JP4367904B2 - Electrochemical gas sensor device - Google Patents

Description

  The present invention relates to an electrochemical gas sensor device that determines whether an electrochemical gas sensor is functioning normally.

  Conventionally, electrochemical gas sensors have characteristics such as low power consumption, linear output characteristics, and excellent gas selectivity. Therefore, industrial gas concentration measuring instruments, detection alarms for carbon monoxide, etc. Widely used.

  Such an electrochemical gas sensor has a working electrode, a counter electrode, a reference electrode, and an electrolyte interposed between the electrodes, and the working electrode is connected to the working electrode, the counter electrode, and the reference electrode by a potentiostat. By keeping the potential constant, when the gas to be detected comes into contact with the working electrode and an oxidation or reduction reaction occurs, a current corresponding to the reaction is output from the working electrode, and the gas concentration corresponding to this output current value Can be detected.

  By the way, when an abnormality such as a short circuit or disconnection between electrodes in an electrochemical gas sensor, a connection failure of a wire connected to each electrode, a disconnection, or a short circuit occurs, the output current is the same as when no gas is detected. Therefore, it cannot be distinguished whether gas is not detected or an abnormality has occurred.

  Various methods for confirming whether or not the electrochemical gas sensor is functioning normally have been proposed. For example, when a transient voltage is applied between the working electrode and the counter electrode and the output current changes at this time if it is normal, it can be determined that there is no change if the output current does not change (for example, Patent Document 1). reference). However, if there is an abnormality such as disconnection in the working electrode or the counter electrode, it can be determined that there is no change in the output current, but it can be determined that there is an abnormality. When there is an abnormality such as, the output voltage may change as in the normal case, and it cannot be accurately determined whether it is functioning normally.

In addition to monitoring the change in output current when a transient voltage is applied between the working electrode and the counter electrode, by monitoring the change in electrolytic voltage between the working electrode and the counter electrode, It can be determined that there is an abnormality in either the working electrode or the counter electrode (for example, see Patent Document 2). However, abnormalities in the working electrode and the counter electrode can be determined, but it cannot be determined even if the reference electrode is broken or the reference electrode is short-circuited to the working electrode or the counter electrode. It cannot be judged accurately.
Japanese Utility Model Publication No. 62-39318 (page 1-2, FIG. 3) Japanese Patent No. 2613316 (page 3, FIG. 1)

  As described above, in the conventional method, it is determined whether the electrochemical gas sensor is functioning normally by applying a transient voltage between the working electrode and the counter electrode. Even if there is an abnormality such as the electrode being short-circuited to the working electrode or the counter electrode, there is a problem that it cannot be accurately determined, and whether it is functioning normally cannot be determined accurately.

  The present invention has been made in view of these points, and an object of the present invention is to provide an electrochemical gas sensor device that can accurately determine whether an electrochemical gas sensor is functioning normally.

  The electrochemical gas sensor device according to claim 1 is an electrochemical gas sensor having a working electrode, a counter electrode, a reference electrode, and an electrolyte interposed between the electrodes, a circuit for operating the electrochemical gas sensor, and the counter electrode A switching means for switching a circuit for applying a voltage between the electrode and a measuring means for measuring a current flowing through one of the working electrode and the counter electrode.

  In this configuration, by applying a voltage between the counter electrode and the reference electrode by the switching unit, charges are stored between the counter electrode and the reference electrodes in a normal state, and the influence of the stored charges is caused. Since the output current flowing through either the working electrode or the counter electrode changes when the voltage application is released, the electrochemical gas sensor functions normally by monitoring the output current when the voltage application is released. Is accurately determined.

  The electrochemical gas sensor device according to claim 2 is the electrochemical gas sensor device according to claim 1, further comprising a potentiostat connected to the working electrode, the counter electrode, and the reference electrode to keep the potential of the working electrode constant. The means opens the potentiostat from the first contact for connecting the potentiostat to the electrochemical gas sensor, the working electrode, the counter electrode, and the reference electrode of the electrochemical gas sensor, and applies a voltage between the counter electrode and the reference electrode. The second contact to be switched is switched.

  In this configuration, when the voltage is applied between the counter electrode and the reference electrode by the switching means, the potentiostat is released from the working electrode, the counter electrode, and the reference electrode. It is possible to prevent the influence and accurately determine from the output current when the voltage application is canceled.

The electrochemical gas sensor device according to claim 3 is the electrochemical gas sensor device according to claim 1 or 2, wherein when the voltage applied between the counter electrode and the reference electrode is released by the switching means, the working electrode and the counter electrode are It comprises a determination means for monitoring an output change of the current flowing through either one and determining an abnormality of the electrochemical gas sensor in accordance with the output change.

In this configuration, when the voltage applied between the counter electrode and the reference electrode is released by the determination unit, the output change of the current flowing through one of the working electrode and the counter electrode is monitored, and the output change is detected. Accordingly, since the abnormality of the electrochemical gas sensor is determined, it is accurately determined whether the electrochemical gas sensor is functioning normally.

  According to the electrochemical gas sensor device of claim 1, by applying a voltage between the counter electrode and the reference electrode by the switching means, in a normal case, an electric charge is stored between the counter electrode and the reference electrode, Since the output current that flows to either the working electrode or the counter electrode changes when the voltage application is canceled due to the effect of the stored charge, the output current when the voltage application is canceled is monitored. It is possible to accurately determine whether the chemical gas sensor is functioning normally.

  According to the electrochemical gas sensor device of claim 2, in addition to the effect of the electrochemical gas sensor device of claim 1, when the voltage is applied between the counter electrode and the reference electrode by the switching means, the working electrode, Since the potentiostat is opened from the electrode and the reference electrode, the influence of the potentiostat at the time of voltage application can be prevented, and accurate determination can be made from the output current when the voltage application is released.

According to the electrochemical gas sensor device of claim 3, in addition to the effect of the electrochemical gas sensor device of claim 1 or 2, when the voltage applied between the counter electrode and the reference electrode is released by the judging means Since the output change of the current flowing through one of the working electrode and the counter electrode is monitored and the abnormality of the electrochemical gas sensor is determined according to the output change, it is possible to accurately determine whether the electrochemical gas sensor is functioning normally. .

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a circuit diagram of an electrochemical gas sensor device. An electrochemical gas sensor device 11 includes a working electrode 12, a counter electrode 13, a reference electrode 14 and an electrolyte (not shown) interposed between the electrodes 12-14. The potentiostat 16 is connected to the working electrode 12, the counter electrode 13, and the reference electrode 14 of the electrochemical gas sensor 15.

  The potentiostat 16 is a negative feedback circuit using the operational amplifier 17, and the inverting input terminal (−) of the operational amplifier 17 is connected to the reference electrode 14 and the non-inverting input terminal (+) of the operational amplifier 17 is grounded and measured. It is connected to the working electrode 12 through the means 20, and the output terminal of the operational amplifier 17 is connected to the counter electrode 13. In this potentiostat 16, the potential difference between the negative feedback voltage from the reference electrode 14 and the voltage from the working electrode 12 input to the inverting input terminal (−) and the non-inverting input terminal (+) of the operational amplifier 17 is zero. As a result, a voltage is applied to the counter electrode 13, and as a result, the potential of the working electrode 12 is kept constant.

  A measuring means 20 for measuring a current flowing through the working electrode 12 is connected to the working electrode 12 of the electrochemical gas sensor 15. For example, the measuring means 20 connects a load resistance between the working electrode 12 and the potentiostat 16, and measures the current flowing through the working electrode 12 from both ends of the load resistance. At this time, the measuring means 20 is connected so as to measure the current flowing through the working electrode 12, but may be connected so as to measure the current flowing through the counter electrode 13.

  A switching means 21 is provided for switching between a circuit for operating the electrochemical gas sensor 15 and a circuit for applying a voltage between the counter electrode 13 and the reference electrode 14. The switching means 21 is provided between the counter electrode 13 and the operational amplifier 17. The switches 22, 23 and 24 are connected between the reference electrode 14 and the operational amplifier 17 and between the working electrode 12 and the measuring means 20, respectively. The switches 22, 23, and 24 are connected to the first contact points A 1, A 2, and A 3 that connect the potentiostat 16 to the electrochemical gas sensor 15, the working electrode 12, the counter electrode 13, and the reference electrode 14 of the electrochemical gas sensor 15. The potentiostat 16 is opened, and the second contacts B1, B2, and B3 for applying the voltage divided by the resistors 25 and 26 from the power source between the counter electrode 13 and the reference electrode 14 are switched. These switches 22, 23 and 24 are switched together in an interlocking manner.

  FIG. 3 is a block diagram of the electrochemical gas sensor device. When the inspection of whether or not the electrochemical gas sensor 15 is functioning normally is performed automatically, based on the output current measured by the measuring means 20. A determination unit 31 that automatically determines whether the electrochemical gas sensor 15 is functioning normally, and a notification unit 32 that notifies when the electrochemical gas sensor 15 is determined to be abnormal are provided.

  The determination unit 31 applies the voltage between the counter electrode 13 and the reference electrode 14 by the switching unit 21 and then changes the output of the electrochemical gas sensor 15 according to the output change of the current flowing through the working electrode 12 when the voltage application is canceled. It is determined whether the function is normal or abnormal.

  Next, the operation of the electrochemical gas sensor device 11 will be described.

  As shown in FIG. 1, in the electrochemical gas sensor device 11, the switches 22, 23, 24 of the switching means 21 are normally connected to the first contacts A1, A2, A3, and the function of the electrochemical gas sensor 15 is normal. In this state, when the potential of the working electrode 12 is kept constant by the potentiostat 16, and the gas to be detected contacts the working electrode 12 to cause an oxidation or reduction reaction, the working electrode 12 responds to the reaction. A current is output, and the gas concentration corresponding to the output current value can be detected.

  When testing whether the electrochemical gas sensor 15 is functioning normally, the switches 22, 23, 24 of the switching means 21 are switched to the second contacts B1, B2, B3, the working electrode 12, the counter electrode 13, and After the potentiostat 16 is opened from the reference electrode 14 and a voltage is applied from the power source between the counter electrode 13 and the reference electrode 14, the switches 22, 23, and 24 are connected to the second contacts B1, B2, and B3. Returning to the first contact A1, A2, A3, the application of voltage between the counter electrode 13 and the reference electrode 14 is released. The voltage is applied for a short time, and a pulse voltage is applied between the counter electrode 13 and the reference electrode 14 as shown in FIG. In FIGS. 1 and 2, the working electrode 12 is denoted by W, the counter electrode 13 is denoted by C, and the working electrode 14 is denoted by R.

  Then, when the electrochemical gas sensor 15 is functioning normally, the switches 22, 23, 24 are switched to the second contacts B1, B2, B3, and the potentiometer from the working electrode 12, the counter electrode 13 and the reference electrode 14 is switched. After the stat 16 is opened and a voltage is applied from the power source between the counter electrode 13 and the reference electrode 14, the switches 22, 23, 24 are switched from the second contacts B1, B2, B3 to the first contacts A1, A2, Returning to A3, when the application of the voltage between the counter electrode 13 and the reference electrode 14 is released, the output current flowing through the working electrode 12 changes.

  This is because charges are stored between the counter electrode 13 and the reference electrode 14 while a voltage is applied between the counter electrode 13 and the reference electrode 14, and the voltage application is canceled due to the effect of the stored charge. When this happens, the output current flowing through the working electrode 12 changes. Then, the charge is released and returns to the original current value. For this reason, the electrochemical gas sensor 15 functions normally by monitoring changes in the output current when the application of voltage is canceled, the peak value of the changed output current, and the time until recovery to the original current value. It is possible to accurately determine whether or not

  Further, when the working electrode 12 and the reference electrode 14 are short-circuited, the reference electrode 14 and the counter electrode 13 are short-circuited, and the working electrode 12, the reference electrode 14 and the counter electrode 13 are short-circuited, When the electrode 12, the reference electrode 14 and the counter electrode 13, the reference electrode 14 and the working electrode 12, and the counter electrode 13 and the working electrode 12 are opened due to poor connection or disconnection, the gap between the working electrode 12 and the reference electrode 14 is Abnormalities such as short-circuit and counter electrode 13 open, reference electrode 14 and counter electrode 13 short-circuited and working electrode 12 open, or electrochemical gas sensor 15 not present There is a case.

  When these abnormalities occur, the switches 22, 23, 24 are switched to the second contacts B1, B2, B3, and the potentiostat 16 is opened from the working electrode 12, the counter electrode 13, and the reference electrode 14. After applying a voltage from the power source between the counter electrode 13 and the reference electrode 14, the switches 22, 23, and 24 are returned from the second contacts B1, B2, and B3 to the first contacts A1, A2, and A3. When the application of the voltage between the electrode 13 and the reference electrode 14 is released, the output current does not change or changes little even if it changes. This is because the output current does not change because charges cannot be stored between the counter electrode 13 and the reference electrode 14 while a voltage is applied between the counter electrode 13 and the reference electrode 14 due to an abnormality. Or, even if it is stored, the output current does not change due to an abnormality in the working electrode 12, or even if it is stored, the stored amount becomes insufficient due to an abnormality inside the sensor, and the change in the output current becomes small.

  Therefore, when the switches 22, 23, and 24 are returned from the second contacts B1, B2, and B3 to the first contacts A1, A2, and A3, and voltage application between the counter electrode 13 and the reference electrode 14 is released. By monitoring this output current, it is possible to confirm that an abnormality has occurred, although it changes more than specified when it is normal but does not change or is small when it is abnormal.

  Further, when the reference electrode 14 is open, when the working electrode 12 and the counter electrode 13 are short-circuited, the working electrode 12 and the counter electrode 13 are short-circuited and the reference electrode 14 is opened. When an abnormality occurs, such as when the output current is normal, the output current during normal time is different from that when the output current is normal, so it can be determined that an abnormality has occurred.

  Further, as another determination means in the case of this abnormality, the switches 22, 23, 24 are switched to the second contacts B1, B2, B3, and the potentiostat 16 is switched from the working electrode 12, the counter electrode 13, and the reference electrode 14. When the switch is opened, the output current becomes zero, and then the switches 22, 23, 24 are returned from the second contacts B1, B2, B3 to the first contacts A1, A2, A3, and the counter electrode 13 and the reference electrode 14 are returned. When the application of the voltage between and is canceled, the output current remains at the original abnormal value and does not return to the normal current value.

  Therefore, by monitoring the output current when the switches 22, 23, and 24 are switched to the contacts A1, A2, and A3, if the output current changes normally, the current value is restored to the original value. In this case, since the value remains changed from zero to an abnormal value, it can be confirmed that an abnormality has occurred.

  As described above, after the voltage is applied between the counter electrode 13 and the reference electrode 14 by the switches 22, 23, and 24 of the switching means 21, the output current changes more than the specified value when the voltage application is canceled. If the current is restored to the original current value, it can be determined that the function of the electrochemical gas sensor 15 is normal, and the voltage is applied between the counter electrode 13 and the reference electrode 14 and then the voltage is applied. Since the function of the electrochemical gas sensor 15 can be determined to be abnormal when there is no change in the output current when released, or when the change does not return to the normal current value after the change, the electrochemical gas sensor 15 It can accurately determine whether it is functioning properly.

  When applying a voltage between the counter electrode 13 and the reference electrode 14 by the switches 22, 23, 24 of the switching means 21, in order to open the potentiostat 16 from the working electrode 12, the counter electrode 13 and the reference electrode 14, The influence of the potentiostat 16 at the time of voltage application can be prevented, and accurate determination can be made from the change in the output current when the voltage application is canceled.

  Here, as one method of the judging means 31, for example, the time is measured from the moment when the switches 22, 23, 24 of the switching means 21 are returned from the second contacts B1, B2, B3 to the first contacts A1, A2, A3. The first measurement time is the time when the change in the output current is almost immediately, that is, several milliseconds to several hundred milliseconds, and the time when the current value is substantially recovered, that is, several seconds to several tens of seconds. A method for determining whether the electrochemical gas sensor 15 is normal or abnormal by verifying each of the output current magnitude in the first measurement time and the output current magnitude in the second measurement time as the second measurement time There is.

  In this case, the output current in the first measurement time and the output current in the second measurement time with respect to the voltage applied between the counter electrode 13 and the reference electrode 14 and the application time thereof are preliminarily measured by a plurality of normal sensors. Measured, and based on this result, the threshold value of the output current (first threshold value) at the first measurement time of the normal sensor and the threshold value of the output current (second threshold value) at the second measurement time. Set the threshold).

  When the output current at the first measurement time is not less than the first threshold value and the output current at the second measurement time is not more than the second threshold value, the electrochemical gas sensor 15 is normal. It can be determined that there is. If the output current at the first measurement time is less than the first threshold value or the output current at the second measurement time exceeds the second threshold value, the electrochemical gas sensor 15 is abnormal. Can be determined.

  The switching means 21 has switches 22, 23, and 24. Even if the switch 24 provided between the working electrode 12 and the measuring means 20 is not provided, the output current pattern is slightly different, but the electrochemical method is similarly used. Whether the gas sensor 15 is normal or abnormal can be determined.

It is a circuit diagram of an electrochemical gas sensor device showing an embodiment of the present invention. It is a waveform diagram of the output current according to the functional state of the electrochemical gas sensor when a pulse voltage is applied between the counter electrode and the reference electrode of the electrochemical gas sensor device. It is a block diagram of an electrochemical gas sensor apparatus same as the above.

Explanation of symbols

11 Electrochemical gas sensor device
12 Working electrode
13 Counter electrode
14 Reference electrode
15 Electrochemical gas sensor
16 Potentiostat
20 Measuring means
21 Switching means
31 Judgment means
A1, A2, A3 First contact
B1, B2, B3 Second contact

Claims (3)

An electrochemical gas sensor having a working electrode, a counter electrode, a reference electrode, and an electrolyte interposed between the electrodes;
Switching means for switching between a circuit for operating the electrochemical gas sensor and a circuit for applying a voltage between the counter electrode and the reference electrode;
An electrochemical gas sensor device comprising: measuring means for measuring a current flowing through one of the working electrode and the counter electrode. A potentiostat connected to the working electrode, the counter electrode and the reference electrode to keep the potential of the working electrode constant;
The switching means opens the potentiostat from the first contact for connecting the potentiostat to the electrochemical gas sensor, the working electrode, the counter electrode, and the reference electrode of the electrochemical gas sensor, and applies a voltage between the counter electrode and the reference electrode. The electrochemical gas sensor device according to claim 1, wherein the second contact point to be applied is switched. When the voltage applied between the counter electrode and the reference electrode is released by the switching means, the output change of the current flowing through one of the working electrode and the counter electrode is monitored, and an abnormality of the electrochemical gas sensor is detected according to this output change. The electrochemical gas sensor device according to claim 1, further comprising: a determination unit that determines

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