JPH0396853A - Dew condensation sensor - Google Patents

Abstract

PURPOSE:To simplify the circuit of a device by providing a catalyst electrode as a positive electrode, a lead electrode as a negative electrode and an electrolyte and an oxygen permeable septum as a detection surface for a dew condensation state. CONSTITUTION:This sensor consists of the catalyst electrode 23 which is effective as the positive electrode to the reduction of oxygen in air, the lead electrode 25 functioning as the negative electrode and the electrolyte 24 and the oxygen permeable septum 22 with which the catalyst electrode 23 is united. This oxygen-lead galvanic battery utilizes large variation in the output value of the battery due to dew condensation on the diaphragm surface. This sensor is basically a galvanic battery, so the sensor itself has a DC output and no external electric circuit is required specially for driving. Consequently, the number of components in use is reduced extremely and the power consumption is reducible.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Applications The present invention relates to a galvanic cell type dew condensation sensor. More specifically, the present invention is a sensor for determining whether the environment is in a condensed state, which comprises a catalytic electrode having an oxygen reduction function as a positive electrode, a lead electrode and an electrolyte serving as a negative electrode. The present invention also relates to a dew condensation sensor that utilizes the fact that in an oxygen-lead battery composed of an oxygen-permeable diaphragm to which a catalyst electrode is integrally joined, the output value of the battery changes significantly due to dew condensation on the diaphragm surface. be.

Dew condensation sensors are used in devices that can cause malfunction or damage if used with condensation, i.e. precision devices such as cameras and VTRs that have high-speed, high-precision sliding properties, and the light-receiving surface must be kept transparent at all times. It is widely used in flame detection type heaters that use optical sensors. In addition, recent developments in electrical and electronic equipment have been remarkable, both for industrial and consumer use, and technologically speaking, higher precision and higher precision are required, and the applications of dew condensation sensors are rapidly expanding. be.

2. Description of the Related Art Dew condensation sensors that have been widely used in the past are made by coating a hard substrate made of ceramic or other material with multiple electrodes printed or vapor-deposited on it and coated with various organic or inorganic moisture-sensitive films.
Generally, the sensor has a J-type structure, is electrically driven from the outside with direct current or high-frequency alternating current between the electrodes, and changes in the electrical conductivity of the moisture-sensitive membrane due to dew condensation are output.

Problems to be Solved by the Invention Such conventional dew condensation sensors are basically passive elements that cannot produce an output by themselves, and always require an external electric circuit to drive them. For this reason, various types of circuits have been devised and put into practical use, but they are not simple, including constant voltage concave circuits, high frequency circuits, etc.

Therefore, the power consumption increases and the number of electrical parts increases, resulting in problems in terms of equipment cost.

Furthermore, the performance of conventional dew condensation sensors is determined by the electrical conductivity of the moisture-sensitive film used, and generally the greater the change in electrical conductivity due to dew condensation, the better the performance. For this reason, the thickness of the moisture-sensitive film is either very thin, or in that case, the heat resistance of the moisture-sensitive film becomes a problem.

Because the thin film-like moisture-sensitive membrane is susceptible to burnout and other damage due to a slight overcurrent or overvoltage, it is necessary to pay sufficient attention to the sensor drive circuit and usage environment. There are also problems with mechanical strength and long-term reliability.

Means for Solving the Problems In view of the above-mentioned problems with dew condensation sensors, the present invention provides a dew condensation sensor based on a completely different principle from the conventional principle. In other words, an oxygen-permeable diaphragm consisting of a catalytic electrode effective in reducing oxygen in the air as a positive electrode, a lead electrode functioning as a negative electrode, an electrolytic solution, and an oxygen-permeable diaphragm to which the catalytic electrode is integrally joined. This method takes advantage of the fact that in a button galvanic cell, the output value of the cell changes significantly due to dew condensation on the surface of the diaphragm.

Since this sensor is basically a galvanic battery, the sensor alone has a DC output, and does not particularly require an external electric circuit for l) v movement.

Therefore, devices using this dew condensation sensor can use a very small number of parts for the sensor.
Since power consumption can also be reduced, cost 1 can be reduced.

In addition, the sensor according to the present invention utilizes changes in the output of a galvanic cell, and does not utilize changes in the electrical conductivity of a moisture-sensitive membrane as in the past. The above-mentioned problems in heat resistance and reliability that occur because of this do not essentially occur.

Function The function of the galvanic cell type dew condensation sensor according to the present invention will be explained with reference to FIG.

After the oxygen contained in the dry environmental atmosphere 21 shown in FIG. 1A reaches the surface of the oxygen permeable membrane 22,
41 and reaches the catalyst electrode layer 23 bonded to one side of the diaphragm. Then, the oxygen causes the electrochemical reaction shown below between the catalyst electrode as the positive electrode, the electrolytic dip 24 and the button electrode 25 as the negative electrode, and based on this reaction, the oxygen-galvanic acid produced by these is output to the seven ponds. is obtained.

? When the electrolyte is acidic] Positive electrode reaction: O■+411++4e →2H20 Negative electrode reaction: 2Pb +2H2 0 -2PbO+48"
+4e total reaction: 0■+2Pb→2Pb0? When the electrolyte is alkaline] Positive electrode reaction: O +282 0 +4e - 408
Negative electrode reaction: 2Pb -t- 4011- →2PbO
+2M20 +4e Total reaction: 0■+2 P b→2Pb
0 Since the oxygen concentration in the atmosphere is approximately constant at 21%, the output of this galvanic cell shows a constant value in a dry state, that is, in a state where the surface of the oxygen permeable membrane is not wet.

On the other hand, in the dew-condensed atmosphere shown in FIG. 1B, a water layer 26 is formed on the surface of the oxygen-permeable diaphragm due to dew condensation. In this state, oxygen in the atmosphere diffuses through the water layer and reaches the oxygen-permeable diaphragm, but since the diffusion rate of oxygen in the water layer is extremely slow, the oxygen involved in the electrochemical reaction mentioned above is The amount of galvanic cells becomes extremely small, and the output of the galvanic cell is significantly reduced.

In this way, it is possible to obtain a galvanic cell type dew condensation sensor that can accurately determine the dew condensation state based on changes in output.

5 6 Example The present invention will be explained below using preferred embodiments.

In order to investigate the performance of the dew condensation sensor of the present invention, a galvanic cell type dew condensation sensor with a rough cross section as shown in FIG. 2 was manufactured as a prototype. The prototype was made as described below.

First, the catalyst electrode 2 was formed to a predetermined thickness by sputtering or vacuum deposition on one side of the fluoropolymer thin film II11 having a thickness of 10 to 50 μm.

Next, there is a button 4 for the negative electrode, a current collector 8 made of porous carphone or the like for collecting current uniformly from the entire surface of the catalyst electrode, a thermistor 6 and a resistor 7 for temperature compensating the sensor output, and a positive electrode for taking out the output.・Negative lead 10. Each of the eleven parts was attached to the sensor container main body 5.

Thereafter, the above-mentioned tactile electrode and diaphragm assembly was attached to the container body using an O-link 9 so as to fit closely into the container body, and an acidic electrolyte 3 consisting of potassium acetate monoacetate and nitric acid was injected as an electrolyte, and a galvanic cell type was used. Although gold was used as the material for the catalyst electrode from which the dew condensation sensor was obtained, the same effect can be obtained by using a noble metal such as platinum or indium.

The output characteristics of the thus obtained sample of the galvanic cell type dew condensation sensor were examined, and the results shown in FIG. 3 were obtained. It can be seen from Figure 3 that the prototype sensor has excellent reversibility of output characteristics and responsiveness.

In addition, the samples of the above-mentioned Examples were held in different atmospheric atmospheres for a long time to examine the stability of the sensor output. That is, 10,000 samples were subjected to a test of 1 hour in a dry atmosphere with a relative humidity of 40 to 60%, 1 hour in a high humidity atmosphere with a relative humidity of 90 to 95%, and 1 hour in a dew atmosphere with a relative humidity of 100%. The test was repeated several times to examine changes in the sensor output. As a result, the values shown in FIG. 3 hardly changed, and the output was extremely stable.

As described above, the present invention makes it possible to obtain a galvanic cell type dew condensation sensor with excellent performance such as output stability and response speed.

Effects of the Invention Since the galvanic cell type dew condensation sensor of the present invention is an active element that itself emits an output, the electric circuit for determining the dew condensation state is greatly simplified. Basically, one inexpensive differential amplifier and one comparator are sufficient, and expensive mechanisms and parts such as a constant voltage generator and a high frequency oscillator are not required at all. Therefore, it greatly contributes to cost reduction of equipment using this.

In addition, the galvanic cell type dew condensation sensor of the present invention uses a chemically very stable and mechanically strong fluororesin film as the detection surface for dew condensation, and its characteristics have long-term reliability. , has excellent stability. therefore,
Failures and accidents caused by dew condensation in devices using this dew condensation sensor can be prevented over a long period of time.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the basic principle of a galvanic cell type dew condensation sensor according to the present invention, where A shows a case where the ambient air is in a dry state, and B shows a case where the ambient air is in a dew state. 21...Environmental atmosphere, 22...Oxygen permeable diaphragm 9 23...Catalyst electrode, 24...Electrolyte 25...Name electrode, 26...Aqueous layer caused by dew condensation in Figure 2 , a cross section of a prototype galvanic cell type dew condensation sensor of the present invention! This is an I4 drawing. 1...Oxygen permeable diaphragm, 2...Catalyst electrode Figure 3 shows:
It is a figure which shows the output characteristic of a sensor when a dry state and a dew state are repeated. 1 0 dice 1 flash 2l 26 2z 23 24 25 evening Z ro 11

Claims (1)

[Claims] A galvanic cell type dew condensation sensor consisting of an oxygen permeable diaphragm as a detection surface for dew condensation, a catalytic electrode as a positive electrode to cause output changes depending on the condensation state, and a lead electrode and electrolyte as a negative electrode.