JPH08233770A - Electrochemical gas sensor - Google Patents

Abstract

PURPOSE: To notify the lifetime of a sensor to a user by detecting the deterioration of sensitivity easily and accurately. CONSTITUTION: A sensor 1 for detecting the ambient temperature is disposed contiguously to a gas sensor element 4. Output from the temperature sensor 1 is sampled at the sampling section 5 of an operating means 2 at a predetermined time interval to obtain a temperature data. The temperature data is converted, at a data calculating section 7, into a lifetime decision data based on a calculation rule prestored at a calculation rule setting memory section 6. A data accumulating section 8 accumulates the numeric values of lifetime decision data and the accumulated value is compared with a predetermined threshold value at a deciding section 9. It is decided that the lifetime of the gas sensor element 4 has expired when the threshold value is exceeded and a signal is delivered to a notifying means 3. Upon receiving the signal, the notifying means 3 notifies the expiration of lifetime to a user by means of voice or light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrochemical gas sensor, and more particularly to an electrolytic type electrochemical gas sensor which detects a specific gas by utilizing an electrochemical redox reaction.

[0002]

2. Description of the Related Art Heretofore, various electrochemical gas sensors have been proposed which detect various gases in the atmosphere, such as carbon monoxide, hydrogen, alcohols, nitrogen compounds, etc., by utilizing an electrochemical redox reaction. (For example, Japanese Patent Laid-Open No. 1-1
See Japanese Patent No. 56657). FIG. 3 shows an example of a conventional electrochemical gas sensor, in which a working electrode 11, a counter electrode 12, and a reference electrode 13 are provided on an insulating substrate 10, and these electrodes are covered with a solid polymer electrolyte membrane 14. It is configured to be electrically connected by doing.

In this electrochemical gas sensor, the working electrode 1
By applying a constant voltage to 1, the gas component of the specific species to be detected causes an oxidation or reduction reaction at the working electrode 11, and the carriers generated by this reaction move in the solid polymer electrolyte membrane 14. A reduction or oxidation reaction occurs at the counter electrode 12, and the working electrode 1 is accompanied by this redox reaction.
Since a current having a level corresponding to the concentration of the reacted gas (hereinafter referred to as a sensor current) flows between 1 and the counter electrode 12,
The concentration of the test gas can be detected by measuring the sensor current value.

[0004]

However, the electrochemical gas sensor having the conventional structure as described above has a problem that the detection sensitivity changes with time and the stability of the performance is deteriorated with time. That is, since the detection sensitivity decreases with time, the concentration of the test gas cannot be accurately detected.

One of the causes of the deterioration of the detection sensitivity over time is that contaminants existing in the air are mixed into the solid polymer electrolyte membrane 14 and, as a result, the solid polymer electrolyte membrane 1
The gas permeability of No. 4 is lowered. When the gas permeability of the solid polymer electrolyte membrane 14 decreases, the amount of the test gas reaching the working electrode 11 decreases, so that a predetermined sensor current according to the concentration of the test gas does not flow.

Speed at which the detection sensitivity deteriorates (degradation speed)
Has been found to be highly dependent on the ambient temperature in which the electrochemical gas sensor is placed (ambient temperature). That is, the higher the ambient temperature, the faster the deterioration rate of the detection sensitivity, and the shorter the life of the electrochemical gas sensor as a sensor. On the other hand, the ambient temperature environment varies depending on the place where the electrochemical gas sensor is used, and even at the same place, the ambient temperature environment changes from moment to moment depending on various conditions such as time, season, presence or absence of air conditioning equipment.

As described above, the deterioration rate of the detection sensitivity depends on the ambient temperature, and the ambient temperature environment is largely different for each gas sensor if there are a plurality of electrochemical gas sensors. Therefore, the sensor life due to the deterioration of the detection sensitivity is judged. In other words, in other words, in order to know whether or not the detection sensitivity maintains a value higher than a predetermined value, the sensor current is measured by actually blowing a test gas of known concentration onto each gas sensor. However, there is a problem that it takes a lot of time to judge the life.

A method has also been proposed in which an oxygen sensor is installed together with a gas sensor, and the sensor current of the oxygen sensor is measured to estimate the degree of deterioration of the detection sensitivity of the gas sensor to determine the life (for example, Japanese Unexamined Patent Publication No. Hei 4). -4395
No. 0), there is a large variation in the characteristics of the oxygen sensor, and accurate results cannot be obtained. The present invention is intended to solve the above-mentioned problems, and it is an object of the present invention to provide an electrochemical gas sensor capable of easily and accurately detecting the degree of deterioration of the detection sensitivity of an electrochemical gas sensor and notifying the life of the sensor. is there.

[0009]

In the present invention, in order to achieve the above object, an electrochemical gas sensor which produces a detection output according to the concentration of this gas by an electrochemical redox reaction with a specific gas. In the above, a temperature detecting means for detecting the ambient temperature, a calculating means for sequentially accumulating life judgment data corresponding to the level of the detection output of the temperature detecting means at a predetermined time interval, and an integrated result by the calculating means. And a notifying means for notifying that the end of life is reached when a predetermined condition is satisfied.

[0010]

According to the above structure, since the deterioration rate of the detection sensitivity depends on the ambient temperature, the deterioration rate at that time is obtained by detecting the ambient temperature by the temperature detection means, and the life judgment corresponding to this deterioration rate is performed. It is possible to know the degree of deterioration of the detection sensitivity by integrating the data over time by the calculating means, and it is determined that the detection sensitivity has dropped below a predetermined value when the integration result satisfies a predetermined condition set in advance. Then, the notification means notifies that the electrochemical gas sensor has reached the end of its life.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram of an electrochemical gas sensor in which a part is omitted in the present embodiment, and FIG. 2 is a gas sensor that causes a redox reaction with a test gas and outputs a sensor current according to the concentration of the test gas. The top view and sectional drawing which show the element 4 are shown.

In this embodiment, the temperature sensor 1 serving as a temperature detecting means for detecting the temperature around the gas sensor element 4.
And a calculation means 2 for integrating the life judgment data corresponding to the level of the detection output of the temperature detection means 1 with time at a predetermined time interval, and when the integration result in the calculation means 2 satisfies a predetermined condition. And an informing means 3 for informing the end of life.

As the temperature sensor 1, various types such as a thermistor, a thermocouple and a platinum temperature measuring element can be used, and the type of sensor is not the gist of the present invention. The calculating means 2 is composed of, for example, a microcomputer, and corresponds to the obtained temperature data, and a sampling section 5 for obtaining temperature data by sampling the detection output from the temperature sensor 1 at predetermined time intervals. Based on this calculation rule, a calculation rule for calculating the life judgment data, that is, a calculation rule setting storage unit 6 in which a conversion rule from the temperature data representing the ambient temperature to the life judgment data representing the deterioration rate is set and stored. A life judgment data calculation unit 7 for calculating life judgment data corresponding to temperature data, and a data integration unit 8 for integrating numerical values of life judgment data obtained at predetermined time intervals and outputting integrated value data.
And a determination unit 9 that compares the integrated value data with a predetermined value determined in advance and outputs a signal when the value exceeds the predetermined value.
It has and.

When the signal from the determination unit 9 of the calculation unit 2 is input, the notification unit 3 indicates that the detection sensitivity of the gas sensor element 4 is below a predetermined value and the end of life is reached by voice, light, or It has a well-known configuration of notifying by an electric signal or the like. Further, the gas sensor element 4 used in this example has a size of 10 mm × 10 mm as shown in FIG.
On the surface of the silicon insulating substrate 10 formed in a rectangular shape and subjected to oxidation insulation treatment, platinum is used as the working electrode 11 and the counter electrode 12 by sputtering, and gold is used as the reference electrode 13.
Films are formed such that the surface of the insulating substrate 10 is exposed between the electrodes, and a perfluorosulfonate polymer (as a solid electrolyte membrane 14 is formed as a solid electrolyte film 14 so as to cover substantially the entire surface of the insulating substrate 10 exposed between the electrodes. Product name Nafio
n: manufactured by DuPont) is formed by a solution casting method, and polytetrafluoroethylene is formed as a protective film 15 on the surface of the solid electrolyte membrane 14 by a plasma polymerization method.

By the way, a voltage of 0.4 V is applied between the working electrode 11 and the reference electrode 13 of the gas sensor element 4 of this embodiment,
When used as a sensor for detecting carbon monoxide (hereinafter abbreviated as CO) gas, the period until the detection sensitivity of the CO gas is reduced by half as compared with the time at the initial manufacturing stage of the gas sensor element 4 and the ambient temperature. The relationship is measured as shown in the table below.

[0016]

[Table 1]

Then, based on the above result, the temperature sensor 1
A conversion rule (calculation rule of life judgment data) from the ambient temperature detected by the above to data representing the deterioration rate is determined as shown in the following table, for example.

[0018]

[Table 2]

Next, the operation of this embodiment will be described. The sampling section 5 of the computing means 2 obtains temperature data by sampling the detection output of the temperature sensor 1 at predetermined time intervals (once every 10 minutes). The life determination data calculation unit 7 calculates the life determination data indicating the deterioration rate based on the calculation rule of the above-mentioned Table 2 which is set and stored in the calculation rule setting storage unit 6.

The calculated life judgment data is integrated over time in the data integrating section 8 and the integrated value is output to the determining section 9. The determination unit 9 determines whether or not the input integrated value exceeds a predetermined threshold value (for example, 1000000), and when the integrated value exceeds this threshold value, the detection sensitivity of the gas sensor element 4 is initialized. It is determined that the signal has deteriorated to half of the detection sensitivity of (1), and a signal is output to the notification means 3. Then, the notification means 3 to which this signal is input notifies the user of the end of the life of the gas sensor element 4 by voice or light.

According to the above configuration, the deterioration rate of the detection sensitivity of the gas sensor element 4 depending on the ambient temperature is determined by the temperature sensor 1.
Can be obtained by detecting the ambient temperature,
The calculation means 2 calculates the life judgment data corresponding to the obtained deterioration rate.
Thus, the degree of decrease in detection sensitivity with time can be easily and accurately detected by integrating over time. Further, when the integrated result satisfies a predetermined condition set in advance, it is judged that the detection sensitivity has dropped to a predetermined value or less, and the notification means 3 notifies that the electrochemical gas sensor has reached the end of its life. You can

Although carbon monoxide was used as an example of the detection gas in this embodiment, the detection gas is not limited to this.
Needless to say, the technical idea of the present invention can be applied to the detection or concentration measurement of various gases other than carbon monoxide. Also, the sampling time interval in the sampling unit 5 is set to 10 minutes in this embodiment, but may be set as appropriate according to the changing speed of the ambient temperature environment. Furthermore, the time when the detection sensitivity drops to half of the initial sensitivity is determined as the end of life of the gas sensor element 4, but a threshold value for determining the end of life may be appropriately set according to the required detection accuracy and the like. Good.

[0023]

INDUSTRIAL APPLICABILITY As described above, the present invention detects the ambient temperature in an electrochemical gas sensor that produces a detection output according to the concentration of this gas by an electrochemical redox reaction with a specific gas. When the temperature detection means, a calculation means for integrating the life judgment data corresponding to the level of the detection output of the temperature detection means over time at a predetermined time interval, and the integration result of this calculation means satisfies a predetermined condition. Since the deterioration rate of the detection sensitivity depends on the ambient temperature, since the deterioration rate of the detection sensitivity depends on the ambient temperature, the deterioration rate at that time is obtained by detecting the ambient temperature by the temperature detection section. It is possible to easily and accurately detect the degree of deterioration of the detection sensitivity with time by integrating the life judgment data corresponding to this deterioration rate with time by the calculating means. The effect that it is possible to notify that the electrochemical gas sensor has reached the end of its life by the notification means by determining that the detection sensitivity has decreased to a predetermined value or less when the result satisfies a predetermined condition set in advance. There is.

[Brief description of drawings]

FIG. 1 is a partially omitted block diagram showing an embodiment of the present invention.

2A and 2B show a gas sensor element used in the above, wherein FIG. 2A is a sectional view and FIG. 2B is a plan view.

3A and 3B show a gas sensor element used in a conventional example, where FIG. 3A is a sectional view and FIG. 3B is a plan view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Temperature sensor 2 Calculation means 3 Notification means 4 Gas sensor element 5 Sampling section 6 Calculation rule setting storage section 7 Life judgment data calculation section 8 Data integration section 9 Judgment section

Claims (1)

[Claims] 1. An electrochemical gas sensor that produces a detection output according to the concentration of this gas by an electrochemical redox reaction with a specific gas, and a temperature detection means for detecting the ambient temperature and a temperature detection means. The calculation means for integrating the life judgment data corresponding to the detection output level of the above with the lapse of time at a predetermined time interval, and when the calculation result of this calculation means satisfies the predetermined condition, the end of life is notified. An electrochemical gas sensor, comprising: