JP7268485B2 - gas detector - Google Patents

Description

The present invention relates to gas detection devices.

2. Description of the Related Art Conventionally, a gas detection device that distinguishes between three types of gas is known (see, for example, Patent Document 1).
Patent document 1 Japanese Patent Application Laid-Open No. 2011-149754

A gas detection device is preferably capable of detecting a wide variety of gases.

SUMMARY OF THE INVENTION In a first aspect of the invention, a gas detection apparatus is provided. A gas detection device includes a gas sensor and a determination unit. The gas sensor has a gas detection layer whose output changes upon contact with a gas to be detected, and a heater layer that heats the gas detection layer. The discriminating portion indicates a first waveform indicating a change in the output of the gas sensor when the temperature of the heater layer is the first temperature, and a change in the output of the gas sensor when the temperature of the heater layer is a second temperature different from the first temperature. The type of gas to be detected is discriminated based on the second waveform.

The determination unit may determine at least three types of detection target gas based on the first waveform and the second waveform.

The determination unit may determine the type of detection target gas based on the change rate of the output value of the first waveform in a predetermined first period.

The determination unit may determine the type of detection target gas based on whether or not the output value of the second waveform converges to a predetermined reference value.

The determination unit may determine the type of detection target gas based on whether or not the second waveform has a minimum value.

The discriminating unit is based on the first waveform, the second waveform, and the third waveform showing the change in the output of the gas sensor when the temperature of the heater layer is a third temperature different from the first temperature and the second temperature. The type of gas to be detected may be determined.

The determination unit may control a predetermined second period of the second waveform based on the first waveform or the second waveform.

The gas detection layer may be heated intermittently by the heater layer. The determination unit may control the intermittent timing based on at least one of the first waveform and the second waveform.

The gas sensing layer may be heated for a first period with the heater layer set to a second temperature. If the output of the gas sensor in a predetermined second period of the second waveform converges to a predetermined first reference value at any detection timing in the first period, the determination unit determines whether the first waveform and the second waveform are equal to each other. The type of gas to be detected may be determined based on the waveform.

The gas sensing layer may be heated for a second period with the heater layer set to the first temperature. If the rate of change in the output value of the first waveform in a predetermined first period is equal to or greater than a predetermined second reference value at any detection timing in the second cycle, the determination unit determines the first waveform and The type of detection target gas may be determined based on the second waveform.

It should be noted that the above summary of the invention does not list all the necessary features of the invention. Subcombinations of these feature groups can also be inventions.

3 illustrates a monitored object 300 according to one embodiment of the present invention; FIG. 1 is a diagram showing an example of a gas detection device 100 according to one embodiment of the invention; FIG. 2 is a diagram showing an example of a cross section of the gas sensor 10; FIG. 4 is a diagram showing an example of the relationship between the temperature of the heater layer 86 of the gas sensor 10 and time. FIG. 4 is a diagram showing an example of the relationship between heating time and output of the gas sensor 10 for gas A. FIG. 4 is a diagram showing an example of a circuit for measuring a change in electrical resistance of the gas detection layer 96 of the gas sensor 10 using a constant voltage; FIG. 4 is a diagram showing an example of the relationship between heating time and output of gas sensor 10 for gas B. FIG. 4 is a diagram showing an example of the relationship between heating time and output of the gas sensor 10 for gas C. FIG. FIG. 4 is a diagram showing a flowchart of determination of detection target gas by the determination unit 20. FIG. 4 is a diagram showing an example of the relationship between the heating time and the output of the gas sensor 10 for four gas species. FIG. FIG. 4 is a diagram summarizing trends of waveforms of gases A to D in a first period ta1, a third period ta3, and a second period ta2. 8 is a diagram showing another example of the relationship between the temperature of the heater layer 86 of the gas sensor 10 and time. FIG. 8 is a diagram showing another example of the relationship between the temperature of the heater layer 86 of the gas sensor 10 and time. FIG.

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. Also, not all combinations of features described in the embodiments are essential for the solution of the invention.

FIG. 1 is a diagram illustrating a monitored object 300 according to one embodiment of the invention. The monitored object 300 in this example comprises a gas detection device 100 and an electrical device 200 . A monitoring target 300 is, for example, a factory, a plant, or the like. The electric device 200 is a device such as a boiler or an air conditioner installed in a factory, plant, or the like, which operates by supplying electricity. The gas detection device 100 detects gas components of combustible gas and incomplete combustion gas due to fuel gas leakage (from the boiler) of the electric device 200 in the monitored object 300 . Moreover, from the viewpoint of disaster prevention, the gas detection device 100 may detect volatile gas components caused by excessive heat generation in the monitored object 300 . The volatile gas component may be a component generated before ignition due to excessive heat generation of the electrical device 200 .

FIG. 2 is a diagram illustrating an example of a gas detection device 100 according to one embodiment of the invention. A gas detection device 100 includes a gas sensor 10 and a determination section 20 . Gas sensor 10 has gas detection layer 96 and heater layer 86 . Heater layer 86 heats gas detection layer 96 .

The output of the gas sensor 10 changes according to contact with the gas to be detected. The gas sensor 10 is preferably a low power consumption gas sensor. The gas sensor 10 of this example is a MEMS (Micro Electro Mechanical System) gas sensor finely processed by semiconductor manufacturing technology. The gas sensor 10 may be formed on a semiconductor substrate such as silicon.

The gas detection device 100 of this example further includes a power supply section 30 . The power supply unit 30 supplies power to the gas sensor 10 . The power supply unit 30 may be a battery. The power supply unit 30 may be a commercial power supply. If the gas sensor 10 is a low power consumption sensor such as a MEMS gas sensor, power can be supplied from a battery for a long period of time. If the gas sensor 10 can be driven by a battery, the gas sensor 10 can be easily provided to various monitored objects 300 . The power supply unit 30 may also supply power to other devices of the monitored object 300 .

When the gas detection layer 96 is heated by the heater layer 86, the output of the gas sensor 10 changes with the lapse of heating time. A waveform indicating a change in the output of the gas sensor 10 when the temperature of the heater layer 86 is the first temperature is referred to as a first waveform. A waveform indicating a change in the output of the gas sensor 10 when the temperature of the heater layer 86 is a second temperature (different from the first temperature) is referred to as a second waveform. The first waveform and second waveform will be described later. The discrimination unit 20 discriminates the type of gas to be detected based on the first waveform and the second waveform.

FIG. 3 is a diagram showing an example of a cross section of the gas sensor 10. As shown in FIG. Gas sensor 10 has gas detection layer 96 and heater layer 86 . The gas sensor 10 of this example further has a semiconductor substrate 80 , a thin film lamination portion 81 , an insulating layer 85 and a gas sensing portion 90 . The semiconductor substrate 80 is, for example, a silicon (Si) substrate. A semiconductor substrate 80 is provided with a diaphragm 88 having a smaller substrate thickness than other regions. The diaphragm 88 may be provided through the semiconductor substrate 80 .

The thin film lamination portion 81 is laminated on the upper surface of the semiconductor substrate 80 . The thin film lamination portion 81 of this example has a thermal oxide film 82 , a nitride film 83 and an oxide film 84 . The thermal oxide film 82 may be formed by thermally oxidizing the upper surface of the semiconductor substrate 80 . The thermal oxide film 82 of this example is a silicon oxide (SiO ₂ ) film.

The nitride film 83 is laminated on the upper surface of the thermal oxide film 82 by plasma CVD, for example. The nitride film 83 of this example is a silicon nitride (Si ₃ N ₄ ) film. The oxide film 84 is laminated on the upper surface of the nitride film 83 by plasma SVD, for example. The oxide film 84 in this example is a silicon oxide (SiO ₂ ) film. The thin film stack 81 functions as a support layer and a thermal insulation layer for the diaphragm structure.

A heater layer 86 is formed on the upper surface of the thin film lamination section 81 . The heater layer 86 is a film containing at least one of platinum, gold and nickel and at least one of chromium and tungsten. The heater layer 86 of this example is provided below the gas sensing portion 90 on the top surface of the oxide film 84 . The heater layer 86 is formed by sputtering, for example.

The insulating layer 85 is formed on the upper surface of the thin film lamination section 81 by, for example, sputtering. An insulating layer 85 is provided to cover the heater layer 86 . The insulating layer 85 in this example is a silicon oxide (SiO ₂ ) film.

The gas sensing portion 90 is provided on the upper surface of the insulating layer 85 . The gas sensing part 90 may be provided in a range overlapping the heater layer 86 when viewed from the top of the semiconductor substrate 80 . The heater layer 86 can efficiently heat the gas sensing portion 90 by providing the gas sensing portion 90 in a range overlapping the heater layer 86 . Further, the diaphragm 88 may be formed in a range overlapping at least one of the gas sensing portion 90 and the heater layer 86 when viewed from above the semiconductor substrate 80 . Provision of the diaphragm 88 suppresses escape of heat from the heater layer 86 to the semiconductor substrate 80 . Also, with the diaphragm 88 provided, the diffusion of heat from the heater layer 86 is faster than when the diaphragm 88 is not provided. Therefore, the heater layer 86 can efficiently heat the gas sensing portion 90 .

Gas sensing portion 90 has selective combustion layer 98 , gas detection layer 96 , electrode 94 and bonding layer 92 . The bonding layer 92 is partially formed on the upper surface of the insulating layer 85 . The gas sensing portion 90 may have two bonding layers 92 for one gas detection layer 96 . The bonding layer 92 may be formed by a sputtering method. The bonding layer 92 of this example is made of a material containing tantalum or titanium.

An electrode 94 is formed on the upper surface of the bonding layer 92 . The electrodes 94 may be formed by a sputtering method. The electrode 94 in this example is made of a material containing platinum or gold. The bonding layer 92 connects the electrode 94 and the insulating layer 85 . The bonding layer 92 may be a film thinner than the electrode 94 . For example, the bonding layer 92 has a thickness of 50 nm and the electrode 94 has a thickness of 200 nm.

The gas detection layer 96 is provided extending from the upper surface of one electrode 94 to the upper surface of the other electrode 94 . A gas detection layer 96 may be provided in contact with the top surface of the insulating layer 85 between the two electrodes 94 . The gas detection layer 96 may be formed by a sputtering method. The gas detection layer 96 of this example is a tin oxide (SnO ₂ ) film doped with antimony (Sb). The gas sensor 10 detects the target gas by detecting the resistance value of the gas detection layer 96 between the two electrodes 94 .

Oxygen (O ₂ ) is negatively charged on the surface of the gas detection layer 96 in an atmosphere in which no gas component exists. When oxygen (O ₂ ) adsorbs a negative charge to the surface of the gas detection layer 96, carrier electrons in the gas detection layer 96 decrease. Therefore, the electrical resistance value of the gas detection layer 96 increases. On the other hand, when a specific gas component exists, oxygen (O ₂ ) adsorbed on the surface of the gas detection layer 96 reacts with the gas component, increasing carrier electrons in the gas detection layer 96 . Therefore, the electrical resistance value of the gas detection layer 96 becomes low. The heater layer 86 heats the gas sensing layers 96 to promote reaction between the adsorbed oxygen and gas components in each gas sensing layer 96 .

A selective combustion layer 98 is provided over the gas detection layer 96 . The selective combustion layer 98 allows specific gas components to pass to the gas detection layer 96 and burns and removes miscellaneous gases such as combustible gases. Also, the selective combustion layer 98 carries a catalyst. By selecting the type of catalyst contained in the selective combustion layer 98, it is possible to select gas components that react with oxygen (O ₂ ) adsorbed on the surface of the gas detection layer 96 with high sensitivity.

The selective combustion layer 98 of this example is a sintered material in which a catalyst is supported on aluminum oxide (Al ₂ O ₃ ). The selective combustion layer 98 may be formed by, for example, baking at 500° C. for 1 hour or more after applying the coating so as to cover the entire gas detection layer 96 by a screen printing method. After forming the selective combustion layer 98 , the lower surface of the semiconductor substrate 80 is etched to form the diaphragm 88 . The selective combustion layer 98 may be applied over the top surface of the gas detection layer 96 .

FIG. 4 is a diagram showing an example of the relationship between the temperature of the heater layer 86 of the gas sensor 10 and time. A plurality of temperatures of the heater layer 86 may be set. In this example, the temperature of the heater layer 86 is set to two types, a first temperature Tp1 and a second temperature Tp2 higher than the first temperature Tp1. The first temperature Tp1 and the second temperature Tp2 may be set according to the type of gas to be detected.

The detection target gas and miscellaneous gas that travel from the outside of the gas sensing section 90 through the selective combustion layer 98 toward the gas detection layer 96 are burned in the selective combustion layer 98 . Miscellaneous gas refers to gas that constantly exists in the monitored object 300 . When the gas sensing portion 90 is heated by the heater layer 86 , combustion of the detection target gas and the miscellaneous gas in the selective combustion layer 98 is promoted. Combustion of the detection target gas in the selective combustion layer 98 will be described later.

Combustion of the detection target gas and the miscellaneous gas in the selective combustion layer 98 is more likely to be promoted as the temperature of the heater layer 86 of the gas sensing section 90 is higher. Since the second temperature Tp2 is higher than the first temperature Tp1, combustion in the selective combustion layer 98 is promoted more when the heater layer 86 is set at the second temperature Tp2 than when it is set at the first temperature Tp1. be done. Therefore, when the detection target gas and the miscellaneous gas are burned in the selective combustion layer 98 for the same period of time, the remaining detection target gas and miscellaneous gas are greater at the first temperature Tp1 than at the second temperature Tp2. Prone.

When the gas to be detected is any one of methane (CH ₄ ), carbon monoxide (CO), hydrogen (H ₂ ), and isobutane (C ₄ H ₁₀ ), the first temperature Tp1 is 60° C. or higher and 350° C. or lower. you can The first temperature Tp1 is 250° C., for example. When the gas to be detected is any one of methane (CH ₄ ), carbon monoxide (CO), hydrogen (H ₂ ), and isobutane (C ₄ H ₁₀ ), the second temperature Tp is 350° C. or higher and 460° C. or lower. you can The second temperature Tp2 is 430° C., for example.

The durations of the first temperature Tp1 and the second temperature Tp2 may be predetermined first period ta1 and second period ta2, respectively. The first period ta1 and the second period ta2 may be set according to at least one of the type and concentration of the gas to be detected. The first period ta1 and the second period ta2 may be longer as the concentration of the detection target gas is higher, and may be shorter as the concentration is lower. The first period ta1 may be determined according to at least one of the first temperature Tp1 and the second temperature Tp2. The second period ta2 may be determined according to at least one of the second temperature Tp2 and the first temperature Tp1.

The first period ta1 and the second period ta2 may be equal or different. In the example of FIG. 4, the first period ta1 and the second period ta2 are equal. The period T1 in the example of FIG. 4 is the sum of the first period ta1 and the second period ta2. Both the first period ta1 and the second period ta2 may be 50 ms or more and 500 ms or less, or may be 50 ms or more and 1000 ms or less. The first period ta1 and the second period ta2 are, for example, 200 ms.

The first period ta1 and the second period ta2 may be continuous or intermittent. In the example of FIG. 4, the first period ta1 and the second period ta2 included in the period T1 are continuous in this order, and the second period ta2 and the first period ta1 in the next (later) period T1 is intermittent. In FIG. 4, the interval between the second period ta2 and the first period ta1 is indicated by T2. A predetermined interval shorter than the interval T2 may be provided between the first period ta1 and the second period ta2 included in the period T1.

Note that the first period ta1 and the second period ta2 included in the period T1 may be continuous in the order of the second period ta2 and the first period ta1. In this case, the first period ta1 and the second period ta2 in the next (later time) period T1 may be intermittent. A predetermined interval shorter than the interval T2 may be provided between the second period ta2 and the first period ta1 included in the period T1.

The interval T2 may be set according to the type of gas to be detected. The interval T2 may be set according to at least one of the first period ta1 and the second period ta2. In this example, the temperature of the heater layer 86 is intermittently set to Tp1 and Tp2 in a cycle (T1+T2).

FIG. 5A is a diagram showing an example of the relationship between the heating time and the output of the gas sensor 10 for gas A. FIG. Gas A is, for example, methane (CH ₄ ). FIG. 5A shows the relationship between the heating time and the output of the gas sensor 10 for four concentrations of gas A (first concentration to fourth concentration). The concentration of gas A is higher in order of first concentration, second concentration, third concentration, and fourth concentration. The case of the first density is indicated by a fine dashed line, the case of the second density by a one-dot chain line, the case of the third density by a coarse dashed line, and the case of the fourth density by a two-dot chain line.

In this example, the first concentration is 300 ppm to 700 ppm, the second concentration is 800 ppm to 1200 ppm, the third concentration is 1500 ppm to 2500 ppm, and the fourth concentration is 3000 ppm to 5000 ppm. The first to fourth concentrations are, for example, 500 ppm, 1000 ppm, 2000 ppm and 4000 ppm, respectively.

In FIG. 5A, the solid line shows the relationship between the heating time and the output of the gas sensor 10 when the gas is air. Air may be a mixture of nitrogen (N ₂ ) and oxygen (O ₂ ) in a volume ratio of about 4:1. Further, in FIG. 5A, the concentration of gas A when the gas is air is so small that it cannot be detected by gas sensor 10 .

5A, the heating start time of the heater layer 86 is assumed to be time 0. In FIG. Further, the heating end time at the first temperature Tp1 and the heating start time at the second temperature Tp1 are defined as time t1. Also, let the heating end time at the second temperature be time t2. Note that the first period ta1 and the second period ta2 shown in FIG. 4 have a length from time 0 to t1 and a length from time t1 to t2, respectively.

A first waveform 42 is the output waveform of the gas sensor 10 when the temperature of the heater layer 86 is the first temperature Tp1 in the first period ta1. The first waveform 42 of this example is the output waveform of the gas sensor 10 when the detection target gas is the gas A. As shown in FIG. A second waveform 44 is the output waveform of the gas sensor 10 when the temperature of the heater layer is the second temperature Tp2 in the second period ta2. The second waveform 44 in this example is the output waveform of the gas sensor 10 when the gas to be detected is the gas A. As shown in FIG.

A waveform 52 is the output waveform of the gas sensor 10 when the temperature of the heater layer 86 is the first temperature Tp1 in the first period ta1. A waveform 52 is an output waveform of the gas sensor 10 when the gas to be detected is air. A waveform 54 is the output waveform of the gas sensor 10 when the temperature of the heater layer is the second temperature Tp2 in the second period ta2. A waveform 54 is an output waveform of the gas sensor 10 when the gas to be detected is air.

The output of the gas sensor 10 is determined by the concentration of combustible components in the detection target gas and the concentration of other gases such as oxygen (O ₂ ) in the monitoring target 300 . The shape of the time waveform of the output of the gas sensor 10 changes according to the type of the contacting gas even when driven under the same heating conditions.

When the detection target gas contains a combustible component (for example, methane (CH ₄ )), when the gas detection layer 96 is heated by the heater layer 86, the component and oxygen (O ₂ ) reacts. Therefore, the electrical resistance of the gas detection layer 96 tends to decrease. Therefore, when the current flowing between the two electrodes 94 is a constant current, the output of the gas sensor 10 tends to decrease. Also, the higher the concentration of the combustible component contained in the gas to be detected, the greater the amount of adsorbed oxygen that reacts with the component. Therefore, the amount of decrease in the output of the gas sensor 10 tends to increase.

In the example shown in FIG. 5A and FIGS. 6 and 7 described later, by passing a constant current between the two electrodes 94, the change in the electrical resistance of the gas detection layer 96 is measured as the change in the output of the gas sensor 10. ing. A change in electrical resistance of gas sensing layer 96 may be measured by a constant voltage.

FIG. 5B is a diagram showing an example of a circuit for measuring a change in electrical resistance of the gas detection layer 96 of the gas sensor 10 using a constant voltage. In the circuit, constant voltage source 110, voltmeter 120, load resistor Rss and gas sensor 10 are connected as shown in FIG. 5B. A constant voltage source 110 generates a constant voltage E. FIG. Let Rs be the sensor resistance between the two electrodes 94 of the gas sensor 10 (the resistance of the gas detection layer 96). A load resistor Rss is provided to monitor the current flowing through the sensor resistor Rs. The resistance value of load resistor Rss is fixed. A voltmeter 120 measures the voltage across the load resistor Rss.

One of the two electrodes 94 is connected to one terminal of the load resistor Rss. A voltage E is applied between the other of the two electrodes 94 and the other terminal of the load resistor Rss. That is, the constant voltage E is applied across the serially connected sensor resistor Rs and load resistor Rss.

The voltage Vss applied across the load resistor Rss has a value obtained by proportionally dividing the constant voltage E by the ratio between the sensor resistor Rs and the load resistor Rss. Assuming that the current flowing through the sensor resistor Rs and the load resistor Rss is I, the following equation holds.

Since the constant voltage E and the load resistance Rss are known, the sensor resistance Rs can be calculated from the equations (1) and (2) by measuring the voltage Vss. That is, the circuit of FIG. 5B can detect changes in the sensor resistance Rs as changes in the voltage Vss. When the combustible component (for example, methane (CH ₄ )) of the gas to be detected reacts with oxygen (O ₂ ) adsorbed on the surface of the gas detection layer 96 and the resistance (sensor resistance Rs) of the gas detection layer 96 decreases. , the voltage Vss increases.

Also, the temperature at which the combustible component contained in the gas to be detected and the oxygen (O ₂ ) adsorbed on the surface of the gas detection layer 96 tend to react varies depending on the component. The higher the temperature of the gas detection layer 96, the easier the reaction between the component and adsorbed oxygen. Therefore, the output of the gas sensor 10 tends to decrease as the temperature of the gas detection layer 96 increases.

Furthermore, the temperature at which combustible components contained in the detection target gas are likely to burn in the selective combustion layer 98 also varies depending on the components contained in the detection target gas. The higher the temperature of the selective combustion layer 98, the more easily the component burns. Therefore, the higher the temperature of the selective combustion layer 98 is, the more difficult it is for the component to reach the gas detection layer 96 . Therefore, the higher the temperature of the selective combustion layer 98, the closer the output of the gas sensor 10 to the output when the gas to be detected is air.

Let the output of the gas sensor 10 at time 0 be MX. At time 0, the reaction between the combustible component contained in the detection target gas and oxygen (O ₂ ) adsorbed on the surface of the gas detection layer 96 has not started, so the output MX is irrespective of the type of detection target gas. likely to be equal.

When the gas to be detected is gas A, the reaction between the combustible component contained in gas A and the oxygen adsorbed to the gas detection layer 96 is accelerated when the first period ta1 starts, so the output of the gas sensor 10 begins to decrease. . The output of the gas sensor 10 converges to a predetermined lower limit MNA (in the case of the fourth concentration) at time t1c, and levels off at the lower limit MNA after time t1c.

Further, when the second period ta2 starts, the reaction between the combustible components contained in the gas A and the oxygen adsorbed to the gas detection layer 96 is further accelerated, so the output of the gas sensor 10 begins to further decrease. Since the combustible components contained in the gas A are difficult to burn off in the selective combustion layer 98 at the second temperature Tp2, the output of the gas sensor 10 in the second period ta2 is the output value of the waveform 54 (for air) (first reference It is difficult to asymptotically approach the value S1 (described later). The output of the gas sensor 10 converges to a predetermined lower limit value different from the lower limit value MNA at time t2c, and levels off at the lower limit value after time tc2.

When the gas to be detected is air, the amount of combustible components such as miscellaneous gases contained in the air is very small. In this case, since the amount of the combustible component that reacts with the oxygen (O ₂ ) adsorbed on the surface of the gas detection layer 96 is very small, it is compared with the case where the detection target gas contains a combustible component such as methane (CH ₄ ). As a result, the electrical resistance of the gas detection layer 96 is less likely to decrease. In the second period ta2, combustible components such as miscellaneous gases contained in the air are likely to burn out, so the waveform 54 converges to the predetermined lower limit. This lower limit value of the waveform 54 is taken as the first reference value S1. FIG. 5A shows the first reference value S1.

FIG. 6 is a diagram showing an example of the relationship between the heating time and the output of the gas sensor 10 for gas B. In FIG. Gas B is, for example, carbon monoxide (CO). FIG. 6 shows the relationship between the heating time and the output of the gas sensor 10 for four concentrations of gas B (first concentration to fourth concentration). Also in this example, the concentration of the gas B is higher in order of the first concentration, the second concentration, the third concentration, and the fourth concentration. As in FIG. 5A, the solid line also shows the relationship between the heating time and the output of the gas sensor 10 when the gas is air.

In this example, the first concentration is 10 ppm to 50 ppm, the second concentration is 60 ppm to 140 ppm, the third concentration is 250 ppm to 350 ppm, and the fourth concentration is 400 ppm to 600 ppm. The first to fourth concentrations are, for example, 30 ppm, 100 ppm, 300 ppm and 500 ppm, respectively.

When the gas to be detected is the gas B, the reaction between the combustible components contained in the gas B and the oxygen adsorbed on the gas detection layer 96 is accelerated when the first period ta1 starts, so the output of the gas sensor 10 begins to decrease. . The output of the gas sensor 10 converges to a predetermined lower limit MNB (in the case of the fourth concentration) at time t1c', and levels off at the lower limit MNB after time t1c'. Note that the lower limit MNB may be different from the lower limit NMA.

Further, when the second period Ta2 starts, the reaction between the combustible component contained in the gas B and the oxygen adsorbed on the gas detection layer 96 is further promoted, so the output of the gas sensor 10 begins to further decrease, and at time t2m Indicates a local minimum. Combustible components contained in the gas B are likely to burn in the selective combustion layer 98 at the second temperature Tp<b>2 , so the components do not easily reach the gas detection layer 96 . Therefore, in the second period ta2, the output of the gas sensor 10 tends to asymptotically approach the output value (first reference value S1) of the waveform 54 (in the case of air).

FIG. 7 is a diagram showing an example of the relationship between the heating time and the output of the gas sensor 10 for gas C. In FIG. Gas C is, for example, hydrogen (H ₂ ). FIG. 7 also shows the relationship between the heating time and the output of the gas sensor 10 for four concentrations of gas C (first concentration to fourth concentration). Also in this example, the concentration of the gas C is higher in the order of the first concentration, the second concentration, the third concentration, and the fourth concentration. 5A and 6, the solid line also shows the relationship between the heating time and the output of the gas sensor 10 when the gas is air.

In this example, the first concentration is 300 ppm to 700 ppm, the second concentration is 800 ppm to 1200 ppm, the third concentration is 1500 ppm to 2500 ppm, and the fourth concentration is 3000 ppm to 5000 ppm. The first to fourth concentrations are, for example, 500 ppm, 1000 ppm, 2000 ppm and 4000 ppm, respectively.

When the gas to be detected is the gas C, the reaction between the combustible components contained in the gas C and the oxygen adsorbed to the gas detection layer 96 is accelerated when the first period ta1 starts, so the output of the gas sensor 10 begins to decrease. . In this example, the output of the gas sensor 10 continues to decrease during the first period ta1. Let the output of the gas sensor 10 at time t1 be MNC (in the case of the fourth concentration).

Note that the output of the gas sensor 10 may converge to a predetermined lower limit value during the first period ta1. In this case, assuming that the time at which the output of the gas sensor 10 converges to the lower limit is t1' (0<t1'<t1), the output of the gas sensor 10 continuously decreases from time 0 to less than time t1'. there is A predetermined output of the gas sensor 10 between time 0 and less than time t1' may be used as the MNC (fourth concentration). Also, in this case, the concentration of gas C may be determined based on the aforementioned converged lower limit.

When the second period ta2 starts, the reaction between the combustible components contained in the gas C and the oxygen adsorbed on the gas detection layer 96 is further promoted. As a result, the output of the gas sensor 10 begins to drop further and reaches a minimum value at time t2m'. Combustible components contained in the gas C are likely to burn in the selective combustion layer 98 at the second temperature Tp<b>2 , so the components are less likely to reach the gas detection layer 96 . Therefore, in the second period ta2, the output of the gas sensor 10 tends to asymptotically approach the output value (first reference value S1) of the waveform 54 (in the case of air).

The discrimination unit 20 (see FIG. 2) discriminates the type of gas to be detected based on the first waveform 42 and the second waveform 44 . 5A, 6 and 7, the first waveform 42 and the second waveform 44 differ depending on the type of gas to be detected. Therefore, the determination unit 20 can determine the type of detection target gas based on the first waveform 42 and the second waveform 44 . In this example, the discrimination unit 20 discriminates at least three types of detection target gases (gases A, B and C) based on the first waveform 42 and the second waveform 44 .

The determination unit 20 may determine the type of detection target gas based on whether or not the output value of the second waveform 44 converges to a predetermined first reference value S. As described above, the first reference value S is the convergence value of the output of the gas sensor 10 when the gas to be detected is air. As described with reference to FIG. 5A, when the output value of the second waveform 44 does not converge to the first reference value S1, the determination unit 20 can determine that the gas to be detected is gas A (eg, methane (CH ₄ )).

The determination unit 20 may determine the type of detection target gas based on whether or not the second waveform 44 has a minimum value. As described with reference to FIG. 5A, when the second waveform 44 levels off after a predetermined time (time tc2 in this example) and there is no minimum value, the determination unit 20 determines that the gas to be detected is gas A (for example, methane (CH ₄ )).

The determination unit 20 may determine the type of detection target gas based on the change rate of the output value of the first waveform 42 during the first period ta1. As described with reference to FIG. 7, when the gas to be detected is the gas C, the output of the gas sensor 10 does not converge to the lower limit value during the first period ta1. Therefore, the rate of change in output value from output MX to output MNC ((MX-MNC)/MX) is the rate of change for gas A ((MX-MNA)/MX) and for gas B There is a high probability that it is greater than the rate of change ((MX-MNB)/MX). Therefore, the determination unit 20 can determine the type of detection target gas based on the change rate of the output value of the first waveform 42 during the first period ta1.

FIG. 8 is a diagram showing a flowchart of determination of detection target gas by the determination unit 20 . In step S200, the determination unit 20 determines whether the output of the gas sensor 10 at time t2 in one detection timing is lower than the first reference value S1 (convergence value of the output of the gas sensor 10 in the case of air). When it is determined that the output of the gas sensor 10 is lower than the output for air, the discrimination unit 20 discriminates the gas to be detected as gas A (eg, methane (CH ₄ )). In this case, the determination unit 20 terminates the determination of the gas to be detected. If it is not determined that the output of the gas sensor 10 is lower than the output for air, the process proceeds to step S202.

In step S202, the determination unit 20 determines whether the output of the gas sensor 10 is lower than the output for air at time t1 at the detection timing next to the one detection timing described above. If it is determined that the output of the gas sensor 10 is lower than the output for air, the process proceeds to step S204. If it is not determined that the output of the gas sensor 10 is lower than the output for air, the determination unit 20 determines that the target gas does not contain the gas component to be detected (no gas). In this case, the determination unit 20 terminates the determination of the gas to be detected.

In step S204, the determination unit 20 determines whether the output of the gas sensor 10 in period ta1 converges to a predetermined lower limit value. When it is determined that the output of the gas sensor 10 converges to the predetermined lower limit value, the discrimination unit 20 discriminates the gas to be detected as gas B (for example, carbon monoxide (CO)). When it is determined that the output of the gas sensor 10 does not converge to the predetermined lower limit value, the discrimination unit 20 discriminates the detection target gas as gas C (for example, hydrogen (H ₂ )). The determination unit 20 may determine the type of detection target gas according to the flowchart shown in FIG. 8 at each intermittent detection timing.

The determination unit 20 may control the second period ta2 based on the first waveform 42. FIG. As described above, when the detection target gas is determined to be the gas C (for example, hydrogen (H ₂ )) in step S204 (during the first period ta1), the determination unit 20 finishes determination of the detection target gas. In this case, the second period ta2 may be long enough to burn and remove miscellaneous gases contained in the monitored object 300 . For this reason, the determination unit 20 may control the second period ta2 to a length that allows the miscellaneous gas to be burned and removed. The determination unit 20 may shorten the second period ta2 when determining that the gas to be detected is the gas C than the second period ta2 when determining that the gas other than the gas C is detected. When the determination unit 20 determines that the gas to be detected is the gas C in the first period ta1, the determination unit 20 may shorten the second period ta2 following the first period ta1. The second period ta2 may be 60 ms or more and 90 ms or less. The second period ta2 is, for example, 90 ms.

The determination unit 20 may control the second period ta2 based on the second waveform 44. FIG. As described above, when the gas to be detected is gas B (eg, carbon monoxide (CO)) or C (eg, hydrogen (H ₂ )), the output of gas sensor 10 asymptotically approaches first reference value S1 in second period ta2. . At time t2 (see FIGS. 6 and 7), the determination unit 20 determines whether the detection target gas is only air based on whether the gas sensor 10 detects gas B or C contained in the monitoring target 300. can be determined. When the gas sensor 10 detects gas B or C, the determination unit 20 determines that gas B or C remains in the monitored object 300 . In this case, the determination unit 20 may extend the second period ta2 so that the remaining gas B or C is burned off. The determination unit 20 may extend the second period ta2 even when the gas sensor 10 detects the gases B and C.

The determination unit 20 may control intermittent heating timing of the gas detection layer 96 based on at least one of the first waveform 42 and the second waveform 44 . The intermittent heating timing of the gas detection layer 96 refers to the period (T1+T2) (see FIG. 4). In the example of the intermittent heating timing shown in FIG. 4, when the discrimination unit 20 discriminates the type of the detection target gas at one detection timing, the detection target gas and the oxygen ( O ₂ ) reacts. Therefore, oxygen (O ₂ ) adsorbed on the gas detection layer 96 is temporarily separated from the gas detection layer 96 . In order for the discrimination unit 20 to discriminate the type of detection target gas at the next detection timing after the current detection timing, it is necessary for the gas detection layer 96 to adsorb a predetermined amount of oxygen (O ₂ ) again. If a predetermined amount of oxygen (O ₂ ) is not adsorbed to the gas detection layer 96 again, at the next detection timing, at least one of the first waveform 42 and the second waveform 44 is applied to the gas detection layer 96 by a predetermined amount. may differ from the waveform when oxygen (O ₂ ) is adsorbed. In this case, the discrimination unit 20 may not be able to discriminate the type of gas to be detected. Therefore, when the determination unit 20 cannot determine the type of detection target gas, the determination unit 20 may increase the period (T1+T2).

FIG. 9A is a diagram showing an example of the relationship between heating time and output of the gas sensor 10 for four gas species. FIG. 9A also shows an example of the relationship between the heating time of the gas sensor 10 and the output for gas D in addition to gases A, B, and C. FIG. The type of gas D is different from any of gases A, B and C. Gas D is, for example _, isobutane ( _C4H10 ). FIG. 9A shows the case of the fourth concentration in FIGS. 5A, 6 and 7 for gases A, B and C, respectively.

The concentration of gas D may be set according to the characteristics of gas sensor 10 . In this example, the concentration of gas D is 3000 ppm or more and 5000 ppm or less. The concentration of gas D is, for example, 4000 ppm.

Also, this example differs from the examples in FIGS. 5A, 6 and 7 in that the heating time further includes a third period ta3. The third period ta3 in this example is provided between the first period ta1 and the second period ta2. During the third period Ta3, the temperature of the heater layer 86 is set to the third temperature Tp3. The third temperature Tp3 may be set according to the type of gas to be detected. The third temperature Tp3 is higher than the first temperature Tp1 and lower than the second temperature Tp2. The third temperature Tp3 may be 300° C. or higher and 400° C. or lower. The third temperature Tp3 is 350° C., for example.

In the third period ta3, a third waveform 46 represents a change in the output of the gas sensor 10 for the detection target gases (gases A to D in this example) when the temperature of the heater layer 86 is the third temperature Tp3. In the third period ta3, a waveform 56 represents a waveform representing a change in the output of the gas sensor 10 when the temperature of the heater layer 86 is the third temperature Tp3.

When the gas to be detected is the gas D, the reaction between the combustible component contained in the gas D and the oxygen adsorbed to the gas detection layer 96 is accelerated when the first period ta1 starts, so the output of the gas sensor 10 is the gas A, Like B and C, it starts to decline. In the first period ta1, the output of the gas sensor 10 converges to a predetermined lower limit value.

When the third period ta3 starts, the reaction between the combustible component contained in each gas and the oxygen adsorbed in the gas detection layer 96 is further promoted for each of the gases A to D. Therefore, for each of the gases A to D, the output of the gas sensor 10 starts to further decrease from the lower limit value converged in the first period ta1.

When the detection target gases are gases A and D, the output of the gas sensor 10 converges to the predetermined lower limit value in the third period ta3. In FIG. 9A, MND is the lower limit value when the detection target gas is gas D, and t3c' is the time when the lower limit value MND is reached. When the detection target gases are gases B and C, the output of the gas sensor 10 shows a minimum value in the third period ta3. In FIG. 9A, the time when this minimum value occurs is indicated by t3c. The time for gas B and the time for gas C may be different. Since the combustible components contained in the gases B and C are likely to burn in the selective combustion layer 98 at the third temperature Tp3, the components do not easily reach the gas detection layer 96 . Therefore, after the output of the gas sensor 10 indicates a minimum value in the third period ta3, it tends to increase toward the output value (first reference value S1) of the waveform 54 (in the case of air).

When the gas to be detected is the gas D, the reaction between the combustible components contained in the gas D and the oxygen adsorbed on the gas detection layer 96 is promoted again when the second period ta2 starts following the third period ta3. Therefore, the output of the gas sensor 10 begins to decrease again and exhibits a minimum value MND2 at time t2m''. Since combustible components contained in the gas D are likely to burn in the selective combustion layer 98 at the second temperature Tp2, the components do not easily reach the gas detection layer 96 . Therefore, in the second period ta2, the output of the gas sensor 10 tends to asymptotically approach the output value (first reference value S1) of the waveform 54 (in the case of air).

FIG. 9B is a diagram summarizing trends of waveforms of gases A to D in the first period ta1, the third period ta3, and the second period ta2. The discrimination section 20 (see FIG. 2) may discriminate the type of detection target gas based on the first waveform 42 , the second waveform 44 and the third waveform 46 . The shapes of the waveforms of the gases A to D over the first period ta1, the third period ta3 and the second period ta2 are different for each of the gases A to D. For example, when the waveform shows a stable downward trend (converges to a predetermined lower limit) in the first period ta1 and the third period ta3, and then the waveform shows a minimum value in the second period ta2, the determination unit 20 The type of gas to be detected can be identified as gas D (for example, isobutane (C ₄ H ₁₀ )). Further, for example, when all of the waveforms of the first period ta1, the third period ta3, and the second period ta2 exhibit a decreasing and stable waveform (converge to a predetermined lower limit value), the discrimination unit 20 determines the type of the gas to be detected as gas. It can be identified as A (for example, methane (CH ₄ )). Further, for example, when the waveform shows a decreasing and stable trend (converges to a predetermined lower limit value) in the first period ta1, and then the waveform shows a minimum value in the third period ta3 and the second period ta2, the determining unit 20 can discriminate the type of gas to be detected as gas B (for example, carbon monoxide (CO)). Further, for example, after the waveform showing a downward trend in the first period ta1 (does not converge to a predetermined lower limit), when the waveform shows a minimum value in the third period ta3 and the second period ta2, the determination unit 20 can discriminate the type of gas to be detected as gas C (for example, hydrogen (H ₂ )).

FIG. 10 is a diagram showing another example of the relationship between the temperature of the heater layer 86 of the gas sensor 10 and time. In this example, the gas detection layer 96 is intermittently heated in the first period TT1 by the heater layer 86 set to the second temperature Tp2. Further, in this example, the discrimination unit 20 discriminates the type of detection target gas at each intermittent detection timing (first period TT1). The duration of the second temperature Tp2 is the second period ta2. In FIG. 10, the second period ta2 is indicated by ta2_1, ta2_2, .

In this example, the temperature of the heater layer 86 is not set to the first temperature Tp1 until the output of the gas sensor 10 at each intermittent detection timing converges to the first reference value S1. The first reference value S1 is the output value of the gas sensor 10 when the gas to be detected is air (see FIGS. 5A, 6 and 7).

In this example, the determination unit 20 acquires the second waveform 44 at each intermittent detection timing, and determines at each intermittent timing whether the output of the gas sensor 10 converges to the first reference value S1. The determination unit 20 may determine whether the output of the gas sensor 10 converges to the first reference value S1 at time t2 shown in FIGS. 5A, 6 and 7 .

When the determination unit 20 determines that the output of the gas sensor 10 has not converged to the first reference value S1, there is a high probability that at least one of the detection target gas and miscellaneous gas remains in the monitoring target 300 . In this case, the determination unit 20 may not be able to accurately detect the type of detection target gas at the next detection timing. In this case, the second period ta2 continues even at the next detection timing so that at least one of the detection target gas and the residual gas is burned and removed. The second periods ta2_1 to ta2_N−2 in FIG. 10 correspond to the second period ta2.

When the determination unit 20 determines that the output of the gas sensor 10 has converged to the first reference value S1, there is a high probability that the detection target gas and residual gas contained in the monitoring target 300 have been burned and removed. In this case, the determination unit 20 sets the first period ta1 at the next detection timing after the detection timing when it is determined that the output of the gas sensor 10 has converged to the first reference value S1. In FIG. 10, the second period ta2_N-1 is the detection timing at which the output of the gas sensor 10 converges to the first reference value S1, and the second period ta2_N is the detection timing at which the first period ta1 is set. In this example, the determination unit 20 determines the type of detection target gas based on the first waveform 42 and the second waveform 44 at the detection timings of the first period ta1 and the second period ta2_N.

FIG. 11 is a diagram showing another example of the relationship between the temperature of the heater layer 86 of the gas sensor 10 and time. In this example, the gas detection layer 96 is intermittently heated at the second period TT2 by the heater layer 86 set to the first temperature Tp1. Further, in this example, the discrimination unit 20 discriminates the type of detection target gas at each intermittent detection timing (second cycle TT2). The duration of the first temperature Tp1 is, for example, the first period ta1. In FIG. 11, the first period ta1 is indicated by ta1_1, ta1_2, . The second period TT2 may be equal to or different from the first period TT1.

In this example, at each intermittent detection timing, the temperature of the heater layer 86 is set to the second temperature Tp2 until the change rate of the output value of the gas sensor 10 reaches or exceeds the predetermined second reference value S2. not. The second reference value S2 may be set by adding or subtracting a predetermined margin to the rate of change in the output value from the output MX to the output MNC ((MX-MNC)/MX) described in FIG.

In this example, the determination unit 20 acquires the first waveform 42 at each intermittent timing, and determines at each intermittent timing whether the change rate of the output of the gas sensor 10 is greater than or equal to the second reference value S2. The determining unit 20 determines whether or not the rate of change in the output of the gas sensor 10 is greater than or equal to the second reference value S2 at each intermittent timing at time t1 shown in FIGS. 5A, 6 and 7. you can

When the determination unit 20 determines that the change rate of the output of the gas sensor 10 is equal to or greater than the second reference value S2, there is a probability that the detection target gas included in the monitoring target 300 is gas C (for example, hydrogen (H ₂ )). expensive. In this case, the determination unit 20 determines that the gas to be detected is the gas C, and terminates the determination of the gas to be detected (step S204 in FIG. 8). Therefore, the determination unit 20 does not need to set the second period ta2 following the first period ta1 at the detection timing when the gas C is detected. Therefore, the determination unit 20 may continue the first period ta1 while determining that the detection target gas is the gas C. In this case, the miscellaneous gas contained in the monitored object 300 is difficult to burn off at the first temperature Tp1, so the miscellaneous gas tends to remain in the monitored object 300 . The first periods ta1_1 to ta1_N−1 in FIG. 11 correspond to the second period ta2.

When the determination unit 20 determines that the change rate of the output of the gas sensor 10 is less than the second reference value S2, there is a probability that the detection target gas included in the monitoring target 300 is not the gas C (for example, hydrogen (H ₂ )). expensive. In this case, the determination unit 20 determines that the detection target gas is not gas C, and continues to determine the type of detection target gas. In this case, the determination unit 20 sets the second period ta2 following the first period ta1 to determine the type of detection target gas. The first period ta1_N in FIG. 11 corresponds to this first period ta1. In this example, the discrimination unit 20 discriminates the type of gas to be detected based on the first waveform 42 and the second waveform 44 at the detection timings of the first period taN and the second period ta2.

Note that the first period ta1 and the second period ta2 may be intermittently alternately set. The first period ta1 and the second period ta2 may be intermittently and randomly set.

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is obvious to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the description of the scope of claims that forms with such modifications or improvements can also be included in the technical scope of the present invention.

The execution order of each process such as actions, procedures, steps, and stages in the devices, systems, programs, and methods shown in the claims, the specification, and the drawings is particularly "before", "before etc., and it should be noted that they can be implemented in any order unless the output of the previous process is used in the subsequent process. Regarding the operation flow in the claims, the specification, and the drawings, even if the description is made using "first,""next," etc. for the sake of convenience, it means that it is essential to carry out in this order. not a thing
[Item 1]
A gas sensor having a gas detection layer whose output changes upon contact with a gas to be detected, and a heater layer for heating the gas detection layer;
a determination unit;
with
The determination unit is
a first waveform showing a change in the output of the gas sensor when the temperature of the heater layer is the first temperature;
a second waveform showing a change in the output of the gas sensor when the temperature of the heater layer is a second temperature different from the first temperature;
A gas detection device that determines the type of the detection target gas based on.
[Item 2]
The gas detection device according to item 1, wherein the discrimination section discriminates at least three types of the detection target gas based on the first waveform and the second waveform.
[Item 3]
3. The gas detection device according to item 1 or 2, wherein the discrimination section discriminates the type of the detection target gas based on a change rate of the output value of the first waveform in a predetermined first period.
[Item 4]
4. Any one of items 1 to 3, wherein the determination unit determines the type of the detection target gas based on whether or not the output value of the second waveform converges to a predetermined first reference value. The gas detection device according to .
[Item 5]
5. The gas detection device according to any one of items 1 to 4, wherein the determination unit determines the type of the detection target gas based on whether or not the second waveform has a minimum value.
[Item 6]
The determination unit is
the first waveform and the second waveform;
a third waveform showing a change in the output of the gas sensor when the temperature of the heater layer is a third temperature different from the first temperature and the second temperature;
5. The gas detection device according to any one of items 1 to 4, wherein the type of the gas to be detected is determined based on.
[Item 7]
7. The gas detection device according to any one of items 1 to 6, wherein the determination unit controls a predetermined second period of the second waveform based on the first waveform or the second waveform.
[Item 8]
The gas detection layer is heated intermittently by the heater layer,
8. The gas detection device according to any one of items 1 to 7, wherein the determination unit intermittently controls the timing based on at least one of the first waveform and the second waveform.
[Item 9]
the gas detection layer is heated in a first cycle by the heater layer set to the second temperature;
When the output of the gas sensor in a predetermined second period of the second waveform converges to a predetermined first reference value at any detection timing of the first period, the determination unit detects the first reference value. 8. The gas detection device according to any one of items 1 to 7, wherein the type of the gas to be detected is determined based on the first waveform and the second waveform.
[Item 10]
the gas detection layer is heated in a second cycle by the heater layer set to the first temperature;
If the rate of change of the output value in a predetermined first period of the first waveform is equal to or greater than a predetermined second reference value at any detection timing of the second period, the determining unit detects the 8. The gas detection device according to any one of items 1 to 7, wherein the type of the gas to be detected is determined based on the first waveform and the second waveform.

DESCRIPTION OF SYMBOLS 10... Gas sensor, 20... Discrimination part, 30... Power supply part, 42... 1st waveform, 44... 2nd waveform, 46... 3rd waveform, 52... Waveform, 54... Waveform, 56... Waveform, 80... Semiconductor substrate, 81... Thin film stack, 82... Thermal oxide film, 83... Nitride film, 84... Oxide film, 85 Insulating layer 86 Heater layer 88 Diaphragm 90 Gas sensing part 92 Junction layer 94 Electrode 96 Gas detection layer Selective combustion layer 100 Gas detection device 110 Constant voltage source 120 Voltmeter 200 Electric device 300 Monitoring object

Claims (13)

A gas sensor having a gas detection layer whose output changes upon contact with a gas to be detected, and a heater layer for heating the gas detection layer;
a determination unit;
with
The determination unit is
a first waveform showing a change in the output of the gas sensor when the temperature of the heater layer is the first temperature;
a second waveform showing a change in the output of the gas sensor when the temperature of the heater layer is a second temperature different from the first temperature;
A gas detection device that determines the type of the detection target gas based on. 2. The gas detection device according to claim 1, wherein said discrimination section discriminates at least three types of said detection target gas based on said first waveform and said second waveform. When the output value of the second waveform does not converge to a predetermined first reference value, the determination unit determines that the type of the detection target gas is the first type of the at least three detection target gases. 3. The gas detection device according to claim 2 , which discriminates a gas to be detected . The determination unit converges the output value of the second waveform to a predetermined first reference value, and the output value of the first waveform is the first reference value at the heating end time at the first temperature. 4. The method according to claim 2, wherein the type of the detection target gas is determined to be the second type or the third type of the detection target gas of the at least three types of the detection target gas when the detection target gas is lower than gas detector. When the output value of the first waveform converges to a predetermined lower limit value in a predetermined first period of the first waveform, the determination unit determines whether the type of the gas to be detected is the second detection target gas. 5. The gas detection device according to claim 4, wherein the type of gas to be detected is discriminated. wherein, in the first period, when the output value of the first waveform does not converge to the lower limit value, the determination unit determines that the type of the detection target gas is the third type of the detection target gas. Item 6. The gas detection device according to item 5. wherein the discrimination unit discriminates the type of the gas to be detected as the second type or the third type based on the rate of change of the output value in a predetermined first period of the first waveform. Item 5. The gas detection device according to item 4. The determination unit determines that the type of the detection target gas is the first type of the detection target gas among the at least three types of the detection target gas when the second waveform does not have a minimum value. 3. The gas detection device according to 2 . The determination unit is
the first waveform and the second waveform;
a third waveform showing a change in the output of the gas sensor when the temperature of the heater layer is a third temperature different from the first temperature and the second temperature;
9. The gas detection device according to any one of claims 1 to 8 , wherein the type of the gas to be detected is determined based on. The gas detection device according to any one of claims 1 to 9 , wherein the determination section controls a predetermined second period of the second waveform based on the first waveform or the second waveform. The gas detection layer is heated intermittently by the heater layer,
The gas detection device according to any one of claims 1 to 10 , wherein the determination unit intermittently controls the timing based on at least one of the first waveform and the second waveform. the gas detection layer is heated in a first cycle by the heater layer set to the second temperature;
When the output of the gas sensor in a predetermined second period of the second waveform converges to a predetermined first reference value at any detection timing of the first period, the determination unit detects the first reference value. The gas detection device according to any one of claims 1 to 10 , wherein the type of the gas to be detected is determined based on the first waveform and the second waveform. the gas detection layer is heated in a second period by the heater layer set to the first temperature;
If the rate of change of the output value in a predetermined first period of the first waveform is equal to or greater than a predetermined second reference value at any detection timing of the second period, the determining unit detects the The gas detection device according to any one of claims 1 to 10 , wherein the type of the gas to be detected is determined based on the first waveform and the second waveform.

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