JP3351508B2 - Electrochemical gas concentration measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrochemical gas concentration measuring apparatus having a function of automatically detecting the operation state of an electrochemical gas sensor and the connection state between the sensor and the measuring apparatus body.

[0002]

2. Description of the Related Art As can be seen in Japanese Patent No. 2613316, immediately after power is supplied to a gas sensor, a preset potential change pulse is applied to the gas sensor, and an output is detected from the gas sensor in response thereto. There has been proposed an apparatus that detects deterioration of a gas sensor. However, since the inspection is performed only immediately after the power is turned on, if continuous operation is required for environmental monitoring or other purposes, it is not possible to confirm during the measurement period because it is performed only once before starting operation. And there is a problem that reliability is low. In order to solve such a problem, it is conceivable to periodically execute a check operation using a timer or the like.However, such an inspection causes an electrochemical change of the sensor. Normally, normal operation cannot be expected for about 30 seconds. Therefore, if the check function is activated during measurement of gas concentration due to gas leakage or the like, measurement becomes impossible, and the reliability of the measurement device is significantly reduced due to problems such as including a large error in the measurement result. Cause problems.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and an object of the present invention is to provide a method for real-time electrical measurement without hindering a measurement operation. An object of the present invention is to provide an electrochemical gas concentration measuring device capable of checking the operating status of a chemical gas sensor and the connection status between the sensor and the measuring device main body to ensure reliability.

[0004]

In order to solve such a problem, the present invention provides a pulse having a time width that does not cause an electrochemical change in a working electrode or a reference electrode constituting an electrochemical gas sensor. A check pulse generation unit that outputs a reference signal, a connection inspection unit that detects a connection state of the electrochemical sensor based on a potential change due to the pulse, and a measurement signal from the electrochemical gas sensor and a reference value. A measurement circuit that suppresses the output when the value is equal to or less than a value, a check potential generating unit that gives the electrode a potential change that causes an electrochemical change in the electrochemical gas sensor, and the electrochemical gas that is caused by the potential change. Function inspection means for determining the function of the electrochemical gas sensor or the measurement circuit based on a signal from a sensor; Control means for operating the check potential generation means and the function inspection means by detecting that the measurement signal is suppressed by the pulse generation means and the connection inspection means in the first cycle and in the second cycle; And was prepared.

[0005]

When no gas is present, the presence or absence of a sensor connection and the functions of the sensor and the measuring circuit are periodically checked in the first and second cycles. On the other hand, when the output of the sensor exceeds the reference value, the measurement operation is continued without activating the check operation, and the measurement operation when gas is present in the environment is maintained.

[0006]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a first embodiment of the present invention. FIG. 1 shows an embodiment of the present invention, in which a sensor 10 is connected to a measuring apparatus main body 20 via a connector or the like. In this embodiment, a working electrode 11, a counter electrode 12, and a reference electrode 13 are connected. It is configured as a three-electrode type constant potential electrolytic gas sensor housed in a container 15 together with the electrolytic solution 14.

The counter electrode 12 is grounded via an impedance element 16, and a connection point P to the impedance element 16 is connected to a check pulse generation means 21 and a connection inspection means 22 including a potential detection circuit and the like. The check pulse generation unit 21 can detect a change in potential by the connection inspection unit 22 and a pulse having a time width that does not cause an electrochemical change in the sensor 10, for example, a pulse of approximately 40 microseconds (FIG. )) And the impedance element 16
A value larger than the impedance between the electrodes constituting 0 is selected.

The working electrode 11 and the reference electrode 13, which receive the action of gas through the diaphragm, are connected to a measuring circuit 24 via a preamplifier 23, and the reference electrode 13 is connected to an amplifier 25.
Is supplied from the check potential generation means 26 via the. The measuring circuit 24 has an offset function for forcibly suppressing the output to a zero level when the level of the input signal is lower than a reference value set to a level slightly higher than a noise component such as a dark current.

The check potential generating means 26 turns on and off the analog switch S, thereby detecting the sensor 10.
The potential of the reference electrode 13 is relatively changed, for example, from 1 to 1 for a time enough to cause electrochemical fluctuation in
It is configured to output a signal that changes by about 0%. The function inspection unit 27 is a circuit that processes the signal of the sensor 10, such as the sensitivity of the sensor 10 itself and the measurement circuit 24 based on the signal output from the sensor 10 due to the potential change caused by the signal of the check potential generation unit 26. It is determined whether the function of the means is normal.

The check control means 28 has a first period T
1, for example, a check pulse is output from the check pulse generation means 21 every 30 seconds, and the connection inspection means 22 inspects the connection state of the sensor 10 and whether there is a break in the lead wire, and a second period T2, for example, 1 It is determined whether the measurement signal of the sensor 10 is suppressed every time or not.
6, a function is determined by the function inspection means 27 based on the response of the sensor 10 to the signal.
In the state where a significant gas-sensitive signal is output from, the measurement operation is continued.

The operation of the above-structured apparatus will be described with reference to the flowchart shown in FIG. When the first cycle T1 set in the timer built in the check control means 28 arrives (step b), the check control means 28 outputs a pulse from the check pulse generation means 21 regardless of the presence or absence of the measurement operation, The potential change at the connection point P is detected by the connection inspection means 22 (step b).

When the sensor 10 is normally connected to the connection means such as a connector and the lead wire is not broken, the pulse from the check pulse generation means 21 flows to the ground via the sensor 10. Since the potential change at the connection point P is extremely small and does not exceed the reference value (step c) (the state before t0 in FIG. 2B), it is determined that the connection is normal and the operation shifts to a normal measurement operation ( Step e).

On the other hand, if the sensor 10 is disconnected from the connector, or if a lead wire connecting the sensor 10 and the circuit is broken, a load voltage is generated by the impedance element 16 and exceeds the reference value. Steps
C) (state after t0 in FIG. 2 (b)), connection inspection means 2
2 issues an alarm such as a sensor dropout by alarm means (not shown) (step d) and stops the measuring operation. Needless to say, the pulse signal from the check pulse generating means 21 is extremely short, about 40 microseconds, and the sensor 10
Since this does not cause a change in the function, the measurement operation can be continued.

Hereinafter, such a connection check operation is performed at a predetermined period, for example, every 30 seconds, and when the period T2 arrives while the measurement operation is continued (step S1).
E) The check control means 28 transmits the signal from the check potential generation means 26 to the sensor 10 only when it is confirmed that the output of the sensor 10 is equal to or less than the reference value based on the signal from the measurement circuit 24 (step f). A signal for increasing the potential of the reference electrode 13 is output for a predetermined time, for example, about 1 second, at which the electrochemical fluctuation can be given (step
G) (FIG. 2 (c)).

Thus, the sensor 10 receives the electrochemical fluctuation and outputs a corresponding signal.
7 indicates that the sensor 10 is normal when the detection sensitivity of the sensor 10 has changed over time or when the measurement circuit 24 and the like are functioning normally (step) by comparing with a preset reference value. After a lapse of time, for example, 30 seconds, until the function is activated (step), the operation shifts to the measurement operation (step e).

On the other hand, as a result of comparison with the reference value, the sensor 1
When an abnormality is detected in the detection sensitivity of 0 or in the function of the measurement circuit 24 or the like (Step T), the function inspection means 27 issues an alarm such as sensor abnormality (Step T) and stops the measurement operation.

On the other hand, if the level of the signal from the sensor 10 exceeds the reference value (step F), there is a high possibility that the sensor 10 is sensitive to gas, and the check control means 28 generates the check potential. Without operating the means 26 (the state at the time t1 in FIG. 2), the measuring operation is continued (step nu). This makes it possible to inspect the functions of the sensors and the like almost in real time while preventing measurement operation from being unnecessarily interrupted when gas is present in the environment and ensuring the reliability of measurement.

In the above-described embodiment, a gas sensor having three working electrodes, a working electrode, a counter electrode, and a reference electrode has been described as an example. However, a two-electrode having only working electrodes and a counter electrode is used. As shown in FIG.
2 and an impedance element 16 are connected between the ground and
A check pulse of the check pulse generating means 21 is applied to the connection point P to detect a potential change of the check pulse.
2, the signal of the check potential generating means 26 may be applied.

In the above-described embodiment, the signal from the sensor is compared with the reference value, and when the signal is less than the reference value, the output of the signal is forcibly suppressed to zero level. Obviously, the same effect can be obtained even if the function is provided.

[0020]

As described above, in the present invention,
Check pulse generation means that outputs a pulse with a time width that does not cause an electrochemical change in the working electrode or reference electrode that constitutes the electrochemical gas sensor, and the connection state of the electrochemical sensor based on the potential change due to the pulse. A connection inspection means for detecting, a measurement circuit for comparing a measurement signal from the electrochemical gas sensor with a reference value, and suppressing an output when the measurement signal is equal to or less than the reference value, and causing an electrochemical fluctuation in the electrochemical gas sensor. Check potential generating means for applying a degree of potential variation to the electrode, function inspection means for determining the function of the sensor or the measurement circuit by a signal from the sensor due to the potential variation, check pulse generation means and connection inspection means in a first cycle, In the second period, it is detected that the measurement signal has received zero suppression, and the check potential generating means and the function test are detected. Control means for operating the means, so that in the absence of gas, the presence or absence of a sensor connection and the function of the sensor and the measuring circuit can be periodically checked in the first and second cycles. If the output from the sensor exceeds zero suppression, the measurement operation is continued without activating the check operation, and without impairing the measurement operation, the operation status of the electrochemical gas sensor as much as possible in real time, In addition, the connection status between the sensor and the measuring device main body can be checked.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an electrochemical gas measuring device according to the present invention.

FIGS. 2A to 2D are waveform diagrams showing signals applied during a check operation of the measuring device and response signals thereto, respectively. FIG. 2A shows a check pulse, and FIG. FIG. 3C shows a response signal, FIG. 3C shows a change in the potential of the sensor by the check potential generating means, and FIG.

FIG. 3 is a flowchart showing an operation of the above device.

FIG. 4 is a block diagram showing an embodiment when the present invention is applied to a two-pole type gas sensor.

[Explanation of symbols]

 10 Electrochemical gas sensor 11 Working electrode 12 Counter electrode 13 Reference electrode

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masaru Ishibashi 2-7-6 Shozuzawa, Itabashi-ku, Tokyo RIKEN Keiki Co., Ltd. (72) Inventor Takanori Tsukahara 2-7-6 Shozuzawa, Itabashi-ku, Tokyo (56) References JP-A-1-172743 (JP, A) JP-A-1-305349 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27 / 416 G01N 27/26 391

Claims (2)

(57) [Claims] 1. A check pulse generating means for outputting a pulse having a time width that does not cause an electrochemical change in a working electrode or a reference electrode constituting an electrochemical gas sensor; and A connection inspection unit for detecting a connection state of the electrochemical sensor, a measurement circuit that compares a measurement signal from the electrochemical gas sensor with a reference value, and suppresses an output when the measurement signal is equal to or less than the reference value; A check potential generating means for applying a potential change to the electrode such that the sensor causes an electrochemical change, and a function of the electrochemical gas sensor or the measuring circuit is determined by a signal from the electrochemical gas sensor due to the potential change. Function checking means, the check pulse generating means and the connection checking means in a first cycle and in a second cycle; An electrochemical gas concentration measurement device comprising: a control unit that detects that the measurement signal is suppressed and activates the check potential generation unit and the function inspection unit. 2. The electrochemical gas concentration measuring device according to claim 1, wherein the first cycle is set shorter than the second cycle.