JP3907543B2 - City gas detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention uses methane (CH ₄ ), which is a main component gas, and ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), and butane (C ₄ H ₁₀ ), which are subcomponent gases, as flammable gases. It is possible to detect the gas component separated by the gas component separation unit and the gas component separation unit that can be separated for each gas component by causing a flow delay according to the molecular weight of the combustible gas. The present invention relates to a city gas detection apparatus including a gas detection unit including a gas detection element and a determination unit that determines whether the gas is a city gas based on an output signal from the gas detection unit.
[0002]
[Prior art]
It is an extremely important issue in terms of gas leakage countermeasures to appropriately detect city gas leaked from underground gas pipes, etc. in underground construction sites or in the vicinity of gas pipe burial facilities. For safety reasons, when these flammable gas leaks occur, the frequency of occurrence of disasters such as explosions decreases if the leaked part can be easily identified quickly.
[0003]
As the city gas, one having methane as a main component or one having propane as a main component is known, but city gas having methane as a main component is methane (CH ₄ ) which is a main component gas. In addition, ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), and butane (C ₄ H ₁₀ ), which are auxiliary component gases, are included as combustible gases (volume ratio is usually methane: ethane: Propane: butane = 88: 6: 4: 2). Therefore, detection of methane, which is the main component gas of city gas, is one of the criteria for determining the presence or absence of city gas leakage.
[0004]
As described above, as a city gas detection device for detecting the leakage of city gas mainly composed of methane, the thermal conductivity change and the electrical conductivity change due to gas adsorption on the metal oxide semiconductor surface are detected by the electrodes, or , A semiconductor gas detector that measures the resistance change as seen from both ends of the noble metal wire coil, or a contact combustion gas detector that measures the temperature rise (resistance value change) of the noble metal wire coil due to gas catalytic combustion on the catalyst surface A device provided with an element can be used.
[0005]
Specifically, as shown in FIG. 8, the city gas detection device X includes a gas detection element S1 having sensitivity to flammable gases such as methane, ethane, propane, and butane, and ethane, propane, and butane (subsidiary). What has a gas detection element S2 that is highly sensitive to the component gas) has been known. Then, the city gas is identified based on the output ratio between the output of the gas detection element S1 and the output of the gas detection element S2 when the gas to be detected is detected.
[0006]
And if this city gas detection apparatus detected methane with subcomponent gas, it judged that the leak of city gas had generate | occur | produced.
[0007]
[Problems to be solved by the invention]
As the gas detection element in the above-described city gas detection device, a catalytic combustion type gas detection element used for detecting a high-concentration combustible gas has been used. In this contact combustion type gas detection element, since the detection limit concentration of the combustible gas is about 1200 to 1500 ppm, it is difficult to detect city gas of 1200 ppm or less.
[0008]
In the city gas having a low concentration of 1200 ppm or less, the content of the auxiliary component gas is small. For example, when the concentration of city gas is 500 ppm, it has a component ratio of 440 ppm of methane, 30 ppm of ethane, 20 ppm of propane, and 10 ppm of butane, but the sensitivity of the catalytic combustion type gas detection element with respect to a subcomponent gas of several tens of ppm is extremely low. Detecting methane as the main component gas, it must be judged as city gas.
[0009]
When city gas leaks from a gas pipe, etc., methane will be present on the ground surface, but on the other hand, methane may occur naturally from the ground, and even in this case, methane will be present on the ground surface. .
Therefore, if the city gas leak standard is only the presence or absence of methane detection, the methane detected when performing the detection work along the road etc. using the city gas detection device described above leaks from the gas pipe etc. buried in the ground. There is a problem that it is difficult to discriminate whether it is derived from city gas or naturally generated.
[0010]
Therefore, a gas that uses a hydrogen flame ionization detector (FID) for detecting the amount of hydrocarbons as a device that can detect the component gas of city gas not only in the main component gas but also in the sub component gas. It is conceivable to detect city gas by chromatography.
In this method, a city gas component is separated by a separation section filled with a separation agent that generates a delayed flow according to the molecular weight of the gas component, and each separated gas component is sequentially detected by a detector.
[0011]
In FIG. 9, the gas sensitivity for each gas component of the city gas in the flame ionization detector is displayed as a relative output when methane is 1. For each gas component, the gas sensitivity at about 50 ppm was measured.
According to this result, it was recognized that the gas sensitivity was approximately the ratio of the number of carbon atoms (C _n ) of hydrocarbons (C _n H _n ). That is, the ratio of gas sensitivity is generally methane: ethane: propane: butane = 1: 2: 3: 4.
Therefore, according to the flame ionization detector, it was recognized that the gas sensitivity of the component gas of city gas increases as the molecular weight increases.
[0012]
FIG. 10 shows the result of detection of city gas using such a flame ionization detector. The measurement was performed according to a conventional method.
[0013]
In this result, the gas component showing the first peak is methane, but the peak showing the presence of ethane is considerably smaller than methane, and the peak showing the presence of propane and butane is not detected. Therefore, it does not have sufficient sensitivity to reliably detect subcomponent gas from city gas. Thus, even when a flame ionization detector is used, it has been recognized that it is difficult to reliably identify city gas by detecting the component gas of the city gas.
[0014]
Accordingly, an object of the present invention is to provide a city gas detection device capable of reliably identifying city gas.
[0015]
[Means for Solving the Problems]
[Configuration 1]
The characteristic configuration of the present invention for achieving this object is as follows:
A city gas having methane (CH ₄ ) as a main component gas and ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ) and butane (C ₄ H ₁₀ ) as combustible gases as flammable gases. A gas component separation unit that can be separated and separated for each gas component by causing a flow delay according to the molecular weight of the combustible gas, and a semiconductor gas that can detect the gas component separated by the gas component separation unit A city gas detection device including a gas detection unit including a detection element and a determination unit that determines whether the gas is a city gas based on an output signal from the gas detection unit,
The semiconductor type gas detection element has a higher sensitivity as a gas component having a higher molecular weight in the combustible gas, and the determination unit performs determination of city gas based on an output signal of the subcomponent gas. The operational effects are as follows.
[0016]
[Function 1]
The present inventors identified that methane may be naturally generated from the ground, so that the detected methane is derived from city gas leaked from a gas pipe or the like buried in the ground or naturally generated. As a result of diligent research focusing on the problem of being difficult, the criteria for determining the presence or absence of city gas leakage are not based on the presence or absence of methane detection, the main component gas of city gas, If it is based on the presence or absence of the detection of propane and butane, it has been newly found out that it is possible to reliably detect and identify city gas, and has reached the present invention.
[0017]
Therefore, in order to distinguish the detection output signal corresponding to the main component gas and the detection output signal corresponding to the subcomponent gas, it is necessary to separate the city gas for each gas component.
In the separation of the city gas for each gas component, the gas component can be separated by the gas component separation unit. That is, the gas component separation unit is constituted by a gas chromatograph device or the like filled with a separating agent that generates a delayed flow according to the molecular weight of the gas component, and the city gas is circulated through the gas chromatograph device, whereby the city gas is gasified. It is separable for every component.
[0018]
Each separated gas component flows with a time lag, and is sequentially detected by a gas detection unit including a semiconductor gas detection element capable of detecting the separated gas component.
[0019]
Here, the reason why the gas detection element is specified as the semiconductor type gas detection element is as follows.
That is, the above-described catalytic combustion type gas detection element is a gas detection element for detecting a high-concentration combustible gas. Furthermore, the present invention needs to detect the subcomponent gas of city gas. When the city gas is detected by the catalytic combustion type gas detection element in such a situation, for example, when the concentration of the city gas is 500 ppm, it has a component ratio of 440 ppm methane, 30 ppm ethane, 20 ppm propane, and 10 ppm butane. The output of the catalytic combustion type gas detection element with respect to the secondary component gas of ppm becomes extremely low. Therefore, it is difficult to use the catalytic combustion type gas detection element for identifying low concentration city gas. Therefore, a semiconductor type gas detection element is used in the gas detection element of the present invention.
[0020]
At this time, as the semiconductor gas detection element, a gas component having a higher molecular weight is used in the combustible gas. Wherein the molecular weight is larger gas component of the combustible gas, it refers to those hydrocarbons (C n _{H n)} of carbon atoms (C _n) is large. If such a semiconductor gas detection element is used, it is possible to detect ethane, propane, and butane, which are subcomponents, with higher sensitivity than methane, which is the main component gas. As described above, city gas has 6%, 4%, and 2% of ethane, propane, and butane, which are subcomponent gases, respectively, but these are much smaller ratios than methane. Therefore, if a semiconductor type gas detection element having a higher sensitivity is used for a gas component having a higher molecular weight (that is, a component gas having a lower content), even a subcomponent gas having a lower content can be detected well. Therefore, gas detection is hardly difficult in the case of a low concentration city gas as in the case of using a catalytic combustion type gas detection element.
[0021]
Furthermore, when the determination unit performs the determination of the city gas based on the output signal of the secondary component gas, the determination of the city gas in the detected gas according to the presence or absence of the output signal of the secondary component gas ethane, propane, or butane. Can determine whether or not. Therefore, it is not necessary to distinguish between methane generated naturally and methane derived from city gas, and it is possible to reliably identify city gas.
[0022]
These can be confirmed in the results shown in Examples described later.
That is, in the examples described later, as shown in FIG. 4, city gas is detected using a city gas detection device including a semiconductor gas detection element that has a higher sensitivity for a gas component having a higher molecular weight. . As a result, a high output can be obtained with respect to the secondary component gas (ethane) having a small abundance ratio (see FIG. 5), and thereby a characteristic output pattern in which the presence of ethane is emphasized can be obtained. It is recognized that it can be done. Therefore, the presence / absence of city gas in the detected gas can be easily determined based on the presence / absence of the sub-component gas (ethane) of the city gas.
[0023]
[Configuration 2]
The characteristic configuration of the present invention for achieving this object is the above-described configuration 1,
Among the output values output from the determination unit, the output signal corresponding to the sub-component gas is multiplied by a predetermined coefficient, and the operation and effect are as follows.
[0024]
[Operation effect 2]
That is, by multiplying the output signal corresponding to the sub-component gas by a predetermined coefficient, the output signal of the sub-component gas (ethane, propane, butane) with a low content can be amplified and output. Gas detection can be performed reliably. Therefore, it is possible to more reliably identify city gas.
[0025]
[Configuration 3]
In order to achieve this object, the characteristic configuration of the present invention is that, in the above configuration 1 or 2, the predetermined coefficient is set to be larger as the secondary component gas has a higher molecular weight. Street.
[0026]
[Operation effect 3]
That is, in general, the gas components contained in city gas are small in the order of methane, ethane, propane, and butane. , Butane, propane and ethane can be set in this order. For this reason, even if the secondary component gas has a large molecular weight and a small component ratio, the output signal can be amplified well, and the secondary component gas can be detected more reliably.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the parts denoted by the same reference numerals as in the conventional example indicate the same or corresponding parts.
[0028]
A schematic diagram of the city gas detector of the present invention is shown in FIG.
The city gas detection device X of the present invention can be employed in, for example, a detector of a gas chromatograph device. The configuration in this case is illustrated below.
[0029]
The city gas detection device X includes a gas component separation unit 10 that generates a flow delay in accordance with the molecular weight of combustible gases such as methane, ethane, propane, and butane, which are components of city gas, and can separate each gas component. , A gas detection unit 20 including a semiconductor gas detection element capable of detecting each gas component separated by the gas component separation unit, and a determination unit that determines whether the gas is a city gas based on an output signal from the gas detection unit 30.
[0030]
The gas component separation unit 10 is constituted by a column filled with a separating agent for separating a gas component of city gas. The separating agent is selected and determined by calcium oxide (CaO), silicon dioxide (SiO ₂ ), activated alumina, PEG-based member, unicarbon member, porous polymer, etc., for example, a mixed powder of calcium oxide and silicon oxide. It is also possible.
[0031]
The gas detection unit 20 includes a hot-wire semiconductor gas detection element capable of detecting each gas component separated by the gas component separation unit. As shown in FIG. 2, the hot-wire semiconductor gas detection element 21 includes a metal oxide such as indium oxide, tungsten oxide, tin oxide, and zinc oxide on a noble metal wire 22 such as platinum, palladium, or platinum-palladium alloy. A gas sensitive part 23 is provided which is coated with a metal oxide semiconductor mainly composed of sinter and dried and sintered.
[0032]
At this time, as the hot-wire semiconductor gas detection element 21, a gas component having a higher molecular weight among the combustible gas is used.
[0033]
This hot-wire semiconductor gas detection element 21 was incorporated in the bridge circuit shown in FIG. At this time, the sensor output is obtained by the following equation.
V = −E {rs / (rs + r0) −r1 / (r1 + r2)}
Here, each variable is as follows.
V: sensor output E: bridge voltage rs: resistance r0 of the hot wire type semiconductor gas detection element 21: resistance r1 of the fixed resistance R0: resistance r2 of the fixed resistance R1: resistance of the fixed resistance R2
The determination unit 30 determines whether the gas to be detected is a city gas based on an output signal from the gas detection unit 20, and calculates a calculation unit 31 based on the output signal from the gas detection unit 20. , A display unit 32 for displaying a calculation result by the calculation unit 31, a storage unit 33 for storing the calculation result, and the like.
[0035]
The calculation unit 31 can be applied to a microcomputer that can perform calculation based on the output signal from the gas detection unit 20, and the display unit 32 can be applied to a monitor that can display the calculation result of the calculation unit 31. Further, the storage unit 33 can be a memory or the like for storing calculation results.
[0036]
The determination unit 30 determines the city gas based on the output signal of the secondary component gas. As a result, the presence or absence of city gas in the gas to be detected can be determined based on the presence or absence of output signals of ethane, propane, and butane, which are subcomponent gases. Therefore, it is not necessary to distinguish between methane generated naturally and methane derived from city gas, and it is possible to reliably identify city gas.
[0037]
Of the output values output from the display unit 32 of the determination unit, it is possible to multiply the output signal corresponding to the sub-component gas by a predetermined coefficient. Thereby, since the output signal of subcomponent gas (ethane, propane, butane) with little content can be amplified and output, subcomponent gas can be detected reliably.
[0038]
The gas component separation unit 10 and the gas detection unit 20 are connected by a pipe 40. From the upstream of the gas component separation unit 10, air introduced from the outside flows through the filter 41. Immediately before the gas component separation unit 10, a detected gas inlet 42 is provided, from which a detected gas is injected. Note that a column filled with activated carbon can be used instead of the filter 41.
[0039]
Further, a pump 43 is connected to the downstream of the gas detection unit 20 via a pipe 40. By operating the pump 43, the gas to be detected and air are sucked, and the gas component separation unit 10 The gas is discharged from the gas exhaust port through the gas detector 20.
[0040]
At this time, the air acts as a carrier gas, is cleaned by the filter 41, and passes through the pipe 40 as a flow path. In this state, when the gas to be detected is supplied from the gas inlet 42, each gas component is separated by the separating agent filled in the gas component separation unit 10 and flows with a time lag. The gas detection element 21 sequentially detects.
[0041]
For the output signal generated as a result of the detection, the city gas component contained in the gas to be detected is calculated by the calculation unit 31 separately, the calculation result is displayed by the display unit 32, and the storage unit 33 as required. Remember. When it is determined that the calculation result is city gas having a concentration equal to or higher than a predetermined value, the alarm unit 45 can notify the user by means of an alarm or the like.
[0042]
In the above embodiment, the pump 43 is arranged on the gas exhaust port side, but it can also be arranged on the air intake side (for example, upstream of the filter 41).
[0043]
【Example】
Embodiments of the present invention are described below with reference to the drawings.
The city gas was detected using the city gas detection device X described above.
The hot-wire semiconductor gas detection element 21 uses a noble metal wire 22 made of platinum, a sensitive layer 23 containing indium oxide as a main component and a silica film chemically vapor-deposited. The gas sensitivity to the component gas is shown in FIG.
In FIG. 4, the gas sensitivities of the subcomponent gases (ethane, propane, isobutane) when the gas sensitivity to methane is set to 1 are relatively shown. For each gas component, the gas sensitivity at about 50 ppm was measured.
[0044]
As a result, when the gas sensitivity to methane is 1, the gas sensitivity to ethane is 4.8, the gas sensitivity to propane is 5.8, and the gas sensitivity to isobutane is 6.7. It was recognized that the element 21 has a higher sensitivity in a gas component having a higher molecular weight in hydrocarbons of methane, ethane, propane, and isobutane.
[0045]
FIG. 5 shows the results of city gas detection using a gas chromatograph device provided with the city gas detection device X having the hot-wire semiconductor gas detection element 21 as a detector. The city gas concentration was 500 ppm.
The experimental conditions in the gas chromatograph apparatus were as follows.
Filler: Porapak N 60-80
Column: 6 mm x 4 mm (diameter), Teflon column temperature: 23 ° C
Carrier gas: Dry air flow rate: 20 mL / min Sample size: 1 mL
Sensitivity: 64
[0046]
The sensor output when the city gas is detected by the city gas detection device X of the present invention is because the gas component of the city gas is separated by the gas component separation unit 10 and each gas component flows with a time lag according to the molecular weight. Each gas component is sequentially detected by the hot-wire semiconductor gas detection element 21. Therefore, the sensor output peak of each gas component is also displayed with a time lag.
That is, the sensor output value in the graph of FIG. 5 is such that the gas component showing the first peak is methane, and the gas component showing the next peak is ethane (methane is about 30 seconds, ethane is about 70 seconds, and peaks). You can get it).
[0047]
Since the volume composition ratio of each component of the city gas is methane: ethane: propane: butane (isobutane) = 88: 6: 4: 2, the sensor output of ethane is considerably smaller than the sensor output of methane. (See Comparative Example 1 described later). However, in the city gas detection device X of the present invention, among the hydrocarbons of methane, ethane, propane, and isobutane, the hot wire type semiconductor gas detection element 21 (that is, ethane is more ethane than methane) that shows a higher sensitivity to a gas component having a higher molecular weight. Can be used to obtain high output for ethane with a small abundance ratio, thereby obtaining a characteristic output pattern that emphasizes the presence of ethane. I was able to. Therefore, the presence / absence of city gas in the detected gas can be easily determined based on the presence / absence of the sub-component gas (ethane) of the city gas.
[0048]
That is, the ratio of gas sensitivity to each gas component of the semiconductor gas detection element in the city gas detection device of the present invention is such that, as described above, the gas component having a higher molecular weight such as methane: ethane = 1: 4.8. It shows high sensitivity. This tendency toward higher sensitivity was more conspicuous than the ratio of gas sensitivity to each gas component (methane: ethane = 1: 2) of the above-described flame ionization detector.
[0049]
In this embodiment, the case where a characteristic output pattern in which the presence of ethane is emphasized is illustrated, but the present invention is not limited to this, and a characteristic output pattern in which the presence of propane or isobutane is emphasized is obtained. If obtained, the presence or absence of city gas in the gas to be detected can be easily determined by the presence or absence of propane or isobutane.
[0050]
To further emphasize the ethane sensor output peak, the output signal corresponding to ethane (that is, the output signal of about 70 seconds) is multiplied by a predetermined coefficient to amplify and display the ethane output signal. Therefore, the secondary component gas can be reliably detected.
This can also be applied to sensor outputs of propane and isobutane. In this case, a characteristic output pattern in which the presence of propane or isobutane is further emphasized can be obtained.
[0051]
(Comparative example)
As a comparative example, city gas was detected under the same conditions as in the above example, except that a hot-wire semiconductor gas detection element 21 ′ having sensitivity to all combustible gases was used.
The hot-wire semiconductor gas detection element 21 ′ uses a noble metal wire 22 having platinum and a sensitive layer 23 having tin oxide as a main component and carrying a trace amount of noble metal, and with respect to the subcomponent gas of the semiconductor gas detection element 21 ′. The gas sensitivity is shown in FIG.
FIG. 6 shows the relative gas sensitivities of the secondary component gases (ethane, propane, isobutane) when the gas sensitivity to methane is 1. For each gas component, the gas sensitivity at about 50 ppm was measured.
[0052]
As a result, when the gas sensitivity to methane is 1, the gas sensitivity to ethane is 1.5, the gas sensitivity to propane is 2.0, and the gas sensitivity to isobutane is 1.8. This hot-wire semiconductor gas detection In the element 21 ′, the sensitivity difference between methane and subcomponent gases (ethane, propane, isobutane) was not recognized as in the hot-wire semiconductor gas detection element 21 in which the gas component having a higher molecular weight showed higher sensitivity.
[0053]
FIG. 7 shows the result of the detection of city gas using the city gas detection device X provided with the hot-wire semiconductor gas detection element 21 ′. The concentration of city gas and the experimental conditions in the gas chromatograph were the same as in the above example.
[0054]
The peak of the sensor output of each gas component in FIG. 7 is also displayed with a time lag. Therefore, the gas component showing the first peak is methane, but the sensor output peak corresponding to ethane is hardly detected.
Therefore, when the city gas is detected using the hot-wire semiconductor gas detection element 21 ′ having sensitivity to all flammable gases, only methane, which is the main component gas of the city gas, can be characteristically identified. It can hardly be expected to obtain a characteristic output pattern in which the presence of subcomponent gases (ethane, propane, isobutane) is emphasized. Therefore, when the hot-wire semiconductor gas detection element 21 ′ having sensitivity to all flammable gases is used, the presence or absence of the city gas in the detected gas cannot be determined based on the presence or absence of the subcomponent gas of the city gas. It was recognized.
[0055]
[Another embodiment 1]
Another embodiment will be described below.
In the above-described embodiment, when it is desired to further emphasize the peak of the sensor output of the sub-component gas, it is possible to multiply the output signal corresponding to the sub-component gas by a predetermined coefficient. You may make it set so that the subcomponent gas with larger molecular weight may be set large. Thereby, normally, a large coefficient can be set in the order of butane, propane, and ethane. For this reason, even if the secondary component gas has a large molecular weight, the output signal can be amplified well, so that the secondary component gas can be detected more reliably.
[0056]
[Another embodiment 2]
In the above-described embodiments, it has been shown that city gas can be identified based on the sensor output of subcomponent gas, but it is conceivable to apply this as follows.
[0057]
That is, a gas detection device including a hot-wire semiconductor gas detection element that exhibits high sensitivity to propane is employed as a detector of the gas chromatograph device. As a result of detecting the gas to be detected using this gas chromatograph apparatus, if a characteristic output pattern in which the presence of propane is emphasized can be obtained, the detected gas contains liquefied petroleum gas. It can be determined that there is.
[0058]
In addition, this invention is not limited to the said embodiment, As long as there exists the same effect, the structure of each part can be changed suitably.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a city gas detector of the present invention. FIG. 2 is a schematic diagram of a hot-wire semiconductor gas detector. FIG. 3 is a schematic diagram of a bridge circuit. Sensitivity to all gas components of the hot-wire semiconductor type gas detection element that performs [Fig. 5] Sensor output for city gas detected by the city gas detection device of the present invention [Fig. 6] Hot-wire semiconductor having sensitivity to all combustible gases Gas Sensing Sensitivity of Gas Components to Gas Components [Fig. 7] Sensor Output for City Gas Detected by Hot-Wire Semiconductor Gas Sensing Elements Sensitive to Combustible Gases [Fig. 8] Conventional City Gas Detection Device Schematic diagram of main parts [Fig. 9] Gas sensitivity of each gas component of city gas in hydrogen flame ionization detector [Fig. 10] Sensor output for city gas detected by hydrogen flame ionization detector [Explanation of symbols]
10 Gas component separation unit 20 Gas detection unit 30 Determination unit

Claims (3)

A city gas having methane (CH ₄ ) as a main component gas and ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ) and butane (C ₄ H ₁₀ ) as combustible gases as flammable gases. A gas component separation unit that can be separated and separated for each gas component by causing a flow delay according to the molecular weight of the combustible gas, and a semiconductor gas that can detect the gas component separated by the gas component separation unit A city gas detection device including a gas detection unit including a detection element and a determination unit that determines whether the gas is a city gas based on an output signal from the gas detection unit,
The semiconductor type gas detection element has a higher sensitivity as a gas component having a higher molecular weight in the combustible gas, and the determination unit performs determination of city gas based on an output signal of the subcomponent gas. The city gas detector that is the thing. The city gas detection device according to claim 1, wherein an output signal corresponding to the sub-component gas is multiplied by a predetermined coefficient among output values output from the determination unit. The city gas detection device according to claim 2, wherein the predetermined coefficient is set to be larger for a secondary component gas having a higher molecular weight.

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