JP4834616B2 - Alarm - Google Patents

Description

  The present invention relates to an alarm device, and more particularly, to an alarm device that self-diagnose whether there is a failure in an electrochemical gas sensor that detects a target gas concentration by a reaction between water vapor from a water container that contains water and the target gas. Is.

  As a device for measuring the CO concentration in the ambient atmosphere, such as a CO alarm device that detects and alarms CO gas due to incomplete combustion of combustion equipment, etc., a device that has conventionally incorporated an electrochemical CO sensor (= gas sensor) Are known.

  As shown in a sectional view in FIG. 7, this electrochemical CO sensor 1 has a proton conductor film 3 installed in an upper opening 4 of a metal can 2 (= water container) in which water 5 is accommodated. The counter electrode 32 is exposed in the metal can 2, and the metal cap 8 including the gas adsorption filter 8 c is overlapped on the opposite detection electrode 31 and is caulked and fixed to the upper opening 4 of the metal can 2.

In the electrochemical CO sensor 1 having the above-described configuration, CO (= target gas) in the ambient atmosphere is introduced into the inside through the introduction hole 8a of the metal cap 8, and the gas adsorption filter 8c made of activated carbon, silica gel, zeolite, or the like. Through the diffusion control hole 7a of the metal diffusion prevention plate 7 interposed between the metal cap 8 and the proton conductor film 3, and reaches the detection electrode 31, where the counter electrode Oxidation reaction using the water 5 in the metal can 2 supplied to the proton conductor film 3 from the 32 side is caused to generate protons (2H ⁺ ) and electrons (2e ⁻ ) at the detection electrode 31.

The electrons (2e ⁻ ) generated in the detection electrode 31 cannot pass through the proton conductor film 3 and therefore stay in the detection electrode 31, while the proton (2H ⁺ ) passes through the proton conductor film 3. It moves to the counter electrode 32, where it causes a reduction reaction with oxygen in the metal can 2 to generate water (H ₂ O) at the counter electrode 32.

  Therefore, between the metal cap 8 that is electrically connected to the detection electrode 31 and functions as its terminal, and the metal can 2 that is electrically connected to the counter electrode 32 via the diffusion prevention plate 7 and functions as its terminal. When a load (not shown) is connected, a flow of electrons (2e−) staying at the detection electrode 31 toward the counter electrode 32 is generated in the load, whereby a short-circuit current flows from the counter electrode 32 to the detection electrode 31 through the load. Therefore, a CO concentration signal having a voltage value corresponding to the CO concentration in the ambient atmosphere can be obtained by current-voltage conversion of the short-circuit current flowing through the load (for example, Patent Documents 1 and 2).

  Further, as described above, as a gas sensor that utilizes the reaction between water vapor from a water container and a target gas, an ion conductive solid electrolytic membrane is provided between two electrodes, and a constant relative humidity is maintained in the ion conductive solid electrolytic membrane. There is a gas sensor including a water container filled with water (for example, Patent Document 3).

  The CO sensor 1 itself does not require an external power supply in order to generate a CO concentration signal having a voltage value corresponding to the CO concentration in the ambient atmosphere. Suitable for use with certain CO alarms.

  By the way, the above-mentioned CO alarm device has conventionally performed self-diagnosis for detecting failures such as “no water”, “disconnection”, and “short circuit” in which water in the metal can 2 is reduced (for example, Patent Document 3). . The self-diagnosis of the CO sensor 1 regards this CO sensor 1 as a kind of capacitor, and uses the fact that the current waveform at the time of discharge differs from the normal state due to failures such as “no water”, “disconnection”, and “short circuit”. Is going.

However, “no water”, “disconnection”, and “short circuit” all have the same current waveform during discharge. Therefore, if the self-diagnosis is performed only with the current waveform at the time of discharge as in the past, it can be understood that it is a failure, but whether the reason for the failure is "no water" or "disconnection" or "short circuit" As a result, there was a problem that failure analysis after failure occurred could not be performed quickly.
JP 2004-170101 A JP 2004-279293 A JP 2000-146908 A

  Accordingly, an object of the present invention is to provide an alarm device that can quickly analyze a failure after the occurrence of a failure by paying attention to the above problems and determining the reason for the failure.

  Invention of Claim 1 made | formed in order to solve the said subject, The electrochemical gas sensor which detects the said object gas concentration by reaction with the water vapor | steam from the water container which accommodates water, or the water vapor | steam in air | atmosphere, and object gas, A discharge resistor connected to the gas sensor; a power source for supplying current to the gas sensor to charge the gas sensor; and a changeover switch provided between the power source and the gas sensor to switch charging and discharging of the gas sensor; Switch control means for turning off the changeover switch to charge the gas sensor after turning on the changeover switch and discharging the gas sensor, and failure of the gas sensor based on a discharge current flowing during discharge of the gas sensor by the switch control means And a first self-diagnosis means for detecting the first self-diagnosis. In response to the detection of the failure of the gas sensor by the stage, if the charging current flowing through the gas sensor during charging of the gas sensor by the switch control means can be regarded as 0, it is determined that there is a disconnection or no water failure, and the switch control means According to the present invention, there is provided an alarm device comprising second self-diagnosis means set so as to determine that a short-circuit fault has occurred when the current flowing through the discharge resistor can be regarded as 0 during charging of the gas sensor.

  The invention according to claim 2 is provided with a current / voltage conversion circuit for converting a discharge current flowing through the gas sensor into a voltage, and the discharge resistor is constituted by an input resistance of the current / voltage conversion circuit. It exists in the alarm device of Claim 1.

The invention according to claim 3 is a first predetermined range in which the second self-diagnostic means can assume that the charging current flowing through the gas sensor is 0 as the output of the current / voltage conversion circuit while the gas sensor is charged by the switch control means. If it is within the range, it is determined that there is a disconnection or no water failure, and the output of the current / voltage conversion circuit is within a second predetermined range in which the current flowing through the input resistance can be regarded as 0 during charging of the gas sensor by the switch control means. If the output of the current / voltage conversion circuit is not in the first predetermined range or the second predetermined range during charging of the gas sensor by the switch control means, it is determined as a circuit failure. It is set as follows, It exists in the alarm device of Claim 2 characterized by the above-mentioned.

  As described above, according to the first aspect of the invention, the second self-diagnostic means can determine whether the reason for the failure is disconnection, water, or short-circuit, so that the failure analysis after the failure occurs can be performed quickly. Can be done.

  According to the second aspect of the present invention, since it is not necessary to provide a discharge resistor separately from the current / voltage conversion circuit, the configuration is simplified and the cost can be reduced.

  According to the invention described in claim 3, since it is possible to determine whether the reason for the failure is a circuit failure by the second self-diagnostic means, the failure analysis after the occurrence of the failure can be further quickly performed.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of a gas alarm device as an alarm device according to an embodiment of the present invention. As shown in the figure, the gas alarm device includes a CO sensor 1 as a gas sensor, a microcomputer (hereinafter referred to as a microcomputer) 10, a self-diagnosis circuit 30, a current / voltage conversion circuit 40, a sound alarm output circuit 50, and the gas alarm. A battery 60 for supplying power to each part of the vessel is provided. The CO sensor 1 is, for example, the electrochemical CO sensor 1 shown in FIG. 7 described above, and outputs a short-circuit current I corresponding to the CO concentration to the current / voltage conversion circuit 40.

  The current / voltage conversion circuit 40 is provided between the operational amplifier 41 having the detection electrode 31 of the CO sensor 1 connected to the negative input terminal and the counter electrode 32 connected to the positive input terminal, and between the negative input terminal and the output terminal of the operational amplifier 41. A voltage signal corresponding to the short-circuit current I is output to the microcomputer 10. A resistor Rs is provided between the detection electrode 31 of the CO sensor 1 and the negative input terminal of the operational amplifier 41. A switch SW2 is provided in parallel with the resistor Rs. The switch SW2 is controlled to be turned on / off by the microcomputer 10.

  The microcomputer 10 includes a CPU 10a that performs various processes according to a processing program, a ROM 10b that stores a program for processing performed by the CPU 10a, a work area that is used in various processes in the CPU 10a, a data storage area that stores various data, and the like. The RAM 10c has a timer 10d for measuring the time set in a predetermined register or the date, time, etc., and these elements are connected by a bus line. The microcomputer 10 samples the voltage signal output from the current / voltage conversion circuit 40 at a predetermined sampling period and measures the CO gas concentration. When the gas concentration reaches or exceeds the alarm set point, a sound alarm is issued. An alarm is issued from the output circuit 50, and the alarm is stopped when the alarm becomes below the alarm release set point.

  Note that CO is known to be generated even when the combustion utensil is used in a normal state, and in particular, when boiling hot water using a cooking utensil such as a pan or a kettle, until the cold cooking utensil warms up. Since CO occurs during this period, even if the CO concentration (gas concentration) exceeds the alarm set point, an alarm is not generated immediately, and the alarm set point is exceeded even after a predetermined delay time has elapsed. If it continues, an alarm may be generated.

  The self-diagnosis circuit 30 is a circuit that executes a self-diagnosis of the CO sensor 1 in accordance with an instruction from the microcomputer 10. The self-diagnosis of the CO sensor 1 by the self-diagnosis circuit 30 is performed by regarding the CO sensor 1 as a kind of capacitor. The self-diagnosis circuit 30 will be described with reference to FIG. FIG. 2 is an equivalent circuit diagram of the gas alarm shown in FIG.

  In FIG. 2, Rd is the input resistance Rd of the current / voltage conversion circuit 40. The input resistance Rd is connected to both ends of the CO sensor 1 and functions as a discharge resistance. The self-diagnosis circuit 30 is provided between the current source 33 and the CO sensor 1 as a power source for supplying current to the CO sensor 1 to charge the CO sensor 1 and charging the CO sensor 1. And a changeover switch SW1 for switching between discharges. The changeover switch SW1 is controlled to be turned on / off by the microcomputer 10.

  Next, the operation at the time of self-diagnosis using the self-diagnosis circuit 30 of the gas alarm will be described. When the changeover switch SW1 is turned on and the switch SW2 is turned off according to an instruction from the microcomputer 10, the CO sensor 1 is charged from the current source 33. At this time, since the switch SW2 is off, the resistor Rs is inserted between the CO sensor 1 and the current / voltage conversion circuit 40, and the input resistance of the current / voltage conversion circuit 40 is increased to Rs + Rd. The CO sensor 1 can be efficiently charged with almost no charging current flowing through the / voltage conversion circuit 40.

  Thereafter, when the changeover switch SW1 is turned off and the switch SW2 is turned on, the charging from the current source 33 to the CO sensor 1 is interrupted, and the electric charge accumulated in the CO sensor 1 is discharged via the input resistor Rd. At this time, since the switch SW2 is on, the resistor Rs is short-circuited, and the input resistance of the current / voltage conversion circuit 40 becomes only Rd and becomes small. For this reason, the time constant becomes small, and the discharge of the CO sensor 1 can be terminated quickly. The current / voltage conversion circuit 40 converts the current flowing through the input resistor Rd into a voltage signal and outputs it to the microcomputer 10. The microcomputer 10 performs self-diagnosis based on the voltage signal output from the current / voltage conversion circuit 40 when the CO sensor 1 is charged and discharged.

  Next, voltage signals output from the current / voltage conversion circuit 40 during charging and discharging of the CO sensor 1 at normal time will be described with reference to FIG. As shown in FIG. 3A, most of the current from the current source 33 flows to the CO sensor 1 immediately after the changeover switch SW1 is turned on and charging is started. Thereafter, the current flowing through the CO sensor 1 decreases transiently toward 0 with a time constant corresponding to the capacity of the CO sensor 1. The current flowing through the input resistor Rd of the current / voltage conversion circuit 40 is 0 immediately after the start of charging, contrary to the current flowing through the CO sensor 1 as shown in FIG. Increase.

  Next, when the changeover switch SW1 is turned off to stop charging and the switch SW2 is turned on to start discharging, as shown in FIG. 3A, the CO sensor 1 has a discharging current in a direction opposite to that during charging. And then transiently decreases to 0 with a time constant corresponding to the capacitance of the CO sensor 1 and the input resistance Rd. As shown in FIG. 3B, the current flowing through the input resistor Rd of the current / voltage conversion circuit 40 flows in the same direction as during charging, and thereafter decreases transiently toward zero. The current / voltage conversion circuit 40 outputs a reference voltage of 2.6V to 2.7V when the current flowing through the input resistor Rd, that is, the current flowing through the current / voltage conversion circuit 0 is 0, and the current flowing through the input resistor Rd. A voltage signal that decreases as the value increases is output. Therefore, as shown in FIG. 3 (C), the voltage signal gradually decreases from 2.6V to 2.7V in response to the start of charging, and decreases rapidly to about 0.2V after about 25 ms when switching from charging to discharging. After that, the waveform increases and returns to 2.6V to 2.7V again.

  Next, voltage signals output from the current / voltage conversion circuit 40 during charging and discharging of the CO sensor 1 at the time of a short circuit failure will be described with reference to FIG. As shown in FIGS. 4A and 4B, when the CO sensor 1 is short-circuited, the current from the current source 33 flows only to the shorted CO sensor 1 and hardly flows to the current / voltage conversion circuit 40. Since no electric charge is accumulated in the CO sensor 1 at the time of a short circuit failure, no current flows through the CO sensor 1 and the current / voltage conversion circuit 40 even when the changeover switch SW1 is turned on to start discharging. Therefore, as shown in FIG. 4C, the voltage signal has a waveform that keeps the vicinity of the reference voltage of 2.6 V to 2.7 V during charging and discharging.

  Next, a voltage signal output from the current / voltage conversion circuit 40 when the CO sensor 1 is charged and discharged when a disconnection or waterless failure occurs will be described with reference to FIG. In the case of a disconnection or waterless failure, both of them have no capacitor component of the CO sensor 1 and are in an open state. Therefore, as shown in FIGS. 5A and 5B, the changeover switch SW1 is turned on to start charging. However, the current from the current source 33 does not flow to the CO sensor 1 but all flows to the current / voltage conversion circuit 40.

  In the case of the disconnection failure or the failure without water, the electric charge does not accumulate in the CO sensor 1, so that no current flows through the CO sensor 1 and the current / voltage conversion circuit 40 even if the changeover switch SW1 is turned on to start discharging. . Therefore, as shown in FIG. 5C, the voltage signal is constant at a voltage lower than the reference voltage of 2.6 V to 2.7 V during charging, and 2.6 V to 2.7 V when switching from charging to discharging. The waveform returns to the reference voltage.

  As shown in FIGS. 3 to 5, the microcomputer 10 performs self-diagnosis by paying attention to the fact that the voltage signal output from the current / voltage conversion circuit 40 is different during normal operation, short circuit, disconnection, or no water. . Specifically, the microcomputer 10 determines that it is normal if the following conditions (1) and (2) are satisfied.

  (1) The voltage signal is 0.2 V or less 25 ms after the start of discharge, and a discharge current flows through the CO sensor 1 after the start of discharge. (2) The voltage signal is 2.3 V to 2.8 V near the reference voltage 10 s after the start of discharge, and the discharge current flowing through the CO sensor 1 becomes 0 after a sufficient time has elapsed from the start of discharge. On the other hand, the microcomputer 10 determines that a failure has occurred unless one of the conditions (1) and (2) is satisfied.

  When the microcomputer 10 detects a failure from the voltage signal at the time of discharging, the microcomputer 10 determines the reason for the failure from the voltage signal at the time of charging. In determining the reason for the failure, the microcomputer 10 determines that the voltage signal immediately before the end of charging is 2.3 V to 2.8 V (= first predetermined range) near the reference voltage, and the current flowing through the input resistor Rd of the current / voltage conversion circuit 40. Is judged as a short-circuit fault. Further, the microcomputer 10 determines that the disconnection or water-free failure occurs when the voltage signal immediately before the end of charging is 0.2 V to 2.3 V (= second predetermined range) and the charging current flowing through the CO sensor 1 can be regarded as 0. To do. Even if the CO sensor 1 fails, as long as the self-diagnosis circuit 30 and the current / voltage conversion circuit 40 operate normally, the voltage signals are 2.3 V to 2.8 V, 0.2 V to 2 It is impossible to get out of the 3V range. Therefore, the microcomputer 10 determines that a circuit failure has occurred unless the voltage signal immediately before the end of charging is either 2.3 V to 2.8 V or 0.2 V to 2.3 V.

  Details of the operation of the gas alarm device during the self-diagnosis described above will be described below with reference to the flowchart shown in FIG. The CPU 10a performs a self-diagnosis process every hour, for example. In the self-diagnosis process, the CPU 10a turns on the changeover switch SW1 (step S1), turns off the switch SW2, and charges the CO sensor 1 (step S2).

  When 5 seconds have elapsed after the start of charging (Y in step S3), the CPU 10a captures the voltage signal at that time as a voltage signal immediately before the end of charging (step S4), and then turns off the switch SW1 and turns on the switch SW2. Then, discharging of the CO sensor 1 is started (step S5). Next, the CPU 10a turns off the switch SW2 (step S7) after 25 ms from the start of discharge and after taking in the voltage signal after 10 s (step S6).

  If the voltage signal 25 ms after the start of discharge is 0.2 V or less and the voltage signal 10 seconds after the start of discharge is 2.3 V to 2.8 V (Y in step S8, And after determining with it being normal (Y in step S9) (step S10), a self-diagnosis process is complete | finished.

  On the other hand, in the CPU 10a, the voltage signal 25 ms after the start of discharge is greater than 0.2V (N in step S8), or the voltage signal 10 seconds after the start of discharge is 2.3V-2. If it is not .8V (N in step S9), it is determined that there is a failure (step S11). Then, if the voltage signal immediately before the end of charging taken in step S4 is in the range of 2.3V to 2.8V (Y in step S12), the CPU 10a determines that a short-circuit fault has occurred (step S13), and then performs self-diagnosis. The process ends.

  On the other hand, if the voltage signal immediately before the end of the discharge taken in step S4 is within the range of 0.2V to 2.3V (Y in step S14), the CPU 10a determines that a disconnection or a waterless failure (step S15). The self-diagnosis process is terminated. Further, the CPU 10a determines that a circuit failure has occurred if the voltage signal immediately before the end of charging taken in step S4 is neither in the range of 2.3V to 2.8V nor in the range of 0.2V to 2.3V (N in step S14). (Step S16), the self-diagnosis process is terminated.

  As is apparent from the above operation, the CPU 10a functions as a switch control unit in steps S2 and S5. Moreover, it functions as a first self-diagnosis unit in steps S8 to S11, and functions as a second self-diagnosis unit in steps S12 to S16.

  According to the gas alarm device described above, when the CPU 10a detects the failure of the CO sensor 1, the charging current that the voltage signal of the current / voltage conversion circuit 40 flows to the CO sensor 1 during charging of the CO sensor 1 can be regarded as 0. If it is within the range of .2V to 2.3V, it is determined that there is a disconnection or a waterless failure, and the current that the voltage signal of the current / voltage conversion circuit 40 flows through the input resistor Rd during charging of the CO sensor 1 can be regarded as zero If it is within the range of 3V to 2.8V, it is determined as a short circuit failure. Thereby, it can be determined whether the reason for the failure is a disconnection, water, or a short circuit, so that failure analysis after the occurrence of failure can be performed quickly.

  Further, according to the gas alarm device described above, since the discharge resistance is configured by the input resistance Rd of the current / voltage conversion circuit 40, it is not necessary to provide a discharge resistance separately from the current / voltage conversion circuit 40, and the configuration Can be simplified and the cost can be reduced.

  Further, according to the gas alarm device described above, the voltage signal of the current / voltage conversion circuit 40 is either in the range of 0.2V to 2.3V or in the range of 2.3V to 2.8V while the CO sensor 1 is being charged. If not, it is determined that there is a circuit failure. Thereby, since it can be determined whether the reason for the failure is a circuit failure, the failure analysis after the occurrence of the failure can be further quickly performed.

  According to the above-described embodiment, the failure of the CO sensor 1 is detected based on the voltage signal 10 ms after 25 ms after starting the discharge of the CO sensor 1, but the present invention is limited to this. It is not a thing. The method for detecting the failure of the CO sensor 1 based on the voltage signal from the start of discharge of the CO sensor 1 is not limited to the above-described embodiment. For example, the voltage signal from the start of discharge of the CO sensor 1 is sampled, and the failure of the CO sensor 1 is detected by comparing with the waveform of the voltage signal at the time of predetermined normality, short circuit failure, disconnection, waterless failure May be. That is, it may be based on the discharge current that flows when the CO sensor 1 is discharged.

  Further, according to the above-described embodiment, the charging current flowing through the CO sensor 1 is regarded as 0 when the voltage signal from the current / voltage conversion circuit 40 is 0.2 V to 2.3 V. It is not limited. The range of the voltage signal in which the charging current flowing through the CO sensor 1 can be regarded as 0 may be appropriately determined for each product depending on the configuration of the current / voltage conversion circuit 40 and the CO sensor 1.

  Further, when the voltage signal from the current / voltage conversion circuit 40 is 2.3 V to 2.8 V, the current flowing through the input resistor Rd is regarded as 0, but the present invention is not limited to this. The range of the voltage signal in which the current flowing through the input resistor Rd can be regarded as 0 may be appropriately determined for each product depending on the configuration of the current / voltage conversion circuit 40 and the CO sensor 1.

  Further, according to the above-described embodiment, the three failure reasons of the short circuit failure, the disconnection or waterless failure, and the circuit failure are determined, but the present invention is not limited to this. For example, two failure reasons such as a short circuit failure, a disconnection, or a waterless failure may be determined.

  In the embodiment described above, the electrochemical CO sensor 1 includes the metal can 2, but the present invention is not limited to this. For example, if the CO sensor 1 can be disposed in a place where a certain amount of water vapor is generated, such as in the exhaust pipe of a water heater, the target gas can be detected without the metal can 2. Even when the metal can 2 is not present, failure such as disconnection or short circuit can be performed as in the above-described embodiment.

  Moreover, although embodiment mentioned above demonstrated the example which applied the alarm device of this invention to the gas alarm device which detects CO density | concentration, this invention is not limited to this. For example, the alarm device of the present invention may be applied to a fire alarm device that detects a fire with smoke + CO concentration.

  Further, the above-described embodiments are merely representative forms of the present invention, and the present invention is not limited to the embodiments. That is, various modifications can be made without departing from the scope of the present invention.

It is a circuit diagram showing one embodiment of a gas alarm as an alarm according to an embodiment of the present invention. It is an equivalent circuit schematic of the gas alarm device shown in FIG. (A) to (C) are time charts of the current flowing through the CO sensor, the current flowing through the current / voltage conversion circuit, and the voltage signal from the current / voltage conversion circuit in a normal state. (A) to (C) are time charts of the current flowing through the CO sensor, the current flowing through the current / voltage conversion circuit, and the voltage signal from the current / voltage conversion circuit when a short circuit failure occurs. (A) to (C) are time charts of the current flowing through the CO sensor, the current flowing through the current / voltage conversion circuit, and the voltage signal from the current / voltage conversion circuit when a disconnection or waterless failure occurs. It is a flowchart which shows the process sequence in the self-diagnosis process of CPU shown in FIG. It is sectional drawing which shows an example of the electrochemical CO sensor which concerns on this invention.

Explanation of symbols

1 CO sensor (gas sensor)
2 Metal can (water container)
10a CPU (switch control means, first self-diagnosis means, second self-diagnosis means)
33 Current source (power supply)
40 Current / voltage conversion circuit Rd Input resistance (discharge resistance)
SW2 selector switch

Claims (3)

An electrochemical gas sensor that detects the concentration of the target gas by a reaction between water vapor from a water container containing water or water vapor in the atmosphere and the target gas, a discharge resistance connected to the gas sensor, and a current to the gas sensor A power supply for charging the gas sensor, a changeover switch provided between the power supply and the gas sensor for switching between charging and discharging of the gas sensor, and turning on the changeover switch to charge the gas sensor and then changing the changeover switch. An alarm device comprising: switch control means for turning off and discharging the gas sensor; and first self-diagnosis means for detecting a failure of the gas sensor based on a discharge current flowing during discharge of the gas sensor by the switch control means.
In response to detecting the failure of the gas sensor by the first self-diagnostic means, if the charging current flowing through the gas sensor during charging of the gas sensor by the switch control means can be regarded as 0, it is determined that there is a disconnection or waterless failure, and And a second self-diagnosis unit set to determine that a short-circuit fault has occurred when the current flowing through the discharge resistor can be regarded as 0 during charging of the gas sensor by the switch control unit. . A current / voltage conversion circuit for converting a discharge current flowing through the gas sensor into a voltage;
The alarm device according to claim 1, wherein the discharge resistance is configured by an input resistance of the current / voltage conversion circuit. If the second self-diagnosis means is within a first predetermined range in which the charging current flowing through the gas sensor can be regarded as 0 during the charging of the gas sensor by the switch control means, no disconnection or no water A failure is determined, and if the output of the current / voltage conversion circuit is within a second predetermined range in which the current flowing through the input resistor can be regarded as 0 during charging of the gas sensor by the switch control means, a short-circuit failure is determined; and When the output of the current / voltage conversion circuit is not in either the first predetermined range or the second predetermined range during charging of the gas sensor by the switch control means, it is determined that a circuit failure is determined. The alarm device according to claim 2, characterized in that:

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