JP3757109B2 - Gas detection device and gas detection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is more sensitive to low concentration gas components generated during a fire than other gases such as carbon monoxide (CO) generated during incomplete combustion or methane (CH ₄ ) generated when city gas leaks. The present invention relates to a gas detection device and a gas detection method for detecting gas in the event of a fire and discriminating between gas generated in a fire and other gas.
[0002]
[Prior art]
As a gas sensor for distinguishing between carbon monoxide generated at the time of incomplete combustion and methane generated at the time of city gas leakage, for example, a semiconductor type gas sensor has been conventionally used, and this semiconductor gas sensor uses catalytic activity. Distinguishing carbon monoxide from methane. FIG. 12 shows gas sensitivity characteristics of a semiconductor gas sensor using a SnO ₂ catalyst.
[0003]
In FIG. 12, the horizontal axis represents the element temperature of the sensor, and the vertical axis represents the sensor resistance. As can be seen from FIG. 12, the SnO ₂ catalyst has a high activity for carbon monoxide at a low temperature range and a high activity for methane at a high temperature range. In other words, carbon monoxide has low sensor resistance at low temperatures and methane has low sensor resistance at high temperatures. Therefore, semiconductor gas sensors have the property of selecting carbon monoxide at low temperatures and methane at high temperatures. .
[0004]
For this reason, one gas sensor provided in the gas detection device is periodically and alternately driven in a low temperature region (for example, 100 ° C.) and a high temperature region (for example, 400 ° C.) by a pulse driving method as shown in FIG. By doing so, the carbon monoxide gas concentration is detected at the CO detection point in the low temperature region (black circle in FIG. 13), and the methane gas concentration is detected at the methane detection point in the high temperature region (black circle in FIG. 13). it can.
[0005]
As a conventional gas detector of this type, for example, a gas leak detector described in Japanese Patent Application Laid-Open No. 59-143948 is known.
[0006]
As shown in FIG. 14, the gas leak detection apparatus described in Japanese Patent Laid-Open No. 59-143948 includes a metal oxide sensitive body 102 whose resistance value decreases when it is exposed to a combustible gas, and this sensitive body 102. , A heater 103 that maintains a predetermined temperature, a voltage discriminating circuit 106 that detects a change in the resistance value of the sensitive body 101, a heater voltage control circuit 105 that changes the heater voltage of the heater 103 based on the output of the voltage discriminating circuit 106, And an arithmetic circuit 108 that detects temperature dependence based on a change in the resistance value of the sensitive body 101 and discriminates the type of combustible gas.
[0007]
According to such a gas leak detection apparatus, when the combustible gas touches the sensitive body 102 and the resistance value decreases and the potential at the point A falls below the set reference potential, the voltage discrimination circuit 106 is activated. The timer circuit 107 is activated, and the voltage applied to the heater 103 is changed by the heater voltage control circuit 105.
[0008]
The potential of the heater 103 before and after the voltage change is calculated by the arithmetic circuit 108, and the temperature dependence of the currently detected gas is calculated, whereby the type of gas can be detected.
[0009]
[Problems to be solved by the invention]
However, the conventional gas detector and the gas leak detector described in Japanese Patent Application Laid-Open No. 59-143948 distinguish between carbon monoxide generated during incomplete combustion and methane generated when city gas leaks. However, it was not possible to distinguish between the gas generated during a fire and the methane generated during leakage of carbon monoxide and city gas generated during incomplete combustion. In addition, even the gas components generated in the event of a fire are not clearly understood.
[0010]
Therefore, the present invention provides a gas detection device capable of easily distinguishing gas components generated during a fire from other gases such as carbon monoxide generated during incomplete combustion and methane generated when a city gas leaks, and It is an object to provide a gas detection method.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention has the following configuration. The gas detector according to claim 1 has a heater coated with an alumina-based catalyst and is provided with a sensor element for detecting gas, and is generated due to combustion heat generated when the gas is burned. A catalytic combustion type gas sensor for detecting a change in the resistance value of the element as a sensor output; and a pulse drive signal in which an off time is set sufficiently long with respect to an on time, and applying the pulse drive signal to the heater. On / off drive of the gas sensor, sensor output detection means for detecting the sensor output value from the sensor element during the on-drive period of the gas sensor, and the sensor output value detected by the sensor output detection means based a gas identifying means for identifying a type of the gas, the gas identifying means, first the sensor output value reaches a predetermined If it is equal to or greater than a threshold value, the gas is determined to be acetic acid gas, and if the sensor output value is equal to or greater than a second threshold value that is smaller than the first threshold value, the gas is oxidized. It is determined to be carbon or methane gas .
[0012]
According to the gas detection device of the first aspect of the invention, the pulse driving means applies a pulse driving signal in which the off time is set sufficiently long with respect to the on time to the heater to drive the gas sensor on / off. When the drive signal OFF time becomes sufficiently long, the sensor sensitivity at the time of low concentration of gas (acetic acid) generated at the time of fire increases rapidly. For this reason, the sensor output value detected by the sensor output detection means also increases, and the gas identification means determines that the gas is acetic acid gas when the sensor output value is equal to or greater than a predetermined first threshold value. When the sensor output value is equal to or larger than the second threshold value smaller than the first threshold value, the gas is determined to be carbon monoxide or methane gas. For this reason , it is possible to easily distinguish the gas components generated at the time of a fire from other gases such as carbon monoxide generated at the time of incomplete combustion and methane generated at the time of leakage of city gas. And fire can be detected without being affected by gases such as methane.
[0017]
The invention of claim 2 is the gas detector of claim 1 Symbol mounting, characterized in that it comprises a notifying means for notifying a result identification of the type of the identified gas by the gas identifying means.
[0018]
Since the notification means of the invention of claim 2 reports the identification result of the gas type identified by the gas identification means, the generated gas type can be easily identified, thereby improving safety. Can do.
[0019]
According to a third aspect of the present invention, there is provided a gas detection method comprising: a sensor having a heater coated with an alumina-based catalyst and a sensor element for detecting gas; and the sensor generated due to combustion heat generated when the gas is burned a heater provided in the catalytic combustion type gas sensor for detecting a change in resistance of the element as a sensor output, generates a pulse drive signal set sufficiently long off-time for the on-time to mark pressurizing the pulse drive signal A pulse driving step for driving the gas sensor on / off, a sensor output detecting step for detecting a sensor output value from a sensor element provided in the gas sensor during the on driving period of the gas sensor, and a detected sensor output look-containing and gas identifying step of identifying the type of the gas, based on the value, the gas identifying step, the sensor output value When it is equal to or greater than a predetermined first threshold value, the gas is determined to be acetic acid gas, and when the sensor output value is equal to or greater than a second threshold value that is smaller than the first threshold value. The gas is determined to be carbon monoxide or methane gas .
[0022]
A fourth aspect of the present invention, in the gas detection method according to claim 3 Symbol mounting, said characterized in that it comprises a notifying step of notifying a gas identification result identifying the type of the identified gas in step, the invention of claim 2 Actions and effects similar to the actions and effects can be obtained.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a gas detection device and a gas detection method of the present invention will be described in detail with reference to the drawings.
[0024]
The gas detection device and the gas detection method of the embodiment have a low-concentration gas component that is generated in the event of a fire, and is higher than other gases such as carbon monoxide that is generated during incomplete combustion and methane that is generated when city gas leaks. Sensitivity is detected and gas generated at the time of fire is distinguished from other gases such as carbon monoxide and methane.
[0025]
(First embodiment)
FIG. 1 is a circuit configuration diagram of a gas detection device according to a first embodiment of the present invention. FIG. 2 is a detailed structural diagram of the gas sensor in the gas detection apparatus of the first embodiment. FIG. 3 is a timing chart of the temperature of the gas sensor in the gas detection apparatus according to the first embodiment.
[0026]
In the gas detection apparatus shown in FIG. 1, the gas sensor 1 is, for example, a catalytic combustion type gas sensor, and this catalytic combustion type gas sensor is a gas detection element having a heater (hereinafter referred to as a sensor element) and a comparison element having a heater. The combustion heat generated when the gas is burned is detected, and the gas is identified based on the obtained sensor output.
[0027]
As shown in FIG. 2, in this gas sensor 1, an element is formed by applying an alumina-based catalyst 51 on a heater 2 made of a platinum coil of 20 μm to 50 μm, and the sensor element 3 having the heater 2 as the element and the heater And a comparison element 4 having 2.
[0028]
The sensor element 3 uses γ-alumina supporting palladium (Pd) as a catalyst, and the comparison element 4 uses γ-alumina or α-alumina as a catalyst. The catalyst 51 generates heat according to the amount of heat generated by the heater 2 and acts as a catalyst for gas combustion.
[0029]
The sensor element 3, the comparison element 4, the resistor R11, and the resistor R12 constitute a bridge circuit 6. And the voltage from the heater drive circuit 5 is applied to the terminal a and the terminal b of the bridge circuit 6, and the output voltage V is taken out from the terminal c and the terminal d as a sensor output. That is, the bridge circuit 6 determines the change in the resistance value of the sensor element 3 and the change in the resistance value of the comparison element 4 caused by the combustion heat generated when the sensor element 3 and the comparison element 4 burn gas. It detects from the connection point of the sensor element 3 and the comparison element 4, and outputs it to the central processing unit (CPU) 11 mentioned later as a sensor output.
[0030]
The power supply circuit 7 supplies power to the timer drive circuit 8 and the heater drive circuit 5. The timer driving circuit 8 receives a power supply from the power supply circuit 7 and drives a timer (not shown). The heater drive circuit 5 generates a pulse drive signal based on a timer signal from a timer driven by the timer drive circuit 8 and applies the generated pulse drive signal to the heater 2 to drive the gas sensor 1 on / off.
[0031]
As shown in FIG. 3, the pulse drive signal is a signal that repeats on / off at a cycle of 10 seconds, and has an on time of 100 ms and an off time of 9900 ms. For this reason, as shown in FIG. 3, the gas sensor 1 is driven off by the pulse drive signal to lower the temperature (RT.degree. C. is maintained for 9900 ms), and the gas sensor 1 is turned on to drive the high temperature (400.degree. C.). Maintained only for 100 ms). The heater driving circuit 5 and the timer driving circuit 8 constitute pulse driving means.
[0032]
Further, as shown in FIG. 1, the CPU 11 includes a sensor output detection unit 13 as a sensor output detection unit and a gas identification unit 15 as a gas identification unit.
[0033]
The sensor output detector 13 detects the sensor element 3 of the gas sensor 1 at the gas detection point DP (black circle in FIG. 3) during the period when the sensor temperature is 400 ° C. (period when the pulse drive signal is on). The sensor output value is detected from
[0034]
When the sensor output value detected by the sensor output detection unit 13 is equal to or greater than a predetermined first threshold value SH1, the gas identification unit 15 determines that the gas to be identified is a gas (acetic acid) generated in the event of a fire. To do.
[0035]
In addition, the gas identification unit 15 determines the identification target when the sensor output value detected by the sensor output detection unit 13 is equal to or larger than a predetermined second threshold value SH2 smaller than the first threshold value SH1. The gas is determined to be a gas (CO or methane, etc.) generated during non-fire
[0036]
The CPU 11 is connected to an LED 21a that is lit to identify a gas such as acetic acid that is generated during a fire, and an LED 21b that is lit to identify a gas such as carbon monoxide or methane during a non-fire. . The speaker 19 informs by voice that it is a gas at the time of a fire or a gas at the time of a non-fire. The speaker 19, the LED 21a, and the LED 21b constitute notification means.
[0037]
Next, prior to the description of the operation of the gas detector of the embodiment configured as described above, the reason why the gas detector of the embodiment employs the pulse drive system as shown in FIG. This will be described with reference to FIG.
[0038]
First, gas generated when the timber was fired, that is, various gases generated in the event of a timber fire were analyzed. FIG. 4 shows the gas analysis results when the timber is fired. The inorganic gas was measured by a gas chromatography method, and the low boiling point compound and the high boiling point compound were measured by a gas chromatography method and a mass spectrometry method. Quantitative analysis of formaldehyde and acetaldehyde was measured by liquid chromatography, and quantitative analysis of acetic acid and formic acid was measured by ion chromatography.
[0039]
As can be seen from FIG. 4, carbon monoxide (gas concentration 1120 ppm) and acetic acid (gas concentration 840 ppm) were detected as the main components of various gases generated during the fire of timber.
[0040]
Next, various gas sensitivity characteristics of the gas sensor 1 when the gas sensor 1 of the embodiment is operated by the pulse drive system as shown in FIG. 3 and the off time is changed are shown in FIGS.
[0041]
FIG. 5 shows the CO concentration versus the sensor output characteristic according to the on / off period of the gas sensor. FIG. 6 shows the methane concentration versus the sensor output characteristic according to the on / off period of the gas sensor. FIG. 7 shows the hydrogen concentration versus the sensor output characteristic according to the on / off period of the gas sensor. FIG. 8 shows isobutane concentration vs. sensor output characteristics according to the on / off period of the gas sensor. FIG. 9 shows the acetic acid concentration versus the sensor output characteristic according to the on / off period of the gas sensor.
[0042]
In the examples shown in FIGS. 5 to 9, the sensor output with respect to the gas concentration is shown when the on time is 100 msec except for continuous energization and the off time is 1 second, 5 seconds, 10 seconds, and 30 seconds. Yes. The sensor output (mV) shown here is obtained by amplifying the sensor output obtained from the sensor element by 50 times.
[0043]
As shown in FIGS. 5 to 8, in general gas species such as CO, methane, hydrogen, and isobutane, the sensitivity basically decreases as the off time increases. On the other hand, as shown in FIG. 9, with acetic acid gas, it can be seen that the sensitivity of the low concentration increases particularly rapidly as the off-time becomes longer.
[0044]
As this factor, acetic acid has high adsorptivity, and acetic acid adsorbed on the surface of the catalyst layer 45 at the time of turning off instantaneously undergoes a combustion reaction at turning on. It is considered that the amount of acetic acid adsorbed increases due to the longer off time, which gives a sensitivity amplification effect. It can also be seen from the fact that CO, which has a relatively high adsorptivity even for gas, shows a slightly higher sensitivity when driven on / off compared to continuous energization.
[0045]
Therefore, in the pulse drive system as shown in FIG. 3, for example, by setting the off time to 5 seconds or more, the acetic acid generated at the time of fire is detected without being affected by other gases such as CO and methane, The fire can be judged.
[0046]
Next, an operation of the gas detection device of the embodiment configured as described above, that is, a gas detection method will be described with reference to a timing chart shown in FIG. 3 and a flowchart shown in FIG.
[0047]
First, a first threshold value and a second threshold value smaller than the first threshold value are set (step S101), and then the heater drive circuit 5 generates a pulse drive signal as shown in FIG. (Step S103), this pulse drive signal is applied to the heater 2 in the bridge circuit 6.
[0048]
That is, the heater 2 is turned on / off by the pulse drive signal, and as shown in FIG. 3, the gas sensor 1 is cooled to a low temperature (RT.degree. C. is maintained only for 9900 ms) by the off drive, and is heated to a high temperature (400.degree. Is maintained for 100 ms) (step S105).
[0049]
Next, the sensor output detection unit 13 detects the sensor output value from the sensor element 3 of the gas sensor 1 at the gas detection point DP (black circle in FIG. 3) during the period when the sensor temperature is 400 ° C. The detected sensor output value is A / D converted by an analog / digital converter (A / D) (not shown) to obtain a voltage value V (step S107).
[0050]
Next, the gas identification unit 15 determines whether or not the obtained voltage value V is greater than or equal to the first threshold value (step S109). If the voltage value V is greater than or equal to the first threshold value, Then, it is determined that the identification target gas is a gas such as acetic acid generated in a fire (step S111).
[0051]
In this case, the LED 21a is turned on by a fire alarm signal from the CPU 11 to perform a fire alarm (step S113), so that it is possible to easily identify that the gas to be identified is a gas such as acetic acid generated at the time of a fire. The speaker 19 can also notify that the gas to be identified is a fire gas.
[0052]
On the other hand, if the obtained voltage value V is less than the first threshold value in step S109, it is determined whether or not the obtained voltage value V is greater than or equal to the second threshold value (step S115). If the voltage value V is greater than or equal to the second threshold value, the gas identification unit 15 determines that the identification target gas is a gas that is generated during a non-fire (step S117).
[0053]
In this case, since the LED 21b is turned on by an alarm signal from the CPU 11, it can be easily identified that the gas to be identified is a gas such as carbon monoxide or methane generated during a non-fire. The speaker 19 can also notify that the identification target gas is a non-fire gas.
[0054]
As described above, according to the gas detection device of the first embodiment, the gas sensor 1 is turned on / off by applying a pulse drive signal in which the off time is set sufficiently longer than the on time to the heater 2. However, when the OFF time of the pulse drive signal becomes sufficiently long, the sensor sensitivity at the time of low concentration of the gas generated at the time of fire increases rapidly. For this reason, the detected sensor output value is also increased, and based on the sensor output value, gas components generated at the time of fire and other gases such as methane generated at the time of leakage of carbon monoxide and city gas generated at the time of incomplete combustion, for example. Thus, it is possible to detect a fire without being affected by gases such as carbon monoxide and methane.
[0055]
In addition, since the fact is notified by the speaker 19 and the LEDs 21a and 21b, the type of gas can be easily identified, and the safety can be improved.
[0056]
In addition, it is necessary to provide a fire sensor or the like because one gas sensor 1 can easily distinguish between gases such as acetic acid gas generated during a fire of wood and other gases such as carbon monoxide gas and methane. Thus, an inexpensive gas detection device can be provided.
[0057]
(Second Embodiment)
Next, a gas detection apparatus according to a second embodiment will be described. The gas detection device of the second embodiment is characterized in that a micro gas sensor is used as the gas sensor. The other configuration of the gas detection device other than the gas sensor is the same as the configuration shown in FIG.
[0058]
FIG. 11 is a detailed structural diagram of a gas sensor in the gas detection device according to the second embodiment. FIG. 11A shows a cross-sectional view of the gas sensor 1, and FIG. 11B shows a top view of the gas sensor. The gas sensor 1 is composed of a microsensor, and includes a heater 2 made of platinum (Pt) for heating a catalyst, a sensor element 3 for detecting various gases, and a comparison element 4. The sensor element 3 and the comparison element 4 is used to detect gas.
[0059]
A substrate 33 made of silicon single crystal is provided on the sensor base 31, and a diaphragm 35 is formed on the substrate 33. The diaphragm 35 is formed by anisotropically etching the substrate 33.
[0060]
Each of the sensor element 3 and the comparison element 4 is provided on the substrate 33 and is in contact with the diaphragm 35 on the oxide film 37 and the Si ₃ N ₄ film 39 made of the SiO ₂ film stacked on the diaphragm 35. Are stacked.
[0061]
Each of the sensor element 3 and the comparison element 4 has a heater 2, the heater 2 of the sensor element 3 is connected to the electrodes 41a and 41b, and the heater 2 of the comparison element 4 is connected to the electrodes 41c and 41d. The electrodes 41a to 41d are fixed by wire bonding of gold (gold wire 43).
[0062]
The sensor element 3 includes a heater 2 and a catalyst layer 45 that is laminated on the heater 2 and uses γ-alumina supported by 5 to 15 wt% of palladium (Pd) as a catalyst. The comparison element 4 includes a heater 2 and a catalyst layer (not shown) laminated on the heater 2 and using γ-alumina or α-alumina as a catalyst. The heater 2 promotes gas combustion, and the catalyst layer 45 generates heat according to the amount of heat generated by the heater 2 and acts as a catalyst for gas combustion.
[0063]
Even when the microsensor having the above configuration is used, the same effect as that of the gas detection device of the first embodiment can be obtained.
[0064]
In addition, this invention is not limited to the gas detection apparatus of embodiment mentioned above. In the embodiment, the on-time is constant at 100 ms, but the on-time may be 1 second, for example, and the off-time may be 30 seconds, for example.
[0065]
【The invention's effect】
According to the gas detection device of the first aspect of the invention and the gas detection method of the third aspect of the invention, a pulse drive signal in which the off time is set sufficiently long with respect to the on time is applied to the heater to turn on / off the gas sensor. Although it is turned off, if the off time of the pulse drive signal becomes sufficiently long, the sensor sensitivity at the time of low concentration of the gas generated at the time of fire suddenly increases. For this reason, the detected sensor output value also increases, and the gas identification means determines that the gas is acetic acid gas when the sensor output value is equal to or greater than a predetermined first threshold value, and the sensor output value is When it is equal to or greater than a second threshold value that is smaller than the first threshold value, the gas is determined to be carbon monoxide or methane gas. For this reason , it is possible to easily distinguish the gas components generated at the time of a fire from other gases such as carbon monoxide generated at the time of incomplete combustion and methane generated at the time of leakage of city gas. And fire can be detected without being affected by gases such as methane.
[0068]
According to the gas detection device of the invention of claim 2 and the gas detection method of the invention of claim 4 , since the identification result of the gas type is notified, the type of the generated gas can be easily identified. Safety can be improved.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram of a gas detection device according to a first embodiment of the present invention.
FIG. 2 is a detailed structural diagram of a gas sensor in the gas detection device according to the first embodiment.
FIG. 3 is a timing chart of the temperature of the gas sensor in the gas detection device according to the first embodiment.
FIG. 4 is a diagram showing a gas analysis result when timber is fired.
FIG. 5 is a graph showing CO concentration versus sensor output characteristics according to the on / off period of the gas sensor.
FIG. 6 is a graph showing methane concentration versus sensor output characteristics according to the on / off period of the gas sensor.
FIG. 7 is a graph showing hydrogen concentration versus sensor output characteristics according to the on / off cycle of the gas sensor.
FIG. 8 is a graph showing isobutane concentration versus sensor output characteristics according to the on / off period of the gas sensor.
FIG. 9 is a graph showing acetic acid concentration versus sensor output characteristics according to the on / off period of the gas sensor.
FIG. 10 is a flowchart for explaining a gas detection method realized by the gas detection device according to the first embodiment;
FIG. 11 is a detailed structural diagram of a gas sensor in a gas detection device according to a second embodiment.
FIG. 12 is a diagram showing gas sensitivity characteristics of a semiconductor gas sensor using a conventional catalyst.
FIG. 13 is a timing chart of the temperature of a gas sensor in a conventional gas detection device.
FIG. 14 is a configuration block diagram of a conventional gas leak detection device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Heater 3 Sensor element 4 Comparison element 5 Heater drive circuit 6 Bridge circuit 7 Power supply circuit 8 Timer drive circuit 11 CPU
13 Sensor output detection part 15 Gas identification part 19 Speaker 21a, 21b LED
31 sensor base 33 substrate 35 diaphragm 37 oxide film 39 Si ₃ N ₄ film 41 electrode 43 gold wire 45 catalyst layer 47 wire mesh 51 catalyst DP gas detection point

Claims (4)

A sensor element having a heater coated with an alumina-based catalyst and detecting gas is provided , and a change in resistance value of the sensor element generated due to combustion heat generated when the gas is burned is detected as a sensor output. A catalytic combustion gas sensor;
Pulse driving means for generating a pulse driving signal in which an off time is set sufficiently long with respect to an on time, and applying the pulse driving signal to the heater to drive the gas sensor on / off;
Sensor output detection means for detecting a sensor output value from the sensor element during the on-drive period of the gas sensor;
Gas identifying means for identifying the type of the gas based on the sensor output value detected by the sensor output detecting means;
Equipped with a,
The gas identifying means determines that the gas is acetic acid gas when the sensor output value is greater than or equal to a predetermined first threshold value, and the sensor output value is smaller than the first threshold value. A gas detection device characterized in that , when it is equal to or greater than a second threshold value, the gas is determined to be carbon monoxide or methane gas. Claim 1 Symbol placement of the gas detection device, comprising a notifying means for notifying the identification result of the type of gas identified by the gas identifying means. A sensor element that has a heater coated with an alumina-based catalyst and that detects gas and detects a change in resistance value of the sensor element that is generated due to combustion heat generated when the gas is burned is detected as a sensor output. a heater provided in the catalytic combustion type gas sensor, generates a pulse drive signal set sufficiently long off-time for the on-time pulse the causes gas sensor on the drive / off driven by indicia pressurizing the pulse drive signal A driving step;
A sensor output detection step of detecting a sensor output value from a sensor element provided in the gas sensor during the on-drive period of the gas sensor;
A gas identification step for identifying the type of the gas based on the detected sensor output value;
Only including,
In the gas identification step, when the sensor output value is equal to or greater than a predetermined first threshold value, the gas is determined to be acetic acid gas, and the sensor output value is smaller than the first threshold value. A gas detection method characterized by determining the gas as carbon monoxide or methane gas when it is equal to or greater than a second threshold value . Gas detection method of claim 3 Symbol mounting, characterized in that it comprises an informing step of informing the recognition result of the type of gas identified by the gas identifying step.

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