JP2006284400A - Electrochemical measuring instrument of gas concentration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochemical measuring instrument of a gas concentration capable of extending the life of an electrochemical sensor. <P>SOLUTION: An air supply pipe 22 is connected to a measuring gas supply pipe 20 through a switching valve SV1, an air discharge pipe 32 is connected to an exhaust pipe 30 through a second switching valve SV2 and the switching valves SV1 and SV2 are intermittently switched by a control part 40 not only to introduce air G, which contains a measuring gas or contains the same according to circumstances, into an electrochemical sensor 11 only for a predetermined time but also to supply air A containing no measuring gas to the electrochemical sensor 11. In a case that the gas concentration of the upper limit of a measurable range is detected, the switching valves SV1 and SV2 are forcibly switched to supply the air A containing no measuring gas to the electrochemical sensor 11. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrochemical gas concentration measuring apparatus.

  The electrochemical gas concentration measuring apparatus includes an electrochemical sensor, an electric circuit that takes out electrons generated by the electrochemical sensor as a current signal and amplifies it to convert it into a voltage or current signal corresponding to the gas concentration of the measurement gas. It is an apparatus provided with the detection part which has.

FIG. 2A is a principle diagram of an electrochemical sensor (constant potential electrolysis sensor), and FIG. 2B is a circuit diagram of a detector using the sensor.
As shown in FIG. 2A, the electrochemical sensor (hereinafter also simply referred to as a sensor) 11 has a sensing electrode S, a counter electrode C, a reference electrode R, an electrolytic solution E, and a diaphragm M. When the measurement gas G is introduced into the sensor 11 so as to come into contact with the diaphragm M, the sensing electrode S (or counter electrode C) passes through the diaphragm M and dissolves in the electrolyte E through the oxidation gas by the measurement gas G. The counter electrode C (or the sensing electrode S) absorbs electrons due to the reverse reduction reaction.
Taking this case of hydrogen sulfide as an example, it can be expressed by the following equation.
Reaction at sensing pole S: H ₂ S + 4H ₂ O → H ₂ SO ₄ + 8H ⁺ + 8e ⁻
Reaction at counter electrode C: 2O ₂ + 8H ⁺ + 8e ⁻ → 4H ₂ O
Note that the oxidation reaction at the sensing electrode and the reduction reaction at the counter electrode may be reversed depending on the measurement gas.
A voltage or current signal corresponding to the gas concentration of the measurement gas G is obtained by extracting and amplifying the generation of such electrons as a current signal using a detection unit 10 having an electric circuit as shown in FIG. The concentration can be displayed by a meter (not shown).

Among electrochemical gas concentration measuring devices, for example, a hydrogen sulfide concentration meter is used for the purpose of monitoring the environment such as a sewage pipe as defined in JIS T 8205 (Non-patent Document 1). It is common to use an electrochemical (constant potential electrolysis) sensor whose principle is excellent in selectivity, and a measurement range of 0 to 30 ppm is also common.
JIS T 8205

For example, since the concentration of gas (hydrogen sulfide) inside the sewer pipe sometimes exceeds several hundred ppm, using the measuring instrument in the general measurement range described above exposes the sensor to high-concentration gas and takes a short time. There is a problem that the lifetime of the sensor is exhausted. The reason for the end of the service life is that the properties of the electrolyte change as the measurement gas dissolves in the electrolyte of the electrochemical sensor.
It may be possible to extend the life of the sensor by taking measures such as making the amount of electrolyte infinite or constantly replenishing fresh electrolyte, but it is impractical to take such measures. Absent. This is because it is impossible to make the amount of the electrolytic solution infinite, and even if the amount of the electrolytic solution is significantly increased, the sensor becomes large in that case. Moreover, if a fresh electrolyte solution is always replenished, the apparatus becomes not only very complicated, but also the accuracy of gas concentration measurement may decrease due to the flow of the electrolyte solution.
An object of the present invention is to provide an electrochemical gas concentration measuring apparatus that can solve the above problems and extend the lifetime of an electrochemical sensor.

In order to achieve the above object, the electrochemical gas concentration measurement apparatus of the present invention intermittently contains a measurement gas (more precisely, a measurement gas (for example, hydrogen sulfide)) with respect to the electrochemical sensor. ) And supply the air that does not contain the measurement gas at other times, thereby extending the lifetime of the electrochemical sensor by shortening the total time for the measurement gas to contact the electrolyte of the electrochemical sensor. Features.
More specifically,
The electrochemical gas concentration measuring apparatus according to claim 1 has a sensing electrode, a counter electrode, an electrolytic solution, and a diaphragm, and allows the measurement gas to pass through the diaphragm and be dissolved in the electrolytic solution, and the oxidation reaction by the dissolved measurement gas is performed. Electrochemical sensor that absorbs the generated electrons by the reverse reduction reaction at the sensing electrode or counter electrode, and the electrons generated by this electrochemical sensor are taken out as current signals and amplified according to the gas concentration of the measurement gas A detector having an electrical circuit for converting to a voltage or current signal;
A measurement gas introduction pipe for introducing into the electrochemical sensor air that contains or may contain the measurement gas in a measurement space that is a gas concentration measurement target;
An exhaust pipe for returning the air exhausted from the electrochemical sensor and containing or possibly containing the measurement gas into the measurement space;
A device comprising:
An air supply pipe that is connected to the measurement gas supply pipe via a switching valve, and supplies the air that does not contain the measurement gas to the electrochemical sensor when the switching valve is open to the air supply side;
The switching valve is operated intermittently, and air containing or containing the measurement gas is intermittently introduced into the electrochemical sensor only for a predetermined time, and air that does not contain the measurement gas is introduced at other times. A control unit for feeding to the electrochemical sensor;
It is characterized by having.
According to such a configuration, the operation of the switching valve by the control unit intermittently introduces air that contains or may contain the measurement gas into the electrochemical sensor only for a predetermined time, and the measurement gas at other times. Since air that does not contain oxygen is supplied to the electrochemical sensor, the total time for which the measurement gas contacts the electrolyte of the electrochemical sensor is shortened, and the lifetime of the electrochemical sensor is extended.
Preferably, the control unit forcibly switches the switching valve to detect the measurement to the electrochemical sensor when the detection unit detects the gas concentration of the upper limit of the measurable range by the electrochemical sensor. It is set as the structure which supplies the air which does not contain gas.
If comprised in this way, the time which high concentration gas contacts the electrolyte solution of an electrochemical sensor can be shortened as much as possible, and the lifetime of an electrochemical sensor can be extended more reliably.
Preferably, an air discharge pipe is connected to the exhaust pipe via a second switching valve that is different from the switching valve, and the control unit uses the switching valve to supply air that does not include the measurement gas to the exhaust pipe. When supplying to the electrochemical sensor, the second switching valve is switched to the air discharge pipe side so that air from the electrochemical sensor is discharged to a place other than the measurement space.
If comprised in this way, the measurement gas concentration fall in the said measurement space by the air which does not contain measurement gas entering into the said measurement space can be prevented, and reliable gas concentration measurement can be performed.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a piping and circuit diagram showing an embodiment of an electrochemical gas concentration measuring apparatus according to the present invention.

As shown in the figure, the electrochemical gas concentration measuring apparatus 1 takes out an electrochemical sensor 11 and electrons generated by the electrochemical sensor 11 as a current signal and amplifies the gas concentration of the measurement gas G. A detector 10 having an electrical circuit for converting it into a corresponding voltage or current signal;
A measurement gas introduction pipe 20 for introducing air (G) containing or containing the measurement gas G in the measurement space SP, which is a gas concentration measurement target, into the electrochemical sensor 11;
An exhaust pipe 30 for returning air discharged from the electrochemical sensor 11 and containing the measurement gas G into the measurement space SP;
When the first switching valve SV1 is connected to the measurement gas supply pipe 20 via the first switching valve SV1, and the first switching valve SV1 is opened to the air supply side, the electrochemical sensor 11 does not contain the measurement gas G. An air supply pipe 22 for supplying
The first switching valve SV1 is operated intermittently, and air (G) containing or containing the measurement gas G is intermittently introduced into the electrochemical sensor 11 only for a predetermined time. And a control unit 40 for supplying the electrochemical sensor 11 with air A that does not contain the measurement gas G.

  The electrochemical gas concentration measuring apparatus 1 of this embodiment is an apparatus for measuring the concentration of hydrogen sulfide as a measurement gas, and the electrochemical sensor 11 is composed of the sensor described above with reference to FIG. ing. Moreover, the detection part 10 also has the electric circuit shown in FIG.2 (b).

One end of the measurement gas introduction pipe 20 is connected to the electrochemical sensor 11 (see FIG. 2B), and the other end is connected to the gas intake pipe 23 and the air supply pipe 22 via the first switching valve SV1. And are connected.
A gas intake port 23a of the gas intake tube 23 opens into the measurement space (for example, a sewage pipe) SP. The air intake 22a of the air supply pipe 22 is isolated from the measurement space SP and opens to a space that does not contain the measurement gas G.
The first switching valve SV1 is a three-way solenoid valve.
Therefore, when the first switching valve SV1 is switched to the gas intake pipe 23 side, the electrochemical sensor 11 includes or includes the measurement gas G from the measurement space SP by the suction action of the pump P described later. When certain air (G) (hereinafter also simply referred to as measurement gas G) is introduced and the first switching valve SV1 is switched to the air supply pipe 22 side, the electrochemical sensor 11 includes air A that does not contain the measurement gas G. Is supplied.

One end of the exhaust pipe 30 is connected to the electrochemical sensor 11 (see FIG. 2B), and the other end is connected to a gas exhaust pipe via a second switching valve SV2 different from the first switching valve SV1. 33 and the air discharge pipe 32 are connected. A pump P is interposed in the exhaust pipe 30.
The gas discharge port 33a of the gas discharge pipe 33 opens into the measurement space (for example, a sewage pipe) SP. The air discharge port 32a of the air discharge pipe 32 opens into a space isolated from the measurement space SP.
The second switching valve SV2 is a three-way solenoid valve.
Therefore, when the second switching valve SV2 is switched to the gas discharge pipe 33 side, the measurement gas G from the electrochemical sensor 11 is discharged to the measurement space SP by the action of the pump P, and the second switching valve SV2 is discharged to the air. When switching to the tube 32 side, the air A from the electrochemical sensor 11 is discharged to a space isolated from the measurement space SP.

  In the figure, “Bypass NV” is a bypass for passing a predetermined flow rate to the electrochemical sensor 11 and bypassing an excessive amount when sucking with a pump P having a suction flow rate larger than the predetermined flow rate. The needle valves “N.V” and “F / M” are a two-dollar valve and a flow meter for adjusting and confirming the flow rate of air flow to the electrochemical sensor 11, and “A / F” is an air filter.

  The detection unit 10 is connected to the digital indicating alarm meter 50 via the transmission loop signal line 12, and the gas concentration detected by the detection unit 10 is converted into a transmission loop signal by the detection unit 10, and the digital indicating alarm meter 50 Concentration display and alarm display / output are performed at.

More specifically, the digital indicator / alarm meter 50 includes first and second switches 51 and 52 that operate according to gas concentration values obtained from the detection unit 10.
The first switch 51 is a switch that is turned on when the gas concentration value becomes 5 ppm or more. When the first switch 51 is turned on, the first alarm signal AL1 is output.
The second switch 52 is a switch that is turned on when the gas concentration value becomes 10 ppm or more. When the second switch 52 is turned on, the second alarm signal AL2 is output.
For example, a remote operation panel (remote monitoring panel) (not shown) is connected to the electrochemical gas concentration measuring apparatus 1 of this embodiment, and when the first alarm signal AL1 is output, for example, The first alarm lamp is turned on or blinks and / or a first alarm sound is emitted. When the second alarm signal AL2 is output, for example, a second alarm lamp on the remote control panel is turned on or blinks and / or a second alarm sound is emitted.

The digital indicating alarm meter 50 has a third switch 53. The third switch 53 is a switch that is turned on when any abnormality occurs in the electrochemical gas concentration measuring apparatus 1, and when the third switch 53 is turned on, a third alarm signal AL3 is output, For example, the third alarm lamp is turned on or blinks and / or a third alarm sound is generated.
T2-1 is a timer switch that operates in conjunction with a second timer T2 described later, and is interposed in the common line of the first to third switches 51 to 53. Reference numeral 55 denotes an analog output unit for displaying the concentration measurement value in an analog manner on the remote control panel. The analog output unit also includes a timer switch T2-2 that operates in conjunction with a second timer T2 described later. It is intervened.

The digital indicating alarm meter 50 has a fourth switch 54. The fourth switch 54 is a switch that is turned on when the gas concentration within the upper limit (or higher) of the measurable range by the electrochemical sensor 11 is detected. When the fourth switch 54 is turned on, the fourth alarm signal is turned on. AL4 is output to the control unit 40.
The gas concentration of the upper limit of the measurable range by the electrochemical sensor 11 in this embodiment is 30 ppm.
Therefore, when the gas concentration value obtained by the detection unit 10 reaches 30 ppm, the fourth switch 54 is turned ON and the fourth alarm signal AL4 is output to the control unit 40.

The control unit 40 includes a first timer T1 and a timer switch TS that is operated by the first timer T1. The aforementioned first switching valve SV1 and second switching valve SV2 are connected to the ON side of the timer switch TS.
The first switching valve SV1 is switched to the air supply pipe 22 when the timer switch TS is OFF, and is switched to the gas intake pipe 23 when the timer switch TS is turned ON.
The second switching valve SV2 is switched to the air discharge pipe 32 when the timer switch TS is OFF, and is switched to the gas discharge pipe 33 when the timer switch TS is turned ON.

Although the set time of the first timer T1 is arbitrary, in this embodiment, the timer is turned on for 1 minute (the timer switch TS is turned on), and then turned off for 14 minutes (the timer switch TS is turned off). It is set to repeat the operation.
Therefore, the detection unit 10 intermittently operates the first and second switching valves SV1 and SV2 to intermittently introduce the measurement gas G into the electrochemical sensor 11 for a predetermined time (in this case, 1 minute) and The measurement gas G from the chemical sensor 11 is discharged into the measurement space SP, and air A containing no measurement gas is supplied to the electrochemical sensor 11 for the other time (in this case, 14 minutes) and the air A from the electrochemical sensor 11 is supplied. Is discharged to a place other than the measurement space SP.

The fourth alarm signal AL4 output to the control unit 40 when the fourth switch 54 in the digital indicator / alarm meter 50 is turned ON causes the timer switch TS to be turned OFF by forcibly resetting the first timer T1. Signal.
Therefore, when the gas concentration value obtained by the detection unit 10 reaches 30 ppm, the timer switch TS is turned off regardless of the above-described ON / OFF cycle of the first timer T1, and the first and second switching valves are turned off. SV1 and SV2 forcibly supply air A that does not contain the measurement gas to the electrochemical sensor 11 and discharge the air A from the electrochemical sensor 11 to locations other than the measurement space SP regardless of the switching cycle described above. It will be switched to the side.

In FIG. 1, 2 is a power switch of the apparatus 1, and 3 is a DC power supply for the control unit 40.
T2 is a second timer provided in the control unit 40, and is a timer for performing a warm-up operation for a predetermined time after the power switch 2 is turned on.
The set time of the second timer T2 is arbitrary, but is set to 1 minute in this embodiment.
When the power switch 2 is turned on, the device 1 starts to operate, the detection unit 10 is also operated via the digital indicating alarm meter 50, and a predetermined voltage is applied to each electrode (S, R, C) of the electrochemical sensor 11. However, since the potential of each electrode of the electrochemical sensor 11 is in an unstable state for a predetermined time (about 30 seconds in this embodiment), the operation of the second timer T2 The alarm signal is not output for one minute after the power switch 2 is turned on. That is, the above-described timer switch T2-1 interlocked with the second timer T2 is OFF for one minute after the power switch 2 is turned ON, and the first to third alarm signals AL1 to AL3 are not output. . Even if the power switch 2 is turned on, the timer switch T2-2 is turned off for one minute thereafter, and an analog signal from the analog output unit 55 is not output.

  In FIG. 1, L1 is a power lamp, L2 is a lamp indicating that air A is supplied to the electrochemical sensor 11, L3 is a lamp indicating that measurement gas G is supplied to the electrochemical sensor 11, R1 is a relay that displays on the remote control panel that the measurement gas G is supplied to the electrochemical sensor 11 and gas concentration measurement is being performed.

The main operation of the electrochemical gas concentration measuring apparatus 1 as described above is as follows.
When the power switch 2 is turned on, the device 1 starts operating. That is, the pump P, the detection unit 10, the control unit 40, and the digital indicating alarm meter 50 start operating. However, as described above, the warm-up operation is performed for one minute. At this time, the timer switch TS of the first timer T1 is OFF, and air A is supplied to the electrochemical sensor 11.
When the power switch 2 is turned on and 14 minutes elapses, the timer switch TS is turned on, the first and second switching valves SV1 and SV2 are switched, and the measurement gas G is introduced into the electrochemical sensor 11, and within the measurement space SP. The gas concentration is measured.
When one minute has elapsed from the start of measurement, the timer switch TS is turned off, the first and second switching valves SV1 and SV2 are switched, air A is supplied to the electrochemical sensor 11, and the measurement remaining in the electrochemical sensor 11 Gas G is scavenged.
When 14 minutes have elapsed from the start of scavenging (air A supply), the timer switch TS is turned on, the first and second switching valves SV1, SV2 are switched, and the measurement gas G is introduced into the electrochemical sensor 11, and within the measurement space SP. The gas concentration is measured.
The operation as described above, that is, the first and second switching valves SV1, SV2 are intermittently operated, and the measurement gas G is intermittently introduced into the electrochemical sensor 11 only for a predetermined time (in this case, 1 minute) The measurement gas G from the chemical sensor 11 is discharged to the measurement space SP, and air A containing no measurement gas is supplied to the electrochemical sensor 11 and air A from the electrochemical sensor 11 is supplied for another time (in this case, 14 minutes). Is repeatedly discharged to a location other than the measurement space SP.

In the process of repeating the above operation, the first alarm signal AL1 is output when the measured gas concentration value is 5 ppm or more, and the second alarm signal AL2 is output when the gas concentration value is 10 ppm or more.
When the gas concentration value reaches 30 ppm, the fourth switch 54 is turned on and the fourth alarm signal AL4 is output to the control unit 40. The first timer T1 is forcibly reset and the timer switch TS is turned off. Regardless of the switching cycle described above, the first and second switching valves SV1 and SV2 are forcibly switched to supply the electrochemical sensor 11 with the air A that does not contain the measurement gas, and the electrochemical sensor 11 is supplied with air. A will be supplied.
If any abnormality occurs while the apparatus 1 is operating, the third alarm signal AL3 is output.

The electrochemical gas concentration measuring apparatus 1 as described above has the sensing electrode S, the counter electrode C, the electrolytic solution E, and the diaphragm M, and the measurement gas G passes through the diaphragm and is dissolved in the electrolytic solution E. An electrochemical sensor 11 that absorbs electrons generated by the oxidation reaction by the measurement gas by a reverse reduction reaction at the counter electrode C, and an electron generated by the electrochemical sensor 11 is extracted as a current signal and amplified to measure the gas. A detector 10 having an electric circuit for converting the voltage or current signal according to the gas concentration of G;
A measurement gas introduction pipe 20 for introducing air (G) containing or containing the measurement gas G in the measurement space SP which is a gas concentration measurement target into the electrochemical sensor 11;
An exhaust pipe 30 for returning air (G) discharged from the electrochemical sensor 11 and containing the measurement gas G into the measurement space SP;
An air supply pipe 22 that is connected to the measurement gas supply pipe 20 via a switching valve SV1 and supplies the air A not containing the measurement gas to the electrochemical sensor 11 when the switching valve SV1 is opened to the air supply side; ,
The switching valve SV1 is operated intermittently, and air (G) that contains or may contain the measurement gas G is intermittently introduced into the electrochemical sensor 11 only for a predetermined time, and air that does not contain the measurement gas at other times. A control unit 40 for supplying A to the electrochemical sensor 11,
Therefore, the operation of the switching valve SV1 by the control unit 40 intermittently introduces air (G) that may contain or contain the measurement gas into the electrochemical sensor 11 only for a predetermined time, and measures the other time. Air A that does not contain gas is supplied to the electrochemical sensor 11.
Therefore, the total time for the measurement gas G to contact the electrolyte E of the electrochemical sensor 11 is shortened, and the lifetime of the electrochemical sensor 11 is extended.
An attempt to shorten the total time in which the measurement gas G contacts the electrolyte E of the electrochemical sensor 11 by turning the pump P on / off is that the measurement gas G in the electrochemical sensor 11 is air A. It is not desirable because it is not scavenged.

Further, when the detection unit 10 detects the gas concentration of the upper limit value of the measurable range by the electrochemical sensor 11, the control unit 40 forcibly switches the switching valve SV1 to supply the measurement gas to the electrochemical sensor 11. Since the air A that is not included is supplied, the time during which the high concentration gas contacts the electrolytic solution E of the electrochemical sensor 11 can be shortened as much as possible.
Therefore, the lifetime of the electrochemical sensor 11 can be extended more reliably.

  In addition, an air discharge pipe 32 is connected to the exhaust pipe 30 via a second switching valve SV2 different from the switching valve SV1. When supplying to the electrochemical sensor 11, the second switching valve SV2 is switched to the air discharge pipe side 32 so that the air A from the electrochemical sensor 11 is discharged to a location other than the measurement space SP. It is possible to prevent a decrease in the concentration of the measurement gas in the measurement space SP due to the entry of the air A that does not contain the measurement gas, and a reliable gas concentration measurement can be performed.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be appropriately modified within the scope of the gist of the present invention.

The piping and circuit diagram which show one Embodiment of the electrochemical type gas concentration measuring apparatus which concerns on this invention. (A) is a principle diagram of an electrochemical sensor, (b) is a circuit diagram of a detection unit using the sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrochemical type gas concentration measuring apparatus 10 Detection part 11 Electrochemical type sensor S Sensing pole C Counter electrode E Electrolyte M Membrane SP Measurement space 20 Measuring gas introduction pipe 22 Air supply pipe 30 Exhaust pipe 32 Air discharge pipe SV1 1st switching valve (switching) valve)
SV2 second switching valve 40 controller

Claims (3)

It has a sensing electrode, a counter electrode, an electrolyte solution, and a diaphragm. The measurement gas passes through the diaphragm and is dissolved in the electrolyte solution. Electrons generated by the oxidation reaction by the dissolved measurement gas are reversed at the sensing electrode or the counter electrode. Detection having an electrochemical sensor to be absorbed by a reduction reaction, and an electric circuit that takes out electrons generated by the electrochemical sensor as a current signal and amplifies it to convert it into a voltage or current signal according to the gas concentration of the measurement gas Part,
A measurement gas introduction pipe for introducing into the electrochemical sensor air that contains or may contain the measurement gas in a measurement space that is a gas concentration measurement target;
An exhaust pipe for returning the air exhausted from the electrochemical sensor and containing or possibly containing the measurement gas into the measurement space;
A device comprising:
An air supply pipe that is connected to the measurement gas supply pipe via a switching valve, and supplies the air that does not contain the measurement gas to the electrochemical sensor when the switching valve is open to the air supply side;
The switching valve is operated intermittently, and air containing or containing the measurement gas is intermittently introduced into the electrochemical sensor only for a predetermined time, and air that does not contain the measurement gas is introduced at other times. A control unit for feeding to the electrochemical sensor;
An electrochemical gas concentration measuring device comprising:   The control unit forcibly switches the switching valve to include the measurement gas in the electrochemical sensor when the detection unit detects the gas concentration of the upper limit value of the measurable range by the electrochemical sensor. The electrochemical gas concentration measuring apparatus according to claim 1, wherein the apparatus is a control unit that supplies non-air.   An air discharge pipe is connected to the exhaust pipe via a second switching valve different from the switching valve, and the control unit uses the switching valve to supply air that does not contain the measurement gas to the electrochemical formula. 2. The control unit according to claim 1, wherein when supplying to the sensor, the control unit is configured to switch the second switching valve to the air discharge pipe side and discharge the air from the electrochemical sensor to a place other than the measurement space. 2. The electrochemical gas concentration measuring apparatus according to 2.

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