JPH0679005B2 - Galvanic battery oxygen sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a structure for improving the temperature characteristics of a galvanic cell type oxygen sensor. More specifically, the present invention relates to a diaphragm in which a catalyst electrode having a function as a positive electrode, a lead electrode having a function as a negative electrode, an electrolytic solution, and a catalyst electrode are integrally joined, and an output of a sensor generated by the diaphragm. The present invention relates to a structure for obtaining good temperature characteristics in a galvanic cell type oxygen sensor composed of an electric resistance element for converting into oxygen.

2. Description of the Related Art Galvanic battery-type oxygen sensors are small, lightweight, operate at room temperature and pressure, and are inexpensive. Therefore, oxygen deficiency conditions in ships, manholes, tunnels, and indoors where a heater is used It is used in a wide range of fields, such as checking and monitoring oxygen concentration in medical devices such as anesthesia machines and artificial respirators. In addition, the sensor is housed in a watertight container so that it can be used in water, and it is used as a dissolved oxygen sensor for aqueous solutions to monitor the dissolved oxygen concentration in fish culture and vegetable hydroponics. .

The galvanic battery type oxygen sensor basically has a structure shown in FIG. That is, in principle, oxygen that has passed through the diaphragm 1 having selective permeability for oxygen is reduced on the catalyst electrode 2 as a positive electrode,
An electrochemical reaction occurs with the negative electrode 4 via the electrolytic solution 3, and as a result, a current corresponding to the oxygen concentration is generated between the catalyst electrode 2 and the negative electrode 4. The current is converted into a voltage signal through the thermistor element 6 for temperature compensation, and a sensor output voltage is obtained. Such a galvanic battery type oxygen sensor has various structures (for example, JP-A-58-187846 and British Patent 12).
[00595) has been devised and put into practical use.

On the other hand, the galvanic cell type oxygen sensor has a strong positive dependence of the current value generated in the sensor on the temperature, due to the principle of reaction. In general, a thermistor element or the like whose resistance value has a similar negative temperature dependence is compensated for so that the sensor output does not fluctuate even if the environmental temperature changes.

However, even if the degree of temperature dependence of the sensor current value and the degree of temperature dependence of the thermistor element resistance value are exactly matched, the rate of change over time, that is, the sensor current value. It is very difficult to match the rate of change of the thermistor element resistance value with the rate of change of the thermistor element value.Therefore, when the temperature of the environment changes suddenly, a mismatch occurs between the sensor current value and the thermistor element resistance value. The output fluctuates.

This will be described in more detail with reference to FIG.
Now, it is assumed that the temperature of the environment where the sensor is placed changes from the temperature T ₁ to T ₂ during the time P ₁ to P ₂ as shown in FIG. 2 (A). At this time, the resistance value of the thermistor element, which is generally excellent in thermal conductivity and has a small volume, changes rapidly, but the current value of the sensor main body, which has a large volume and has poor thermal conductivity, changes later than that. To do. This state is schematically shown in FIG. The resistance value of the thermistor element is from R ₁
The time Pr required to reach R ₂ and the sensor current value from I ₁ to I ₂
Since the time P ₁ required for the sensor to be different is different, the output voltage value of the sensor fluctuates.

In this way, even if the oxygen concentration does not change, if the temperature changes, the sensor output voltage value fluctuates for a while, which causes malfunction of equipment such as an oxygen concentration meter that uses the sensor. Is.

Conventionally, in order to avoid this problem, the thermistor element is encapsulated with a resin or the like, and the thermal conductivity of the thermistor element is deteriorated to approach the thermal conductivity of the sensor body.

However, even if the periphery of the thermistor element is covered with a resin that does not have good heat conduction, heat is transferred from the lead wire connected to the thermistor element, and the characteristics vary depending on the amount of resin to be encapsulated. The sensor output voltage value could not be completely stabilized against the conditions.

Means for Solving the Problems The present invention considers that the above-mentioned problems are caused by the absence of heat exchange between the thermistor element and the sensor body, and the thermistor element for temperature compensation has an extremely high thermal conductivity. By encapsulating the inside of the sensor body with a high thermal conductivity resin and making the thermal conditions the same as the sensor body, the rate of change of the thermistor element resistance value when the temperature changes matches the rate of change of the sensor current value. By doing so, it is intended to solve the above-mentioned problems.

When the thermistor element for working temperature compensation is enclosed in the sensor body with high thermal conductivity resin, the rate of change of the thermistor element resistance value is governed by the rate of change of the temperature of the sensor body, which has a large heat capacity. For example, when the ambient temperature of the sensor rises, if the temperature of the thermistor element rises faster than that of the sensor body, the thermistor element and the sensor body are always kept at the same temperature by being quickly cooled from the sensor body side through the high thermal conductive resin. . As a result, the resistance value of the thermistor element and the changing speed of the current value of the sensor always match, and the output voltage of the sensor does not change.

This will be described in more detail with reference to FIG.
Now, as in the case where the temperature of the environment where the sensor is placed is as shown in FIG. 2 (A) above, from the time T ₁ to the time P ₁ to P ₂
Suppose it has changed to T ₂ . At this time, in the conventional sensor, the resistance value of the thermistor element tends to change faster than the sensor current value as described with reference to FIG. 2B, but in the product of the present invention, the thermistor element has a high thermal conductivity resin. Through the through, the sensor body side is quickly cooled and kept at the same temperature as the sensor body. Therefore, the time required for the resistance value of the thermistor element to change from R ₁ to R ₂ as schematically shown in FIG.
Time required for the current value of Pr and the sensor to change from I ₁ to I ₂ P ₁
And the output voltage value of the sensor does not fluctuate.

Even when the ambient temperature decreases, the thermistor element is quickly warmed from the sensor body side through the high thermal conductive resin, and the sensor output voltage does not fluctuate.

In this way, by enclosing the thermistor element in the sensor body with the high thermal conductive resin, it is possible to obtain a galvanic cell type oxygen sensor having excellent output stability.

Examples Hereinafter, the present invention will be described using preferred examples.

In order to know the effect of the present invention, a galvanic cell type oxygen sensor having a sectional structure shown in FIG. The prototype was manufactured as described below. First, a catalyst electrode 2 made of a noble metal such as gold or platinum or iridium was formed as a positive electrode on one surface of a diaphragm 1 made of a fluoropolymer thin film having a thickness of 10 to 50 μm to a predetermined thickness by sputtering or vacuum deposition. Next, the above-mentioned assembly of the catalyst electrode and the diaphragm, the lead 4 of the negative electrode, the current collector 7 made of porous carbon or the like for uniformly collecting current from the entire surface of the catalyst electrode, the thermistor element for temperature compensating the sensor output. 6. The positive and negative leads 9 and 10 for taking out the output were mounted on the container body 5 of the sensor. Then, after injecting an acidic electrolytic solution 3 composed of acetic acid-potassium acetate-lead acetate as an electrolytic solution, a high thermal conductive resin 8
Was filled into the entire mounting portion of the thermistor element to obtain a prototype.

In order to make the effect of the present invention, that is, the effect that the thermistor element and the sensor body are always kept at the same temperature, the prototype is more complete, the thermistor element has the largest heat capacity and the temperature of the sensor current value. The structure is such that it is projected into the electrolytic solution, which is the most dominant factor in the change.

As a material of the high thermoelectric resin, as a result of various examinations, a high thermal conductive compound type resin (trade name: Lambdite) manufactured by Denki Kagaku Kogyo Co., Ltd., model name A-120H, was cured with a curing agent R-1. Was good. The thermal conductivity of this material is 2.0 J / ° K · m · s, which is much higher than that of general epoxy resin (0.1 to 0.5 J / ° K · m · s).

With respect to the obtained galvanic cell type oxygen sensor, the ambient temperature was rapidly changed between 5 and 40 ° C. and the stability of the sensor output was examined. The result is shown in FIG. For comparison, the characteristics of the sensor in which the thermistor element is filled and sealed with an epoxy resin, for example, a brand name Araldite manufactured by Ciba-Geigy Co., Ltd. and the other structures are the same as those of the present invention are also shown in the figure for comparison.

The sensor according to the present invention was very stable with almost no change in output even when the ambient temperature changed.

The same effect was observed when using a high thermal conductivity resin having a thermal conductivity of 1.0 J / ° K · m · s or more, but the thermal conductivity was 1.5 J /
A more remarkable effect was obtained when a high thermal conductivity resin having a temperature of ° K · m · s or more was used.

As described above, according to the present invention, it is possible to obtain a galvanic cell type oxygen sensor having excellent performance such as output stability and response speed.

EFFECTS OF THE INVENTION The galvanic cell type oxygen sensor according to the present invention has extremely excellent stability against changes in ambient temperature.
By using this sensor, a highly reliable oxygen concentration meter and an oxygen deficiency alarm without malfunction etc. can be obtained, which is extremely useful for industrial purposes.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a general galvanic cell type oxygen sensor. FIG. 2 is a diagram for explaining that the output of the conventional galvanic cell type oxygen sensor fluctuates when the ambient temperature changes. FIG. 3 is a diagram for explaining that the output of the galvanic cell type oxygen sensor of the present invention does not fluctuate when ambient temperature changes. FIG. 4 is a view showing a sectional structure of the galvanic cell type oxygen sensor of the present invention. 1 ... diaphragm, 2 ... catalyst electrode, 3 ... electrolyte, 4 ... negative electrode, 5 ... container body, 6 ... thermistor element, 7 ... current collector, 8 ... high thermal conductive resin No. 5 The figure shows a comparison of the output characteristics of the galvanic cell type oxygen sensor of the embodiment of the present invention and the conventional galvanic cell type oxygen sensor when the ambient temperature changes.

Claims (1)

[Claims] 1. A galvanic cell oxygen sensor comprising a catalyst electrode having a function as a positive electrode, a lead electrode having a function as a negative electrode, an electrolytic solution, and a diaphragm in which the catalyst electrode is integrally joined. A galvanic battery type oxygen sensor characterized in that a thermistor for temperature compensation is filled and sealed with a high thermal conductive resin having a thermal conductivity of 1.0 J / ° K · m · s or more.