JP2772330B2 - Initial stabilization method of solid electrolyte type carbon dioxide sensor and solid electrolyte type carbon dioxide detection 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 initial stabilization method for a solid oxide carbon dioxide sensor and a solid oxide carbon dioxide detector.

[0002]

2. Description of the Related Art Conventionally, there is a solid electrolyte type sensor as one of sensors for detecting a gas component existing in an atmosphere.
This sensor comprises a gas detecting section and a heater section for heating the gas detecting section to an operating temperature. As shown in the schematic diagram of FIG. 3, the gas detection unit 1 generally includes a sensor electrode 12 having a detection electrode 12 a and a reference electrode 12 b with a solid electrolyte serving as an ion conductor 11 interposed therebetween. This conductor 11
As an ion conductor that moves specific ions,
Metal such as platinum is used for the detection electrode 12a and the reference electrode 12b. Then, the detection electrode is coated with the compound 13 containing both the specific ion and the gas component to be detected, and heated so that only one of them contacts the test gas,
The gas concentration is detected by measuring the electromotive force generated between both electrodes.

In a solid electrolyte type carbon dioxide sensor in which the gas to be detected is carbon dioxide, an alkali metal ion conductor made of a solid electrolyte is usually used for the ion conductor 11. Also, the detection electrode 12a sandwiching the ion conductor 11
Is coated with a compound 13 composed of an alkali metal carbonate using a platinum net or the like, and the reference electrode 12b is sealed in air or carbon dioxide gas composed only of platinum. Therefore, the test gas is the detection electrode 12a.
, But not with the reference electrode 12b.

When the sensor electrode 12 is heated from about 400 ° C. to 600 ° C. in a carbon dioxide gas atmosphere as a test gas by a heater (not shown), the detection electrode 12 is heated.
The alkali metal carbonate a reaches dissociation equilibrium with carbon dioxide in the atmosphere, and an electromotive force is generated between both electrodes. By connecting the load LD between both electrodes, a current corresponding to the electromotive force flows through the load LD. Since this electromotive force changes according to the concentration of carbon dioxide, the concentration of carbon dioxide in the atmosphere can be detected from the amount of change.

FIG. 4 shows an electric circuit of a solid electrolyte type carbon dioxide gas detection device using the above-mentioned solid electrolyte type carbon dioxide gas sensor. The device is composed of a solid electrolyte type carbon dioxide gas sensor and a heater section 2 which is a heating means of the sensor. And a power switch 4 for turning on / off the power supply from the power supply 3 to the heater section 2 and a high input impedance circuit 5 for lowering the output impedance of a sensor having an extremely large internal impedance. . The heating of the heater section 2 is performed by turning on a power switch 4 and applying a voltage of a heater power supply 3 to the heater section 2.

The principle of generation of electromotive force will be described below with reference to the schematic diagram of the sensor section 1 described above with reference to FIG. It is considered that the compound 13 composed of the heated metal carbonate has reached a dissociation equilibrium by a chemical reaction represented by the following formula (1). At this time, the ion conductor 11
In the case of N (sodium ion conductive ceramic), it is considered that the equilibrium as in the following equation (2) is established.

[0007]

Embedded image

When a load LD is connected to both electrodes 12a and 12b of the sensor section 1, in a state where the partial pressure of CO ₂ is small, the left side is promoted in the equation (1) and decomposition of the carbonate proceeds. Accordingly, it is considered that Na ₂ O is generated on the reference electrode 12b side of the ion conductor 11 made of NASICON. Further, an electromotive force is generated between the two electrodes 12a and 12b according to the CO ₂ concentration. Next, when the partial pressure of CO ₂ increases on the side of the detection electrode 12a, this reaction is suppressed, and the decomposition of Na ₂ CO ₃ is reduced or increased, and as a result, the decomposition is caused according to the partial pressure of CO _2. Power is reduced.

[0009]

However, when the conventional carbon dioxide gas sensor is heated from the non-operated state to the sensor electrode and brought into the operating state, the alkali metal carbonate dissociates with carbon dioxide in the atmosphere and dissociates. The time it takes to reach is long, and if the concentration of carbon dioxide in the atmosphere is high, the generated electromotive force is small, but if the concentration of carbon dioxide is as low as about 350 ppm as in normal atmosphere, the dissociation is large and the electromotive force is also large. large.

For this reason, it may take a long time to reach the above-mentioned first equilibrium state (atmospheric CO ₂ concentration) at the start of use. The time until this stabilization increases depending on the number of days left without energizing and heating, the temperature and humidity of the leaving environment, and the like. When the test sample is left for one day, for example, as shown in FIG. 5, it takes 30 minutes or more for the electromotive force to gradually rise and become substantially stable,
If left for one month, it takes several hours to one day.

For this reason, there is a problem that the accuracy of the measured value cannot be increased in the case of a portable measuring instrument which needs to complete the measurement in a short time. If the electromotive force changes slowly from low to high (high to low in the density display) when using a densitometer, the display will exceed the meter setting when the electromotive force is low, and whether a trouble has occurred. There is a problem that the judgment cannot be made.

As a method of resolving this drawback and achieving an initial stabilization, a heat-up method for temporarily increasing a heating voltage performed by various gas sensors at the start of use, and a method for temporarily applying a voltage directly to the sensor from outside. In addition, a method of helping to reach a stable electromotive force (Japanese Patent Application No. 3-29638) and a method of preventing heating and occasional change during standing (Japanese Patent Application Laid-Open No. 4-22)
No. 861) has been considered, but none of these methods has been satisfactory yet.

[0013] Accordingly, the present invention has been made in view of the above-mentioned conventional problems, and provides an alkali metal ion conductor comprising a solid electrolyte.
In the solid electrolyte type carbon dioxide sensor having to shorten the initial stabilization time from the heated sensor electrode until stable steady operating state which can be used, initial that enable and improve the accuracy of measurement of the carbon dioxide concentration It is a first object to provide a stabilization method.

Further, in view of the above-mentioned conventional problems, the present invention has an alkali metal ion conductor comprising a solid electrolyte.
Electrolyte type with a solid electrolyte type carbon dioxide sensor
A second object of the present invention is to provide a solid electrolyte type carbon dioxide gas detection device capable of shortening an initial stabilization time until a stable operation state after turning on a power supply and improving measurement accuracy of a carbon dioxide gas concentration. It has two purposes.

[0015]

Means for Solving the Problems] initial stabilization method for a solid electrolyte type carbon dioxide gas sensor was made by the present invention for achieving the above first object, an alkali metal consisting of a solid electrolyte
A metal ion conductor, opposed to each other across the ion conductor,
A sensor electrode including a detection electrode and a reference electrode that generate an electromotive force corresponding to the concentration of the contacting carbon dioxide gas, an alkali metal carbonate covering the detection electrode, and heating the sensor electrode and the alkali metal carbonate. A solid electrolyte type carbon dioxide gas sensor comprising a heating unit, wherein during the period in which the heating unit does not heat the sensor electrode and the alkali metal carbonate, a constant voltage having an opposite polarity to an electromotive force generated between the sensor electrodes is applied. continuously applied between the sensor electrodes
It is characterized in that that.

In order to achieve the second object, the solid electrolyte type carbon dioxide detection device according to the present invention is opposed to and contacts an alkali metal ion conductor made of a solid electrolyte with the ion conductor interposed therebetween. A sensor electrode composed of a detection electrode and a reference electrode for generating an electromotive force corresponding to the concentration of carbon dioxide gas, an alkali metal carbonate covering the detection electrode, and a power switch that is turned on, the sensor electrode and the alkali metal carbonate are turned on. A solid electrolyte type carbon dioxide gas detection device having a solid electrolyte type carbon dioxide gas sensor having a heating means for heating a salt, wherein the heating means does not heat the sensor electrode and the alkali metal carbonate.
In the meantime, there is provided an initial stabilizing means for continuously applying a constant voltage having a polarity opposite to that of the electromotive force generated between the sensor electrodes between the sensor electrodes.

[0017] The initial stabilization means, in conjunction with the power switch for turning on and off the power supply to the heating means
A switch that is turned on and off, and a voltage application circuit that applies a constant voltage having a polarity opposite to that of an electromotive force generated between the sensor electrodes through the switch when the power supply to the heating unit is turned off. It is characterized by becoming.

[0018]

According to the above method, a constant voltage having a polarity opposite to that of the electromotive force generated between the sensor electrodes is continuously applied between the sensor electrodes while the heating means is not heating the sensor electrodes and the alkali metal carbonate. So alkali gold left unattended
The progress of decomposition of the genus carbonate can be suppressed.

Further, according to the above-described apparatus configuration, during a period in which the heating means does not heat the sensor electrode and the alkali metal carbonate by the heating means, the initial stabilizing means is opposite to the electromotive force generated between the sensor electrodes. Apply a constant voltage between the sensor electrodes
Continues to Runode, it is possible to suppress the progress of the decomposition of alkali metal carbonate during standing.

In the initial stabilizing means, when a power switch for turning on / off the power supply to the heating means turns off the power supply to the heating means, a voltage application circuit is connected between the sensor electrodes through a switch interlocked with the power switch. a constant voltage of the electromotive force polarity opposite that occurs is applied between the sensor electrode connection
Ketei Runode, without performing any special operation, A in the left
The progress of the decomposition of the rukari metal carbonate can be suppressed.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an electric circuit showing an embodiment of a solid electrolyte type carbon dioxide gas detecting apparatus which is initially stabilized by the method according to the present invention, and the same parts as those of the conventional apparatus described above with reference to FIG. And a detailed description is omitted.

Although the method for stabilizing the initial state of the solid electrolyte type carbon dioxide sensor according to the present invention is actually very complicated and cannot be clearly explained, one of the factors that occurs during the standing of the sensor and hinders the initial stabilization is as follows. Considering the decomposition of carbonate that proceeds very slowly during standing, the direction in which decomposition of carbonate does not proceed during standing, that is, the electromotive force generated between the sensor electrodes while the sensor electrode and the carbonate are not heated And a constant voltage having a polarity opposite to that of the sensor electrode is artificially applied between the sensor electrodes.

In order to carry out this method for initial stabilization,
As shown in FIG. 1, the solid-electrolyte-type carbon dioxide detection device according to the present invention has a configuration in which the sensor electrode 12 and the carbonate (not shown) are not heated by the heater section 2.
An initial stabilizing circuit 5 is provided as initial stabilizing means for applying a constant voltage having a polarity opposite to that of an electromotive force generated between the sensor electrodes.

The initial stabilizing circuit 5 turns on / off a DC power supply 51 which may be a dry battery, adjustable semi-fixed resistors VR1 and VR2 for dividing the voltage of the DC power supply 51, and power supply to the heater section 2. A switch 52 that is turned on and off in conjunction with the power switch 4, and a circuit 5 that connects the + side of the DC power supply 51 to the detection electrode 12 a of the sensor electrodes 12.
3 and a circuit 54 for connecting the voltage divided by the semi-fixed resistors VR1 and VR2 to the reference electrode 12b of the sensor electrodes 12. The circuits 53 and 54 constitute a voltage application circuit that applies a constant voltage having a polarity opposite to that of the electromotive force generated between the sensor electrodes 12 through the switch 52 when the power supply to the heater unit 2 is turned off. ing.

With this configuration, when the power supply to the heater section 2 is turned off by turning off the power switch 4, the switch 52 in the initial stabilizing means 5 is turned on, and the sensor section 12 and the carbonate (not shown) are turned on by the heater section 2. During a period in which is not heated, a constant voltage having a polarity opposite to that of the electromotive force generated between the sensor electrodes 12 is applied between the sensor electrodes.

[0026] Now, the initial stabilization time when the test sample to generate an electromotive force of about 287mV was started again used to stand for 1 week in CO ₂ concentration in the atmosphere during heating use, the initial stabilization means 5 described above As is clear from the graph of FIG.
In the former case shown by the dotted line, it takes 1 to return to about 287 mV.
It takes about one hour, while the latter shown by a solid line is about 1 hour.
It can be seen that the stable range was reached in about 0 minutes.

It is preferable that the voltage and current applied during the standing are higher than the electromotive force of the sensor in the atmosphere, but if it is too high, the electromotive force decreases at the start of energization, and conversely, the stability is deteriorated. become.

In the illustrated example, a 1.5 V AA battery is used for the DC power supply 51, and each half-fixed resistor VR1, approximately 1 MΩ is used.
A voltage of about 0.75 V divided by VR2 is applied to the sensor electrode 12. The voltages and currents thus applied need to be adjusted to some extent by semi-fixed resistors VR1 and VR2 for voltage division by individual sensors, and it is also necessary to consider the sensor leaving time. The application of this voltage does not affect the sensitivity and the response speed.

It has been confirmed that when the polarity of the voltage applied during the standing is reversed, the sensitivity and the response speed are remarkably deteriorated.

According to the above-described embodiment, the time until the solid electrolyte type carbon dioxide sensor is stabilized after the initial energization is equal to:
Even if it is left for a long time of one month or more, it will be within 5 to 10 minutes of the waiting time until practical measurement is started.

[0031]

As described above, according to the present invention, it is possible to suppress the progress of the decomposition of the alkali metal carbonate during standing, so that the sensor electrode can be stably used after heating the sensor electrode. It is possible to shorten the initial stabilization time and improve the measurement accuracy of the carbon dioxide concentration.

Further , the initial stabilizing means continues to apply a constant voltage having a polarity opposite to that of the electromotive force generated between the sensor electrodes during the standing, so that the decomposition of the alkali metal carbonate proceeds during the standing. Since it can be suppressed, the initial stabilization time until the operation becomes stable after the power is turned on can be shortened, and the measurement accuracy of the carbon dioxide concentration can be improved. In particular, a constant voltage of the opposite polarity to the electromotive force generated automatically between the sensor electrodes when the heating is stopped will continue to be applied between the sensor electrodes, so that no special operation is performed. The decomposition of the alkali metal carbonate during the standing can be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an electric circuit of a carbon dioxide gas detection device implementing a method according to the present invention.

FIG. 2 is a graph for explaining the effect obtained by the method according to the present invention and the carbon dioxide gas detection apparatus implementing the method.

FIG. 3 is a schematic diagram showing a structure of a sensor unit of the solid electrolyte type carbon dioxide sensor.

FIG. 4 is a diagram showing an example of a conventional carbon dioxide gas detection device.

FIG. 5 is a graph for explaining a problem of a conventional method and apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sensor part of solid electrolyte type carbon dioxide sensor 11 Ion conductor 12 Sensor electrode 12a Detection electrode 12b Reference electrode 13 Carbonate (compound) 2 Heating means (Heater part) 4 Power switch 5 Initial stabilization means (Initial stabilization circuit) 52 Switches 53, 54 Voltage application circuit (circuit)

Claims (3)

(57) [Claims] 1. A sensor electrode comprising a detection electrode and a reference electrode which are opposed to each other through an alkali metal ion conductor made of a solid electrolyte, and generate an electromotive force corresponding to the concentration of carbon dioxide gas in contact therewith. When the alkali metal carbonate to coat the sensing electrode, the sensor electrode and the a
A solid electrolyte type carbon dioxide gas sensor comprising: a heating unit for heating the alkali metal carbonate, wherein the heating unit includes the sensor electrode and the alkali.
An initial stabilization method for a solid oxide carbon dioxide sensor, wherein a constant voltage having a polarity opposite to that of an electromotive force generated between the sensor electrodes is continuously applied between the sensor electrodes while the metal carbonate is not heated. 2. A sensor electrode comprising a detection electrode and a reference electrode which are opposed to each other with an alkali metal ion conductor made of a solid electrolyte therebetween and generate an electromotive force corresponding to the concentration of carbon dioxide gas in contact with the alkali metal ion conductor. And an alkali metal carbonate covering the sensing electrode, and turning on a power switch.
The sensor electrode and the alkali in the solid electrolyte type carbon dioxide gas detection device including a solid electrolyte type carbon dioxide gas sensor and a heating means for heating the sensor electrode and the alkali metal carbonates, by the heating means Te
A solid electrolyte type having initial stabilizing means for continuously applying a constant voltage having a polarity opposite to that of an electromotive force generated between the sensor electrodes during a period in which the metal carbonate is not heated , between the sensor electrodes. Carbon dioxide detector. 3. The apparatus according to claim 1, wherein said initial stabilizing means is linked to said power switch for turning on / off a power supply to said heating means.
A switch that is turned on and off, and a voltage application circuit that applies a constant voltage having a polarity opposite to the electromotive force generated between the sensor electrodes through the switch when the power supply to the heating unit is turned off, between the sensor electrodes. The solid electrolyte type carbon dioxide detection device according to claim 2, comprising: