Gas detector and method for diagnosing of gas detector

Abstract

To provide a gas detector capable of precisely diagnosing a gas sensor for malfunctions.SOLUTION: A gas detector 100 has a control unit 1 for diagnosing a gas sensor 21 for malfunctions on the basis of output from the gas sensor 21 when a charge state of storing charges in the gas sensor 21 including an action electrode 21a and a counter electrode 21b and a discharge state of releasing charges in the gas sensor 21 are switched. The control unit 1 determines whether the gas sensor 21 is malfunctioning, on the basis of output acquired after discharge of the gas sensor 21 and a predetermined threshold value based on output at a predetermined time before diagnosis of the gas sensor 21 is started.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a gas detection device and a diagnostic method for a gas detection device, and particularly to a gas detection device for diagnosing a failure of a gas sensor and a diagnostic method for a gas detection device.

Background Art

[0002] Conventionally, a gas detection device for diagnosing a failure of a gas sensor has been known (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses an alarm (gas detection device) including a gas sensor including a sensing electrode and a counter electrode, a current / voltage conversion circuit that converts a current flowing through the gas sensor into a voltage, and a self-diagnosis means that diagnoses a failure of the gas sensor based on the output voltage of the current / voltage conversion circuit. In the alarm of Patent Document 1, the self-diagnosis means stores and charges electric charges between the sensing electrode and the counter electrode of the gas sensor, then discharges, and diagnoses a failure of the gas sensor based on the output voltage of the current / voltage conversion circuit at that time. Further, the self-diagnosis means diagnoses a failure of the gas sensor by comparing the output voltage of the current / voltage conversion circuit at a preset time point during charging and discharging of the gas sensor with a preset threshold value.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1 described above, the self-diagnosis means diagnoses the failure of the gas sensor by comparing the output voltage of the current / voltage conversion circuit at a preset time point during charging and discharging of the gas sensor with a preset threshold value. For this reason, when the output voltages during charging and discharging of the gas sensor vary due to individual differences in the gas sensors, the magnitude relationship with respect to the preset threshold value will be different. As a result, it is difficult to accurately diagnose the failure of the gas sensor.

[0006] The present invention has been made to solve the above problems, and one object of the present invention is to provide a gas detection device and a diagnosis method for a gas detection device capable of accurately diagnosing the failure of a gas sensor.

Means for Solving the Problems

[0007] In order to achieve the above object, a gas detection device according to a first aspect of the present invention includes a control unit that diagnoses the failure of a gas sensor based on an output from the gas sensor when switching between a charging state of storing charge in the gas sensor including a working electrode and a counter electrode and a discharging state of discharging the charge stored in the gas sensor. The control unit determines whether the gas sensor is faulty based on the output obtained after discharging of the gas sensor and a predetermined threshold value based on the output at a predetermined time point before the start of diagnosis of the gas sensor.

[0008] In the gas detection device according to the first aspect of the present invention, as described above, a control unit is provided that determines whether the gas sensor is faulty based on the output obtained after discharging of the gas sensor and a predetermined threshold value based on the output at a predetermined time point before the start of diagnosis of the gas sensor. Thereby, even when the output voltages during charging and discharging of the gas sensor vary due to individual differences in the gas sensors, a predetermined threshold value can be set based on the detection signal at a predetermined time point before the start of diagnosis of the gas sensor. As a result, when the gas sensor is charged and then discharged, the detection signal returns to the value before charging, so that even when there are individual differences in the gas sensors, the failure of the gas sensor can be accurately diagnosed.

[0009] The diagnostic method of the gas detection device according to the second aspect of the present invention is a diagnostic method for performing a failure diagnosis of a gas sensor based on an output from the gas sensor when switching between a charging state in which charges are stored in the gas sensor including a working electrode and a counter electrode and a discharging state in which the charges stored in the gas sensor are discharged. In this diagnostic method, based on the output obtained after discharging the gas sensor and a predetermined threshold value based on the output at a predetermined time point before the start of the diagnosis of the gas sensor, it is determined whether the gas sensor is faulty.

[0010] In the diagnostic method of the gas detection device according to the second aspect of the present invention, as described above, based on the output obtained after discharging the gas sensor and a predetermined threshold value based on the output at a predetermined time point before the start of the diagnosis of the gas sensor, it is determined whether the gas sensor is faulty. Thereby, even when the output voltages during charging and discharging of the gas sensor vary due to individual differences in the gas sensor, a predetermined threshold value can be set based on the detection signal at a predetermined time point before the start of the diagnosis of the gas sensor. As a result, when the gas sensor is charged and then discharged, since the detection signal returns to the value before charging, it is possible to provide a diagnostic method for a gas detection device capable of accurately diagnosing the failure of the gas sensor even in the case of individual differences in the gas sensor.

Effects of the Invention

[0011] According to the present invention, as described above, the failure of the gas sensor can be accurately diagnosed.

Brief Description of the Drawings

[0012]

Figure 1

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Figure 13

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0014] With reference to FIGS. 1 to 13, the configuration of a gas detection device 100 according to an embodiment will be described.

[0015] (Configuration of the Alarm System) As shown in FIG. 1, the gas detection device 100 is configured to detect a gas to be detected and give an alarm.

[0016] As shown in FIG. 1, the gas detection device 100 includes a control unit 1, a sensor unit 2, an alarm unit 3, and a power supply unit 4.

[0017] The control unit 1 is configured to control each part of the gas detection device 100. Further, the control unit 1 includes a processor such as an MCU (Micro Controller Unit) that executes a program to perform processing, and a memory that stores the program.

[0018] The sensor unit 2 is configured to detect a gas to be detected. The sensor unit 2 detects, for example, CO gas, methane gas, propane gas, etc. as the gas to be detected. The sensor unit 2 includes an electrochemical gas sensor. The sensor unit 2 detects the gas when the output voltage changes when the gas to be detected is present.

[0019] The alarm unit 3 is configured to issue an alarm to the surroundings when the gas to be detected is detected by the sensor unit 2. The alarm unit 3 issues an alarm, for example, by a buzzer sound, a voice message, a light output, a display of information, etc. The alarm unit 3 includes, for example, a speaker, a light emitting unit, a display screen, etc.

[0020] The power supply unit 4 supplies power to each part of the gas detection device 100. The power supply unit 4 includes a power conversion circuit connected to a commercial power supply. Further, the power supply unit 4 may be, for example, a battery.

[0021] As shown in FIG. 2, the sensor unit 2 includes a gas sensor 21, a constant voltage circuit unit 22, and a signal output unit 23. The gas sensor 21 includes a working electrode 21a and a counter electrode 21b.

[0022] As shown in FIG. 2, the gas sensor 21 can be represented as a circuit having a resistance component Rs, a capacitance component Cp, and a resistance component Rp. That is, each element of the gas sensor 21 as a circuit can be regarded as being arranged as follows. The resistance component Rs is arranged on the working electrode 21a side and is connected in series with the capacitance component Cp and the resistance component Rp connected in parallel. The capacitance component Cp and the resistance component Rp connected in parallel are arranged on the counter electrode 21b side.

[0023] Also, a resistor R3 is provided in parallel with the gas sensor 21. Further, a resistor R4 is connected to the working electrode 21a side of the gas sensor 21. Also, a resistor R5 is connected to the counter electrode 21b side of the gas sensor 21.

[0024] The constant voltage circuit section 22 generates a reference voltage for the sensor section 2. As shown in FIG. 2, the constant voltage circuit section 22 is connected to the counter electrode 21b side of the gas sensor 21. The constant voltage circuit section 22 includes a resistor R1, a resistor R2, a capacitor C1, a capacitor C2, and an OP amplifier U1. The resistor R1 is connected to the voltage VCC supplied from the power supply section 4. The resistor R2 is connected in series to the resistor R1 and is connected to the ground potential. The capacitor C1 is connected in parallel with the resistor R2, in series to the resistor R1, and is connected to the ground potential. The OP amplifier U1 has its plus side connected between the resistors R1 and R2, and its minus side connected to the output. The capacitor C2 is connected between the voltage VCC of the OP amplifier U1 and the ground potential.

[0025] The signal output section 23 is connected to the gas sensor 21 and outputs a detection signal based on the power input from the gas sensor 21. The signal output section 23 converts a current into a voltage and outputs a detection signal. As shown in FIG. 2, the signal output section 23 includes a resistor R6, a resistor R7, a resistor R9, a capacitor C3, a capacitor C4, and an OP amplifier U2. The resistor R6 is connected to the working electrode 21a side of the gas sensor 21 and to the minus side of the OP amplifier U2. The resistor R7 is connected to the counter electrode 21b side of the gas sensor 21 and to the plus side of the OP amplifier U2. The resistor R9 and the capacitor C3 are connected in parallel with the resistor R6 and the OP amplifier U2 to the working electrode 21a side of the gas sensor 21. The capacitor C4 is connected between the voltage VCC of the OP amplifier U2 and the ground potential.

[0026] A resistor R8 is connected between the resistor R7 and the positive side of the operational amplifier U2. The resistor R8 has a switch Q1 connected to it. The switch Q1 can be switched between an on state in which a current flows from the resistor R8 side to the ground potential according to an on-off control signal from the control unit 1, and an off state in which no current flows from the resistor R8 side to the ground potential.

[0027] A resistor R10 is connected to the output side of the operational amplifier U2. A detection signal is output from the resistor R10 to the control unit 1. Specifically, the detection signal is amplified by an amplifier circuit and then input to the control unit 1. Also, a capacitor C5 is connected between the resistor R10 and the ground potential.

[0028] The switch Q1 switches the circuit between a charging state in which charges are stored between the working electrode 21a and the counter electrode 21b of the gas sensor 21 and a discharging state in which the charges between the working electrode 21a and the counter electrode 21b of the gas sensor 21 are released. Specifically, when the switch Q1 is in the on state, it is in a charging state in which charges are stored between the working electrode 21a and the counter electrode 21b of the gas sensor 21. Also, when the switch Q1 is in the off state, it is in a discharging state in which the charges between the working electrode 21a and the counter electrode 21b of the gas sensor 21 are released. Also, the switch Q1 is in the off state when detecting gas.

[0029] As shown in FIG. 3, when the switch Q1 before charging is in the off state, the gas sensor 21 usually has no current flowing when the gas to be detected is not present. Since no current flows through the gas sensor 21 before charging, due to the negative feedback action of the operational amplifier U2, the working electrode 21a and the counter electrode 21b are at the same potential. That is, the capacitive component Cp is in a state without charge.

[0030] As shown in Fig. 4, when switch Q1 is turned on for charging, resistor R8 is connected to the ground potential, and the voltage on the positive side of operational amplifier U2 is pulled down (in+ < in-). That is, the voltage on the positive side of operational amplifier U2 becomes the voltage obtained by dividing the reference voltage Vref with resistors R7 and R8. As a result, the balance of the input terminal voltage of operational amplifier U2 is disrupted, and the output voltage of operational amplifier U2 decreases.

[0031] As a result, current flows through the path of reference voltage Vref → resistor R5 → capacitive component Cp / / resistive component Rp → resistive component Rs → resistor R4 → capacitor C3 / / resistor R9 → the output side of operational amplifier U2. As a result, a potential difference is generated across the capacitive component Cp of gas sensor 21, and the capacitive component Cp is charged.

[0032] As shown in Fig. 5, when switch Q1 is turned off for discharging after charging, resistor R8 becomes open, and the voltage on the positive side of operational amplifier U2 returns to the original reference voltage Vref. As a result, since the potential on the negative side of operational amplifier U2 has decreased due to charging (in+ > in-), the voltage on the output side of operational amplifier U2 increases. As a result, current flows through the path of the output side of operational amplifier U2 → capacitor C3 / / resistor R9 → resistor R4 → resistive component Rs → capacitive component Cp / / resistive component Rp → resistor R5 → reference voltage Vref. As a result, the potential difference of gas sensor 21 gradually disappears. As the disappearance of the potential difference of gas sensor 21 progresses, the output voltage from operational amplifier U2 gradually decreases and finally converges to the state before charging.

[0033] As shown in Fig. 6, at time T0, charging starts, and then, at time T1, it is switched from charging to discharging. When charging starts, the detection signal decreases to 0V. And when it is switched from charging to discharging, the detection signal rises, exceeds the voltage before charging, and then converges to the voltage before charging.

[0034] Also, as shown in FIG. 7, due to individual differences, the reference voltage of the gas sensor 21 may vary. In this case, when discharging after charging, the detection signal converges to the reference voltage after exceeding the reference voltage which is the voltage before charging.

[0035] Also, as shown in FIG. 8, due to individual differences, when discharging after charging, the voltage return of the gas sensor 21 may be slow. That is, for the gas sensor 21, the time until the voltage returns after discharging after charging may vary due to individual differences.

[0036] Also, as shown in FIG. 9, when the gas sensor 21 fails due to a sensor open, since the capacitance component Cp disappears, even if the switch Q1 is turned on, the gas sensor 21 is not charged. That is, when the gas sensor 21 fails due to a sensor open, even if the switch Q1 is turned on and the voltage on the output side of the OP amplifier U2 drops to draw in current, the gas sensor 21 is not charged. Also, since the gas sensor 21 is not charged, even if the switch Q1 is switched from the on state to the off state, the voltage of the detection signal does not increase significantly.

[0037] That is, when the gas sensor 21 fails due to a sensor open, as shown in FIG. 10, even if the switch Q1 is turned on at time T0, the detection signal does not drop to 0V. Also, even if the switch Q1 is turned off at time T1, the detection signal does not exceed the original voltage and converges to the original voltage.

[0038] Also, as shown in FIG. 11, when the gas sensor 21 fails due to a sensor short, since the capacitance component Cp disappears, even if the switch Q1 is turned on, the gas sensor 21 is not charged. That is, when the gas sensor 21 fails due to a sensor short, even if the switch Q1 is turned on and the voltage on the output side of the OP amplifier U2 drops to draw in current, the gas sensor 21 is not charged. Also, since the gas sensor 21 is not charged, even if the switch Q1 is switched from the on state to the off state, the voltage of the detection signal does not increase significantly.

[0039] That is, when the gas sensor 21 malfunctions due to a sensor short circuit, as shown in FIG. 12, when the switch Q1 is turned on at time T0, the detection signal drops to 0V. Then, even when the switch Q1 is turned off at time T1, the detection signal converges to the original voltage without exceeding the original voltage.

[0040] Here, in the present embodiment, the control unit 1 determines whether the gas sensor 21 is malfunctioning based on the output of the detection signal acquired after the discharge of the gas sensor 21 and a predetermined threshold based on the output of the detection signal at a predetermined time point before the diagnosis of the gas sensor 21. Specifically, the control unit 1 determines that the gas sensor 21 is malfunctioning based on the fact that the detection signal acquired after charging and then discharging the gas sensor 21 is less than or equal to a predetermined threshold based on the detection signal at a predetermined time point before the diagnosis of the gas sensor 21.

[0041] That is, the control unit 1 sets a predetermined threshold based on the detection signal before charging the gas sensor 21. For example, as shown in FIG. 7, the control unit 1 sets a predetermined threshold based on the detection signal before charging. In FIG. 7, in the case of the gas sensor 21 having a broken-line waveform with a relatively small value of the detection signal before charging, a predetermined threshold Th1 is set based on the detection signal before charging. Also, in the case of the gas sensor 21 having a solid-line waveform with a relatively large value of the detection signal before charging, a predetermined threshold Th2 (Th2 > Th1) is set based on the detection signal before charging.

[0042] Further, the control unit 1 may set a predetermined threshold based on the output of the detection signal at that time based on the previous diagnosis result of the gas sensor 21. Also, the control unit 1 may set a predetermined threshold based on the detection signal at the time of manufacturing, factory shipment, or installation of the gas detection device 100.

[0043] Further, the control unit 1 sets a value larger than the detection signal at a predetermined time point before the start of diagnosis of the gas sensor 21 as a predetermined threshold value. For example, the control unit 1 sets, as the predetermined threshold value, a value obtained by adding a uniform numerical value to the detection signal at a predetermined time point before the start of diagnosis of the gas sensor 21. Further, the control unit 1 sets, as the predetermined threshold value, a value obtained by increasing the detection signal before charging by a predetermined ratio (for example, about 1% to 10%).

[0044] Also, in the present embodiment, the control unit 1 performs a failure diagnosis of the gas sensor 21 based on the detection signal from the signal output unit 23 when switching the charging (on state) and discharging (off state) of the gas sensor 21 by the switch Q1. Specifically, the control unit 1 acquires a plurality of detection signals after discharging of the gas sensor 21 at different times, and determines whether the gas sensor 21 is faulty based on all the detection signals. Specifically, the control unit 1 determines that the gas sensor 21 is faulty based on the fact that all of the acquired detection signals are below a predetermined threshold value.

[0045] For example, as shown in FIG. 6, the control unit 1 acquires detection signals at times T2, T3, and T4 after charging and then discharging. In the example shown in FIG. 6, between time T1 and time T2 after charging and then discharging, the value of the detection signal exceeds a predetermined threshold value Th1. That is, the detection signal exceeds the predetermined threshold value Th1 at times T2, T3, and T4. In this case, the control unit 1 determines that the gas sensor 21 is normal.

[0046] Also, in the example shown in FIG. 10, after charging (switch Q1 in the on state) and then discharging (switch Q1 in the off state), the detection signal does not exceed the predetermined threshold value Th1. That is, the detection signal is below the predetermined threshold value Th1 at any of times T2, T3, and T4. In this case, the control unit 1 determines that the gas sensor 21 is faulty.

[0047] Also, in the case of the example shown in FIG. 12, after charging (switch Q1 is in the ON state) and then discharging (switch Q1 is in the OFF state), the detection signal does not exceed a predetermined threshold Th1. That is, the detection signal is equal to or less than the predetermined threshold Th1 at any of times T2, T3, and T4. In this case, the control unit 1 determines that the gas sensor 21 is malfunctioning.

[0048] Further, when the control unit 1 charges the gas sensor 21 and the detection signal obtained after discharging exceeds a predetermined threshold value, the control unit 1 may determine that the gas sensor 21 is normal and stop acquiring detection signals for subsequent fault diagnosis. For example, in the example shown in FIG. 6, the control unit 1 acquires a detection signal at time T2 after charging and then discharging. Since the detection signal acquired by the control unit 1 at time T2 exceeds the predetermined threshold Th1, the control unit 1 determines that the gas sensor 21 is normal. Further, the control unit 1 does not acquire detection signals for fault diagnosis at subsequent times T3 and T4. Also, in the example shown in FIG. 8, the control unit 1 acquires a detection signal at time T2 after charging and then discharging. Since the detection signal acquired by the control unit 1 at time T2 is equal to or less than the predetermined threshold Th1, the control unit 1 acquires a detection signal at time T3 after charging and then discharging. Since the detection signal acquired by the control unit 1 at time T3 exceeds the predetermined threshold Th1, the control unit 1 determines that the gas sensor 21 is normal. Further, the control unit 1 does not acquire detection signals for fault diagnosis at the subsequent time T4.

[0049] Also, the control unit 1 acquires detection signals at every predetermined interval after charging the gas sensor 21 and determines whether the gas sensor 21 is normal or malfunctioning based on the plurality of acquired detection signals. Specifically, as shown in FIG. 6, the control unit 1 acquires detection signals at every time interval Ta starting from the start of discharging. For example, the time interval Ta is about 0.1 second to several seconds. Preferably, the time interval Ta is about 1 second.

[0050] Further, after charging the gas sensor 21, the control unit 1 acquires detection signals at predetermined intervals longer than the time for charging the gas sensor 21 after discharge, and determines whether the gas sensor 21 is normal or faulty based on the plurality of acquired detection signals. For example, the control unit 1 acquires detection signals for determining a fault at predetermined time intervals that are several to several tens of times the charging time.

[0051] Further, after charging the gas sensor 21, the control unit 1 acquires detection signals at three or more different times after discharge, and determines whether the gas sensor 21 is normal or faulty based on the three or more acquired detection signals. For example, as shown in FIG. 6, the control unit 1 acquires detection signals for determining a fault at three different times, namely, times T2, T3, and T4 after discharge.

[0052] Further, in the present embodiment, at a first time point, the control unit 1 acquires a first difference, which is the difference between a detection signal exceeding a predetermined threshold after discharging the gas sensor 21 and the predetermined threshold. Specifically, at the first time point, the control unit 1 acquires, from among the plurality of detection signals acquired at different times after discharging the gas sensor 21, the first difference, which is the difference between the detection signal exceeding the predetermined threshold and the predetermined threshold. Further, at a second time point after the first time point, the control unit 1 acquires a second difference, which is the difference between a detection signal exceeding a predetermined threshold after discharging the gas sensor 21 and the predetermined threshold. Specifically, at the second time point after the first time point, the control unit 1 acquires, from among the plurality of detection signals acquired at different times after discharging the gas sensor 21, the second difference, which is the difference between the detection signal exceeding the predetermined threshold and the predetermined threshold. Then, the control unit 1 compares the first difference and the second difference to determine the deterioration state of the gas sensor 21.

[0053] For example, as shown in FIG. 13, when the determination of a failure is first made at time point A1, then at time point A2, and then at time point A3, over time, the return of the detection signal after discharge may become slower. Therefore, the difference exceeding a predetermined threshold value at each time point is compared to determine the degradation state. Note that the time points for determining a failure are, for example, time points every one day to several months.

[0054] In the example shown in FIG. 13, at time point A1, at time T2, since the detection signal exceeds a predetermined threshold value Th1, the difference at time T2 is acquired. At time point A2, at time T2, since the detection signal exceeds a predetermined threshold value Th1, the difference at time T2 is acquired. At time point A3, at time T3, since the detection signal exceeds a predetermined threshold value Th1, the difference at time T3 is acquired.

[0055] The control unit 1 determines the degradation state of the gas sensor 21 based on, for example, the change rate or change amount of the difference at each time point.

[0056] Further, the control unit 1 sets a predetermined threshold value according to the charging time during the failure diagnosis of the gas sensor 21. Specifically, the control unit 1 changes the charging time according to the state of the gas sensor 21. Then, when the charging time is long, the control unit 1 sets a large predetermined threshold value based on the detection signal before charging, and when the charging time is short, the control unit 1 sets a small predetermined threshold value based on the detection signal before charging.

[0057] Also, when the detection signal acquired after discharging the gas sensor 21 after charging is near a predetermined threshold value, the control unit 1 may increase the charging time and perform the failure diagnosis again. For example, when the detection signal after discharging during the failure diagnosis is approximately equal to the predetermined threshold value and the detection signal is a value such that it exceeds or does not exceed the predetermined threshold value, the control unit 1 increases the charging time and performs the failure diagnosis again.

[0058] In addition, when the detection signal satisfies a predetermined condition, the control unit 1 does not perform a failure diagnosis of the gas sensor 21. For example, the control unit 1 may not perform a failure diagnosis of the gas sensor 21 when the detection signal detects a gas at the alarm level. That is, in the gas detection device 100 of the present embodiment, it is possible to perform a failure diagnosis of the gas sensor 21 regardless of the atmosphere. However, for example, from the viewpoint of protecting the user, the alarm may be prioritized, or the diagnosis may not be performed in consideration of the load on the gas sensor 21. Further, the control unit 1 may not perform a failure diagnosis of the gas sensor 21 when the output of the detection signal reaches a predetermined value once or a plurality of times within a predetermined period. Further, the control unit 1 may not perform a failure diagnosis when the output of the detection signal maintains a value equal to or greater than a predetermined value for a predetermined period.

[0059] In addition, the control unit 1 detects the gas to be detected based on the cumulative value of the detection signals other than during the failure diagnosis. That is, when detecting the gas to be detected, the control unit 1 starts detecting the gas in a reset state when the detection signal during the failure diagnosis is accumulated.

[0060] (Effect of the present embodiment) In the present embodiment, the following effects can be obtained.

[0061] Further, in the present embodiment, as described above, based on the output of the detection signal acquired after the discharge of the gas sensor 21 and a predetermined threshold value based on the output of the detection signal at a predetermined time point before the start of the diagnosis of the gas sensor 21, a control unit 1 for determining whether the gas sensor 21 is faulty is provided. Thereby, even when the output voltages during charging and discharging of the gas sensor 21 vary due to the presence of the gas to be detected in the atmosphere, a predetermined threshold value can be set based on the detection signal at a predetermined time point before the start of the diagnosis of the gas sensor 21. As a result, when the gas sensor 21 is charged and then discharged, the detection signal returns to the value before charging, so that a predetermined threshold value for performing a failure diagnosis can be set to an appropriate value according to the atmosphere. As a result, the failure of the gas sensor 21 can be accurately diagnosed regardless of the atmosphere.

[0062] (Modification example) It should be noted that the embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims rather than the description of the above embodiments, and further includes all modifications (modification examples) within the meaning and scope equivalent to the claims.

[0063] For example, in the above embodiment, an example in which one gas sensor is provided in the gas detection device is shown, but the present invention is not limited to this. In the present invention, a plurality of gas sensors for detecting gases with different detection targets may be provided in the gas detection device. In this case, the control unit may perform the diagnosis of the present invention for at least one gas sensor.

[0064] In addition, the gas detection device may be provided with other warning functions. For example, the gas detection device may be provided with a function of fire alarm (fire notification).

[0065] Also, in the above embodiment, an example in which detection signals are acquired at a plurality of different times after charging and discharging when diagnosing the gas sensor is shown, but the present invention is not limited to this. In the present invention, a detection signal may be acquired at a certain one time after charging and discharging.

[0066] Also, in the above embodiment, an example in which detection signals are acquired at three different times after charging and discharging when diagnosing the gas sensor is shown, but the present invention is not limited to this. In the present invention, detection signals may be acquired at two or a plurality of four or more different times after charging and discharging.

[0067] Also, in the above embodiment, an example in which detection signals are acquired at predetermined intervals after charging and discharging when diagnosing the gas sensor is shown, but the present invention is not limited to this. In the present invention, when diagnosing the gas sensor, a plurality of detection signals may be acquired continuously after charging and discharging. Also, when diagnosing the gas sensor, detection signals may be acquired at different time intervals after charging and discharging.

[0068] In addition, in the above-described embodiment, an example of a configuration is shown in which it is determined that the gas sensor is faulty based on the fact that the output of the gas sensor after discharge is equal to or less than a predetermined threshold value based on the output at a predetermined time point before the start of diagnosis of the gas sensor. However, the present invention is not limited to this. In the present invention, it may be determined that the gas sensor is faulty based on the fact that the output of the gas sensor after discharge is equal to or greater than a predetermined threshold value based on the output at a predetermined time point before the start of diagnosis of the gas sensor. For example, when the output increases due to charging of the gas sensor and decreases due to discharge, and the output of the gas sensor after discharge does not become smaller than the threshold value, it may be determined that the gas sensor is faulty.

[0069] Also, a predetermined range may be set from a predetermined threshold value based on the output at a predetermined time point before the start of diagnosis of the gas sensor, and it may be determined that there is a fault when the output of the gas sensor after discharge is within or outside the predetermined range.

Explanation of Reference Numerals

[0070] 1 Control unit 21 Gas sensor 21a Working electrode 21b Counter electrode 100 Gas detection device

Claims

Claim 1 A control unit is provided for performing failure diagnosis of a gas sensor based on an output from the gas sensor when switching between a charged state in which charge is stored in the gas sensor including a working electrode and a counter electrode and a discharged state in which the charge stored in the gas sensor is discharged. The control unit determines whether the gas sensor has failed based on the output obtained after discharging of the gas sensor and a predetermined threshold value based on the output at a predetermined time point before the start of diagnosis of the gas sensor. A gas detection device. Claim 2 In a diagnostic method for performing failure diagnosis of a gas sensor based on an output from the gas sensor when switching between a charged state in which charge is stored in the gas sensor including a working electrode and a counter electrode and a discharged state in which the charge stored in the gas sensor is discharged. A diagnostic method for a gas detection device, wherein it is determined whether the gas sensor has failed based on the output obtained after discharging of the gas sensor and a predetermined threshold value based on the output at a predetermined time point before the start of diagnosis of the gas sensor.

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