WO2006022003A1 - Electrochemical gas sensor self-diagnosis method and gas sensor - Google Patents

Abstract

Using the output waveform of when the power supply of an electrochemical gas sensor is turned on after the power supply is kept off for a short time and the output waveform of when the power supply is turned on after it is kept off for a long time, the gas sensor is self-diagnosed. If the gas sensor is normal, a bottom appears in the potential at the sensing electrode when the power supply is turned on after a short-time off, and a peak appears in the potential at the sensing electrode when the power supply is turned on after a long-time off. Thus, the electrochemical gas sensor is self-diagnosed without using a pulse power supply for self-diagnosis, and the dead time from the self-diagnosis to the sensing start can be shortened.

Description

 Specification

 Self-diagnosis method and gas detector for electrochemical gas sensor

 Technical field

 [0001] The present invention relates to a self-diagnosis of an electrochemical gas sensor using an electrolyte such as a proton conductor or a liquid electrolyte.

 Background art

 As a structure of a proton conductor gas sensor, there is one described in Patent Document 1. In this gas sensor, the bottom of the metal can is used as a water reservoir, and the body of the CO sensor is held through the constriction at the top. The body of the CO sensor is composed of a MEA composed of a proton conductor film and front and back electrodes, and a porous carbon sheet serving both as gas diffusion and conductive contact. The bottom of the sensor body is brought into contact with a metal washer provided with a water vapor introduction hole, and the upper part is brought into contact with a metal washer provided with a diffusion control hole. Also, support the bottom washer with the constriction of the metal can, provide a gasket between the upper washer and the metal can, caulk the top of the metal can, and connect the upper and lower metal plates (brushers) and the sensor body between them to the metal can. Attach to. The sensor body is held by pressure, and the connection between the upper and lower metal plates and the carbon sheet of the sensor body is maintained.

 [0003] For example, Patent Document 2 proposes self-diagnosis of a proton conductor gas sensor.

 Measure the capacitance after turning off the pulse by applying a short voltage pulse for a short time between the sensing and counter electrodes of the gas sensor. It is said that self-diagnosis is possible because the capacitance differs between normal and bad sensors. Electrochemical gas sensor has low internal resistance of Ω order, but even if it is a weak pulse for a short time, if voltage is applied between both electrodes, there is a possibility that the electrolyte and its electrode may change or hysteresis may occur. . In addition, a pulse power supply is required for self-diagnosis, and detection becomes impossible until the hysteresis disappears after the pulse is received.

 Patent Document 1: US Patent 5650054

 Patent Document 2: US Patent 6200443

Disclosure of the invention Problems to be solved by the invention

 [0004] An object of the present invention is to make it possible to easily perform self-diagnosis of an electrochemical gas sensor and to reduce the influence of the self-diagnosis on the electrochemical method and its electrodes.

 Means for solving the problem

 [0005] The present invention is a self-diagnosis method for an electrochemical gas sensor, comprising an electrolyte, a detection electrode, and a counter electrode, wherein the detection electrode and the counter electrode are connected by an amplifier circuit, wherein the detection electrode and the counter electrode are connected to each other. The gas sensor is self-diagnosed from the presence or absence of the peak or bottom of the output of the gas sensor when it is connected again after being opened.

 [0006] Preferably, the gas sensor is normal when the output peak exists, and the gas sensor is defective when the peak does not exist.

 Particularly preferably, after the connection is opened for less than a predetermined time at the first frequency, the gas sensor is self-diagnosed at the first frequency from the presence or absence of the bottom of the output after being connected again, and further, The self-diagnosis of the gas sensor is performed at a second frequency lower than the first frequency based on the presence or absence of the output peak after the electrical connection is opened for a predetermined time and then reconnected. .

[0007] The present invention is a gas detection device in which a detection electrode and a counter electrode of a gas sensor having an electrolyte, a detection electrode, and a counter electrode are connected by an amplifier circuit, wherein the detection electrode and the counter electrode of the gas sensor are connected to each other. A switch for opening and closing the output and the peak or bottom of the output of the amplifier circuit after reconnecting after opening the connection is detected, and the gas sensor is operated normally when the bottom or peak is detected. If it is not, a self-diagnosis means for giving a self-diagnosis result as a failure and a display means for displaying the self-diagnosis result are provided.

 [0008] Preferably, the self-diagnosis means detects the peak of the output when the connection is re-established after the connection has been opened for a predetermined time, and the gas sensor is not detected. Defective.

Particularly preferably, the connection is reconnected after being released at the first frequency, and the connection is reconnected after being released at a second frequency lower than the first frequency for a time longer than a predetermined time. Means for driving the switch, and Self-diagnosis of the gas sensor from the presence or absence of the bottom of the output after opening the connection for a time less than the predetermined time, and the presence or absence of a peak of the output after releasing the connection for a time longer than the predetermined time To further self-diagnose the gas sensor.

 Preferably, the switch is a power switch of the amplifier circuit or a switch for electrically connecting / disconnecting the electrochemical gas sensor to the amplifier circuit.

In this specification, the output of the electrochemical gas sensor and the amplification circuit is 10 when current flows from the detection electrode to the counter electrode in the sensor, and − when current flows from the counter electrode to the detection electrode. The output + corresponds to the presence of CO, H2, etc. For example, if C〇 is present, CO + H2 0 → C 0 2 ⁺ 2H ⁺ 2e-

 Opposite

 2H + + 2e "+ 1/202 → H20

 The reaction proceeds. Therefore, the output peak is the output in the same direction as the output when it contacts the reducing gas, and the output bottom is set in the incidental circuit with the counter electrode and the detection electrode reversed, and the output when CO is present The direction of the output when the reducing gas concentration becomes negative is the same as the direction of. In the embodiment, a specific structure of the gas sensor, an electrolyte and an electrode material, and a specific amplifier circuit are shown, but these are optional.

 For example, when one of the detection electrode and the counter electrode is connected to one input of the operational amplifier and the other is connected to the other input of the operational amplifier, the operational amplifier is connected.

 The invention's effect

[0010] According to the present invention, after the connection between the detection electrode and the counter electrode of the electrochemical gas sensor is opened, the gas sensor performs self-diagnosis from the output waveform when it is connected again. For this reason, a special power supply for self-diagnosis is not required, and voltage is not stored between the detection electrode and the counter electrode of the sensor, so there is no risk of sensor deterioration due to voltage pulses for self-diagnosis. In the inventor's experiment, the dead time until the detection becomes possible after reconnecting the detection electrode and the counter electrode is, for example, 20 seconds or less. Can be shortened. In the self-diagnosis of the present invention, in addition to poor contact or disconnection between the detection electrode or counter electrode and the external terminal, short-circuit between the detection electrode and the counter electrode, etc., the sensor sensitivity decreases, or the 0 gas level shifts to an abnormal position. Can also be detected. [0011] There are two types of transient waveforms when the detection electrode and the counter electrode are connected again. When the connection is opened and connected again for a short time, for example, 1 minute or less, the bottom of the output is observed. On the other hand, when the connection was opened and reconnected for a long time, for example, more than 5 minutes, the peak of the output was detected. The bottom of the output after a short opening was observed even with a gas sensor with poor sensitivity, and it was difficult to distinguish between a normal gas sensor and a gas sensor with poor sensitivity. Simple faults such as force, wire breakage and short-circuit could be detected reliably. Next, at the peak of the output after the connection was released for a long time, it was possible to distinguish between a normal gas sensor and a gas sensor with poor sensitivity. In this case, the output peak was generated only in a normal gas sensor, and the output peak did not occur due to poor sensitivity, zero gas level shift, disconnection, or short circuit.

 [0012] Therefore, by using the characteristics when the connection is reconnected after opening the connection for a short time or for a long time, ie, the presence or absence of the bottom or peak, simple defects such as disconnection or short-circuit can be reliably detected, and the sensitivity Defects can be detected to some extent. Using the output peak after opening for a long time, it is possible to reliably detect poor sensitivity. In addition, since the dead time of detection increases when it is opened for a long time, self-diagnosis that opens for a long time is performed at a low second frequency such as once a month, and self-diagnosis that opens for a short time is high such as once a day. If performed at the first frequency, a reliable self-diagnosis is possible. Alternatively, even if the mode is opened repeatedly for a short time, the detection reliability can be increased.

 [0013] When the gas detection device is driven by a battery power supply, an amplifier circuit or a signal processing microcomputer is started every predetermined time to save power, and these operations are stopped at other times. It is done. Therefore, when the amplifier circuit is turned off, the connection between the detection electrode and the counter electrode is cut off, and when the power supply is turned on and the detection electrode and the counter electrode are connected, self-diagnosis can be performed using the on / off of the amplifier circuit.

 Brief Description of Drawings

 [0014] [Figure 1] Cross section of electrochemical gas sensor

 [Figure 2] Block diagram of electrochemical gas detector

[Figure 3] Operational waveform diagram of electrochemical gas detector, 1) switch S1 operation, 2) switch S2 operation, 3) short-time switch S1 open, presence or absence of bottom 4) shows self-diagnosis based on the presence or absence of a peak after opening switch S1 for a long time. [Figure 4] Flow chart of self-diagnostic algorithm for electrochemical gas sensor

5] Diagram showing sensitivity characteristics of normal electrochemical gas sensor

6] Diagram showing sensitivity characteristics of an abnormal electrochemical gas sensor

7] Diagram showing sensitivity characteristics of other abnormal electrochemical gas sensors

8] Diagram showing the bottom of the output that appears when the electrochemical gas sensor in Fig. 5 is turned on after being turned off for 5 seconds.

9] Diagram showing the bottom of the output that appears when the electrochemical gas sensor in Fig. 6 is turned on after turning it off for 5 seconds.

10] Diagram showing the output pattern that appears when the electrochemical gas sensor in Fig. 7 is turned on after being turned off for 5 seconds.

 [Fig. 11] A diagram showing the peak of output that appears when the electrochemical gas sensor of FIG. 5 is turned on after turning it off for one hour.

 [Fig. 12] Diagram showing the output pattern of the electrochemical gas sensor in Fig. 6 when the power is turned on after turning it off for 1 hour

13] Diagram showing the output pattern of the electrochemical gas sensor in Fig. 7 when the power is turned on after turning it off for 1 hour

14] A diagram showing the bottom of the output when a normal electrochemical gas sensor is powered on for 5 seconds.

15] A diagram showing the bottom of the output when the electrochemical gas sensor with short circuit or wire breakage is turned on after being turned off for 5 seconds.

 [Figure 16] Diagram showing the bottom of the output when the electrochemical gas sensor in Figure 14 is turned on for 5 minutes.

 [Fig.17] Response characteristics when 50mV voltage is applied for 4 seconds between the sensing electrode Z and the counter electrode of the electrochemical gas sensor in Fig. 14

 [Fig.18] Response characteristic diagram when 50mV voltage (opposite polarity from Fig.17) is applied for 4 seconds between the sensing electrode Z and the counter electrode of the electrochemical gas sensor in Fig. 14

19] Block diagram of a modified electrochemical gas detector

Explanation of symbols Electrochemical gas sensor Sensor body

MEA

 Diffusion control plate Sealing body

 Cap Bottom plate

 Filter material, 24 openings

 Diffusion control hole Washer

 Steam inlet metal can

 Gel

 Recess

 Gasket Proton conductor membrane Detection electrode

 Opposite electrode

, 46 Conductive carbon sheet Power supply

 Reset switch Microcomputer

AD computer

CO detection unit Self-diagnosis unit Power supply control unit

LED drive 60 LEDs

 61 Buzzer drive

 62 Buzzer

 63 LCD driver

 64 LCD

 65 EEPROM

 66 Reset controller

 67 Battery check

 68 timer

 69 RAM

 Rl, R10 resistance

 CI to C5 capacitor

 IC1, IC3 operational amplifier

 si-, S4 switch

 + Vcc circuit power supply

 BEST MODE FOR CARRYING OUT THE INVENTION

[0016] An optimum embodiment for carrying out the present invention will be described below.

 Example

 FIG. 1 shows a structure of a proton conductor gas sensor 2 as an example of an electrochemical gas sensor. FIG. 2 is a block diagram of a gas detection apparatus using the gas sensor 2, and FIG. 3 is an operation waveform diagram thereof. Fig. 4 is a flowchart showing the self-diagnosis algorithm of the electrochemical gas sensor. In this example, as a switch for operating the connection between the detection electrode D and the counter electrode C of the gas sensor 2, when the power switch S1 is used and when the switch S1 is turned off, the connection between the detection electrode D and the counter electrode C is broken. When turned on, these are connected.

[0018] Figures 5 to 7 show the sensitivity patterns (CO30-400ppm) of normal gas sensors (Figure 5: number of sensors 5) and bad gas sensors (Figure 6: number of sensors 3, Figure 7: number of sensors 2). . Fig. 8 to Fig. 10 are waveform diagrams of the output when the power of these gas sensors and their associated circuits is turned off for 5 seconds and then turned on again. If the power is turned off for a short time, the bottom of the output is (Negative peak) occurs, and this bottom is an output waveform in which the detected CO concentration is negative. Using this bottom, it is possible to distinguish between the defective sensor in FIG. 7 and the normal sensor in FIG. 5. It is difficult to distinguish the defective sensor in FIG. 6 from the normal sensor in FIG.

 FIG. 11 and FIG. 13 show the outputs when the power of the electrochemical gas sensor of FIGS. 5 to 7 is turned off for 1 hour including the accompanying circuits and then turned on again. A normal sensor produces an output peak, and a defective sensor does not produce a peak. Therefore, the normality / defectiveness of the sensor can be reliably identified, but since the power is turned off for a long time, detection dead time occurs.

 FIG. 14 shows an output waveform when twelve normal electrochemical gas sensors are turned on again after being turned off for 5 seconds. Each sensor indicates the bottom of the output. Figure 15 shows the output waveforms under the same conditions for three sensors with disconnections and shorts. Fig. 16 shows the output waveform when the gas sensor in Fig. 14 is turned on after being turned off for 5 minutes. Although it is smaller than Fig. 11, output peaks occur in all sensors.

 [0021] FIG. 17 and FIG. 18 show the relationship between eight normal electrochemical gas sensors between the detection electrode and the counter electrode.

 ± 50mV x Output waveform after capturing a voltage pulse for 4 seconds. It takes about 500 seconds for the output to return to a steady value, and the detection dead time required for self-diagnosis is long.

 In FIG. 1, 2 is a proton conductor gas sensor, 4 is a sensor body, and comprises MEA 10, diffusion control plate 12, sealing body 14, and metal washer 28. As shown on the right side of FIG. 1, the MEA 10 is provided with a sensing electrode 43 and a counter electrode 44 on both sides of the proton conductor film 42, which are made of conductive carbon sheets 45 and 46 (film thickness of about 40 / im). It is coated. For the proton conductor film 42, a persulfonic acid-based solid polymer electrolyte (SPE), for example, a film made by Goa Co., having a film thickness of about 20 μΐη was used here. Each of the sensing electrode 43 and the counter electrode 44 is obtained by dispersing Pt in carbon and impregnating an electrochemical polymer (film thickness of about 10 zm each). Conductive carbon sheets 45 and 46 need not be provided. The material and film thickness of MEA10 are arbitrary. Gas sensor 2 has two poles and no reference pole.

The diffusion control plate 12 is made of a thin plate such as titanium, and has a thickness of about 0.1 mm, for example, and is provided with a diffusion control hole 26 having a diameter of about 0.1 mm by punching or the like. The sealing body 14 is upstream of the diffusion control plate 12 and is used to remove poisonous substances and gases that cause false alarms. The sealing body 14 is composed of a metal cap 16 and a metal bottom plate 18 between which a gas is interposed. Activated carbon, silica gel, and Filled with filter material 20 made of orite.

 [0024] The bottom plate 18 has, for example, an opening 22 at the center, and an opening 24 is provided on the side surface of the cap 16, and the opening 22 and the opening 24 are arranged so as not to overlap with each other in the axial direction of the sealing body 14. It is preferable to provide a plurality of openings 22, 24. The washer 28 is made of a metal plate such as stainless steel or titanium, and is thicker than the diffusion control plate 12, for example, 0.5 mm thick. Supply. The water vapor introduction hole 30 is, for example, about 0.5 mm in diameter and larger than the diffusion control hole 26.

 [0025] 32 is a metal can. Here, a gel 34 obtained by gelling pure water is used as a water reservoir. Reference numeral 36 denotes a recess, which supports the metal bush 28, and 38 denotes a gasket, which is disposed between the sealing body 14 and the metal can 32. Then, the sensor body is fixed to the metal can 32 by pressing and tightening the upper part of the metal can 32, the sealing body 14 is insulated from the metal can 32, and the electrical continuity in each part of the sensor body 4 and the I do.

 [0026] A CO detection mechanism is shown. The ambient atmosphere that has passed through the sealing body 14 reaches the detection electrode 43 through the diffusion control hole 26. During this time, CO in the ambient atmosphere is detected at the detection electrode 43.

 CO + H20 → C02 + 2H + + 2e—

 Protons are generated by this reaction. Water necessary for this reaction is supplied from the water vapor introduction hole. At counter electrode 14,

 2H + + 1 / 2〇2 + 2e— → H20

 Reaction occurs. The oxygen concentration in the ambient atmosphere is much higher than the CO concentration, so there is always enough oxygen at the counter electrode 44 to fully oxidize CO.

 FIG. 2 shows the configuration of the gas detection device. Reference numeral 50 denotes a power source using a battery or the like, and 51 denotes a reset switch. The normally open power switch S1 is used to turn on and off the power supply to the gas sensor 2 and its amplification circuit. R1-R10 are resistors, and C1 and C5 are capacitors. The power supply of the amplifier circuit is represented by + Vcc. The detection electrode D and the counter electrode C of the gas sensor 2 are imaginary shorted at both inputs of the operational amplifier IC2, and are electrically connected while the operational amplifier IC2 is turned on.

[0028] A positive bias voltage determined by the resistor R1ZR2, here + 1 V, is received at the counter electrode C of the gas sensor 2 via the operational amplifier IC1, thereby making it easy to detect the bottom of the output. In addition The main function of the operational amplifier IC1 is to remove lip glue from the power supply, and this need not be provided when the battery power supply 50 is used. The current flowing from the detection electrode D of the gas sensor 2 to the counter electrode C is converted into a voltage by the resistor R5. The internal resistance between the sensing electrode D and the counter electrode C is about 1 Ω, and the resistance value of the resistor R5 is about 100 Ω. In the operational amplifier IC3, amplification is performed at a magnification determined by the resistance ratio between the resistor R6 and the resistor R8. Here, resistance R6 is about 3Ω, and resistance R8 is about 100Ω. As a result, when InA current flows from the detection electrode D to the counter electrode C, the output voltage Vout of the operational amplifier IC3 is 3 mV. For example, when CO600ppm is present, the output of the operational amplifier IC3 increases by 3V from the 0 gas level, and in the gas sensor 2, the detection electrode D force also flows to the counter electrode C at about 1 μA. The resistor R9 connected to the operational amplifier IC3 is an adjustment resistor for making the output Vout IV at 0 gas level.

[0029] The resistor R10 has a resistance of about 1Ω, and is connected to the gas sensor 2 in parallel with the normally closed switch S2. The resistor R10 is a resistor for preventing the gas sensor 2 from being polarized during inventory of the gas detection device, and the resistor R10 and the switch S2 need not be provided. Also, the resistance value of the resistor R10 is much higher than the resistance value of the gas sensor 2, and the influence on the detection signal of gas is negligible. Switch S2 is opened while switch S1 is open for gas sensor 2 self-diagnosis, and is closed during the subsequent bottom and peak observation times, but the bottom and peak observation times are also open. Good. Resistor R10 and switch S2 need not be provided.

 [0030] In the embodiment, two stages of operational amplifiers IC2 and IC3 are used for current amplification, but these may be arranged in one stage. In addition, in the embodiment, the force bias potential obtained by applying a bias potential of + IV to the counter electrode C can be changed between, for example, lOOmV—about 2V, and instead of using a single power source such as + 5V as the circuit power source + Vcc. When the operational amplifiers IC1 and IC3 are driven by dual power supplies such as ± 5V, the bias potential can be set to 0, for example. In the example, rather than performing self-diagnosis using the capacitance between the sensing electrode D and the counter electrode C, phenomena such as the generation of polarization, local potential, and mixed potential at the sensing electrode D and the counter electrode C can be observed. Use to self-diagnose.

[0031] The resistors Rl, R2-R10, operational amplifiers IC1, IC3, and the like constitute an amplifier circuit of the gas sensor 2. The microcomputer 54 processes the output signal Vout. 55 is an AD converter, 56 is a C0 detector, which compares the output Vout with a predetermined threshold. Calculate the CO concentration. Reference numeral 57 denotes a self-diagnosis unit that performs a self-diagnosis of the gas sensor 2 from a transient waveform of the output Vout when the power supply 50 is turned off for a predetermined time. If the amplifier circuit is defective, the output Vout shows an abnormal value, so the amplifier circuit can be checked.

 [0032] Reference numeral 58 denotes a power control unit that turns on / off the switch S1. The microcomputer 54 has two modes, an operation mode and a standby mode. In the standby mode, for example, only the timer 68 is operated to manage the standby time, and in addition to supplying power to the RAM 69 to store data, It has stopped. When the standby mode is entered, switch S1 is opened in synchronism, and the power supply to gas sensor 2 and the amplifier circuit is shut off. When the switch S1 is turned off for a predetermined time by the timer 68, the microcomputer 54 shifts to the standby mode force and the operation mode, and in synchronization with this, the switch S1 is closed and the gas sensor 2 and its amplification circuit are turned on. . Then, the self-diagnosis of the gas sensor 2 is performed from the output waveform for a predetermined time after the power is turned on, for example, 5 seconds to 15 seconds.

 [0033] Reference numeral 59 denotes an LED drive unit that drives an LED group 60 composed of a plurality of LEDs, and the display state of the LED group 60 includes normal / gas detection device not operating normally / low concentration CO. For example, there are four types of high-concentration CO. The buzzer driving unit 61 drives the buzzer 62. For example, the buzzer 62 is driven when high concentration CO exists or when low concentration CO exceeds the allowable time. The LCD drive unit 63 drives the LCD 64 to display the CO concentration, and also displays that the gas detection device is not operating normally or that a reset is required.

 The EEPROM 65 is for storing main data even when the power is turned off by the reset switch 51. The main data includes CO detection history, gas detection device self-diagnosis history, and total power usage time. The reset control unit 66 initializes the microcomputer 54 when the reset switch 51 is turned on. The battery check unit 67 checks the circuit power supply + Vcc value, etc., and checks whether the power supply 50 needs to be replaced. It is assumed that the circuit power supply + Vcc is input to the battery check unit 67 via an AD converter (not shown).

[0035] The timer 68 determines various operation cycles of the microcomputer 54, and in particular, determines the opening / closing cycle of the switch S1. For example, switch S 1 is opened for 40 seconds, then switch S 1 is closed for 20 seconds. First, switch SI is driven in 60 seconds per cycle. Then, the self-diagnosis of the gas sensor 2 is performed using the first 15 seconds of the on-time of the switch 20 seconds, and CO is detected using the last 5 seconds. Normally, the gas sensor 2 operates at a cycle of 1 minute, for example, once every month, that is, at an interval longer than the above 1-minute cycle, for example, for 1 hour after turning off the switch S1 and turning off the switch S1 from off. Perform self-diagnosis of gas sensor 2 using 15 seconds. As described above, when the switch S1 is open, the microcomputer 54 is also in the standby mode. The RAM 69 stores various data necessary for the operation of the microcomputer 54.

 FIG. 3 shows the operation of the gas detection device in self-diagnosis. Switches SI and S2 are opened periodically for a predetermined time. During this time, switches SI and S2 are opened to disconnect the sensing and counter electrodes. Next, switch S1 is closed, and it is detected whether the bottom or peak of the output occurs during a predetermined time. During the detection period, switch S2 may be closed or open.

 FIG. 4 shows a self-diagnosis algorithm in the embodiment. If the time during which switch S1 is off is less than force minutes, for example, 40 seconds in the case of the embodiment, an abnormality is checked from the presence or absence of an output bottom when switch S1 is on. For example, if the off time is 5 minutes or more, check for abnormalities based on the presence or absence of the output peak after switch S 1 is turned off. In the embodiment, for example, 1 hour is used as the power off time of the long side. The off time of the power source on the long side is preferably 3 minutes to 24 hours, more preferably 5 minutes to 12 hours, and even more preferably 5 minutes to 1 hour. The power off time on the short side is, for example, 1 minute or less, preferably 0.1 seconds or more, more preferably 1 minute or less, 1 second or more, and even more preferably 40 seconds or less, 3 seconds or more. The boundary between the long off time side and the short side is, for example, 3 minutes, a time longer than 3 minutes is, for example, more than a predetermined time, and a time shorter than 3 minutes is, for example, less than the predetermined time.

[0038] If an abnormality is detected in the gas sensor, the fact is stored in EEPROM or RAM. If an abnormality is detected when the short side is turned off, the power is automatically turned off again with the switch S1, for example, for 40 seconds, and the self-diagnosis is performed again. In this way, for example, when an abnormality is detected twice in succession, the LCD 64 is displayed to request a reset. If reset is performed with an abnormality recorded in the EEPROM, the switch S1 is turned off, for example, for 5 minutes when returning from reset, and a long time off is forcibly executed. Check the abnormality from the output pattern afterwards. If any abnormality is confirmed here, for example, permanent failure is recorded in the EEPROM, and LED60 and

Do not turn off the abnormal display on LCD64.

[0039] If an abnormality is detected after turning off the switch S1 for a long time, the abnormality is similarly written to the EEPROM and a reset is requested. Then, after resetting, the power is turned off again with the switch S1 for a long time. If an abnormality is detected again, for example, a permanent abnormality is detected.

Write to M and display that on the LCD or LED.

[0040] If an abnormality is not detected, or if an abnormality is not reproduced by resetting even if an abnormality is detected, CO is detected and the power is turned off at predetermined intervals. Transition to standby mode.

 [0041] Fig. 5 shows the output waveforms of five normal gas sensors. The current flowing from the sensing electrode D to the counter electrode C is 0.7 µΑ at C 0400 ppm. The sensor output is proportional to the C0 concentration. Figure 6 shows the waveforms of the three sensors, with the two sensor waveforms overlapping on the output IV line. These sensors have poor or no CO sensitivity. Figure 7 shows the waveforms of the two gas sensors, which have an abnormal zero level and low CO sensitivity.

 [0042] FIGS. 8 to 10 show the characteristics of these gas sensors after the switch S1 is opened for 5 seconds, the power is turned off, and then the power is turned on again. In the normal gas sensor in Fig. 5 and the two gas sensors in the abnormal gas sensor in Fig. 6 (Fig. 9), an output bottom appears when the power is turned on. On the other hand, the bottom of output does not occur in the gas sensor of Fig. 7 (Fig. 10).

 [0043] For detecting the bottom, for example, a threshold value of 0.95 V obtained by lowering the 50 mV potential from the bias is used. After the power is turned on, for example, within a window within 15 seconds, the output passes the threshold value from top to bottom. It is only necessary to detect passing from the bottom to the top. Alternatively, the time derivative of the output voltage after the power is turned on and the output shows the peak of IV may be used. The output bottom detection method itself is arbitrary.

FIG. 11 and FIG. 13 show the characteristics when the power of the gas sensor of FIGS. 5 to 7 is turned on again after turning off the power for one hour. Assume that the power is turned on at 5 seconds. The gas sensor in Fig. 5 shows the peak of all output. In contrast, the gas sensor of FIG. 6 does not generate an output peak, and can be distinguished from the gas sensor of FIG. 5 and the gas sensor of FIG. 6 by lengthening the power-off time. The gas sensor in Fig. 7 is the same whether the power off time is long or short. The behavior is shown (Fig. 10, Fig. 13).

FIG. 14 shows the characteristics when twelve normal gas sensors are turned on after the power is turned off for 5 seconds. In any sensor, when the power supply is changed from OFF to ON, the output bottom force S is generated. In the gas sensor of Fig. 15, the detection electrode and the counter electrode are short-circuited, or the detection electrode and the counter electrode are floating from the terminal. In this case, there are three types of output waveforms: the noise voltage IV appears as it is, or the ground voltage 0 volts and the circuit voltage + Vcc 5V appear. In either case, the transient waveform after changing the power supply from off to on is not seen.

 [0046] FIG. 16 shows a waveform when the normal sensor of FIG. 14 is turned on after the power is turned off for 5 minutes. When the power supply was changed from off to on, the output peak occurred in all 12 sensors. The threshold value was bias +100 mV.

 [0047] As described above, the self-diagnosis of the electrochemical gas sensor 2 can be performed from the transient waveform after the power source is changed from OFF to ON. When the power off time is short, for example 5 seconds, the output waveform bottoms out, and when the power on time is long, for example 5 minutes or longer, the output peak occurs. In these two self-tests, longer power off times are more reliable. Increasing the power off time while pushing, increases the CO detection dead time. For this reason, both self-diagnosis with a short off-time and self-diagnosis with a long off-time are performed. Self-diagnosis with a short off-time is relatively frequent, and self-diagnosis with a long off-time is relatively infrequent. Good. The power supply necessary for the self-diagnosis can be turned off by using a standby mode for resting the battery power supply 50.

 FIG. 17 and FIG. 18 show waveforms after applying ± 50 mV potential for 4 seconds to 8 other normal electrochemical gas sensors. Fig. 17 shows the waveform when the detection electrode is + and 50mV is applied between the detection electrode and the counter electrode. Fig. 18 shows the waveform when -50mV is applied to the detection electrode.

[0049] When a voltage of 50 mV x 4 seconds is applied, the sensor signal is stable for about 500 seconds thereafter. This increases the detection dead time. Next, when a voltage of 50 mV is applied between the sensing electrode and the counter electrode, a current of 10 mA or more flows between both electrodes. Gas sensor 2 is designed to pass a current of about 1 μA at C 600 ppm. There is a possibility that the interface with the electric film may be affected or the hysteresis may remain.

 [0050] As described above, in the embodiment, the self-diagnosis of the electrochemical gas sensor can be performed by using the power on / off between the standby mode and the operation mode. Self-diagnosis can detect not only simple things such as short-circuits and short-circuits, but also those with poor sensitivity and floating sensor output.

 [0051] In FIG. 19, the switches S3 and S4 are connected to the detection electrode D and the counter electrode C of the gas sensor 2, and the control signal P2 from the microcomputer causes the detection electrode Z and the counter electrode to pass through the switches S3 and S4. An example of opening and closing a connection is shown. In this example, the switch S1 for power saving, the control signal Pl, and the switches S3 and S4 for self-diagnosis can be opened and closed independently. This modification is otherwise the same as the embodiment of FIG. 1 and FIG. 18, the same reference numerals denote the same parts, and the microcomputer 54 of FIG. 2 is connected to the output side of the operational amplifier IC3.

 [0052] The gas sensor is not limited to the proton conductor gas sensor, and any type of electrolyte may be used as long as it is a sulfuric acid electrolyte, an alkaline electrolyte, a simple water, or a liquid electrolyte gas sensor using an electrolyte such as an ionic liquid. The inventor confirmed that the same characteristics as in Fig. 8 to Fig. 18 were obtained even with a gas sensor using 0.1N KOH7 solution as the electrolyte.

Claims

The scope of the claims  [1] A method for self-diagnosis of an electrochemical gas sensor comprising an electrolyte, a detection electrode, and a counter electrode, wherein the detection electrode and the counter electrode are connected by an amplifier circuit.  A self-diagnosis method for an electrochemical gas sensor, characterized by self-diagnosis of the gas sensor based on the presence or absence of an output peak or bottom of the gas sensor when the detection electrode and the counter electrode are disconnected and then reconnected.  2. The self-diagnosis method for an electrochemical gas sensor according to claim 1, wherein the gas sensor is normal when the output peak exists, and the gas sensor is defective when the peak does not exist.  [3] After releasing the connection at a first frequency for less than a predetermined time and then reconnecting, the gas sensor performs self-diagnosis based on the presence or absence of the bottom of the output at the first frequency. The self-diagnosis of the gas sensor is performed at a second frequency lower than the first frequency after the electrical connection is released for a predetermined period of time and then the presence or absence of the output peak after the connection is reconnected. The self-diagnosis method of the electrochemical gas sensor according to claim 1,  [4] A gas detection device for an electrochemical gas sensor having an electrolyte, a detection electrode, and a counter electrode, in which the detection electrode and the counter electrode are connected by an amplification circuit,  A switch for opening and closing the connection between the detection electrode and the counter electrode of the gas sensor, and detecting the output peak or bottom of the amplifier circuit after the connection is opened and then reconnecting, and the bottom or peak is detected. Self-diagnostic means for self-diagnostic results as if the gas sensor is normal when detected, and defective when it is not,  And a display means for displaying the self-diagnosis result.  [5] The self-diagnosis means determines that the gas sensor is normal if the output peak is detected and the gas sensor is defective if the peak is not detected when the connection is reconnected after being opened for a predetermined time. The gas detection device according to claim 4, wherein: [6] To reconnect after releasing the connection at a first frequency, and reconnect after releasing the connection at a second frequency lower than the first frequency for a time exceeding a predetermined time, in front Means for driving the switch; and  Self-diagnosis of the gas sensor from the presence or absence of the bottom of the output after opening the connection for a time less than the predetermined time, and further from the presence or absence of the peak of the output after opening the connection for a time longer than the predetermined time 5. The gas detection device according to claim 4, wherein the self-diagnosis means is configured to further self-diagnose the gas sensor. 5. The gas detection device according to claim 4, wherein the switch is a power switch of the amplifier circuit or a switch that electrically connects / disconnects the gas sensor to / from the amplifier circuit.