JPH0695083B2 - Humidity sensor, its manufacturing method and atmospheric humidity measuring method - Google Patents

Description

The present invention relates to a humidity sensor for detecting atmospheric humidity.

[Conventional technology]

With the recent spread of air-conditioning equipment, the demand for not only indoor temperature control but also humidity control has become more sophisticated. Furthermore, highly reliable humidity measurement in the presence of various pollutants is also required for humidity control in factories and the like.

Humidity sensors used for this purpose include those that utilize the hygroscopicity of electrolytes and polymer materials to detect changes in the electrical resistance and capacitance of these hygroscopic materials, metal and ceramic materials, etc. It is known to detect changes in electric resistance of materials adsorbed with water by utilizing the water adsorption phenomenon. However, these conventional humidity sensors can only detect changes in the characteristics of the material due to the physical adsorption and desorption of water at around room temperature, and also require heating cleaning to eliminate interference due to adsorption of various substances. I had to do it.

[Problems to be Solved by the Invention]

Under the circumstances as described above, the present invention provides a highly reliable humidity sensor that is not easily interfered by substances other than moisture, can perform continuous measurement at high temperature for a long time, and has high responsiveness and durability. It is intended to be provided.

[Means for Solving the Problems]

The humidity sensor of the present invention is provided with a moisture-sensitive resistance element in which a metallic resistance wire is surrounded by an active ceramics layer containing activated zeolite as a main material, and compensation to be combined with such a humidity-sensitive resistance element. The resistance element includes a metal resistance conductor wire surrounded by an inert ceramic layer.

The activated zeolite used in the humidity sensor of the present invention is one obtained by activating a hydrous aluminosilicate by removing a part or most of the water of crystallization and activating the zeolite. Any material may be used as long as it is stable and exhibits excellent water adsorption ability. However, when mass-producing a humidity sensor whose performance is controlled industrially, it is preferable to use an industrially synthesized zeolite. Among them, an A-type zeolite having a small pore size used as an adsorbent, that is, a mole of aluminum and silicon is used. Zeolite having a ratio of about 1 can be preferably used, but it is not necessarily limited to this.

Such zeolite is sufficiently pulverized into a fine powder, which is
800 ℃ or less, preferably 400 ~ 750 ℃, more preferably 600
Activate by heat treatment at ~ 700 ° C for 30 minutes to 2 hours. Such heat treatment conditions are important for maintaining a balance between the durability and sensitivity of the humidity-sensitive resistance element, the sensitivity decreases when the heat treatment temperature is too high, and the durability is insufficient when the heat treatment temperature is too low. Easy to become

The activated zeolite thus obtained is further sufficiently crushed, and after crushing and mixing a binder such as clay or aluminum hydroxide, a paste-like coating material is prepared using water or an organic solvent. At this time, a thickener or the like may be added as long as the activity of the zeolite is not impaired.

The metallic resistance lead wire used for producing the humidity sensor of the present invention may be one having resistance to corrosion and oxidation and having a stable temperature coefficient of electric resistance. For example, a platinum wire is preferably used. Such a resistance wire can be used, for example, in the form of a coil directly or indirectly supported on an inert insulating support.

Moisture-sensitive resistance element in the present invention, on the surface of the metal resistance conducting wire as described above, a coating containing activated zeolite as described above is applied to a thin and uniform thickness and dried, It is obtained by heat-treating and fixing the zeolite under conditions not exceeding the activation treatment temperature.

On the other hand, the compensating resistance element in the present invention can be prepared by a similar method by using an inert ceramic instead of the activated zeolite used in the above-mentioned humidity sensitive resistance element. The inert ceramics used here are
It is only necessary that the property of adsorbing water is significantly inferior to that of the above-mentioned activated zeolite, and it is desirable that the other physical properties are not significantly different from those of zeolite. From this point of view, as the preferable inert ceramics, those obtained by inactivating zeolite by heat treatment at a temperature exceeding 800 ° C., especially the same zeolite as that used for preparing the humidity-sensitive resistance element is 800 The crystal structure may be changed by heat treatment at a temperature higher than 0 ° C, for example, a temperature higher than 850 ° C. In this way, when making a compensating resistance element using inert zeolites that differ only in heat treatment temperature, the exact same procedure is used as in the case of making the above-mentioned moisture-sensitive resistance element, and the shape and dimensions are also the same. More preferably,

The moisture-sensitive resistance element and the compensation resistance element created as described above are combined so as to form a bridge by connecting them in series, for example, and the temperature of the electric wire is 300- Adjust so that it is within the range of 500 ℃.

When the humidity sensor in which the humidity sensitive resistance element and the compensation resistance element are combined is brought into contact with the humidity measurement target atmosphere as described above, a difference in electric resistance value occurs between the humidity sensitive resistance element and the compensation resistance element. It can be detected as a voltage change. The voltage change, that is, the output voltage, increases in accordance with the increase of the water vapor content in the atmosphere, that is, the humidity, but is hardly affected by the change of the temperature of the atmosphere and the existence of various vapors of gas. Furthermore, it quickly follows changes in the humidity of the atmosphere and exhibits high responsiveness, so that deterioration does not occur even when continuous measurement is performed for a long period of time.

〔Example〕

A-type zeolite (Molecular Sieve 5A) was finely pulverized by a vibrating mill, placed in an electric furnace, and heat-treated at 650 ° C. for 1 hour for activation. Aluminum hydroxide was added to this to be 10% by weight, and the mixture was further sufficiently pulverized and mixed by a vibration mill, and then water and glycerin were added to prepare a paste-like coating material A.

Further, the same zeolite as described above was heat-treated at 850 ° C. for 1 hour to obtain an inactivated zeolite whose crystal structure was destroyed, and a paint B was prepared by the same composition and procedure as above.

On the other hand, two ends of a platinum wire coil with a diameter of 30 μm and a length of 50 mm were fixed by spot welding to two pins made of constantan penetrating through the pedestal of the heat resistant material at intervals of 5 mm, and the above-mentioned portion was fixed to this coil portion by spot welding. After the coating material A or the coating material B was applied and dried, a voltage was applied between the electrodes to heat the coil to heat-treat at 650 ° C. for 2 hours. The element (FIG. 1) thus obtained was covered with a cover made of stainless wire mesh press-formed into a bowl shape and caulked and fixed.

The moisture-sensitive resistance element A and the compensation resistance element B thus created are mounted adjacent to each other on the substrate as shown in FIG. Was supplied to reach a steady state, and then the water content in the air supplied into the measuring tank C was changed to measure the output V. At this time, the temperature of the atmosphere was 40 ° C., but the temperature of the platinum wire calculated from the electric resistance value of the platinum wire was about 420 ° C. The humidity sensitivity characteristics of the humidity sensor thus obtained are shown in FIG. From this result, it can be seen that the humidity sensor of the present invention shows an output that is almost proportional to the absolute humidity.

Similarly, the output change was measured when the atmospheric temperature was changed while keeping the water content constant. The result is shown in FIG. 4. From this result, it is understood that the output of the humidity sensor of the present invention is determined by the absolute humidity.

Further, FIG. 5 shows the result of measuring the output when hydrogen or ethanol vapor coexists in the atmosphere while keeping the temperature and humidity constant. The results show that the presence of such gas does not interfere with the measurement by the humidity sensor of the present invention. It was confirmed that the output slightly decreased when the coexisting gas concentration was extremely high, but it was confirmed that the output quickly returned to the original value when the coexisting gas disappeared from the atmosphere.

Next, 20.7 g / m absolute humidity of the atmosphere in the measuring tank from 6.9 g / m ³
When the response characteristics were examined when the value was increased to ³ and vice versa, the results shown in FIG. 6 were obtained. From this result, it can be seen that the humidity sensor of the present invention responds quickly to changes in humidity and has stable output characteristics with excellent reproducibility.

〔The invention's effect〕

As described above, the humidity sensor of the present invention is provided with the humidity sensitive resistance element in which the metallic resistance wire is surrounded by the activated zeolite layer, and the humidity sensor hardly affects the fluctuation of the atmospheric temperature and the coexisting gas. It gives a highly reproducible measurement value corresponding to the moisture content in the atmosphere, that is, absolute humidity without receiving it, and it is possible to perform stable measurement continuously for a long time without performing cleaning regeneration. There is a feature that does not cause deterioration.

[Brief description of drawings]

FIG. 1 is an external view of an embodiment of a humidity sensitive resistance element used in the humidity sensor of the present invention, and FIG. 2 is a circuit diagram for humidity measurement using the humidity sensor of the present invention. FIG. 3 is a graph of the humidity sensitivity characteristic of the embodiment of the humidity sensor of the present invention, FIG. 4 is a graph showing the influence of the ambient temperature on the output, and FIG. 5 is the same as the ambient temperature of the output. FIG. 6 is a graph showing the effect of the seed gas, and FIG. 6 is a graph showing the output response characteristics to changes in the atmospheric humidity. A ... Moisture-sensitive resistance element, B ... Compensation resistance element, C ... Measuring tank, E ... Power supply, V ... Output.

Claims (7)

[Claims] 1. A humidity sensor comprising a humidity-sensitive resistance element in which a metallic resistance wire is surrounded by an active ceramics layer containing activated zeolite as a main material. 2. A moisture-sensitive resistance element in which a metallic resistance wire is surrounded by an active ceramics layer containing activated zeolite as a main material, and a compensation resistance element in which a metal resistance wire is surrounded by an inactive ceramics layer. Humidity sensor characterized by having. 3. The humidity sensor according to claim 1, wherein the activated zeolite is A-type zeolite. 4. The humidity sensor according to claim 1, wherein the activated zeolite has been activated at a temperature of 800 ° C. or lower. 5. The humidity sensor according to claim 2, wherein the inert ceramic is zeolite that has been inactivated at a temperature exceeding 800 ° C. 6. A coating comprising a powder of activated zeolite heat-treated at a temperature of 800 ° C. or lower and an inorganic binder is applied to a metallic resistance wire and then heat-treated at a temperature of 800 ° C. or lower to form an active ceramic layer. A moisture-sensitive resistance element obtained by conversion, a coating containing a powder of inactivated zeolite heat-treated at a temperature of more than 800 ° C. and an inorganic binder is applied on a metallic resistance wire and then heat-treated to produce an inert ceramic. A method of manufacturing a humidity sensor, characterized in that a compensation resistance element obtained by converting into a layer is coupled to form a bridge. 7. A moisture-sensitive resistance element in which a metallic resistance wire is surrounded by an active ceramics layer containing activated zeolite as a main material, and a compensation resistance element in which a metal resistance wire is surrounded by an inactive ceramics layer. For combined humidity sensor,
Maintaining the temperature of the metallic resistance wire within the range of 300 to 550 ° C. and simultaneously contacting the atmosphere to be measured with humidity,
An atmospheric humidity measuring method, wherein a difference in electric resistance between the humidity-sensitive resistance element and the compensation resistance element is detected as an output voltage.