has been considered to provide a compensation circuit using a thermistor or a humidity sensor, but the above problem has not been sufficiently solved.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas detection device having high detection accuracy and a gas detection method capable of improving detection accuracy.

[0005]

According to the first aspect of the present invention, there is provided a gas sensor using a metal oxide semiconductor as a gas-sensitive body, and a load resistance connected in series to the gas-sensitive body. An alternating voltage output circuit for applying a detection voltage consisting of an alternating voltage to a series circuit of a gas-sensitive body and a load resistor;
And a detection circuit for detecting a change in the voltage across the load resistor, which can increase the sensitivity and the sensitivity as compared with a case where a DC voltage is used as the detection voltage. , The humidity dependency can be reduced, and the detection accuracy can be increased.

[0006] A second aspect of the present invention is the above-mentioned first aspect, wherein the frequency of the detection voltage is approximately 10 Hz to approximately 1 MHz, which is a desirable embodiment. According to a third aspect of the present invention, in the first or second aspect of the present invention, the heater for heating the gas-sensitive body and the energization of the heater are controlled to control the gas-sensitive body in accordance with the type of the gas to be detected. Means for varying the temperature, wherein the means alternately sets a high-temperature period in which the temperature of the gas-sensitive body is high and a low-temperature period in which the temperature is low. Since the detection period for detecting the detection target gas is set in the period, the degree of freedom in selecting the detection target gas is increased, and power can be saved.

According to a fourth aspect of the present invention, there is provided a gas detecting apparatus according to the third aspect, wherein a flammable gas such as methane, propane, hydrogen or the like, and carbon monoxide are used as a detection target gas. The temperature is set at a temperature at which the sensitivity of carbon monoxide to the sensitivity of the oxidizing gas is sufficiently low, and the temperature during the low temperature period is set at a temperature at which the sensitivity of the flammable gas to the sensitivity of carbon monoxide is sufficiently low. By detecting flammable gas and detecting carbon monoxide during a low temperature period, both flammable gas and carbon monoxide can be detected with high sensitivity.

According to a fifth aspect of the present invention, in a gas sensor using a metal oxide semiconductor as a gas-sensitive body, a load resistor is connected in series to the gas-sensitive body, and an alternating voltage is connected to a series circuit of the gas-sensitive body and the load resistor. It is characterized by detecting a gas by applying a detection voltage consisting of a load and detecting the gas by the change in the voltage between both ends of the load resistance. The sensitivity is higher than when a DC voltage is used as the detection voltage and the sensitivity is dependent on humidity. Becomes smaller,
Detection accuracy is increased.

A sixth aspect of the present invention is a preferred embodiment in which the frequency of the detection voltage is approximately 10 Hz to approximately 1 MHz in the fifth aspect of the invention. According to a seventh aspect of the present invention, in the fifth or sixth aspect, a heater is provided in the gas sensor, and by controlling energization of the heater, a high-temperature period in which the temperature of the gas-sensitive body is high and a temperature in which the temperature is low. Since the low-temperature period and the low-temperature period are set alternately, and the detection period for performing gas detection is set in the high-temperature period or the low-temperature period or in both periods, the degree of freedom in selecting the detection target gas is increased, and power saving can be achieved. .

[0010] The invention of claim 8 is a gas detection method according to the invention of claim 7, wherein a flammable gas such as methane, propane, hydrogen or the like and carbon monoxide is a detection target gas. Set the temperature at which the sensitivity of carbon monoxide to the sensitivity of flammable gas is sufficiently low, and set the temperature during the low temperature period to the temperature at which the sensitivity of flammable gas to the sensitivity of carbon monoxide is sufficiently low. Since flammable gas is detected and carbon monoxide is detected during a low temperature period, both flammable gas and carbon monoxide can be detected with high sensitivity.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a gas detection device according to the present embodiment comprises a gas sensor S having a metal oxide semiconductor as a gas-sensitive body 24 and having a heater 25 for heating the gas-sensitive body 24; Load resistance R connected in series to gas sensing element 24
L, an alternating voltage output circuit 1 for applying a detection voltage composed of an alternating voltage to a series circuit of the gas sensitive body 24 and the load resistor RL.
A detection circuit 4 composed of a microcomputer for detecting gas based on a change in the voltage across the load resistor RL; and a heater power supply circuit (not shown) for varying the temperature of the gas-sensitive body 24 by energizing the heater 25. And

The alternating voltage output circuit 1 outputs the DC rectangular wave voltage (the voltage at the point in FIG.
2 (a) is converted into a DC triangular wave voltage (the voltage at the point in FIG. 1 is shown in FIG. 2 (b)) by the integrating circuit 2, and this triangular wave voltage is converted into an AC rectangular wave voltage (FIG. The voltage at point 1 is converted into that shown in FIG. 2C), and this AC rectangular wave voltage is applied to a series circuit of the gas sensing element 24 and the load resistor RL. The voltage between both ends of the load resistor RL is input to the detection circuit 4 via the rectifying and integrating circuit 5. The circuit configuration of the alternating voltage output circuit 1 is shown in FIG.
The present invention is not limited to the configuration described above, and any configuration that outputs an alternating voltage may be used.

That is, in the present embodiment, as shown in FIG. 3, a predetermined voltage V _H is applied between both ends of the heater 25 to heat the gas-sensitive body 24, and the gas-sensitive body 24 and the load resistance RL are connected to each other. A detection voltage V _C consisting of an alternating voltage is applied between both ends of the series circuit, and the load resistance RL across the load resistor RL is changed due to a change in the resistance value of the gas-sensitive body 24 caused by the gas contacting the surface of the gas-sensitive body 24. Gas is detected by a change in the voltage Vout.

The gas sensor S has, for example, a structure as shown in FIG. 4 and includes a base 30 serving also as a bottom of a sensor housing (not shown) formed of a bottomed cylindrical body, and a sensor housing penetrating through the base 30. Three terminals 10 ₁ , 1 protruding in and out
0 ₂ and 10 _3, and a gas-sensitive body 24 made of a metal oxide semiconductor supported by connecting and fixing a lead wire to a terminal. The gas-sensitive body 24 is formed in an elliptical sphere having a diameter in the longitudinal direction of about 0.4 mm to about 0.8 mm and a diameter in the transverse direction of about 0.2 mm to about 0.7 mm, and includes an electrode coil of a noble metal wire. The heater 25 is embedded and the heater 2
5, a detection electrode 20 made of a noble metal wire is provided. The gas sensor S of the present embodiment is a gas sensor 2
4 is a sintered type sensor in which a heater 25 is embedded, but the gas sensor S is not limited to the sintered type sensor, and it is sufficient that the gas sensor S includes a metal oxide semiconductor and a heater. It may be a type sensor.

Here, Sn, which is a main component of the gas-sensitive body 24, is used.
Explaining the adjustment of O ₂ , first, an aqueous solution of SnCl ₄ is hydrolyzed with NH ₄ to obtain a stannate sol, and the obtained stannate sol is air-dried, for example, at 550 ° C. in air.
Sintering is performed at a temperature of about 700 ° C. for 1 hour to obtain SnO ₂ . This S
Impregnated with an aqueous solution of Pd in nO ₂ , for example, 50
The powder is calcined at 0 ° C. for 1 hour in the air to carry Pd. Here, the role of Pd is to give the gas sensor appropriate sensitivity to each gas and to improve the response speed to various gases, and may not be added depending on the application. Also, instead of Pd, Pt, Rh, Au
And the like can be used.

In the present embodiment, a flammable gas such as methane, propane, hydrogen or the like or carbon monoxide is used as a detection target gas, and a predetermined voltage V between both ends of the heater 25 according to the detection target gas.
_H is applied to heat the gas-sensitive body 24, and a detection is made of an AC square wave voltage (alternating voltage) having a frequency of about 10 Hz to about 1 MHz between both ends of a series circuit of the gas-sensitive body 24 and the load resistor RL. The voltage Vc is applied, the gas is detected by the change in the voltage Vout across the load resistor RL, and the sensitivity indicated by the ratio of the resistance at both ends of each gas to the resistance at both ends of the gas sensing element 24 in the clean atmosphere (that is, The sensitivity is indicated by the ratio of the voltage across the load resistance RL when the gas sensitive body 24 is in gas to the voltage across the load resistance RL when the gas sensitive body 24 is in the clean atmosphere.
It has been confirmed that the humidity dependency of the sensitivity can be reduced as compared with the related art, and the detection accuracy is improved.

Further, the above-mentioned heater power supply circuit allows
A high-temperature period in which the gas-sensitive body 24 is heated by the heater 25 for one second for 80 seconds is set, and a low-temperature period in which the gas-sensitive body 24 is not heated by the heater 25 is set for the remaining 179 seconds. If methane is used as the gas to be detected during the high temperature period when heating is performed and carbon monoxide is used as the gas to be detected during the low temperature period when the gas-sensitive body 24 is not heated, a power-saving gas detection device that can be driven by a battery is provided. Can be configured. Also in this case, the humidity dependency of the sensitivity could be made smaller than before by setting the frequency of the detection voltage Vc, which is an alternating voltage, to approximately 100 Hz to approximately 100 kHz. Note that the voltage V _H applied to the heater 25 is appropriately set according to the detection target gas.

The detection voltage Vc is approximately 10H
Although it is not clear why the humidity dependency of the sensitivity is reduced by using the alternating voltage of z to about 1 MHz as compared with the case of using the conventional DC voltage, the water adsorbed on the surface of the gas sensitive body 24 is not clear. It is presumed that the quantity or the quality of the adsorbed water is related. That is, the detection voltage Vc is approximately 10
By using an AC voltage of about 1 MHz to about 1 MHz,
Whether the amount of water adsorbed on the surface of the gas-sensitive body 24 is reduced,
Alternatively, it is presumed that the interaction between the water adsorbed on the surface of the gas-sensitive body 24 and the surface of the gas-sensitive body 24 decreases, and the humidity dependency decreases.

In each of the embodiments described below, measurement was performed using a gas detector having the circuit of FIG. (Embodiment 1) In this embodiment, a voltage of 0.9 V is applied to the heater 25 so that the temperature of the gas-sensitive body 24 becomes approximately 400 ° C. in the gas detection device shown in FIG. In this embodiment, the frequency of the alternating voltage applied to the detection voltage Vc is variously changed (the effective voltage is kept constant at 5 V and the frequency is changed in the range of 1 Hz to 100 MHz).
When the relative humidity dependency of the sensitivity to pm) was measured, measurement results as shown in FIG. 5 were obtained. Note that the sensitivity corresponds to the ratio of the resistance value at both ends of the gas-sensitive body 24 in the gas to the resistance value at both ends of the gas-sensitive body 24 in the clean atmosphere, and the sensitivity is higher as this value is smaller than 1. . The temperature of the atmosphere in which the measurement was performed was constant at 20 ° C., and the relative humidity of the atmosphere was 20%, 40%, 60%, and 80%.

Here, the frequency (1H) in FIG.
When z is set, c (▲) is when the frequency is 10 Hz, d (◇) is when the frequency is 100 Hz, e (□) is when the frequency is 100 kHz, and f (○) is when the frequency is 1 MHz. In the case of doing, each result is shown.
It should be noted that when the frequency of the detection voltage Vc is 10 MHz, it is omitted because the reliability of the measurement data is lacking.
In FIG. 5, a (●) shows the result when a DC power supply is provided in place of the alternating voltage output circuit 1 and the measured voltage is a DC voltage of 5 V, which corresponds to a conventional example. .

From this measurement result, in the present embodiment, by using an alternating voltage having a frequency of about 10 Hz to about 1 MHz as the detection voltage Vc, the methane emission is reduced as compared with the conventional example using a DC voltage as the detection voltage Vc. It was found that as the sensitivity increased, the humidity dependency of the sensitivity became smaller and the detection accuracy could be increased. (Embodiment 2) In this embodiment, a voltage of 0.3 V is applied to the heater 25 so that the temperature of the gas-sensitive body 24 becomes approximately 100 ° C. in the gas detection device shown in FIG. In the present embodiment, the frequency of the alternating voltage applied to the detection voltage Vc is variously changed (the effective voltage is kept constant at 5 V and the frequency is changed in the range of 1 Hz to 100 MHz).
When the relative humidity dependency of the sensitivity to (ppm) was measured, the measurement results as shown in FIG. 6 were obtained. Note that the sensitivity corresponds to the ratio of the resistance value at both ends of the gas-sensitive body 24 in the gas to the resistance value at both ends of the gas-sensitive body 24 in the clean atmosphere, and the sensitivity is higher as this value is smaller than 1. . The temperature of the atmosphere in which the measurement was performed was constant at 20 ° C., and the relative humidity of the atmosphere was 20%, 40%, 60%, and 80%.

Here, the frequency (1H) in FIG.
When z is set, c (▲) is when the frequency is 10 Hz, d (◇) is when the frequency is 100 Hz, e (□) is when the frequency is 100 kHz, and f (○) is when the frequency is 1 MHz. In the case of doing, each result is shown.
It should be noted that when the frequency of the detection voltage Vc is 10 MHz, it is omitted because the reliability of the measurement data is lacking.
6 shows the result when a DC power supply is provided in place of the alternating voltage output circuit 1 and the measured voltage is a DC voltage of 5 V, which corresponds to a conventional example. .

From this measurement result, in the present embodiment, by using an alternating voltage having a frequency of about 10 Hz to about 1 MHz as the detection voltage Vc, compared to the conventional example using a DC voltage as the detection voltage Vc, It was found that the sensitivity to carbon became higher and the humidity dependency of the sensitivity became smaller, and the detection accuracy could be improved. (Embodiment 3) In this embodiment, the heater 25 is set so that the temperature of the gas-sensitive body 24 becomes approximately 400 ° C. only for one second every 180 seconds.
The heater voltage V _H of 0.9V is applied to the remaining 179 seconds are substantially zero V heater voltage V _H as the temperature of the gas-sensitive body 24 is equal to about room temperature. In the present embodiment, methane is used as a detection target gas in the last preset first detection period of the one-second high-temperature period in which the heater 25 is heating the gas-sensitive body 24, and the next 179-second low-temperature period is used. The carbon monoxide is used as the gas to be detected in the last preset second detection period.

In this embodiment, the frequency of the alternating voltage applied to the detection voltage Vc is variously changed (the frequency is changed in the range of 1 Hz to 100 MHz while the effective voltage is fixed at 5 V).
The relative humidity dependence of the sensitivity to methane (1000 ppm) was measured during the first detection period, and the relative humidity dependence of the sensitivity to carbon monoxide (100 ppm) was measured during the second detection period. The measurement results as shown were obtained, and the measurement results as shown in FIG. 8 were obtained for carbon monoxide. Note that the sensitivity corresponds to the ratio of the resistance value at both ends of the gas-sensitive body 24 in the gas to the resistance value at both ends of the gas-sensitive body 24 in the clean atmosphere, and the sensitivity is higher as this value is smaller than 1. . The temperature of the atmosphere in which the measurement was performed was constant at 20 ° C., the relative humidity of the atmosphere was 20%,
40%, 60% and 80%.

Here, in FIG. 7 and FIG. 8, (b) indicates a case where the frequency is 1 Hz, (c) indicates a case where the frequency is 10 Hz, and (d) indicates a case where the frequency is 100 Hz.
E (□), when the frequency is 100 kHz, F (○)
Indicates the respective results when the frequency is 1 MHz. It should be noted that when the frequency of the detection voltage Vc is 10 MHz, it is omitted because the reliability of the measurement data is lacking. 7 (a) and 7 (b) show the results when a DC power supply is provided in place of the alternating voltage output circuit 1 and the measured voltage is a DC voltage of 5V, which corresponds to a conventional example. .

By the way, no carbon monoxide was detected in the first detection period, and no methane was detected in the second detection period. Therefore, by setting the temperatures of the high temperature period and the low temperature period as described above,
It has been found that combustible gas such as methane and carbon monoxide can be selectively detected. Further, by using an alternating voltage having a frequency of approximately 10 Hz to approximately 1 MHz as the detection voltage Vc, the sensitivity to methane (1000 ppm) and carbon monoxide (100 ppm) is higher than that of a conventional example using a DC voltage as the detection voltage Vc. It was found that the sensitivity became less dependent on humidity and the detection accuracy could be increased.

In the first and third embodiments, only data using methane as a detection target gas is given. However, the effect of reducing the relative humidity dependence of the sensitivity of hydrogen and propane is obtained as in the case of methane. And selectivity for carbon monoxide was obtained.

[0028]

According to the first aspect of the present invention, there is provided a gas sensor using a metal oxide semiconductor as a gas-sensitive body, a load resistor connected in series to the gas-sensitive body, and a series circuit of the gas-sensitive body and the load resistor. It has an alternating voltage output circuit that applies a detection voltage consisting of an alternating voltage, and a detection circuit that detects a change in the voltage across the load resistor, so that a DC voltage is used as the detection voltage. And the sensitivity can be made less dependent on humidity, and the detection accuracy can be increased.

The invention of claim 3 is the invention of claim 1 or claim 2.
In the invention of the present invention, a heater for heating the gas-sensitive body,
Means for varying the temperature of the gas-sensitive body in accordance with the type of the gas to be detected by controlling the energization of the heater, wherein the high-temperature period in which the temperature of the gas-sensitive body is high and the temperature in which the temperature is low The low-temperature period is set alternately, and the detection circuit sets a detection period in which the detection target gas is detected in the high-temperature period or the low-temperature period or both periods, so that the degree of freedom in selecting the detection target gas increases. In addition, there is an effect that power can be saved.

According to a fourth aspect of the present invention, there is provided the gas detecting apparatus according to the third aspect of the present invention, wherein a flammable gas such as methane, propane, and hydrogen and carbon monoxide are used as the detection target gas. The temperature is set at a temperature at which the sensitivity of carbon monoxide to the sensitivity of the oxidizing gas is sufficiently low, and the temperature during the low temperature period is set at a temperature at which the sensitivity of the flammable gas to the sensitivity of carbon monoxide is sufficiently low. By detecting the flammable gas and detecting carbon monoxide during the low temperature period, there is an effect that both the flammable gas and carbon monoxide can be detected with high sensitivity.

According to a fifth aspect of the present invention, in a gas sensor using a metal oxide semiconductor as a gas-sensitive body, a load resistor is connected in series to the gas-sensitive body, and an alternating voltage is connected to a series circuit of the gas-sensitive body and the load resistor. Since a gas is detected by applying a voltage for detection consisting of a change in the voltage across the load resistor, the sensitivity is higher and the humidity dependency of the sensitivity is smaller than when a DC voltage is used as the voltage for detection. This has the effect of increasing the detection accuracy.

The invention of claim 7 is the invention of claim 5 or claim 6.
In the invention according to the invention, a heater is provided in the gas sensor, and a high-temperature period in which the temperature of the gas-sensitive body is high and a low-temperature period in which the temperature is low are alternately set by controlling the energization of the heater. Alternatively, since the detection period in which the gas detection is performed is set in both periods, the degree of freedom in selecting the detection target gas is increased, and there is an effect that power saving can be achieved.

According to an eighth aspect of the present invention, there is provided a gas detection method according to the seventh aspect, wherein a flammable gas such as methane, propane, hydrogen or the like and carbon monoxide are used as detection target gases. Set the temperature at which the sensitivity of carbon monoxide to the sensitivity of flammable gas is sufficiently low, and set the temperature during the low temperature period to the temperature at which the sensitivity of flammable gas to the sensitivity of carbon monoxide is sufficiently low. Since flammable gas is detected and carbon monoxide is detected during a low temperature period, there is an effect that both flammable gas and carbon monoxide can be detected with high sensitivity.

[Brief description of the drawings]

FIG. 1 is a circuit example diagram of a gas detection device according to an embodiment.

FIG. 2 is an operation explanatory view of the above.

FIG. 3 is an explanatory diagram of a detection principle according to the first embodiment.

FIG. 4 is a schematic configuration diagram of a gas sensor used in the same.

FIG. 5 is a graph showing the humidity dependence of sensitivity to methane at each detection voltage in Example 1.

FIG. 6 is a graph showing humidity dependency of sensitivity to carbon monoxide at each detection voltage in Example 2.

FIG. 7 is a graph showing the humidity dependence of sensitivity to methane at each detection voltage in Example 3.

FIG. 8 is a graph showing the humidity dependency of sensitivity to carbon monoxide at each detection voltage in Example 3.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 alternating voltage output circuit 2 integration circuit 3 differentiation circuit 4 detection circuit 5 rectification integration circuit S gas sensor RL load resistance 24 gas sensitive body 25 heater

Claims (8)

[Claims] 1. A gas sensor using a metal oxide semiconductor as a gas-sensitive body, a load resistance connected in series with the gas-sensitive body, and a detection voltage comprising an alternating voltage in a series circuit of the gas-sensitive body and the load resistance. A gas detection device comprising: an alternating voltage output circuit for applying a voltage; and a detection circuit for detecting a voltage based on a change in voltage across the load resistor. 2. The gas detection device according to claim 1, wherein the frequency of the detection voltage is approximately 10 Hz to approximately 1 MHz. 3. A heater for heating a gas-sensitive body, and means for varying the temperature of the gas-sensitive body in accordance with the type of a gas to be detected by controlling energization of the heater. The high temperature period in which the temperature of the gas body becomes high and the low temperature period in which the temperature becomes low are alternately set, and the detection circuit sets the detection period for detecting the detection target gas in the high temperature period or the low temperature period or both periods. The gas detection device according to claim 1, wherein the gas detection device is configured to perform the above operation. 4. A gas detection device using a combustible gas such as methane, propane, hydrogen or the like and carbon monoxide as a detection target gas, wherein the temperature of the high-temperature period is such that the sensitivity of the carbon monoxide to the sensitivity of the combustible gas is sufficient. 4. The gas detection device according to claim 3, wherein the temperature is set to a lower temperature, and the temperature during the low temperature period is set to a temperature at which the sensitivity of the combustible gas to the sensitivity of carbon monoxide is sufficiently low. 5. A gas sensor using a metal oxide semiconductor as a gas-sensitive body, a load resistor connected in series to the gas-sensitive body, and a detection voltage comprising an alternating voltage in a series circuit of the gas-sensitive body and the load resistor. And detecting a gas based on a change in voltage across the load resistor. 6. The gas detection method according to claim 5, wherein the frequency of the detection voltage is approximately 10 Hz to approximately 1 MHz. 7. A high-temperature period in which the temperature of the gas-sensitive body is high and a low-temperature period in which the temperature is low are alternately set by providing a heater to the gas sensor and controlling energization of the heater. 7. The gas detection method according to claim 5, wherein a detection period for performing gas detection is set in the period or both periods. 8. A gas detection method using a combustible gas such as methane, propane, hydrogen or the like and carbon monoxide as a detection target gas, wherein the temperature of the high-temperature period is determined by determining the sensitivity of the carbon monoxide to the sensitivity of the combustible gas. In addition to setting the temperature to be sufficiently low, the temperature in the low temperature period is set to a temperature at which the sensitivity of the flammable gas to the sensitivity of carbon monoxide is sufficiently low. 8. The gas detection method according to claim 7, wherein carbon is detected.