JP2018205210A - Gas sensor, gas alarm, controller, and control method - Google Patents

Abstract

To provide a gas sensor in which the selectivity of a detection object gas is heightened.SOLUTION: The gas sensor comprises: a measurement unit 20 for measuring the resistance value of a gas-sensing layer; a heating control unit 30 for controlling a heater so as to heat the gas-sensing layer; a first acquisition unit 50 for acquiring a first resistance value of the gas-sensing layer that is measured by the measurement unit while the temperature of a gas-sensing layer 12 is controlled at a first temperature by the heating control unit; a second acquisition unit 60 for acquiring a second resistance value of the gas-sensing layer that is measured by the measurement unit while the temperature of the gas-sensing layer is controlled at a second temperature lower than the first temperature by the heating control unit when the first resistance value is smaller than or equal to a predetermined first threshold; a third acquisition unit 70 for acquiring a third resistance value of the gas-sensing layer that is measured by the measurement unit while the temperature of the gas-sensing layer is controlled at a third temperature higher than the second temperature by the heating control unit when the second resistance value is smaller than or equal to a predetermined second threshold; and an identification unit 80 for identifying the type of existing gas on the basis of the third resistance value.SELECTED DRAWING: Figure 1

Description

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

Conventionally, a gas detection method that performs preliminary detection and main detection according to the result of the preliminary detection is known (see, for example, Patent Document 1). In Patent Document 1, the preliminary detection and the main detection are performed at different temperatures. Further, as a related technique, a technique that enables detection of three or more kinds of gases by controlling the gas sensor to at least three different temperatures and executing gas detection at different temperatures is known (for example, Patent Document 2).
[Prior art documents]
[Patent Literature]
[Patent Document 1] JP 2010-54213 [Patent Document 2] JP 2005-13411 A

  In the gas sensor, it is desirable to prevent the detection target gas from being detected by reacting with a substance such as alcohol other than the detection target gas even though the detection target gas is not present. Accordingly, in the gas sensor, it is desirable to increase the selectivity of the detection target gas with respect to a substance such as alcohol.

  In a first aspect of the present invention, a gas sensor is provided. The gas sensor may include a gas sensing layer and a heater for heating the gas sensing layer. The gas sensor may detect the detection target gas based on the resistance value of the gas sensing layer heated by the heater. The gas sensor may include a measurement unit, a heating control unit, a first acquisition unit, a second acquisition unit, a third acquisition unit, and a determination unit. The measurement unit may measure a resistance value of the gas sensing layer. The heating control unit may control the heater to heat the gas sensing layer. The first acquisition unit may acquire a first resistance value of the gas sensing layer. The first resistance value may be measured by the measurement 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 measurement unit 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 by the measurement unit 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 determination unit may determine the existing gas type based on the third resistance value.

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

  The detection target gas may be LP gas. The determination unit may determine that the detection target gas exists when the third resistance value is equal to or greater than the third threshold value. The determination unit may determine that a gas other than the detection target gas exists when the third resistance value is smaller than the third threshold value.

  The detection target gas may be methane gas. The determination unit may determine that the detection target gas exists when the third resistance value is equal to or less than the third threshold value. The determination unit may determine that there is a gas other than the detection target gas when the third resistance value is greater than the third threshold value.

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

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

  The detection target gas may be LP gas. The determination unit may determine that the detection target gas exists when the temporal change rate of the third resistance value is equal to or greater than a predetermined change rate threshold value. The determination unit may determine that there is a gas other than the detection target gas when the time change rate of the third resistance value is smaller than the change rate threshold.

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

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

  The detection target gas may be LP gas. The determination unit may determine that the detection target gas exists when the third resistance value starts to increase within a predetermined time. The determination unit may determine that there is a gas other than the detection target gas when the third resistance value is stagnant or decreased even after a predetermined time has elapsed.

  The detection target gas may be methane gas. The determination unit may determine that the detection target gas exists when the third resistance value is stagnant or decreased even after a predetermined time has elapsed. The determination unit may determine that a gas other than the detection target gas exists when the third resistance value starts to increase within a predetermined time.

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

  The third acquisition unit may change the timing for acquiring the third resistance value according to the second resistance value. The determination 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 detection target gas.

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

  The third temperature may be higher than the first temperature. The gas alarm may include a gas sensor. The gas alarm device may include an alarm generation unit. The alarm generation unit may generate an alarm when detecting the detection target gas.

  In a second aspect of the present invention, a control device is provided. The control device may control the gas sensor. The gas sensor may include a gas sensing layer and a heater for heating the gas sensing layer. The gas sensor may detect the detection target gas 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 determination unit. The heating control unit may control the heater to heat the gas sensing layer. The first acquisition unit may acquire a 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 determination unit may determine 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 include a gas sensing layer and a heater for heating the gas sensing layer. The gas sensor may detect the detection target gas 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 determination stage. In the first temperature control step, the temperature of the gas sensing layer may be controlled to the first temperature. In the first acquisition step, 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 step, the temperature of the gas sensing layer may be controlled 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. In the second acquisition step, a 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, the temperature of the gas sensing layer may be controlled to a third temperature higher than the second temperature when the second resistance value is equal to or lower than a predetermined second threshold value. In the third acquisition step, a 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 determination step, the existing gas type may be determined based on the third resistance value acquired in the third acquisition step.

  It should be noted that the above summary of the invention does not enumerate all the necessary features of the present invention. In addition, a sub-combination of these feature groups can also be an invention.

It is a figure showing the outline of gas sensor 100 of a 1st embodiment of the present invention. 2 is a cross-sectional view illustrating a schematic configuration of a detection unit 10. It is a figure which shows an example of a heater drive pattern in case a 1st resistance value is larger than a 1st threshold value. It is a figure which shows an example of a heater drive pattern in case a 2nd resistance value is larger than a 2nd threshold value. It is a figure which shows an example of a heater drive pattern in case a 2nd resistance value is below a 2nd threshold value. It is a figure which shows an example of a heater drive pattern in case a 2nd resistance value is below a 2nd threshold value. It is a figure which shows an example of the resistance change of the gas sensing layer 12 at the time of driving the heater 14 to a High state. It is a figure which shows an example of resistance change of the gas sensing layer 12 at the time of driving the heater 14 to a Low state. It 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 kind discrimination | determination process in case detection target gas is LP gas. It is a figure which shows an example of the gas kind discrimination | determination process in case detection target gas is methane gas. It is a figure which shows the gas sensitivity with respect to LP gas, and the gas sensitivity with respect to methane gas. 3 is a flowchart showing an example of processing contents of a gas sensor 100. 3 is a flowchart showing an example of processing contents of a gas sensor 100. It is a figure which shows the outline of the gas sensor 100 of 2nd Embodiment of this invention. It is a figure which shows an example of the time change rate in resistance of the gas sensing layer 12 at the time of driving the heater 14 to a High state. It is a flowchart which shows an example of the gas kind discrimination | determination process in case detection target gas is LP gas. It is a flowchart which shows an example of the gas kind discrimination | determination process in case detection target gas is methane gas. It is a figure which shows the outline of the gas sensor 100 of 3rd Embodiment of this invention. It is a flowchart which shows an example of the gas kind discrimination | determination process in case detection target gas is LP gas. It is a flowchart which shows an example of the gas kind discrimination | determination process in case 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 invention according to the claims. In addition, not all the combinations of features described in the embodiments are essential for the solving means of 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 a detection target gas. The detection target gas (abbreviated as “target gas”) may be a combustible gas. The target gas may be LP gas mainly composed of propane and butane. Alternatively, the target gas may be a city gas whose main component is methane gas.

  The gas sensor 100 of the present example not only performs the detection at the first temperature T1 and the detection at the second temperature T2 lower than the first temperature T1, but also performs the second detection according to the detection result at the second temperature T2. The heater 14 is driven to a third temperature T3 that 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. As a result, the target gas is distinguished from a gas such as alcohol.

  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 may not include the temperature measurement unit 16. The gas sensing layer 12 is a sensor resistance whose resistance value varies 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 determination unit 80, and a storage unit 90. However, the alarm generation unit 40 is not necessarily an essential component for the control device 200. When the gas sensor 100 is a gas alarm device, 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 determination unit 80 may be realized as a function of a microcomputer. The measurement unit 20 measures the electrical resistance value of the gas sensing layer 12. For example, the measurement unit 20 measures the voltage across the gas sensing layer 12 by passing a current through the gas sensing layer 12. Measuring the resistance value of the gas sensing layer 12 may include measuring an electrical characteristic such as voltage or current associated with the resistance value of the gas sensing layer 12. Obtaining the measured resistance value may include obtaining an electrical characteristic such as voltage or current associated with the resistance value. Comparing the resistance value with the threshold value may include comparing a voltage or current associated with the resistance value with the threshold value. In one example, the resistance value of the gas sensing layer 12 being greater than the threshold value may include a voltage across the gas sensing layer 12 being greater than the threshold value, and a current flowing through the gas sensing layer 12 being less than the threshold value. May be included. The resistance value of the gas sensing layer 12 being smaller than the threshold value may include a voltage across the gas sensing layer 12 being smaller than the threshold value, and a current flowing through the gas sensing layer 12 being 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. In the first detection process, when there is a possibility that the target gas exists, the heating control unit 30 causes 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. The heater 14 is controlled. Furthermore, when there is a possibility that the target gas exists as a result of the second detection process, the heating control unit 30 sets the temperature of the gas sensing layer 12 to the first temperature in order to increase the selectivity of the target gas with respect to a gas such as alcohol. The heater 14 is controlled so that the third temperature T3 is higher than the second 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 an electric resistance value of the gas sensing layer 12 measured by the measurement unit 20 in a state where the temperature of the gas sensing layer 12 is controlled to the first temperature T1 by the heating control unit 30. The second resistance value is an electric resistance value of the gas sensing layer measured by the measurement unit 20 in a state where the temperature of the gas sensing layer 12 is controlled to the second temperature T2 lower than the first temperature T1 by the heating control unit 30. . The third resistance value is an electric resistance value of the gas sensing layer measured by the measurement unit 20 in a state where the temperature of the gas sensing layer 12 is controlled to the third temperature T3 higher than the second temperature T2 by the heating control unit 30. .

  The first temperature T1 and the third temperature T3 are higher 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 a low state and controls the temperature of the gas sensing layer 12 to be the second temperature T2. The second temperature T2 may be preferably 250 ° C. or higher and 350 ° C. or lower.

  The determination unit 80 determines the existing gas type based on the third resistance value. The determination 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 illustrating a schematic configuration of the detection unit 10. The detection unit 10 of this example is a semiconductor thin film gas sensor. The detection unit 10 of this example includes a silicon substrate 2, a thermal insulation support layer 3, a heater layer that functions as a heater 14, an electrical insulation layer 4, and a gas detection unit 5. A through hole 6 is provided in the silicon substrate 2. 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. For example, the gas sensing layer 12 is formed as a sensing layer mainly composed of a metal oxide such as SnO ₂ , In ₂ O ₃ , WO ₃ , ZnO, and TiO ₂ .

The selective combustion layer 9 is a sintered body supporting at least one kind of 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 mainly contains 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 based on the resistance value of the gas sensing layer 12 when the gas sensing layer 12 is heated by the heater 14.

  Next, driving of the heater 14 by the heating control unit 30 will be described. FIG. 3 is a diagram illustrating an example of a heater driving pattern when the first resistance value is greater than the first threshold value. The heating control unit 30 intermittently drives the heater 14. The heating control unit 30 periodically applies a pulse voltage as a heater driving voltage to the heater 14. The heating control unit 30 may apply a pulsed voltage to the heater 14 with 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). In order to set the temperature of the gas sensing layer 12 to the first temperature T1, a voltage to be applied to the heater 14 may be set in advance. 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 over a predetermined heating time. In one example, the heating time in the first detection process is 30 milliseconds to 100 milliseconds, and more preferably 40 milliseconds to 90 milliseconds.

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

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

  The heating control unit 30 performs the first determination. The first determination is a determination as to whether the first resistance value is equal to or less than a predetermined first threshold value. However, the first determination may be performed 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 energization of the heater 14 as shown in FIG. 3 assuming that the target gas has not been detected. Therefore, the heating time can be shortened and power saving can be realized.

  FIG. 4 is a diagram illustrating an example of a heater driving pattern when the second resistance value is larger than the second threshold value. When the first resistance value is equal to or lower 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 over a predetermined heating time. In one example, the heating time in the second detection process may be not less than 160 milliseconds and not more than 200 milliseconds.

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

  The heating control unit 30 performs the second determination. The second determination is a determination as to whether the second resistance value is equal to or less than a predetermined second threshold value. However, the second determination may be performed 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 has not been detected. Therefore, the heating time is shortened and power saving can be realized.

  FIG. 5 is a diagram illustrating an example of a heater driving pattern when the second resistance value is equal to or smaller 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, it is determined that the target gas has been detected if the second resistance value is equal to or less than the second threshold value. On the other hand, unlike this case, the gas sensor 100 of this example further executes control for improving the selectivity with alcohol other than the target gas. Specifically, when the second resistance value is equal to or lower than the second threshold value, the heating control unit 30 sets the temperature of the gas sensing layer 12 to a third temperature T3 (which is higher than the second temperature T2) as shown in FIG. High).

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

  The determination unit 80 determines the existing gas type based on the third resistance value. The determination 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 illustrating an example of a heater driving pattern when the second resistance value is equal to or smaller than the second threshold value. As shown in FIG. 6, the third temperature T3 may be higher than the first temperature T1. By making 3rd temperature T3 higher than 1st temperature T1, the selectivity of object gas and alcohol can further be improved.

  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 entire heating time can be shortened as compared with the case where the temperature is always controlled to the first temperature T1, the second temperature T2, and the third temperature T3.

  FIG. 7 is a diagram illustrating 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 a measurement result when the temperature of the gas sensing layer 12 is held 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 air (indicated as Air), LP gas (indicated as LP, isobutane, etc.), hydrogen gas (indicated as H 2), ethanol (indicated as ETOH). ) And methane gas (denoted as CH4).

  As shown in FIG. 7, the resistance value of the gas sensing layer 12 is lower when any gas other than the atmosphere exists compared to the atmosphere. In the atmosphere, the resistance value of the gas sensing layer 12 becomes stable when about 40 milliseconds have elapsed after the start of heating. On the other hand, in LP gas and hydrogen gas, after the resistance value of the gas sensing layer 12 is greatly reduced compared to that in the atmosphere, the resistance value of the gas sensing layer 12 gradually increases in the atmosphere after starting to rise around 40 milliseconds. Approaching. The resistance value of the gas sensing layer 12 gradually decreases in alcohol such as ethanol. Also in the case of methane gas, the resistance value of the gas sensing layer 12 gradually decreases.

  Therefore, for example, in the time range from 30 milliseconds to 100 milliseconds 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 be a value that can distinguish between a case in the atmosphere and a case in which any gas other than the atmosphere exists. In this example, the first threshold L1 is set between 40 kΩ and 100 kΩ. However, the threshold value differs depending on the detection unit 10, and is not limited to this case.

  The first resistance value of the gas sensing layer 12 measured by the measurement unit 20 in a state where the temperature of the gas sensing layer 12 is controlled to the first temperature T1 by the heating control unit 30 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 because 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 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 illustrating an example of a change in resistance of the gas sensing layer when the heater is driven to a low state. FIG. 8 shows a measurement result when the temperature of the gas sensing layer 12 is held 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 becomes stable when about 60 milliseconds elapse after the start of heating. Further, in hydrogen gas, the resistance value of the gas sensing layer 12 is greatly reduced as compared with that in the atmosphere, and then gradually approaches the resistance value in the atmosphere. In the case of LP gas, alcohol such as ethanol, and methane gas, the resistance value of the gas sensing layer 12 gradually decreases.

  Therefore, for example, in the time range from 160 ms to 200 ms after the start of heating in the low state, the resistance value of the gas sensing layer 12 in LP gas and alcohol, and the gas sensing layer in hydrogen gas There is a difference between the resistance value. 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 for 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 L2 (L2 ′) is set between 30 kΩ and 300 kΩ. In the temperature region 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 L2 ′ when the target gas is methane gas may be set to a value higher than the second threshold 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 and is not a target gas. Therefore, the heating control unit 30 stops energization to the heater 14. On the other hand, when the second resistance value is equal to or smaller 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 change in resistance of the gas sensing layer when the heater is driven to a high state for 200 msec. FIG. 9 shows a measurement result when the temperature of the gas sensing layer 12 is held 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 with reference to FIG. 7, in the atmosphere, the resistance value of the gas sensing layer 12 is stabilized when about 40 milliseconds have elapsed after the start of heating. On the other hand, in the case of LP gas (such as isobutane) and in the case of hydrogen gas, the resistance value of the gas sensing layer 12 greatly decreases compared to that in the atmosphere, and then starts to increase around 40 milliseconds, 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 milliseconds 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 as the heating time elapses is greater than in the case of alcohol. Due to the difference in the increase rate, for example, in the time range from 160 ms to 200 ms 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 A difference occurs between 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. The third threshold 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 determination unit 80 can determine whether the gas present 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 and the third threshold value L3. When the target gas is LP gas, the determination unit 80 may determine that LP gas that is target gas exists when the third resistance value is equal to or greater than the third threshold value. On the other hand, the determination unit 80 may determine that there is a gas other than the target gas when the third resistance value is smaller than the third threshold value. Specifically, the determination unit 80 may determine that there is a gas containing alcohol when the third resistance value is smaller than the third threshold value. 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 less likely to change in the time range from 40 ms to 200 ms after decreasing to 40 ms 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 after the elapse of 160 milliseconds after the start of heating, a difference occurs 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, the third threshold 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 determination unit 80 can determine 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 and the third threshold value L3. The determination unit 80 may determine that methane gas that is the target gas exists when the third resistance value is equal to or less than the third threshold value. On the other hand, when the third resistance value is larger than the third threshold value, the determination unit 80 may determine that there is a gas other than the target gas. Specifically, the determination unit 80 may determine that a gas containing alcohol is present when the third resistance value is greater than the third threshold value. 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 for discrimination between the alcohol and the target gas, while the second temperature T2 is used to increase the gas sensitivity in order to determine the concentration of the target gas. The second resistance value measured in step 1 may be used. For example, when the target gas is LP gas, it is advantageous to use a resistance value measured at a third temperature of 400 ° C. or higher for discrimination between alcohol and the target gas. Then, the sensitivity to the target gas (the amount of change in the resistance value with respect to the gas concentration) is 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 using the second resistance value measured at a second temperature around 330 ° C. with high gas sensitivity. Good. Thereby, the selectivity with respect to alcohol can be improved, maintaining the detection sensitivity of gas. On the other hand, when the target gas is methane gas, since the gas sensitivity is higher in the case of the third temperature than in the case of the second temperature, the measured third resistance value at the third temperature is used. The concentration of the target gas may be determined as well as the discrimination between the alcohol and the target gas.

  FIG. 10 is a flowchart showing an example of processing contents of the gas sensor 100 according to the first embodiment of the present invention. FIG. 10 shows an example of a method for controlling the gas sensor 100. The heating control unit 30 applies a voltage to the heater 14 and controls 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 a first temperature control stage in which the temperature of the gas sensing layer 12 is controlled to the first temperature T1. The process in step S101 may also serve as a process for 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 a 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. Therefore, the heating control unit 30 stops energizing the heater 14 and turns off the heater 14. 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, heating can be stopped immediately. Thereby, 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 exists. 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 higher temperature range than when the gas sensitivity of the target gas is the first temperature T1. For example, when the target gas is LP gas, the gas sensitivity is higher at the second temperature T2 that is 250 ° C. or more and 350 ° C. or less than the first temperature T1 that is 400 ° C. or more and 500 ° C. or less. Therefore, the concentration of the target gas can be accurately determined by measuring the resistance value at the second temperature T2. Thereby, it is possible to reliably detect the target gas in a predetermined concentration range. Moreover, the heating control part 30 may change 2nd temperature T2 according to the kind of object gas so that it may mention later. The process of step S104 corresponds to a second temperature control stage in which the temperature of the gas sensing layer 12 is controlled 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). For example, the second acquisition unit 60 acquires, as the second resistance value, the resistance value of the gas sensing layer 12 measured in the time region of 160 ms to 200 ms after the start of heating. The process of step S105 corresponds to a 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 greater 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 energization of the heater 14 and turns off the heater 14 (step S110). Thereby, when the second resistance value is greater than the second threshold value L2 and there is no gas other than the atmosphere, heating is immediately stopped and power consumption is reduced.

  When the second resistance value is equal to or smaller than the second threshold value L2 (step S106: YES), there is a possibility that the target gas exists. 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 approximate. 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 smaller than the second threshold value L2 (step S106: YES), the heating control unit 30 sets the heater 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 stage in which the temperature of the gas sensing layer 12 is controlled 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., LP gas cannot be completely desorbed, and 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 lowered, 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 lowered, 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). For example, the third acquisition unit 70 acquires, as the third resistance value, the resistance value of the gas sensing layer 12 measured in the time region of 160 milliseconds to 200 milliseconds after the start of heating. The process of step S108 corresponds to a 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 determination unit 80 performs a gas type determination process for determining a gas type based on the third resistance value (step S109). The process of step S109 corresponds to a determination step of determining an 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 a heater driving period 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 illustrating an example of a gas type determination process when the target gas is LP gas. FIG. 11 is an example of the process in step S109 of FIG. The comparison unit 82 compares the third resistance value with a predetermined third threshold value L3 (step S201). When the third resistance value is greater than or equal to the third threshold value L3 (step S201: YES), it is considered that the target gas actually exists rather than the influence of the miscellaneous gas containing alcohol, as described in FIG. Therefore, the determination 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 a gas containing alcohol is present (step S203). If it is determined that LP gas is present, the alarm generation unit 40 issues a gas leak alarm (step S204). On the other hand, if it is determined that there is a gas containing alcohol, the alarm generation unit 40 may return without issuing a gas leak alarm.

  FIG. 12 is a flowchart illustrating an example of a gas type determination 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 a 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), it is considered that the target gas actually exists, not the influence of the miscellaneous gas containing alcohol, as described in FIG. . Therefore, the determination 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 L3 ′ (step S301: NO), it is determined that there is a gas containing alcohol (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, if it is determined that there is a gas containing alcohol, the alarm generation unit 40 may return without issuing a gas leak alarm.

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

  According to the control method of this example, the heater driving 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 entire heating time can be shortened compared to the case where the temperature is always controlled to the first temperature T1, the second temperature T2, and the third temperature T3. Therefore, power consumption can be reduced.

  In the case where the second resistance value is equal to or smaller than the second threshold value L2, the gas sensor 100 of this example immediately executes a gas determination process without immediately conclude that the target gas exists. Therefore, the selectivity of the target gas with respect to a gas such as alcohol is increased. Therefore, it is possible to reduce the possibility that the alarm generation 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. Moreover, the heating control part 30 may change the 3rd temperature T3 according to the kind of object gas. FIG. 13 is a diagram illustrating gas sensitivity to LP gas and gas sensitivity to methane gas. The second temperature T2 may be set in a higher temperature region than the case where the gas sensitivity (detection sensitivity) of the target gas is 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 for methane gas is located on the higher temperature side than the peak of gas sensitivity for LP gas. Therefore, the heating control unit 30 may set the second temperature T2 when the target gas is methane gas higher than the second temperature T2 when the target gas is LP gas. For example, the second temperature T2 when the target gas is methane gas may be 350 ° C., and the second temperature T2 when the target gas is LP gas may be 330 ° C.

  In addition, 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 long in the heating time held at the third temperature T3. 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 increases. And if the 3rd temperature T3 becomes high, such a tendency will become strong. Accordingly, when the target gas is methane gas, the selectivity with respect to 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 processing contents of the gas sensor 100. 14 are the same as steps S101 to S106 in FIG. 10, and steps SS408 to S412 in FIG. 14 are the same as steps S107 to S111 in FIG. The process shown in FIG. 14 is different from the process shown in FIG. 10 in that step S407 is added. Therefore, repetitive description of steps similar to those in the process of FIG. 10 is 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 amount of the gas component adhering to the gas sensing layer 12 increases as the second resistance value decreases. When there are many gas components adhering to the gas sensing layer 12, it takes time to desorb the gas components by driving the High and heating the gas sensing layer 12 to the third temperature T3. Therefore, the third temperature T3 may be increased as the second resistance value is decreased.

  When the second resistance value is low, the heating control unit 30 increases the third temperature T3, thereby promoting the desorption of LP gas adhering to the gas sensing layer 12. Therefore, it becomes easy to ensure 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 increases the third temperature T3, thereby promoting the desorption of the alcohol adhering to the gas sensing layer 12. Therefore, it becomes easy to ensure 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 illustrating an example of processing contents of the gas sensor 100. Steps S501 to S507 in FIG. 15 are the same as steps S101 to S107 in FIG. 10, and steps SS509 to S512 in FIG. 15 are the same as steps S108 to S111 in FIG. The process shown in FIG. 15 is different from the process shown in FIG. 10 in that step S508 is added. Therefore, repetitive description of steps similar to those in the process of FIG. 10 is omitted.

  In step S508, the third acquisition unit 70 changes the timing for acquiring the third resistance value according to the second resistance value. Accordingly, 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, a 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 can be ensured. Further, the detachment of alcohol adhering to the gas sensing layer 12 is promoted. Therefore, 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 can be ensured. Further, the determination unit 80 may change the third temperature T3 according to the second resistance value. For example, the determination 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 third threshold value may be decreased as the second resistance value is decreased.

  FIG. 16 is a diagram schematically illustrating the gas sensor 100 according to the second embodiment of the present invention. The gas sensor 100 of the second embodiment is the same as the structure of the gas sensor 100 of the first embodiment, except that the determination unit 80 includes a change rate calculation unit 84. Therefore, repeated description is omitted.

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

FIG. 17 is a diagram illustrating an example of a time change rate of resistance of the gas sensing layer 12 when the heater 14 is driven to a high state. FIG. 17 shows the rate of change over time of the resistance of the gas sensing layer 12 when the temperature of the gas sensing layer 12 is maintained at the third temperature T3. In FIG. 17, the vertical axis indicates a 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 milliseconds have elapsed after the start of heating. Specifically, when the third resistance value of the gas sensing layer 12 at the elapse of 200 milliseconds after the start of heating is R ₂₀₀ and the third resistance value of the gas sensing layer 12 at an arbitrary time X is R _X , FIG. The rate of change shown on the vertical axis is calculated by the formula R ₂₀₀ / R _X.

  As shown in FIG. 17, the time change rate of the resistance value of the gas sensing layer 12 in LP gas is about 3.2 at the maximum. Specifically, in LP gas, the third resistance value of the gas sensing layer 12 when 40 seconds have elapsed after the start of heating is equal to 3. 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 at the elapse of 100 seconds after the start of heating is 2.3 of the third resistance value of the gas sensing layer 12 at the elapse of 200 seconds after the start of heating. Doubled. Therefore, when the target gas is LP gas, the change rate threshold L4 may be set between 2.3 times and 3.2 times.

  Moreover, 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 change rate threshold L4 ′ may be set between 2.3 times and 1 time. As described above, the determination unit 80 determines 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 contents of the gas sensor 100 of the second embodiment as described above are the same as the processing contents shown in FIGS. 10, 14, and 15 except for the gas type determination process.

  FIG. 18 is a flowchart illustrating an example of a gas type determination process when the target gas is LP gas. FIG. 18 shows an example of the processing in step S109 in FIG. 10, step S410 in FIG. 14, and step S510 in 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 is not limited to the maximum time change rate as long as it indicates the degree of temporal change in the third resistance value.

  The discriminating unit 80 discriminates the existing gas type based on the calculated time change rate. Specifically, the determination unit 80 determines whether or not the time change rate of the third resistance value is equal to or greater than a predetermined change rate threshold L4 (step S602). When the temporal change rate of the third resistance value is equal to or greater than a predetermined change rate threshold L4 (step S602: YES), the determination 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 L4 (step S602: NO), it is determined that a gas containing alcohol is present (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 illustrating an example of a gas type determination process when the target gas is methane gas. FIG. 19 shows an example of the processing in step S109 in FIG. 10, step S410 in FIG. 14, and step S510 in 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 L4 ′ (step S702). If the time change rate of the third resistance value is equal to or less than the predetermined change rate threshold L4 ′ (step S702: YES), the determination unit 80 determines that methane gas is present (step S702). S703). on the other hand. When the time change rate of the third resistance value is larger than the change rate threshold L4 ′ (step 702: NO), it is determined that a 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 schematically illustrating 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 determination unit 80 includes a timing detection unit 86. Therefore, repeated description is omitted.

  The timing detector 86 detects the timing at which the third resistance value starts to increase with the elapse of the heating time from the start of heating. In the present embodiment, the third resistance value is acquired at a plurality of times. The timing at which the third resistance value starts to increase may be detected from the plurality of third resistance values acquired at a plurality of times. Specifically, the time from the start of heating to the time when the third resistance value starts to increase may be detected.

  Referring 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 milliseconds have elapsed after the start of heating, and then the resistance value of the gas sensing layer 12 is To increase. Therefore, in LP gas, the timing at which the third resistance value starts to increase may be about 40 milliseconds after the start of heating. On the other hand, in alcohol, the timing at which the third resistance value starts to increase may be about 100 milliseconds after the start of heating. In methane gas, the third resistance value is stagnant or decreased even after about 200 milliseconds have elapsed 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 contents of the gas sensor 100 of the third embodiment as described above are the same as the processing contents shown in FIGS. 10, 14, and 15 except for the gas type determination process. FIG. 21 is a flowchart illustrating an example of a gas type determination process when the target gas is LP gas. FIG. 21 shows an example of the processing in step S109 in FIG. 10, step S410 in FIG. 14, and step S510 in FIG.

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

  The discriminating unit 80 discriminates the existing gas type at the timing when the third resistance value starts to increase. Specifically, the determination 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 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 milliseconds and shorter than 100 milliseconds.

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

  FIG. 22 is a flowchart illustrating an example of a gas type determination process when the target gas is methane gas. FIG. 22 shows an example of the processing in step S109 in FIG. 10, step S410 in FIG. 14, and step S510 in FIG. The timing detector 86 detects the timing at which the third resistance value starts to increase with the elapse of the heating time from the start of heating (step S901).

  The determination unit 80 determines whether or not the third resistance value starts 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 increase and shorter than the time when the third resistance value in methanol starts increasing. In the example shown in FIG. 9, the predetermined time may be longer than 100 milliseconds and shorter than 200 milliseconds.

  If the third resistance value is stagnant or decreasing after the predetermined time has elapsed (step S902: NO), the determination 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 determination unit 80 determines that there is a gas other than the target gas. Specifically, the determination unit 80 determines that there is a gas containing alcohol (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 smaller than the second threshold value L2, it is not immediately concluded that the target gas exists, and a gas discrimination process is further executed. Therefore, the selectivity of the target gas with respect to a gas such as alcohol is increased. Therefore, it is possible to reduce the possibility that the alarm generation unit 40 issues an alarm even though the target gas does not exist.

  As described above, the present invention has been described using the embodiment, but each embodiment in the present specification can be appropriately combined. The technical scope of the present invention is not limited to the scope described in the above embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above embodiment. It is apparent from the description of the scope of claims that embodiments with such changes or improvements can be included in the technical scope of the present invention.

  The execution order of each process such as operation, procedure, step, and stage in the apparatus, system, program, and method shown in the claims, the description, and the drawings is particularly “before” or “prior to”. It should be noted that the output can be realized in any order unless the output of the previous process is used in the subsequent process. Even if the operation flow in the claims, the description, and the drawings is described using “first”, “next”, etc. for the sake of convenience, it means that it is essential to carry out in this order. It is not a thing.

2 .... Silicon substrate, 3 .... Thermal insulation support layer, 4 .... Electrical insulation layer, 5 .... Gas detection part, 6 .... Through-hole, 7 ... Bonding layer, 8 ... Gas detection layer electrode, 9 ...・ Selective combustion layer, 10. 50 .. First acquisition unit, 60... Second acquisition unit, 70... Third 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 measurement unit for measuring a resistance value of the gas sensing layer;
A heating controller that controls the heater to heat the gas sensing layer;
A first acquisition unit for acquiring a first resistance value of the gas sensing layer measured by the measurement unit in a state where the temperature of the gas sensing layer is controlled to the first temperature by the heating control unit;
When the first resistance value is less than or equal to a predetermined first threshold, the measurement unit measures the temperature of the gas sensing layer controlled to a second temperature lower than the first temperature by the heating control unit. A second acquisition unit for acquiring a second resistance value of the gas sensing layer,
When the second resistance value is less than or equal to a predetermined second threshold, the measurement is performed by the measurement unit 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 for acquiring a third resistance value of the gas sensing layer,
A discriminating unit for discriminating an existing gas type based on the third resistance value;
With gas sensor. The determination 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 determination unit determines 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 determination unit determines that the detection target gas is present when the third resistance value is equal to or greater than the third threshold value, and determines that the third resistance value is smaller than the third threshold value, The gas sensor according to claim 2, wherein it is determined that a gas other than the detection target gas exists. The detection target gas is methane gas,
The determination unit determines that the detection target gas exists when the third resistance value is equal to or less than the third threshold value, and determines that the detection target gas is greater than the third threshold value when the third resistance value is greater than the third threshold value. The gas sensor according to claim 2, wherein it is determined that a gas other than the detection target gas exists. The gas sensor according to claim 3 or 4, wherein the gas other than the detection target gas includes alcohol. The determination unit includes a change rate calculation unit that calculates a time change rate of the third resistance value.
The gas sensor according to claim 1, wherein the determination unit determines an existing gas type based on a time change rate of the third resistance value. The detection target gas is LP gas,
The determination unit determines that the detection target gas exists when the time change rate of the third resistance value is equal to or higher than a predetermined change rate threshold value, while the time of the third resistance value is determined. The gas sensor according to claim 6, wherein when the change rate is smaller than the change rate threshold, it is determined that a gas other than the detection target gas exists. The detection target gas is methane gas,
The determination unit determines that the detection target gas exists when the time change rate of the third resistance value is equal to or less than a predetermined change rate threshold value, while the time of the third resistance value is determined. The gas sensor according to claim 6, wherein when the rate of change is larger than the change rate threshold, it is determined that a gas other than the detection target gas exists. The determination unit includes a timing detection unit that detects a timing at which the third resistance value starts to increase,
The gas sensor according to claim 1, wherein the determination unit determines an existing gas type based on a timing at which the third resistance value starts to increase. The detection target gas is LP gas,
The discriminating unit discriminates that the detection target gas exists when the third resistance value starts to increase within a predetermined time, while the predetermined time elapses. The gas sensor according to claim 9, wherein when the three resistance value is stagnant or decreased, it is determined that a gas other than the detection target gas exists. The detection target gas is methane gas,
The determination unit determines that the detection target gas exists when the third resistance value is stagnant or decreased even after a predetermined time elapses, and 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 exists. The gas sensor according to any one of claims 1 to 11, wherein the heating control unit changes the third temperature in accordance with the second resistance value. The gas sensor according to any one of claims 1 to 11, wherein the third acquisition unit changes a timing at which the third resistance value is acquired according to the second resistance value. The gas sensor according to any one of claims 2 to 5, wherein the determination 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 a 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. A gas sensor according to any one of claims 1 to 16, comprising:
A gas alarm device further comprising an alarm generation unit that generates an alarm when the detection target gas is detected. A control device that controls a gas sensor that has a gas sensing layer and a heater for heating the gas sensing layer, and detects a detection target gas based on a resistance value of the gas sensing layer heated by the heater. ,
A heating controller that controls the heater to heat the gas sensing layer;
A first acquisition unit configured to acquire a 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;
The gas measured when the temperature of the gas sensing layer is controlled to a second temperature lower than the first temperature by the heating control unit when the first resistance value is equal to or lower than a predetermined first threshold value. A second acquisition unit for acquiring a second resistance value of the sensing layer;
The gas measured when the temperature of the gas sensing layer is controlled to a third temperature higher than the second temperature by the heating controller when the second resistance value is equal to or lower than a predetermined second threshold value. A third acquisition unit for acquiring a third resistance value of the sensing layer;
A determining unit that determines an existing gas type based on the third resistance value. A gas sensor control method comprising: 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 first temperature control step of controlling the temperature of the gas sensing layer to a first temperature;
A first obtaining step of obtaining a 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;
A second temperature control step of controlling 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 lower than a predetermined first threshold;
A second obtaining step of obtaining a 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;
A third temperature control step of controlling the temperature of the gas sensing layer to a third temperature higher than the second temperature when the second resistance value is equal to or lower than a predetermined second threshold;
A third obtaining step of obtaining a 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 determination step of determining an existing gas type based on the third resistance value acquired in the third acquisition step.

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