JP6863102B2 - Gas sensors, gas alarms, control devices, and control methods - Google Patents

Description

The present invention relates to a gas sensor, a gas alarm, a control device, and a control method.

Conventionally, a gas detection method that executes preliminary detection and main detection according to the result of preliminary detection is known (see, for example, Patent Document 1). In Patent Document 1, the preliminary detection and the main detection are executed at different temperatures. Further, as a related technique, a technique is known that enables detection of three or more types of gas by controlling a gas sensor to at least three different temperatures and performing gas detection at different temperatures (for example,). See Patent Document 2).
[Prior art literature]
[Patent Document]
[Patent Document 1] Japanese Unexamined Patent Publication No. 2010-54213 [Patent Document 2] Japanese Unexamined Patent Publication No. 2005-134311

In the gas sensor, it is desirable to prevent the detection target gas from being determined to be present by reacting with a substance such as alcohol other than the detection target gas even though the detection target gas does not exist. Therefore, in the gas sensor, it is desirable to enhance the selectivity of the detection target gas for substances such as alcohol.

In the first aspect of the present invention, a gas sensor is provided. The gas sensor may have a gas sensing layer and a heater for heating the gas sensing layer. The gas sensor may detect the gas to be detected based on the resistance value of the gas sensing layer heated by the heater. The gas sensor may include a measuring unit, a heating control unit, a first acquisition unit, a second acquisition unit, a third acquisition unit, and a discrimination unit. The measuring unit may measure the resistance value of the gas sensing layer. The heating control unit may control the heater so as to heat the gas sensing layer. The first acquisition unit may acquire the first resistance value of the gas sensing layer. The first resistance value may be measured by the measuring unit in a state where the temperature of the gas sensing layer is controlled to the first temperature by the heating control unit. The second acquisition unit may acquire the second resistance value of the gas sensing layer when the first resistance value is equal to or less than a predetermined first threshold value. The second resistance value may be measured by the measuring unit in a state where the temperature of the gas sensing layer is controlled by the heating control unit to a second temperature lower than the first temperature. The third acquisition unit may acquire the third resistance value of the gas sensing layer when the second resistance value is equal to or less than a predetermined second threshold value. The third resistance value may be measured by the measuring unit in a state where the temperature of the gas sensing layer is controlled by the heating control unit to a third temperature higher than the second temperature. The discriminating unit may discriminate the existing gas type based on the third resistance value.

The discrimination unit may include a comparison unit. The comparison unit may compare the third resistance value with a predetermined third threshold value. The discriminating unit may discriminate the existing gas type based on the comparison result between the third resistance value and the third threshold value.

The detection target gas may be LP gas. When the third resistance value is equal to or higher than the third threshold value, the discriminating unit may determine that the detection target gas exists. When the third resistance value is smaller than the third threshold value, the discriminating unit may determine that a gas other than the detection target gas exists.

The detection target gas may be methane gas. When the third resistance value is equal to or less than the third threshold value, the discriminating unit may determine that the detection target gas exists. When the third resistance value is larger than the third threshold value, the discriminating unit may determine that a gas other than the detection target gas exists.

The gas other than the detection target gas may contain alcohol.

The determination unit may include a rate of change calculation unit. The rate of change calculation unit may calculate the rate of change over time of the third resistance value. The discriminating unit may discriminate the existing gas type by the time change rate of the third resistance value.

The detection target gas may be LP gas. When the time change rate of the third resistance value is equal to or higher than a predetermined change rate threshold value, the discriminating unit may determine that the detection target gas exists. When the time change rate of the third resistance value is smaller than the change rate threshold value, the discriminating unit may determine that a gas other than the detection target gas exists.

The detection target gas may be methane gas. When the time change rate of the third resistance value is equal to or less than a predetermined change rate threshold value, the discriminating unit may determine that the detection target gas exists. When the time change rate of the third resistance value is larger than the change rate threshold value, the detection target gas may be determined to have a gas other than the detection target gas.

The determination unit may include a timing detection unit. The timing detection unit may detect the timing at which the third resistance value starts to increase. The discriminating unit may discriminate the existing gas type according to the timing at which the third resistance value starts to increase.

The detection target gas may be LP gas. When the third resistance value starts to increase within a predetermined time, the discriminating unit may determine that the detection target gas exists. If the third resistance value is stagnant or lowered even after the elapse of a predetermined time, the discriminating unit may determine that a gas other than the detection target gas is present.

The detection target gas may be methane gas. If the third resistance value is stagnant or lowered even after the elapse of a predetermined time, the discriminating unit may determine that the detection target gas is present. When the third resistance value starts to increase within a predetermined time, the discriminating unit may determine that a gas other than the detection target gas exists.

The heating control unit may change the third temperature according to the second resistance value.

The third acquisition unit may change the timing of acquiring the third resistance value according to the second resistance value. The discriminating unit may change the third threshold value according to the second resistance value.

The heating control unit may change the second temperature according to the type of the detection target gas.

The heating control unit may change the third temperature according to the type of the detection target gas.

The third temperature may be higher than the first temperature. The gas alarm may include a gas sensor. The gas alarm may include an alarm generator. The alarm generating unit may generate an alarm when it detects the detection target gas.

In the second aspect of the present invention, a control device is provided. The control device may control the gas sensor. The gas sensor may have a gas sensing layer and a heater for heating the gas sensing layer. The gas sensor may detect the gas to be detected based on the resistance value of the gas sensing layer heated by the heater. The control device may include a heating control unit, a first acquisition unit, a second acquisition unit, a third acquisition unit, and a discrimination unit. The heating control unit may control the heater so as to heat the gas sensing layer. The first acquisition unit may acquire the first resistance value of the gas sensing layer. The first resistance value may be measured in a state where the temperature of the gas sensing layer is controlled to the first temperature by the heating control unit. The second acquisition unit may acquire the second resistance value of the gas sensing layer when the first resistance value is equal to or less than a predetermined first threshold value. The second resistance value may be measured in a state where the temperature of the gas sensing layer is controlled to a second temperature lower than the first temperature by the heating control unit. The third acquisition unit may acquire the third resistance value of the gas sensing layer when the second resistance value is equal to or less than a predetermined second threshold value. The third resistance value may be measured in a state where the temperature of the gas sensing layer is controlled to a third temperature higher than the second temperature by the heating control unit. The discriminating unit may discriminate the existing gas type based on the third resistance value.

In the third aspect of the present invention, a control method is provided. The control method may be a gas sensor control method. The gas sensor may have a gas sensing layer and a heater for heating the gas sensing layer. The gas sensor may detect the gas to be detected based on the resistance value of the gas sensing layer heated by the heater. The control method may include a first temperature control stage, a first acquisition stage, a second temperature control stage, a second acquisition stage, a third temperature control stage, a third acquisition stage, and a discrimination stage. In the first temperature control stage, the temperature of the gas sensing layer may be controlled to the first temperature. In the first acquisition stage, the first resistance value of the gas sensing layer may be acquired. The first resistance value may be measured in a state where the temperature of the gas sensing layer is controlled to the first temperature. In the second temperature control stage, when the first resistance value is equal to or less than a predetermined first threshold value, the temperature of the gas sensing layer may be controlled to a second temperature lower than the first temperature. In the second acquisition step, the second resistance value of the gas sensing layer may be acquired. The second resistance value may be measured in a state where the temperature of the gas sensing layer is controlled to the second temperature. In the third temperature control stage, when the second resistance value is equal to or less than a predetermined second threshold value, the temperature of the gas sensing layer may be controlled to a third temperature higher than the second temperature. In the third acquisition step, the third resistance value of the gas sensing layer may be acquired. The third resistance value may be measured in a state where the temperature of the gas sensing layer is controlled to the third temperature. In the discrimination step, the existing gas type may be discriminated based on the third resistance value acquired in the third acquisition step.

The outline of the above invention does not list all the necessary features of the present invention. Sub-combinations of these feature groups can also be inventions.

It is a figure which shows the outline of the gas sensor 100 of 1st Embodiment of this invention. It is sectional drawing which shows the schematic structure of the detection part 10. It is a figure which shows an example of the heater drive pattern when the 1st resistance value is larger than the 1st threshold value. It is a figure which shows an example of the heater drive pattern when the 2nd resistance value is larger than the 2nd threshold value. It is a figure which shows an example of the heater drive pattern when the 2nd resistance value is not more than 2nd threshold value. It is a figure which shows an example of the heater drive pattern when the 2nd resistance value is not more than the 2nd threshold value. It is a figure which shows an example of the resistance change of a gas sensing layer 12 when the heater 14 is driven to a high state. It is a figure which shows an example of the resistance change of the gas sensing layer 12 when the heater 14 is driven to the Low state. This is an example of a resistance change of the gas sensing layer 12 when the heater 14 is driven to a high state for 200 msec. It is a flowchart which shows an example of the processing content of the gas sensor 100 of 1st Embodiment of this invention. It is a flowchart which shows an example of the gas type discrimination process when the detection target gas is LP gas. It is a figure which shows an example of the gas type discrimination process when the detection target gas is methane gas. It is a figure which shows the gas sensitivity to LP gas and the gas sensitivity to methane gas. It is a flowchart which shows an example of the processing content of a gas sensor 100. It is a flowchart which shows an example of the processing content of a gas sensor 100. It is a figure which shows the outline of the gas sensor 100 of the 2nd Embodiment of this invention. It is a figure which shows an example of the time change rate in the resistance of a gas sensing layer 12 when the heater 14 is driven to a high state. It is a flowchart which shows an example of the gas type discrimination process when the detection target gas is LP gas. It is a flowchart which shows an example of the gas type discrimination process when the detection target gas is methane gas. It is a figure which shows the outline of the gas sensor 100 of the 3rd Embodiment of this invention. It is a flowchart which shows an example of the gas type discrimination process when the detection target gas is LP gas. It is a flowchart which shows an example of the gas type discrimination process when the detection target gas is methane gas.

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the inventions that fall within the scope of the claims. Also, not all combinations of features described in the embodiments are essential to the means of solving the invention.

FIG. 1 is a diagram showing an outline of a gas sensor 100 according to a first embodiment of the present invention. The gas sensor 100 of this example detects the gas to be detected. The detection target gas (abbreviated as “target gas”) may be a flammable gas. The target gas may be an LP gas containing propane and butane as main components. Alternatively, the target gas may be a city gas containing methane gas as a main component.

The gas sensor 100 of this example not only executes the detection at the first temperature T1 and the detection at the second temperature T2 lower than the first temperature T1, but also further, according to the detection result at the second temperature T2, the second The heater 14 is driven to a third temperature T3, which is higher than the temperature T2. That is, the gas sensor 100 of this example may drive the heater 14 in the order of the first temperature T1 (High), the second temperature T2 (Low), and the third temperature T3 (High) according to the detection result. Thereby, the target gas and the gas such as alcohol are distinguished.

The gas sensor 100 includes a detection unit 10 and a control device 200. The detection unit 10 includes a gas sensing layer 12 and a heater 14. The detection unit 10 of this example includes a temperature measurement unit 16 that measures the temperature of the heater 14. Unlike this example, the detection unit 10 does not have to include the temperature measurement unit 16. The gas sensing layer 12 is a sensor resistor whose resistance value changes depending on the gas. The heater 14 heats the gas sensing layer 12. The gas sensor 100 detects the target gas based on the resistance value of the gas sensing layer 12 heated by the heater 14.

The control device 200 controls the gas sensor 100. In this example, both the detection unit 10 and the control device 200 are built in the gas sensor 100. However, the control device 200 may be a control device externally attached to the gas sensor 100. The control device 200 may include a measurement unit 20, a heating control unit 30, an alarm generation unit 40, a first acquisition unit 50, a second acquisition unit 60, a third acquisition unit 70, a discrimination unit 80, and a storage unit 90. However, the alarm generation unit 40 is not necessarily indispensable for the control device 200. When the gas sensor 100 is a gas alarm, an alarm generation unit 40 may be provided.

At least a part of the heating control unit 30, the alarm generation unit 40, the first acquisition unit 50, the second acquisition unit 60, the third acquisition unit 70, and the discrimination unit 80 may be realized as a function of the microcomputer. The measuring unit 20 measures the electric resistance value of the gas sensing layer 12. For example, the measuring unit 20 passes a current through the gas sensing layer 12 to measure the voltage across the gas sensing layer 12. Measuring the resistance value of the gas sensing layer 12 may include measuring electrical properties such as voltage or current associated with the resistance value of the gas sensing layer 12. Acquiring the measured resistance value may include acquiring electrical properties such as voltage or current associated with the resistance value. Comparing a resistance value to a threshold may include comparing the voltage or current associated with the resistance value to the threshold. In one example, the resistance value of the gas sensing layer 12 being larger than the threshold value may include that the voltage across the gas sensing layer 12 is larger than the threshold value, and the current flowing through the gas sensing layer 12 is smaller than the threshold value. May be included. The fact that the resistance value of the gas sensing layer 12 is smaller than the threshold value may include that the voltage across the gas sensing layer 12 is smaller than the threshold value and that the current flowing through the gas sensing layer 12 is larger than the threshold value. Good.

The heating control unit 30 controls the voltage applied to the heater 14. In particular, the heating control unit 30 controls the heater 14 so that the temperature of the gas sensing layer 12 becomes the first temperature T1 in the first detection process. When there is a possibility that the target gas may be present in the first detection process, the heating control unit 30 sets the temperature of the gas sensing layer 12 to be the second temperature T2 lower than the first temperature T1 in the second detection process. Controls the heater 14. Further, when there is a possibility that the target gas may be present as a result of the second detection process, the heating control unit 30 sets the temperature of the gas sensing layer 12 to be higher in order to increase the selectivity of the target gas with respect to the gas such as alcohol. The heater 14 is controlled so that the third temperature T3 is higher than the two temperature T2.

The alarm generation unit 40 issues an alarm when the target gas is detected. The first acquisition unit 50 acquires the first resistance value of the gas sensing layer 12. The second acquisition unit 60 acquires the second resistance value of the gas sensing layer 12. The third acquisition unit 70 acquires the third resistance value of the gas sensing layer 12.

The first resistance value is the electric resistance value of the gas sensing layer 12 measured by the measuring unit 20 in a state where the temperature of the gas sensing layer 12 is controlled by the heating control unit 30 to the first temperature T1. The second resistance value is the electric resistance value of the gas sensing layer measured by the measuring unit 20 in a state where the temperature of the gas sensing layer 12 is controlled by the heating control unit 30 to the second temperature T2 which is lower than the first temperature T1. .. The third resistance value is the electric resistance value of the gas sensing layer measured by the measuring unit 20 in a state where the temperature of the gas sensing layer 12 is controlled by the heating control unit 30 to the third temperature T3 higher than the second temperature T2. ..

The first temperature T1 and the third temperature T3 are higher temperatures than the second temperature T2. The heating control unit 30 drives the heater 14 to a high state and controls the temperature of the gas sensing layer 12 to be the first temperature T1 or the third temperature T3. The first temperature T1 and the third temperature T3 may be preferably 400 ° C. or higher and 500 ° C. or lower, and more preferably 400 ° C. or higher and 450 ° C. or lower. On the other hand, the second temperature T2 is lower than the first temperature T1 and the third temperature T3. The heating control unit 30 drives the heater 14 to the Low state and controls the temperature of the gas sensing layer 12 to be the second temperature T2. The second temperature T2 is preferably 250 ° C. or higher and 350 ° C. or lower.

The discriminating unit 80 discriminates the existing gas type based on the third resistance value. The discrimination unit 80 in this example includes a comparison unit 82. The comparison unit 82 compares the third resistance value with a predetermined third threshold value. The discriminating unit 80 discriminates the existing gas type based on the comparison result between the third resistance value and the third threshold value. The storage unit 90 may store information or parameters necessary for the heating control unit 30 to control the heater 14.

FIG. 2 is a cross-sectional view showing a schematic configuration of the detection unit 10. The detection unit 10 of this example is a semiconductor type thin film gas sensor. The detection unit 10 of this example includes a silicon substrate 2, a heat insulation support layer 3, a heater layer that functions as a heater 14, an electrical insulation layer 4, and a gas detection unit 5. The silicon substrate 2 is provided with a through hole 6. The through hole 6 constitutes a diaphragm structure. The gas detection unit 5 includes a bonding layer 7, a gas sensing layer electrode 8, a gas sensing layer 12, and a selective combustion layer 9. The gas sensing layer 12 is formed as a sensing layer containing metal oxides such as _{SnO 2} , In ₂ O ₃ , WO ₃ , ZnO, and TiO _{2 as main components.}

The selective combustion layer 9 is a sintered body carrying at least one catalyst such as Pd, PdO, and Pt. The selective combustion layer 9 is also called a catalyst layer. In one example, the selective combustion layer 9 is a catalyst-supported Al ₂ O ₃ sintered body, and is mainly composed of metal oxides such as _{Cr 2} O ₃ , Fe ₂ O ₃ , Ni ₂ O ₃ , ZrO ₂ , SiO _{2, and zeolite.} It may be formed as a component. The silicon substrate 2 is composed of a silicon wafer. The heater 14 heats the gas detection unit 5. The detection unit 10 detects the target gas by the resistance value of the gas sensing layer 12 when the gas sensing layer 12 is heated by the heater 14.

Next, the driving of the heater 14 by the heating control unit 30 will be described. FIG. 3 is a diagram showing an example of a heater drive pattern when the first resistance value is larger than the first threshold value. The heating control unit 30 intermittently drives the heater 14. The heating control unit 30 periodically applies a pulsed voltage to the heater 14 as a heater drive voltage. The heating control unit 30 may apply a pulsed voltage to the heater 14 at a period P of 30 seconds or more and 60 seconds or less.

The heating control unit 30 controls the temperature of the gas sensing layer 12 to the first temperature T1 (High). The voltage to be applied to the heater 14 may be preset in order to set the temperature of the gas sensing layer 12 to the first temperature T1. The heating control unit 30 may apply a preset voltage to the heater 14. The heating control unit 30 may maintain the temperature of the gas sensing layer 12 at the first temperature T1 for a predetermined heating time. In one example, the heating time in the first detection process may be 30 msec to 100 msec, more preferably 40 msec or more and 90 msec.

The first acquisition unit 50 acquires the first resistance value of the gas sensing layer 12 measured by the measuring unit 20 in a state where the temperature of the gas sensing layer 12 is controlled by the heating control unit 30 to the first temperature T1. The resistance value of the gas sensing layer 12 is acquired at any time from the start of heating until, for example, 100 msec elapses. In particular, the first resistance value may be acquired when 40 msec or more and 90 msec elapses from the start of heating to the first temperature T1.

In one example, the measuring unit 20 constantly measures the electrical resistance value of the gas sensing layer 12. The first acquisition unit 50 samples and AD-converts (analog-digital conversion) the measurement result by the measuring unit 20 at the timing when the temperature of the gas sensing layer 12 is controlled to the first temperature T1. 1 The resistance value may be acquired. The second acquisition unit 60 may have the same configuration.

The heating control unit 30 executes the first determination. The first determination is a determination as to whether or not the first resistance value is equal to or less than a predetermined first threshold value. However, the first determination may be executed by a control unit other than the heating control unit 30. When the first resistance value is larger than the first threshold value, the heating control unit 30 stops energizing the heater 14 as shown in FIG. 3, assuming that the target gas is not detected. Therefore, the heating time can be shortened and power saving can be realized.

FIG. 4 is a diagram showing an example of a heater drive pattern when the second resistance value is larger than the second threshold value. When the first resistance value is equal to or less than the first threshold value, the heating control unit 30 controls the temperature of the gas sensing layer 12 to a second temperature T2 (Low) lower than the first temperature T1 as shown in FIG. .. The heating control unit 30 may maintain the temperature of the gas sensing layer 12 at the second temperature T2 for a predetermined heating time. In one example, the heating time in the second detection process may be 160 msec or more and 200 msec or less.

The second acquisition unit 60 acquires the second resistance value of the gas sensing layer 12 measured by the measuring unit 20 in a state where the temperature of the gas sensing layer 12 is controlled by the heating control unit 30 to the second temperature T2. The resistance value of the gas sensing layer 12 is acquired at any time from the start of heating to, for example, 200 msec. In particular, the second resistance value may be acquired when 160 msec or more and 200 msec elapses from the start of heating to the second temperature T2.

The heating control unit 30 executes the second determination. The second determination is a determination as to whether or not the second resistance value is equal to or less than a predetermined second threshold value. However, the second determination may be executed by a control unit other than the heating control unit 30. When the second resistance value is larger than the second threshold value, the heating control unit 30 stops energizing the heater 14 as shown in FIG. 4, assuming that the target gas is not detected. Therefore, the heating time is shortened, and power saving can be realized.

FIG. 5 is a diagram showing an example of a heater drive pattern when the second resistance value is equal to or less than the second threshold value. In the case of the control of the preliminary detection in the general High state and the main detection in the Low state, if the second resistance value is equal to or less than the second threshold value, it is determined that the target gas has been detected. On the other hand, unlike this case, the gas sensor 100 of this example further executes control for improving the selectivity with alcohol or the like other than the target gas. Specifically, when the second resistance value is equal to or less than the second threshold value, the heating control unit 30 sets the temperature of the gas sensing layer 12 higher than the second temperature T2 at the third temperature T3 (as shown in FIG. 5). High) is controlled.

The heating control unit 30 may maintain the temperature of the gas sensing layer 12 at the third temperature T3 for a predetermined heating time. For example, the heating time is 160 msec or more and 200 msec. The third acquisition unit 70 acquires the third resistance value of the gas sensing layer 12 measured by the measuring unit 20 in a state where the temperature of the gas sensing layer 12 is controlled by the heating control unit 30 to the third temperature T3. The third resistance value of the gas sensing layer 12 is acquired at any time from the start of driving the heater 14 to the high state again and the start of heating, for example, up to 200 msec. In particular, the third resistance value may be acquired when 160 msec or more and 200 msec elapses from the start of heating to the third temperature T3.

The discriminating unit 80 discriminates the existing gas type based on the third resistance value. The discrimination unit 80 in this example includes a comparison unit 82. The comparison unit 82 compares the third resistance value with a predetermined third threshold value. The discriminating unit 80 discriminates the existing gas type based on the comparison result between the third resistance value and the third threshold value.

In the example shown in FIG. 5, the first temperature T1 and the third temperature T3 are the same. However, the gas sensor 100 of this example is not limited to this case. FIG. 6 is a diagram showing an example of a heater drive pattern when the second resistance value is equal to or less than the second threshold value. As shown in FIG. 6, the third temperature T3 may be higher than the first temperature T1. By setting the third temperature T3 higher than the first temperature T1, the selectivity between the target gas and alcohol can be further enhanced.

The gas sensor 100 of this example switches the heater drive pattern as shown in FIGS. 3, 4, and 5 according to the values of the first resistance value and the second resistance value. Therefore, the overall heating time can be shortened as compared with the case where the temperatures are always controlled to the first temperature T1, the second temperature T2, and the third temperature T3.

FIG. 7 is a diagram showing an example of a change in resistance of the gas sensing layer when the heater 14 is driven to a high state. FIG. 7 shows the measurement results when the temperature of the gas sensing layer 12 is maintained at the first temperature T1. Specifically, FIG. 7 shows the measurement results when the temperature of the gas sensing layer 12 is 430 ° C. In FIG. 7, the atmosphere in which the detection unit 10 of the gas sensor 100 is placed is the atmosphere (displayed as Air), LP gas (displayed as LP. Isobutane, etc.), hydrogen gas (displayed as H2), ethanol (displayed as ETOH). ), And the case of methane gas (denoted as CH4) are shown.

As shown in FIG. 7, the resistance value of the gas sensing layer 12 is lower when any gas other than the atmosphere is present as compared with the case of the atmosphere. In the atmosphere, the resistance value of the gas sensing layer 12 stabilizes about 40 msec after the start of heating. On the other hand, in LP gas and hydrogen gas, the resistance value of the gas sensing layer 12 decreases significantly as compared with the case of the atmosphere, and then starts to increase in about 40 ms and gradually increases in the resistance value of the gas sensing layer 12 in the atmosphere. Approaching. In alcohol such as ethanol, the resistance value of the gas sensing layer 12 gradually decreases. Even in methane gas, the resistance value of the gas sensing layer 12 gradually decreases.

Therefore, for example, in the time range of 30 msec to 100 msec after the start of heating, there is a difference between the resistance value of the gas sensing layer 12 in the atmosphere and the resistance value of the gas sensing layer 12 in each gas. .. Therefore, the presence or absence of gas can be determined based on the resistance value of the gas sensing layer 12. Specifically, the first threshold value L1 is set so as to have a value that can distinguish between the case of being in the atmosphere and the case of being present in any gas other than the atmosphere. In this example, the first threshold value L1 is set between 40 kΩ and 100 kΩ. However, since the threshold value differs depending on the detection unit 10, the threshold value is not limited to this case.

The first resistance value of the gas sensing layer 12 measured by the measuring unit 20 in a state where the temperature of the gas sensing layer 12 is controlled by the heating control unit 30 to the first temperature T1 is compared with the first threshold value L1. When the first resistance value is larger than the first threshold value L1, the heating control unit 30 stops energizing the heater 14 on the assumption that any gas other than the atmosphere is not detected. On the other hand, when the first resistance value is equal to or less than the first threshold value L1, the target gas may be detected. Therefore, the heating control unit 30 controls the temperature of the gas sensing layer 12 to the second temperature T2, which is lower than the first temperature T1, so that the resistance of the gas sensing layer 12 easily changes depending on the concentration of the target gas.

FIG. 8 is a diagram showing an example of a change in resistance of the gas sensing layer when the heater is driven to the Low state. FIG. 8 shows the measurement results when the temperature of the gas sensing layer 12 is maintained at the second temperature T2. Specifically, FIG. 8 shows the measurement results when the temperature of the gas sensing layer 12 is 330 ° C. The gas species shown in FIG. 8 are the same as the gas species shown in FIG.

In the atmosphere, the resistance value of the gas sensing layer 12 stabilizes about 60 msec after the start of heating. Further, in hydrogen gas, the resistance value of the gas sensing layer 12 is significantly reduced as compared with the case in the atmosphere, and then gradually approaches the resistance value in the atmosphere. The resistance value of the gas sensing layer 12 gradually decreases in the case of LP gas, alcohol such as ethanol, and methane gas, respectively.

Therefore, for example, in the time range of 160 msec to 200 msec after the start of heating in the Low state, the resistance value of the gas sensing layer 12 in the case of LP gas and the case of alcohol and the gas sensing layer in hydrogen gas There is a difference from the resistance value of. Therefore, it is possible to distinguish whether the existing gas is hydrogen gas based on the resistance value of the gas sensing layer.

The difference between the resistance value of the gas sensing layer 12 in the case of methane gas and the resistance value of the gas sensing layer 12 in the case of hydrogen gas increases as the heating time increases. Therefore, when the target gas is methane gas, the timing of acquiring the second resistance value may be delayed as compared with the case where the target gas is LP gas. In this example, the second threshold value L2 (L2') is set between 30 kΩ and 300 kΩ. In the temperature range shown in FIG. 8, the resistance value of the gas sensing layer 12 in methane gas is higher than the resistance value of the gas sensing layer 12 in LP gas. Therefore, the second threshold value L2'when the target gas is methane gas may be set to a value higher than the second threshold value L2 when the target gas is LP gas.

The second resistance value of the gas sensing layer 12 is compared with the second threshold value L2. When the second resistance value is larger than the second threshold value L2, the existing gas is a miscellaneous gas such as hydrogen gas, not a target gas. Therefore, the heating control unit 30 stops energizing the heater 14. On the other hand, when the second resistance value is equal to or less than the second threshold value L2, there is a possibility that the target gas exists. The heating control unit 30 of this example controls the temperature of the gas sensing layer 12 to be a third temperature T3 higher than the second temperature T2 in order to select and detect the target gas with respect to alcohol such as methanol. ..

FIG. 9 is an example of a resistance change of the gas sensing layer when the heater is driven to the high state for 200 msec. FIG. 9 shows the measurement results when the temperature of the gas sensing layer 12 is maintained at the third temperature T3. Specifically, FIG. 9 shows the measurement results when the temperature of the gas sensing layer 12 is 430 ° C.

As described in FIG. 7, in the atmosphere, the resistance value of the gas sensing layer 12 stabilizes when about 40 msec has elapsed after the start of heating. On the other hand, in the case of LP gas (isobutane or the like) and the case of hydrogen gas, the resistance value of the gas sensing layer 12 decreases significantly as compared with the case of the atmosphere, and then starts to increase around 40 msec and gradually increases to the atmosphere. It approaches the resistance value of the gas sensing layer 12 inside. In alcohol such as ethanol, the resistance value of the gas sensing layer 12 gradually decreases, and the resistance value of the gas sensing layer 12 gradually increases from about 100 msec after the start of heating.

In the case of LP gas, the rate of increase in the resistance value of the gas sensing layer 12 with the passage of the heating time is larger than that in the case of alcohol. Due to the difference in the rate of increase, for example, in the time range of 160 msec or more and 200 msec after the start of heating, the resistance value of the gas sensing layer 12 in LP gas and the resistance value of the gas sensing layer 12 in alcohol. There is a difference between and. Specifically, the resistance value of the gas sensing layer 12 in LP gas is higher than the resistance value of the gas sensing layer 12 in alcohol. A third threshold value L3 may be set between the resistance value of the gas sensing layer 12 in LP gas and the resistance value of the gas sensing layer 12 in alcohol.

The discrimination unit 80 can discriminate whether the existing gas is LP gas or alcohol based on the resistance value of the gas sensing layer 12. The comparison unit 82 may compare the third resistance value of the gas sensing layer 12 with the third threshold value L3. When the target gas is LP gas, the discriminating unit 80 may determine that LP gas, which is the target gas, is present when the third resistance value is equal to or higher than the third threshold value. On the other hand, the discrimination unit 80 may determine that a gas other than the target gas exists when the third resistance value is smaller than the third threshold value. Specifically, when the third resistance value is smaller than the third threshold value, the discriminating unit 80 may determine that a gas containing alcohol is present. Therefore, when the target gas is LP gas, the target gas can be detected separately from miscellaneous gases such as alcohol.

In the case of methane gas, the resistance value of the gas sensing layer 12 is unlikely to change in the time range from 40 msec to 200 msec after decreasing to 40 msec after the start of heating. On the other hand, in the case of alcohol such as ethanol, the resistance value of the gas sensing layer 12 gradually increases from around 100 msec after the start of heating. Therefore, for example, in the time range 160 msec after the start of heating, there is a difference between the resistance value of the gas sensing layer 12 in methane gas and the resistance value of the gas sensing layer 12 in alcohol. Specifically, the resistance value of the gas sensing layer 12 in methane gas is lower than the resistance value of the gas sensing layer 12 in alcohol. Therefore, when methane gas is the target gas, a third threshold value L3'may be set between the resistance value of the gas sensing layer 12 in methane gas and the resistance value of the gas sensing layer 12 in alcohol.

The discrimination unit 80 can discriminate whether the existing gas is methane gas or alcohol based on the resistance value of the gas sensing layer 12. The comparison unit 82 may compare the third resistance value of the gas sensing layer 12 with the third threshold value L3. When the third resistance value is equal to or less than the third threshold value, the discriminating unit 80 may determine that methane gas, which is the target gas, is present. On the other hand, when the third resistance value is larger than the third threshold value, the discrimination unit 80 may determine that a gas other than the target gas exists. Specifically, when the third resistance value is larger than the third threshold value, the discriminating unit 80 may determine that a gas containing alcohol is present. Therefore, when the target gas is methane gas, the target gas can be detected separately from miscellaneous gases such as alcohol.

The third resistance value measured at the third temperature T3 is used to distinguish the alcohol from the target gas, while the second temperature T2 is used to determine the concentration of the target gas in order to increase the gas sensitivity. The second resistance value measured in may be used. For example, when the target gas is LP gas, it is advantageous to use the resistance value measured at a third temperature of 400 ° C. or higher for distinguishing between alcohol and the target gas, but the temperature is 400 ° C. or higher. In that case, the sensitivity to the target gas (the amount of change in the resistance value with respect to the gas concentration) becomes low, which is disadvantageous for determining the concentration of the target gas. Therefore, when it is determined that the target gas is LP gas instead of alcohol, the concentration of the target gas is determined by using the second resistance value measured at the second temperature of around 330 ° C., which has high gas sensitivity. Good. This makes it possible to increase the selectivity for alcohol while maintaining the detection sensitivity of the gas. On the other hand, when the target gas is methane gas, the gas sensitivity is higher when the temperature is the third temperature than when the temperature is the second temperature. Therefore, the third resistance value measured at the third temperature is used. Not only the alcohol and the target gas may be discriminated, but also the concentration of the target gas may be determined.

FIG. 10 is a flowchart showing an example of the processing content of the gas sensor 100 according to the first embodiment of the present invention. FIG. 10 shows an example of a control method of the gas sensor 100. The heating control unit 30 applies a voltage to the heater 14 to control the heater 14 so that the temperature of the gas sensing layer 12 becomes the first temperature T1 (step S101). The process of step S101 corresponds to the first temperature control step of controlling the temperature of the gas sensing layer 12 to the first temperature T1. The process of step S101 may also serve as a process of cleaning the gas sensing layer 12.

The first acquisition unit 50 acquires the first resistance value of the gas sensing layer 12 (step S102). The process of step S102 corresponds to the first acquisition step of acquiring the first resistance value of the gas sensing layer 12 measured in a state where the temperature of the gas sensing layer 12 is controlled to the first temperature T1.

The heating control unit 30 determines whether the first resistance value is equal to or less than the first threshold value L1 (step S103). When the first resistance value is larger than the first threshold value L1 (step S103: NO), it is considered that the target gas does not exist, so that the heating control unit 30 stops the energization of the heater 14 and turns the heater 14 on. Turn off (step S110). Therefore, when the first resistance value is larger than the first threshold value L1 and there is no gas other than the atmosphere, the heating can be stopped immediately. As a result, power consumption can be reduced.

When the first resistance value is equal to or less than the first threshold value L1 (step S103: YES), there is a possibility that some gas is present. Therefore, the heating control unit 30 controls the heater 14 so that the temperature of the gas sensing layer 12 becomes the second temperature T2 (step S104). The second temperature T2 is lower than the first temperature T1. In particular, the second temperature T2 may be 250 ° C. or higher and 350 ° C. or lower. The second temperature T2 may be set in a temperature region in which the gas sensitivity of the target gas is higher than that in the case of the first temperature T1. For example, when the target gas is LP gas, the gas sensitivity of the second temperature T2 of 250 ° C. or higher and 350 ° C. or lower is higher than that of the first temperature T1 of 400 ° C. or higher and 500 ° C. or lower. Therefore, the concentration of the target gas can be accurately determined by measuring the resistance value at the second temperature T2. As a result, the target gas can be reliably detected in a predetermined concentration range. Further, the heating control unit 30 may change the second temperature T2 according to the type of the target gas, as will be described later. The process of step S104 corresponds to a second temperature control step of controlling the temperature of the gas sensing layer 12 to a second temperature T2 lower than the first temperature T1 when the first resistance value is equal to or less than a predetermined first threshold value. To do.

The second acquisition unit 60 acquires the second resistance value of the gas sensing layer 12 (step S105). The second acquisition unit 60 acquires, for example, the resistance value of the gas sensing layer 12 measured in the time region of 160 msec or more and 200 msec or less after the start of heating as the second resistance value. The process of step S105 corresponds to the second acquisition step of acquiring the second resistance value of the gas sensing layer 12 measured in a state where the temperature of the gas sensing layer 12 is controlled to the second temperature T2.

The heating control unit 30 determines whether the second resistance value is equal to or less than the second threshold value L2 (step S106). When the second resistance value is larger than the second threshold value L2 (step S106: NO), it is considered that the target gas does not exist. Therefore, the heating control unit 30 stops the energization of the heater 14 and turns off the heater 14 (step S110). As a result, when the second resistance value is larger than the second threshold value L2 and there is no gas other than the atmosphere, the heating is immediately stopped and the power consumption is reduced.

When the second resistance value is equal to or less than the second threshold value L2 (step S106: YES), the target gas may be present. The target gas may be LP gas or methane gas. However, for example, depending on the concentration of LP gas and the concentration of alcohol or the like, the resistance value of the gas sensing layer 12 in LP gas and the resistance value of the gas sensing layer 12 in alcohol are similar. Therefore, it may be difficult to determine the gas type based on the second resistance value.

Therefore, in this example, when the second resistance value is equal to or less than the second threshold value L2 (step S106: YES), the heating control unit 30 heats the gas sensing layer 12 so that the temperature of the gas sensing layer 12 becomes the third temperature T3. 14 is controlled (step S107). The process of step S107 corresponds to a third temperature control step of controlling the temperature of the gas sensing layer 12 to a third temperature T3 higher than the second temperature T2 when the second resistance value is equal to or less than a predetermined second threshold value. To do.

The third temperature T3 may be 400 ° C. or higher and 500 ° C. or lower, and more preferably 400 ° C. or higher and 450 ° C. or lower. When the target gas is LP gas, if the third temperature T3 is set lower than 400 ° C., the LP gas cannot be completely desorbed and the LP gas remains in the gas sensing layer 12 or the like. Therefore, the resistance value of the gas sensing layer 12 with the heating time remains low, and it becomes difficult to distinguish between LP gas and alcohol. When the target gas is methane gas, if the third temperature T3 is set lower than 400 ° C., the resistance value in alcohol such as ethanol remains low, and it may be difficult to distinguish between methane gas and alcohol. On the other hand, if the third temperature T3 is higher than 500 ° C., the detection unit 10 may be deteriorated.

The third acquisition unit 70 acquires the third resistance value of the gas sensing layer 12 (step S108). The third acquisition unit 70 acquires, for example, the resistance value of the gas sensing layer 12 measured in the time region of 160 msec or more and 200 msec or less after the start of heating as the third resistance value. The process of step S108 corresponds to the third acquisition step of acquiring the third resistance value of the gas sensing layer 12 measured in a state where the temperature of the gas sensing layer 12 is controlled to the third temperature T3.

The discrimination unit 80 executes a gas type discrimination process for discriminating the gas type based on the third resistance value (step S109). The process of step S109 corresponds to the discrimination step of discriminating the existing gas type based on the third resistance value acquired in the third acquisition step (step S108). The heating control unit 30 stops energizing the heater 14 and turns off the heater 14 (step S110). For example, the heating control unit 30 waits for the heater drive cycle P of 30 seconds or more and 60 seconds or less to elapse (step S111: YES) so that the temperature of the gas sensing layer 12 becomes the first temperature T1 again. The heater 14 is controlled (step S101).

FIG. 11 is a flowchart showing an example of gas type discrimination processing when the target gas is LP gas. FIG. 11 is an example of the process of step S109 of FIG. The comparison unit 82 compares the third resistance value with the predetermined third threshold value L3 (step S201). When the third resistance value is equal to or higher than the third threshold value L3 (step S201: YES), it is considered that the target gas actually exists, not the influence of the miscellaneous gas containing alcohol, as described in FIG. Therefore, the discriminating unit 80 determines that LP gas is present (step S202).

On the other hand, when the third resistance value is smaller than the third threshold value L3 (step S201: NO), it is determined that the gas containing alcohol exists (step S203). When it is determined that LP gas is present, the alarm generation unit 40 issues a gas leak alarm (step S204). On the other hand, when it is determined that the gas containing alcohol is present, the alarm generation unit 40 may return without issuing a gas leak alarm.

FIG. 12 is a flowchart showing an example of the gas type discrimination process when the target gas is methane gas. FIG. 12 is an example of the process of step S109 of FIG. The comparison unit 82 compares the third resistance value with the predetermined third threshold value L3'(step S301). When the third resistance value is equal to or less than the third threshold value L3'(step S301: YES), as described in FIG. 9, it is considered that the target gas actually exists, not the influence of the miscellaneous gas containing alcohol. .. Therefore, the discriminating unit 80 determines that methane gas is present (step S302).

On the other hand, when the third resistance value is larger than the third threshold value L3'(step S301: NO), it is determined that the gas containing alcohol exists (step S303). When it is determined that methane gas is present, the alarm generation unit 40 issues a gas leak alarm (step S304). On the other hand, when it is determined that the gas containing alcohol is present, the alarm generation unit 40 may return without issuing a gas leak alarm.

As described above, according to the control method of this example, when the first resistance value is equal to or less than the first threshold value L1 (step S103: YES in FIG. 10) and the second resistance value is equal to or less than the second threshold value L2. Only in (step S105: YES in FIG. 10), the process of holding the temperature of the gas sensing layer 12 at the third temperature T3 (step S107 and step S108) is executed. Therefore, in each cycle P, the power consumption can be reduced as compared with the case of executing the process of holding the temperature of the gas sensing layer 12 at the third temperature T3 for a relatively long time.

According to the control method of this example, the heater drive pattern is switched as shown in FIGS. 3, 4, and 5 according to the values of the first resistance value and the second resistance value. Therefore, in each cycle P, the overall heating time can be shortened as compared with the case where the temperatures are always controlled to the first temperature T1, the second temperature T2, and the third temperature T3. Therefore, the power consumption can be reduced.

When the second resistance value is equal to or less than the second threshold value L2, the gas sensor 100 of this example does not immediately conclude that the target gas exists, and further executes the gas discrimination process. Therefore, the selectivity of the target gas with respect to the gas such as alcohol is enhanced. Therefore, it is possible to reduce the possibility that the alarm generating unit 40 issues an alarm even though the target gas does not exist.

In the gas sensor 100 of this example, the heating control unit 30 may change the second temperature T2 according to the type of the target gas. Further, the heating control unit 30 may change the third temperature T3 according to the type of the target gas. FIG. 13 is a diagram showing the gas sensitivity to LP gas and the gas sensitivity to methane gas. The second temperature T2 may be set in a temperature region in which the gas sensitivity (detection sensitivity) of the target gas is higher than that in the case of the first temperature T1. However, depending on the gas type, the gas temperature of the target gas at the second temperature T2 may be lower than that at the first temperature T1. The peak of gas sensitivity to methane gas is located on the higher temperature side than the peak of gas sensitivity to LP gas. Therefore, the heating control unit 30 may set the second temperature T2 when the target gas is methane gas to be higher than the second temperature T2 when the target gas is LP gas. For example, when the target gas is methane gas, the second temperature T2 may be 350 ° C., and when the target gas is LP gas, the second temperature T2 may be 330 ° C.

Further, as shown in FIG. 9, the difference between the resistance value of the gas sensing layer 12 in LP gas and the resistance value of the gas sensing layer 12 in alcohol such as ethanol is such that the heating time held at the third temperature T3 is long. I see, it gets smaller. On the other hand, the difference between the resistance value of the gas sensing layer 12 in methane gas and the resistance value of the gas sensing layer 12 in alcohol increases as the heating time held at the third temperature T3 becomes longer. Then, as the third temperature T3 becomes higher, such a tendency becomes stronger. Therefore, when the target gas is methane gas, the selectivity with alcohol may be increased by setting the third temperature T3 to a higher value than when the target gas is LP gas.

FIG. 14 is a flowchart showing an example of the processing content of the gas sensor 100. Steps S401 to S406 of FIG. 14 are the same as steps S101 to S106 of FIG. 10, and steps SS408 to S412 of FIG. 14 are the same as steps S107 to S111 of FIG. The process shown in FIG. 14 differs from the process shown in FIG. 10 in that step S407 is added. Therefore, the repetition of the steps similar to the process of FIG. 10 will be omitted.

In step S407, the heating control unit 30 may change the third temperature T3 according to the second resistance value. Specifically, it is estimated that the lower the second resistance value, the larger the amount of gas components adhering to the gas sensing layer 12. When there are many gas components adhering to the gas sensing layer 12, it takes time to drive the gas sensing layer 12 to a third temperature T3 to remove the gas components. Therefore, the lower the second resistance value, the higher the third temperature T3 may be.

When the second resistance value is low, the heating control unit 30 raises the third temperature T3 to promote the desorption of LP gas adhering to the gas sensing layer 12. Therefore, it becomes easy to secure the difference between the resistance value of the gas sensing layer 12 in LP gas and the resistance value of the gas sensing layer 12 in alcohol. Further, when the second resistance value is low, the heating control unit 30 raises the third temperature T3 to promote the desorption of alcohol adhering to the gas sensing layer 12. Therefore, it becomes easy to secure the difference between the resistance value of the gas sensing layer 12 in methane gas and the resistance value of the gas sensing layer 12 in alcohol.

FIG. 15 is a flowchart showing an example of the processing content of the gas sensor 100. Steps S501 to S507 of FIG. 15 are the same as steps S101 to S107 of FIG. 10, and steps SS509 to S512 of FIG. 15 are the same as steps S108 to S111 of FIG. The process shown in FIG. 15 differs from the process shown in FIG. 10 in that step S508 is added. Therefore, the repetition of the steps similar to the process of FIG. 10 will be omitted.

In step S508, the third acquisition unit 70 changes the timing of acquiring the third resistance value according to the second resistance value. Along with this, the heating control unit 30 may lengthen the heating time for heating the gas sensing layer 12 to the third temperature T3. By lengthening the heating time, desorption of LP gas adhering to the gas sensing layer 12 is promoted. Therefore, it is possible to secure the difference between the resistance value of the gas sensing layer 12 in LP gas and the resistance value of the gas sensing layer 12 in alcohol. In addition, the desorption of alcohol adhering to the gas sensing layer 12 is promoted. Therefore, it is possible to secure the difference between the resistance value of the gas sensing layer 12 in methane gas and the resistance value of the gas sensing layer 12 in alcohol. Further, the discriminating unit 80 may change the third temperature T3 according to the second resistance value. For example, the discriminating unit 80 determines the third threshold value by looking at the ratio between the second threshold value L2 and the second resistance value. For example, the lower the second resistance value, the smaller the third threshold value may be.

FIG. 16 is a diagram showing an outline of the gas sensor 100 according to the second embodiment of the present invention. The gas sensor 100 of the second embodiment has the same structure as the gas sensor 100 of the first embodiment, except that the discrimination unit 80 includes the rate of change calculation unit 84. Therefore, the repetitive description will be omitted.

The change rate calculation unit 84 calculates the time change rate of the third resistance value with the lapse of the heating time from the start of heating. In the present embodiment, the third resistance value may be acquired at a plurality of times. The time change rate of the third resistance value is calculated from the plurality of third resistance values acquired at the plurality of times. The change rate calculation unit 84 may calculate the maximum time change rate (maximum ratio) of the third resistance value with reference to the third resistance value at a specific time.

FIG. 17 is a diagram showing an example of the time change rate of the resistance of the gas sensing layer 12 when the heater 14 is driven to the high state. FIG. 17 shows the time change rate of the resistance of the gas sensing layer 12 when the temperature of the gas sensing layer 12 is held at the third temperature T3. In FIG. 17, the vertical axis shows the ratio based on the resistance value of the gas sensing layer 12 at a predetermined time. In this example, the ratio is shown based on the resistance value of the gas sensing layer 12 when 200 msec has elapsed after the start of heating. Specifically, when the third resistance value of the heating after the start 200m seconds elapse time of the gas sensing layer 12 and R _200, a third resistance value of the gas sensing layer 12 at an arbitrary time X and R _X, in FIG. 17 the rate of change shown in the ordinate axis is calculated by the formula of _R 200 / _{R X.}

As shown in FIG. 17, the time change rate of the resistance value of the gas sensing layer 12 in the LP gas is about 3.2 at the maximum. Specifically, in LP gas, the third resistance value of the gas sensing layer 12 40 seconds after the start of heating is the third resistance value of the gas sensing layer 12 200 seconds after the start of heating. It will be doubled. On the other hand, the time change rate of the resistance value of the gas sensing layer 12 in alcohol such as ethanol is about 2.3 at the maximum. Specifically, in ethanol, the third resistance value of the gas sensing layer 12 100 seconds after the start of heating is 2.3 of the third resistance value of the gas sensing layer 12 200 seconds after the start of heating. Double. Therefore, when the target gas is LP gas, the rate of change threshold L4 may be set between 2.3 times and 3.2 times.

Further, the time change rate of the resistance value of the gas sensing layer 12 in methane gas is about 1 at the maximum. Therefore, when the target gas is methane gas, the rate of change threshold L4'may be set between 2.3 times and 1 time. As described above, the discriminating unit 80 discriminates the existing gas type based on the time change rate of the third resistance value. In particular, when the target gas is methane gas, it is effective in increasing the selectivity of the target gas for substances such as alcohol. The processing content of the gas sensor 100 of the second embodiment as described above is the same as each processing content shown in FIGS. 10, 14, and 15 except for the processing of determining the gas type.

FIG. 18 is a flowchart showing an example of gas type discrimination processing when the target gas is LP gas. FIG. 18 is an example of the processing of step S109 of FIG. 10, step S410 of FIG. 14, and step S510 of FIG.

The change rate calculation unit 84 calculates the time change rate of the third resistance value with the passage of time from the start of heating (step S601). The time change rate may be the maximum time change rate (maximum ratio) of the third resistance value as described in FIG. However, the time change rate may be any one indicating the degree of time change of the third resistance value, and is not limited to the maximum time change rate.

The discriminating unit 80 discriminates the existing gas type based on the calculated time change rate. Specifically, the discriminating unit 80 determines whether or not the time change rate of the third resistance value is equal to or higher than the predetermined change rate threshold value L4 (step S602). When the time change rate of the third resistance value is equal to or higher than the predetermined change rate threshold value L4 (step S602: YES), the discriminating unit 80 determines that LP gas is present (step S603). on the other hand. When the time change rate of the third resistance value is smaller than the change rate threshold value L4 (step S602: NO), it is determined that the gas containing alcohol exists (step S604). If it is determined that LP gas is present, the alarm generation unit 40 may issue a gas leak alarm (step S605).

FIG. 19 is a flowchart showing an example of gas type discrimination processing when the target gas is methane gas. FIG. 19 is an example of the processing of step S109 of FIG. 10, step S410 of FIG. 14, and step S510 of FIG. The change rate calculation unit 84 calculates the time change rate of the third resistance value with the passage of time from the start of heating (step S701).

The determination unit 80 determines whether or not the time change rate of the third resistance value is equal to or less than a predetermined change rate threshold value L4'(step S702). When the time change rate of the third resistance value is equal to or less than the predetermined change rate threshold value L4'(step S702: YES), the discrimination unit 80 determines that methane gas is present (step). S703). on the other hand. When the time change rate of the third resistance value is larger than the change rate threshold value L4'(step 702: NO), it is determined that the gas containing alcohol is present (step 704). If it is determined that methane gas is present, the alarm generation unit 40 may issue a gas leak alarm (step S705).

FIG. 20 is a diagram showing an outline of the gas sensor 100 according to the third embodiment of the present invention. The gas sensor 100 of the third embodiment is the same as the structure of the gas sensor 100 of the first or second embodiment except that the discrimination unit 80 includes the timing detection unit 86. Therefore, the repetitive description will be omitted.

The timing detection unit 86 detects the timing at which the third resistance value begins to increase as the heating time elapses from the start of heating. In the present embodiment, the third resistance value is acquired at a plurality of times. From a plurality of third resistance values acquired at a plurality of times, the timing at which the third resistance value begins to rise may be detected. Specifically, the time from the start of heating to the time when the third resistance value starts to increase may be detected.

With reference to FIG. 9 described above, in the case of LP gas, the resistance value of the gas sensing layer 12 shows a minimum value when about 40 msec has elapsed after the start of heating, and then the resistance value of the gas sensing layer 12 changes. To increase. Therefore, in the LP gas, the timing at which the third resistance value starts to increase may be about 40 msec after the start of heating. On the other hand, in alcohol, the timing at which the third resistance value begins to increase may be about 100 msec after the start of heating. In methane gas, the third resistance value is stagnant or decreased even after about 200 msec has passed since the start of heating. Therefore, in methane gas, the timing at which the third resistance value starts to increase may be after about 200 msec after the start of heating. Here, "stagnation" may mean that a predetermined numerical range is maintained.

The processing content of the gas sensor 100 of the third embodiment as described above is the same as each processing content shown in FIGS. 10, 14, and 15 except for the processing of determining the gas type. FIG. 21 is a flowchart showing an example of gas type discrimination processing when the target gas is LP gas. FIG. 21 is an example of the processing of step S109 of FIG. 10, step S410 of FIG. 14, and step S510 of FIG.

The timing detection unit 86 detects the timing at which the third resistance value begins to increase as the heating time elapses from the start of heating (step S801). The timing at which the third resistance value begins to increase may be the timing at which the third resistance value changes from decreasing to increasing as the heating time elapses from the start of heating. Alternatively, the timing at which the third resistance value begins to increase may be the timing at which the third resistance value increases by a predetermined value from the minimum value as the heating time elapses from the start of heating.

The discriminating unit 80 discriminates the existing gas type according to the timing at which the third resistance value starts to increase. Specifically, the discriminating unit 80 determines whether or not the third resistance value starts to increase within a predetermined time (step S802). The predetermined time may be set to be longer than the time when the third resistance value in the LP gas starts to rise and shorter than the time when the third resistance value in the alcohol starts to rise. In the example shown in FIG. 9, the predetermined time may be set to a time longer than 40 ms and shorter than 100 ms.

When the third resistance value starts to increase within a predetermined time (step S802: YES), the discriminating unit 80 determines that LP gas is present (step S803). On the other hand, if the third resistance value is stagnant or decreased even after the lapse of a predetermined time (step S802: NO), the discriminating unit 80 determines that a gas other than the target gas is present. Specifically, the discriminating unit 80 determines that a gas containing alcohol is present (step S804). If it is determined that LP gas is present, the alarm generation unit 40 may issue a gas leak alarm (step S805). If the third resistance value starts to increase within a predetermined time (step S802: YES), the heating control unit 30 may stop energizing the heater 14.

FIG. 22 is a flowchart showing an example of the gas type discrimination process when the target gas is methane gas. FIG. 22 is an example of the processing of step S109 of FIG. 10, step S410 of FIG. 14, and step S510 of FIG. The timing detection unit 86 detects the timing at which the third resistance value begins to increase as the heating time elapses from the start of heating (step S901).

The determination unit 80 determines whether or not the third resistance value has started to increase within a predetermined time (step S902). The predetermined time may be set to be longer than the time when the third resistance value in alcohol starts to rise and shorter than the time when the third resistance value in methanol starts to rise. In the example shown in FIG. 9, the predetermined time may be longer than 100 ms and shorter than 200 ms.

If the third resistance value is stagnant or decreased even after the lapse of a predetermined time (step S902: NO), the discriminating unit 80 determines that methane gas is present (step S903). On the other hand, when the third resistance value starts to increase within a predetermined time (step S902: YES), the discriminating unit 80 determines that a gas other than the target gas is present. Specifically, the discriminating unit 80 determines that a gas containing alcohol is present (step S904). If it is determined that methane gas is present, the alarm generation unit 40 may issue a gas leak alarm (step S905).

Also in this example, when the second resistance value is equal to or less than the second threshold value L2, the gas discrimination process is further executed without immediately concluding that the target gas exists. Therefore, the selectivity of the target gas with respect to the gas such as alcohol is enhanced. Therefore, it is possible to reduce the possibility that the alarm generating unit 40 issues an alarm even though the target gas does not exist.

Although the present invention has been described above using the embodiments, the embodiments in the present specification can be combined as appropriate. The technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various changes or improvements can be made to the above embodiments. It is clear from the description of the claims that such modified or improved forms may also be included in the technical scope of the present invention.

The execution order of each process such as operation, procedure, step, and step in the device, system, program, and method shown in the claims, the specification, and the drawing is particularly "before" and "prior to". It should be noted that it can be realized in any order unless the output of the previous process is used in the subsequent process. Even if the scope of claims, the specification, and the operation flow in the drawings are explained using "first", "next", etc. for convenience, it means that it is essential to carry out in this order. It's not a thing.

2 ... Silicon substrate, 3 ... Thermal insulation support layer, 4 ... Electrical insulation layer, 5 ... Gas detector, 6 ... Through hole, 7 ... Bonding layer, 8 ... Gas sensing layer electrode, 9 ...・ Selective combustion layer, 10 ・ ・ Detection unit, 12 ・ ・ Gas sensing layer, 14 ・ ・ Heater, 16 ・ ・ Temperature measurement unit, 20 ・ ・ Measurement unit, 30 ・ ・ Heating control unit, 40 ・ ・ Alarm generation unit, 50 ... 1st acquisition unit, 60 ... 2nd acquisition unit, 70 ... 3rd acquisition unit, 80 ... discrimination unit, 82 ... comparison unit, 84 ... change rate calculation unit, 86 ... timing detection unit , 90 ... storage unit, 100 ... gas sensor, 200 ... control device

Claims (19)

A gas sensor having a gas sensing layer and a heater for heating the gas sensing layer, and detecting a detection target gas based on a resistance value of the gas sensing layer heated by the heater.
A measuring unit that measures the resistance value of the gas sensing layer,
A heating control unit that controls the heater so as to heat the gas sensing layer,
A first acquisition unit that acquires the first resistance value of the gas sensing layer measured by the measuring unit while the temperature of the gas sensing layer is controlled to the first temperature by the heating control unit.
When the first resistance value is equal to or less than a predetermined first threshold value, the measurement unit measures the temperature of the gas sensing layer controlled by the heating control unit to a second temperature lower than the first temperature. A second acquisition unit that acquires the second resistance value of the gas sensing layer, and
When the second resistance value is equal to or less than a predetermined second threshold value, the measurement unit measures the temperature of the gas sensing layer controlled by the heating control unit to a third temperature higher than the second temperature. A third acquisition unit that acquires the third resistance value of the gas sensing layer, and
A discriminating unit that discriminates an existing gas type based on the third resistance value, and
Gas sensor equipped with. The discrimination unit includes a comparison unit that compares the third resistance value with a predetermined third threshold value.
The gas sensor according to claim 1, wherein the discrimination unit discriminates an existing gas type based on a comparison result between the third resistance value and the third threshold value. The detection target gas is LP gas.
The discriminating unit determines that the detection target gas exists when the third resistance value is equal to or higher than the third threshold value, and when the third resistance value is smaller than the third threshold value, the discrimination unit determines that the detection target gas exists. The gas sensor according to claim 2, wherein it is determined that a gas other than the detection target gas is present. The detection target gas is methane gas.
The discriminating unit determines that the detection target gas exists when the third resistance value is equal to or less than the third threshold value, and when the third resistance value is larger than the third threshold value, the discrimination unit determines that the detection target gas exists. The gas sensor according to claim 2, wherein it is determined that a gas other than the detection target gas is present. The gas sensor according to claim 3 or 4, wherein the gas other than the detection target gas contains alcohol. The discriminating unit includes a change rate calculation unit that calculates the time change rate of the third resistance value.
The gas sensor according to claim 1, wherein the discrimination unit discriminates an existing gas type based on the time change rate of the third resistance value. The detection target gas is LP gas.
When the time change rate of the third resistance value is equal to or higher than a predetermined change rate threshold value, the discriminating unit determines that the detection target gas exists, while the time of the third resistance value. The gas sensor according to claim 6, wherein when the rate of change is smaller than the rate of change threshold value, it is determined that a gas other than the detection target gas is present. The detection target gas is methane gas.
When the time change rate of the third resistance value is equal to or less than a predetermined change rate threshold value, the discriminating unit determines that the detection target gas exists, while the time of the third resistance value. The gas sensor according to claim 6, wherein when the rate of change is larger than the rate of change threshold value, it is determined that a gas other than the detection target gas is present. The discriminating unit includes a timing detecting unit that detects the timing at which the third resistance value starts to increase.
The gas sensor according to claim 1, wherein the discrimination unit discriminates an existing gas type according to a timing at which the third resistance value starts to increase. The detection target gas is LP gas.
When the third resistance value starts to increase within a predetermined time, the discriminating unit determines that the detection target gas exists, and on the other hand, even if the predetermined time elapses, the first 3. The gas sensor according to claim 9, wherein when the resistance value is stagnant or lowered, it is determined that a gas other than the detection target gas is present. The detection target gas is methane gas.
If the third resistance value is stagnant or lowered even after a predetermined time has elapsed, the discriminating unit determines that the detection target gas exists, while within the predetermined time. The gas sensor according to claim 9, wherein when the third resistance value starts to increase, it is determined that a gas other than the detection target gas is present. The gas sensor according to any one of claims 1 to 11, wherein the heating control unit changes the third temperature according to the second resistance value. The gas sensor according to any one of claims 1 to 11, wherein the third acquisition unit changes the timing of acquiring the third resistance value according to the second resistance value. The gas sensor according to any one of claims 2 to 5, wherein the discriminating unit changes the third threshold value according to the second resistance value. The gas sensor according to any one of claims 1 to 14, wherein the heating control unit changes the second temperature and / or the third temperature according to the type of the detection target gas. The gas sensor according to any one of claims 1 to 15, wherein the third temperature is higher than the first temperature. The gas sensor according to any one of claims 1 to 16 is provided.
A gas alarm further including an alarm generating unit that generates an alarm when the detection target gas is detected. A control device having a gas sensing layer and a heater for heating the gas sensing layer, and controlling a gas sensor that detects a gas to be detected based on a resistance value of the gas sensing layer heated by the heater. ,
A heating control unit that controls the heater so as to heat the gas sensing layer,
The first acquisition unit that acquires the first resistance value of the gas sensing layer measured in a state where the temperature of the gas sensing layer is controlled to the first temperature by the heating control unit, and
When the first resistance value is equal to or less than a predetermined first threshold value, the gas measured in a state where the temperature of the gas sensing layer is controlled to a second temperature lower than the first temperature by the heating control unit. The second acquisition unit that acquires the second resistance value of the sensing layer, and
When the second resistance value is equal to or less than a predetermined second threshold value, the gas measured in a state where the temperature of the gas sensing layer is controlled to a third temperature higher than the second temperature by the heating control unit. A third acquisition unit that acquires the third resistance value of the sensing layer, and
A control device including a discriminating unit for discriminating existing gas types based on the third resistance value. It is a control method of a gas sensor having a gas sensing layer and a heater for heating the gas sensing layer, and detecting a gas to be detected based on a resistance value of the gas sensing layer heated by the heater.
A first temperature control step that controls the temperature of the gas sensing layer to the first temperature, and
The first acquisition step of acquiring the first resistance value of the gas sensing layer measured in a state where the temperature of the gas sensing layer is controlled to the first temperature, and
A second temperature control step that controls the temperature of the gas sensing layer to a second temperature lower than the first temperature when the first resistance value is equal to or less than a predetermined first threshold value.
A second acquisition step of acquiring the second resistance value of the gas sensing layer measured in a state where the temperature of the gas sensing layer is controlled to the second temperature, and
When the second resistance value is equal to or less than a predetermined second threshold value, a third temperature control step for controlling the temperature of the gas sensing layer to a third temperature higher than the second temperature, and
A third acquisition step of acquiring the third resistance value of the gas sensing layer measured in a state where the temperature of the gas sensing layer is controlled to the third temperature, and
A control method including a discrimination step of discriminating an existing gas type based on a third resistance value acquired in the third acquisition step.

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