JP2005069820A - Electrochemical gas detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochemical gas detector capable of detecting gas with high reliability over a long period of time. <P>SOLUTION: This electrochemical gas detector is equipped with an electrochemical sensor and constituted so as to detect the concentration of the gas to be detected on the basis of the output value from the electrochemical sensor. The electrochemical gas detector is also equipped with an indication value correcting means for performing correction so as to increase the indication value of the concentration of the gas to be detected to the output value from the electrochemical sensor with the elapse of time and the gas to be detected is preferably a carbon monoxide gas. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrochemical gas detector.

  As a gas detector for detecting carbon monoxide gas, a gas detector including an electrochemical gas sensor such as a constant potential electrolysis gas sensor or a galvanic cell gas sensor is known (for example, Patent Document 1 to Patent Document). 3).

  As a certain type of electrochemical gas sensor, for example, an electrolyte cell having an opening for accommodating an electrolyte solution and having two openings that are closed by a porous sheet having gas permeability And a working electrode provided on the surface of one porous sheet for electrolyzing carbon monoxide gas as a detection target gas, provided on the other porous sheet, a counter electrode for the working electrode, and the other A constant potential electrolytic gas sensor is used which is provided on a porous sheet separately from a counter electrode and includes a reference electrode for controlling the potential of the working electrode.

  Such an electrochemical gas sensor including a porous sheet, an electrode, an electrolytic solution, and an electrolytic cell as a constituent element is a gas to be detected at the working electrode in a state where the working electrode, the counter electrode, and the reference electrode are immersed in the electrolytic solution. As a result of the electrolysis, the output value indicated by the electrolytic current value generated due to the electrochemical reaction occurring at the working electrode and the counter electrode is proportional to the concentration of the gas to be detected. The detection target gas concentration is detected by measuring the output value.

However, in the electrochemical gas detector, the electrochemical gas sensor has a large characteristic change over time due to, for example, contamination of the porous sheet, oxidation of the metal constituting the electrode, deterioration of the catalytic action of the electrolytic solution, etc. As the usage time increases, the output value varies and the gas detection performance is lowered. Therefore, there is a problem that the gas concentration detection performance is gradually lowered.
The problem of the gas concentration detection performance degradation in such an electrochemical gas detector is, for example, when it is used in a poor environment such as in a tunnel on a motorway, during the initial period when the electrochemical gas detector starts operation. It will be remarkable.

Japanese Patent Laid-Open No. 05-11020 Japanese Patent Laid-Open No. 05-223777 Japanese Patent Laid-Open No. 06-058906

  The present invention has been made based on the above circumstances, and an object thereof is to provide an electrochemical gas detector capable of performing gas detection with high reliability over a long period of time.

The electrochemical gas detector of the present invention is an electrochemical gas detector that includes an electrochemical sensor and detects a detection target gas concentration based on an output value from the electrochemical sensor,
The apparatus is characterized by comprising an instruction value correcting means for correcting the instruction value of the detection target gas concentration with respect to the output value from the electrochemical sensor to increase with time.

  In the electrochemical gas detector of the present invention, the detection target gas is preferably carbon monoxide gas.

  In the electrochemical gas detector of the present invention, it is preferable that the indicated value correcting means corrects at a correction rate smaller than the correction rate of the initial use period after the initial use period has elapsed.

The electrochemical gas detector of the present invention is suitably used for detecting the concentration of a gas to be detected in a tunnel on an automobile road.
In such a case, the detected gas concentration to be detected can be used for controlling the exhaust mechanism in the tunnel.

  According to the electrochemical gas detector of the present invention, the indicated value correcting means for correcting the indicated value of the gas concentration to be detected is provided, and the detected gas performance that occurs over time in the electrochemical gas sensor by this indicated value correcting means. Can be compensated by increasing the indicated value of the gas concentration to be detected with respect to the output value of the electrochemical gas sensor according to the degree of the decrease, and therefore, the characteristic change with time of the electrochemical gas sensor occurs. However, since the gas concentration detection performance is prevented from being lowered at the indicated value of the detection target gas concentration, as a result, highly reliable gas detection can be performed over a long period of time.

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is an explanatory diagram showing an example of the configuration of the electrochemical gas detector of the present invention.
The electrochemical gas detector 10 uses a constant potential electrolytic gas sensor as an electrochemical gas sensor, and introduces a gas for introducing a gas to be inspected (hereinafter also referred to as “inspected gas”). A gas cell 13 having a port 13A and a gas discharge port 13B, a constant potential electrolytic gas sensor 20 connected to the gas cell 13, and a control unit (not shown) for operating the constant potential electrolytic gas sensor 20 The gas detector main body 11 comprised by these is provided.

Then, the electrochemical gas detector 10 includes an instruction value correction means for correcting the instruction value of the gas concentration to be detected with respect to the output value from the constant potential electrolysis gas sensor 20 in the gas detector body 11 to increase with time (FIG. Not shown).
Here, the “indicated value” is determined based on the magnitude of the output value using the fact that the magnitude of the output value from the constant potential electrolytic gas sensor 20 and the concentration of the detection target gas are in a proportional relationship. Is a value indicating the concentration of the detection target gas.
In the example of this figure, the initial value of the indication value of the detection target gas concentration with respect to the output value of the constant potential electrolytic gas sensor 20 is recorded in the control unit.

The constant potential electrolytic gas sensor 20 forms an electrolytic solution housing space 21A for containing an electrolytic solution made of an aqueous sulfuric acid solution, and includes a first opening 23 provided with a cylindrical connecting member 22 extending outwardly, An electrolyte solution cell 21 made of, for example, polycarbonate, vinyl chloride or the like, having a circular second opening 24 provided at a position facing the first opening 23, is provided. A first gas permeable film 31 that has a size suitable for the first opening 23 and is provided so as to close the first opening 23 and that does not allow the electrolyte solution to pass therethrough, and the first gas permeable film 31. The working electrode 34 for electrolyzing the gas to be detected, which is formed on the surface facing the electrolytic solution containing space 21 </ b> A, has a size suitable for the second opening 24, and closes the second opening 24. The electrolyte solution The second gas permeable membrane 32 that is not to be made, and the counter electrode 35 that is formed on the surface of the second gas permeable membrane 32 that faces the electrolytic solution housing space 21A, and the action that is provided separately from the counter electrode 35. A reference pole 36 for controlling the potential of the pole 34 is provided.
In the example of this figure, 21B is an opening for adjusting the pressure inside the electrolyte cell 21.

  In the constant potential electrolytic gas sensor 20, the working electrode 34 and the reference electrode 36 are connected to, for example, a potentiostat circuit 39, and a counter electrode 35 is also connected to the potentiostat circuit 39 via a resistor R.

In the potentiostatic gas sensor 20, as the working electrode 34, the counter electrode 35, and the reference electrode 36, an electrode made of an electrode material metal such as platinum, gold, silver, copper, ruthenium, ruthenium oxide, or a mixture thereof is used. Can do.
Moreover, as each of the 1st gas permeable film 31 and the 2nd gas permeable film 32, porous sheets, such as a product made from polytetrafluoroethylene resin (PTFE resin), can be used, for example.

  As the instruction value correcting means, for example, a microcomputer can be used.

  The correction by the indicated value correcting means can be in an appropriate mode according to the environmental conditions in which the electrochemical gas detector 10 is used. For example, an indication of the detection target gas concentration with respect to the output value from the constant potential electrolytic gas sensor 20 The value may be increased stepwise as the time changes, or may be increased gradually.

As a preferred mode of correction by the instruction value correction means, the correction rate after the use initial period has elapsed is made smaller than the correction rate for the use initial period.
Here, the “initial period of use” refers to a period in which the characteristic change over time is extremely large from the deterioration characteristics of the electrochemical gas sensor itself such as the constant potential electrolytic gas sensor 20, and specifically, for example, for two months. is there.
In addition, this initial use period is a period related to the use time in the constant potential electrolytic gas sensor 20.

  By making the correction rate after the initial period of use less than the correction rate of the initial use period, a large correction is performed in the initial use period according to the deterioration state derived from the deterioration characteristics of the constant potential electrolytic gas sensor 20, and After the initial period of use, a correction that is smaller than the correction is performed, so that more reliable gas detection can be reliably performed.

  The degree of correction of the indicated value of the gas concentration to be detected by the indicated value correcting means is determined by measuring the deterioration characteristics of the gas detector main body 11 itself in an environment where the electrochemical gas detector 10 is actually used. It can be determined as appropriate based on the measurement result.

  As a specific example of the correction by the instruction value correction means, during the initial use period of 2 months, the monthly correction rate is set to 5 to 10% of the initial value. The correction rate is 1 to 3% of the initial value.

  The electrochemical gas detector 10 having such a configuration includes at least a working electrode 34, a counter electrode 35, and a counter electrode 35 in the electrolyte solution containing space 21 </ b> A of the electrolyte cell 21 in the constant potential electrolytic gas sensor 20 in the gas detector body 11. A gas detection operation can be performed by accommodating an appropriate amount of electrolyte in which the reference electrode 36 is immersed, and during the gas detection operation, the potentiostat circuit 39 and the working electrode 34, When the potential between the reference electrode 36 is kept constant and the gas to be inspected is introduced into the gas cell 13 through the gas inlet 13A, the detection target gas existing in the gas to be inspected is fixed. By passing through the first gas permeable membrane 31 of the electrolysis gas sensor 20, it is electrolyzed at the working electrode 34, and the working electrode 34 and the counter electrode 35 are respectively An output value indicated by the value of the electrolytic current flowing between the working electrode 34 and the counter electrode 35 due to the occurrence of the electrochemical reaction is measured in the control unit, and the magnitude of the output value and the concentration of the detection target gas are determined. Using the proportional relationship, the control unit specifies the detection target gas concentration based on the indication value of the detection target gas concentration with respect to the output value of the constant potential electrolytic gas sensor 20, and as a result, the detection target in the gas to be inspected. Gas concentration can be detected.

In the electrochemical gas detector 10 described above, as the usage time increases, for example, contamination of the first gas permeable membrane 31 and the second gas permeable membrane 32, the working electrode 34, the counter electrode 35, and the reference electrode 36 are removed. The output value of the constant potential electrolysis gas sensor 20 varies due to oxidation of the constituent metals, deterioration of the catalytic action of the electrolyte, and the like, and the gas detection performance deteriorates. As a result, the initial value is recorded in the control unit in advance. The detection target gas concentration specified in accordance with the indicated value of the detection target gas concentration will be smaller than the actual detection target gas concentration. The indicated value of the gas concentration to be detected with respect to the output value of the constant potential electrolysis gas sensor 20 increases according to the degree of deterioration in gas detection performance that occurs over time. It is possible to cormorants corrected and compensated, even temporal characteristic change in potential electrolysis type gas sensor 20 occurs, the indicated value of the detection target gas concentration, gas concentration detection performance is suppressed to decrease.
Therefore, the electrochemical gas detector 10 can perform highly reliable gas detection over a long period of time.
In practice, such an electrochemical gas detector 10 is preferably used as one that detects the concentration of a gas to be detected in a poor environment in which, for example, an automobile exhaust gas or the like stays in a tunnel on a motorway. it can.

  In addition, according to the electrochemical gas detector 10, since a highly reliable gas detection can be performed over a long period of time, a maintenance period between one maintenance and the next maintenance is increased. For maintenance of the gas detector, for example, when it is used in a tunnel of an automobile road where it is necessary to temporarily stop the traffic of the automobile, there is an advantage that the number of maintenance can be reduced.

  Furthermore, the electrochemical gas detector 10 is, for example, a detection target gas in a control device that controls the operation of the exhaust mechanism in a tunnel having an exhaust mechanism for maintaining the concentration of the detection target gas in the interior below a certain level. It can be used as a gas detection unit that detects the concentration. In this case, the gas detection unit detects the concentration of the detection target gas detected in the gas detection unit, so that the gas detection unit As a result, the operation of the exhaust mechanism can be reliably controlled by the control device.

  The electrochemical gas detector 10 can suitably use carbon monoxide gas as a detection target gas.

In the above, the electrochemical gas detector provided with the constant potential electrolytic gas sensor as the electrochemical gas sensor has been described, but the present invention is not limited to this, and the concentration of the detection target gas concentration with respect to the output value from the electrochemical sensor is not limited to this. Various other members can be used as long as they include instruction value correction means for correcting the instruction value to increase over time.
For example, a galvanic cell type gas sensor can be used as the electrochemical gas sensor.

  Hereinafter, experiments conducted for confirming the effects of the present invention will be described.

[Experimental Example 1]
In accordance with the configuration of FIG. 1, an electrochemical gas sensor including a constant potential electrolytic gas sensor as an electrochemical gas sensor and using carbon monoxide gas as a detection target gas (hereinafter also referred to as “electrochemical gas detector (1)”). Was made.
In this electrochemical gas detector (1), as the indicated value correction means, during the initial period of 2 months, the monthly correction rate is set to 6% of the initial value. A microcomputer that performs correction with a correction rate of 2% of the initial value was used.

  The produced electrochemical gas detector (1) was placed in a carbon monoxide gas atmosphere at a concentration of 100 ppm for 6 months, and a gas detection test was performed to confirm the gas detection results every month. In the meantime, it was confirmed that the gas concentration detection performance without any practical problem was maintained.

[Comparative Experiment Example 1]
The electrochemical gas detector (1) has the same configuration as the electrochemical gas detector (1) except that it does not include the indicated value correction means (hereinafter referred to as “comparison electrochemical gas detector”). (Also referred to as “vessel (1)”).

  When a gas detection test was performed on the produced comparative electrochemical gas detector (1) by the same method as in Experimental Example (1), it was confirmed that the gas concentration detection performance deteriorated as the usage time increased. It was.

  According to the experimental example (1) and the comparative experimental example (1), the electrochemical gas detector (1) according to the present invention can detect the gas concentration even if the electrochemical gas sensor changes in characteristics over time. It was confirmed that it can suppress that falls.

[Experiment 2]
The electrochemical gas detector (1) in the experimental example (1) is placed in a tunnel on the motorway for 210 days, and a gas with a carbon monoxide concentration of 100 ppm is periodically introduced into the gas cell as a gas to be inspected. A gas detection test was conducted to confirm the concentration of carbon monoxide gas detected by the test. The result is shown by curve a in FIG.

[Comparative Experiment 2]
In Experimental Example (2), the same as in Experimental Example (2) except that the electrochemical gas detector for comparison (1) in Comparative Experimental Example (1) was used instead of the electrochemical gas detector (1). The gas detection test was conducted by the method. The result is shown by curve b in FIG.

  From the above experimental example (2) and comparative experimental example (2), according to the electrochemical gas detector (1) according to the present invention, an inferior environment in which the exhaust gas of a car such as in a tunnel of a motorway stays. It has been confirmed that the gas concentration detection performance can be prevented from being lowered even at the bottom.

  From the above results, it was confirmed that the electrochemical gas detector (1) according to the present invention can perform highly reliable gas detection over a long period of time.

It is explanatory drawing which shows an example of a structure of the electrochemical gas detector of this invention. It is explanatory drawing which shows the relationship between the elapsed days and the detected carbon monoxide gas density | concentration which concern on Experimental example (2) and Comparative experimental example (2).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electrochemical gas detector 11 Gas detector main body 13 Gas cell 13A Gas inlet 13B Gas outlet 20 Constant potential electrolytic gas sensor 21 Electrolyte cell 21A Electrolyte storage space 21B Opening 22 Connecting member 23 First Opening 24 Second opening 31 First gas permeable membrane 32 Second gas permeable membrane 34 Working electrode 35 Counter electrode 36 Reference electrode 39 Potentiostat circuit

Claims (5)

In an electrochemical gas detector that includes an electrochemical sensor and detects a gas concentration to be detected based on an output value from the electrochemical sensor,
An electrochemical gas detector, comprising: an instruction value correction means for performing correction to increase the instruction value of the detection target gas concentration with respect to the output value from the electrochemical sensor over time.   The electrochemical gas detector according to claim 1, wherein the detection target gas is carbon monoxide gas.   3. The electrochemical gas detector according to claim 1, wherein the indicated value correcting means corrects at a correction rate smaller than the correction rate of the initial use period after the initial use period has elapsed. .   The electrochemical gas detector according to any one of claims 1 to 3, wherein the electrochemical gas detector is used for detecting a concentration of a gas to be detected in a tunnel of an automobile road.   5. The electrochemical gas detector according to claim 4, wherein the detected gas concentration to be detected is used for controlling an exhaust mechanism in the tunnel.

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