JPH03220448A - humidity sensor - Google Patents

Abstract

PURPOSE:To restrict the sensitivity to combustible gases thereby to improve the response, durability and reliability by using a resistance element subjected to catalytic action with a compound selected from organic oxysilanes, silicic acids and silicates. CONSTITUTION:A platinum wire or the like is used for a metallic resistance conductor of this sensor. The wire is formed in the shape of a coil etc. and supported on an inactive insulative supporting body. A resistance element constituting the sensor is obtained by applying a thin film of a paint on the surface of the resistance conductor and fixing the same through thermal treatment. For obtaining the paint, active ceramics are crushed and mixed with a binding agent such as clay, then turned into paste with use of water or an organic solvent. At this time, a means for catalytic action with a compound selected from organic oxysilane such as alkoxysilane (for example, methyl silicate), silicic acid such as silicic acid sol or the like, and silicate such as sodium silicate etc. is added. This resistance element is used at least as a humidity sensitive resistance element at the side exposed to the atmosphere. A resistance element for temperature compensation may be any that has the same temperature characteristic of resistance as the humidity sensitive resistance element.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Use] The present invention relates to a humidity sensor for detecting atmospheric humidity.

[Prior Art] With the recent spread of air conditioning equipment, demands for not only indoor temperature control but also humidity control have become more sophisticated. Furthermore, humidity control in factories and the like requires highly reliable humidity measurement in the presence of various pollutants.

Humidity sensors used for such purposes include electrolytes, polymer materials, etc. There are methods that detect changes in the electrical resistance and capacitance of materials that have absorbed moisture by using the
A device is known that utilizes the phenomenon of moisture adsorption to metals, ceramic materials, etc., and detects changes in the electrical resistance of the materials to which moisture has been adsorbed. However, these conventional humidity sensors can only detect changes in material properties due to physical adsorption and desorption of water at around room temperature, and also require heating cleaning to eliminate interference due to adsorption of various substances. There was a need to do something.

On the other hand, humidity sensors constructed by combining a humidity-sensitive resistance element, which is made by surrounding a metallic resistance conductor wire with an active ceramic layer, and a compensating resistance element are durable enough to carry out long-term continuous measurements, but are flammable. It had the disadvantage of being easily interfered with by harmful gases and having low reliability.

:Problems to be Solved by the Invention] Under these circumstances, the present invention is not susceptible to interference by substances other than moisture, is capable of long-term continuous measurement at high temperatures, and has high responsiveness and durability. The purpose of this invention is to provide a highly reliable humidity sensor that has the following features.

: Means for Solving the Problems] The humidity sensor of the present invention is a combination of a set of resistance elements, each consisting of a metal resistance conductor surrounded by an active ceramic layer, in which one side is exposed to the atmosphere and the other is shielded from the atmosphere. In this humidity sensor, a resistance element that has been subjected to contact treatment with a compound selected from organic oxysilanes, silicic acids, and silicates is used as at least the resistance element on the side exposed to the atmosphere.

The metal resistance conductor used in the humidity sensor of the present invention may be any wire as long as it is corrosion-resistant and oxidation-resistant and has a stable temperature coefficient of electrical resistance. For example, a platinum wire is preferably used. Such a resistance conductor can be used, for example, in the form of a coil supported directly or indirectly on an inert insulating support.

The active ceramics used in the humidity sensor of the present invention are:
For example, it may be activated alumina or activated zeolite, and it is preferable to heat-treat hydrated alumina or hydrated aluminosilicate to remove part or most of the crystal water and activate it, but it is not necessarily limited thereto. It's not something you can do. Such activated ceramics are thoroughly ground, mixed with a binder such as clay or aluminum hydroxide, and then made into a paste-like paint using water, an organic solvent, and, if necessary, a thickener. .

The resistance element constituting the humidity sensor of the present invention is produced by coating the previously prepared paint on the surface of the metal resistance conductor wire so as to have a thin and uniform thickness and drying it. It can be manufactured using conventional methods such as heat treatment and fixing under temperature conditions that do not cause loss of color. That is, in order to manufacture the resistive element as described above, organic oxanes such as alkoxysilanes such as methyl silicate and ethyl silicate, aryloxysolanes, alkyliminooxanes, etc., e.g. A means for contact treatment with a compound selected from silicic acids such as silicic acid sol and silicates such as sodium silicate is added, but treatment using such compounds will reduce the metallic resistance. Contact treatment with such compounds may be carried out only on the conductor wires, or may be carried out after the ceramic paint has been applied, or after heat treatment of the applied ceramic paint. In addition to methods such as applying a solution containing a concentration of may be done.

In the humidity sensor of the present invention, a resistance element subjected to contact treatment with such a compound is used at least in the humidity-sensitive resistance element and L on the side exposed to the atmosphere, but the resistance element on the side that is shielded from the atmosphere is used. Basically, the resistance element for temperature compensation is a resistance element that has the same resistance-temperature characteristics as the resistance element on the moisture-sensitive side, even if it has been subjected to contact treatment with the above-mentioned compound. It may not be added.

The humidity sensor of the present invention, which combines the humidity-sensitive resistance element obtained as described above and the compensating resistance element, detects humidity using a measuring circuit as shown in FIG. 1, for example.
is a humidity sensitive resistance element, and B is a compensation resistance element, to which a current is supplied from a power source E to obtain an output (2).

[For production]

The humidity sensor of the present invention is composed of a humidity-sensitive resistance element that has been subjected to contact treatment with a compound as described above, but the humidity-sensing characteristics are completely suppressed (there is no effect and only the sensitivity to flammable gas is significantly suppressed). This makes it possible to measure humidity with high sensitivity without compromising detection accuracy.

[Example 1] A platinum wire with a diameter of 30 μm and a length of 50 wires was wound into a coil with a diameter of 0.8 mm around two pins made of Konsukunkun that penetrated a base made of heat-resistant material and were planted at 5IW1 intervals. Both ends were fixed by spot welding.

The coil was placed in a closed container containing a small amount of ethyl silicate, and while exposed to the vapor of ethyl silicate, the coil was energized to about 600"C and subjected to contact treatment for 10 hours.

After that, aluminum hydroxide was added to the A-type zeolite (Molecular Sieve 5A) powder that had been heat-treated at 650°C for 1 hour to a concentration of 10% by weight, and after thorough pulverization and mixing, water and glycerin were added to make a paste. A shaped activated ceramic paint was applied to the coil and dried.

Next, a voltage is applied between the electrodes to generate heat in the coil, and the coil is heated at 650°C for 2 hours to perform firing.
Furthermore, a cover made of stainless wire mesh press-molded into a bowl shape was applied and fixed by caulking, thereby producing a resistance element (a).

In addition, a comparative resistance element (b) was prepared in exactly the same manner as above except that the treatment with ethyl silicate was not performed.

Furthermore, a temperature compensation resistance element (C) was made in the same manner as the comparison resistance element (b), except that a cap made of a stainless steel plate was attached instead of the stainless steel wire mesh cover and sealed by caulking. did.

Using these resistance elements, the humidity sensor (a) of the present invention
+ (C) and control humidity sensor (b) + (C
) was assembled and its moisture sensitivity characteristics were investigated. The results are shown in Figure 2.

In addition, variations in the sensor output haze were investigated by changing the concentration of ethanol in air at a temperature of 25°C and a relative humidity of 40%. The results are shown in Figure 3.

From these results, it can be seen that the humidity sensor using the resistive element (a) treated with ethyl silicate has significantly less influence on the output due to ethanol.

(Example 2) Methyl silicate/L, 5 instead of treatment with ethyl silicate
In addition to performing the above processing, a resistive element (d) was created in exactly the same manner as in Example 1, and a humidity sensor (d) and a sensor (C) were assembled and their humidity sensitivity characteristics and the effect of ethanol on the output were measured. I looked into it.

When we investigated the humidity sensitivity characteristics of the humidity sensor (d); (C) of this example, we found that the humidity sensor (a) + (
It was found that it had almost the same characteristics as C).

[Example 3] A platinum wire coil was coated with activated ceramic paint and fired in the same manner as in the preparation of the comparative resistor elements in Example 1, and then silicic acid was applied in the same manner as in Example 1. After treatment with ethyl, the resistive element (e
)It was created.

A humidity sensor (e) ± (C) was assembled using this resistance element (e) and the temperature compensation resistance element (C) obtained in Example 1, and the humidity sensor characteristics were investigated. It was found that it had almost the same characteristics as the humidity sensor (a) + (C).

[Example 4] A resistance element was obtained by coating a platinum wire coil with activated ceramic paint and firing it in the same manner as in the preparation of the comparative resistance element (g) in Example 1. The sample was placed in a sealed container into which a small amount of pentylidene(2)-iminooxy(trimethoxy)silane was injected, and exposed to the atmosphere for one hour. Electricity was applied between the electrodes to bring the temperature to about 500°C, and contact treatment was carried out for 1 hour.

Using the resistance element (f) obtained in this way and the resistance element (C) for temperature compensation obtained in Example 1, a humidity sensor is created (±(C)).
When the humidity sensor (a) + (C) in Example 1 was assembled and its moisture sensitivity characteristics were examined, it was found that it had the same characteristics as the humidity sensor (a) + (C) in Example 1.

[Example 5] Instead of the steam exposure treatment in Example 4, silicate sol (
A resistive element (river) was prepared in the same manner as in Example 4, except that a 25% aqueous solution was applied, impregnated, and dried.

Using the resistance element (g) thus obtained and the temperature compensation resistance element (C) obtained in Example 1, a humidity sensor (g) +
When (C) was assembled and its moisture sensitivity characteristics were examined, it was found that it had almost the same characteristics as the humidity sensor (a) + (C) in Example 1.

; Example 6] The same procedure as in Example 1 was followed except that instead of the ethyl silicate treatment of the platinum wire coil in Example 1, the platinum wire coil was immersed in a 30% aqueous solution of water glass and dried. , resistance element th) was created.

Using the resistance element (h) thus obtained and the resistance element (C) for temperature compensation obtained in Example 1, a humidity sensor (h) ± (C
) assemble,! g Humidity When the moisture property was investigated, it was found that the humidity sensor had almost the same characteristics as the humidity sensor (a) + (C) in Example I.

〔Effect of the invention〕

The humidity sensor of the present invention is a combination of a humidity-sensitive resistance element whose sensitivity to flammable gas is suppressed by contact treatment with a specific compound and a compensating resistance element, and the humidity sensor does not lose its sensitivity to humidity. It has both high precision and high sensitivity, and also has excellent durability.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a humidity measurement circuit using the humidity sensor of the present invention, Fig. 2 is a graph showing the humidity sensitivity characteristics of the humidity sensor of the present invention and the conventional humidity sensor, and Fig. 3 is a graph showing the humidity sensitivity characteristics of the humidity sensor of the present invention and the conventional humidity sensor. It is a graph showing the relationship between concentration and sensor output. A...Moisture sensitive resistance element, B...Compensation resistance element, E...
・Power supply, ■...output.

Claims (1)

[Claims] A humidity sensor consisting of a set of resistance elements consisting of a metallic resistance conductor surrounded by an active ceramic layer, one of which is exposed to the atmosphere and the other of which is shielded from the atmosphere, is made of organic oxysilanes, silicic acids and silicates. A humidity sensor characterized in that a resistance element that has been subjected to contact treatment with a selected compound is used as at least the resistance element on the side exposed to the atmosphere.