Humidity sensor and a method of producing the humidity sensor

Electrical resistors – Resistance value responsive to a condition – Gas – vapor – or moisture absorbing or collecting

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352963, H01C 700

Patent

active

056083742

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a humidity sensor which detects humidity by utilizing a change in electric characteristics of the device corresponding to a change in the humidity.


BACKGROUND ART

Along with the recent increase in number of the fields where measurement and control of humidity is required, the importance of the humidity sensor has been appreciated.
The humidity sensor which detects humidity by utilizing a change in electric characteristics of the device corresponding to a change in the humidity includes those of an electrolyte type, a metal type, a polymer type and a ceramics type, and various materials have been investigated in each type, however, at moment, humidity sensors of a polymer type and a ceramics type have been practically used. Both types of the sensors utilize their property that the impedance or the electric capacity of the device is changed by absorption and desorption of the water onto the device.
However, the prior art humidity sensors have some problems in their downsizing. When the prior art technique is employed for producing a humidity sensor of a small size, the impedance is raised and the fluctuation of the impedance from one device to another is increased. Besides, the dynamic range of the impedance becomes too big or too small. Accordingly, it has been difficult to produce a small hydrometer of high precision.
Many of the prior art humidity sensors have a slow response, thus it has been impossible to measure the humidity change correctly.
From the view point of the reliability, the prior art humidity sensors are not resistant to a high temperature, high humidity or an organic solvent, and when they are immersed in water, many of them are deteriorated. Furthermore, when they are contacted with an electrolyte solution such as a salt water, even after being dried, the electrolyte remains in the humidity sensing body, and the characteristics are very much changed to make the device unusable. With an organic solvent, as the humidity sensing body is dissolved in it, the characteristics are very much changed and the device becomes unusable.
The present invention is to solve these problems, and its object is to provide a humidity sensor having, in addition to a quick response and high environmental resistance, a low impedance and an appropriate dynamic range of the impedance even after the sensor is downsized.


DISCLOSURE OF THE INVENTION

According to one aspect of the present invention, there is provided a humidity sensor employing a humidity sensing body containing manganese oxide, lead oxide and an alkali metal compound as the main components.
According to another aspect of the present invention, there is provided a humidity sensor employing a humidity sensing body containing manganese oxide and an alkali metal compound as the main components.
According to still another aspect of the present invention, there is provided a humidity sensor employing a humidity sensing body containing lead oxide and an alkali metal compound as the main components.
By the use of the humidity sensing body having such components, a humidity sensor which has a low impedance and an appropriate dynamic range of the impedance, can be obtained even when the sensor is downsized.
By forming the humidity sensing body in the form of a film on a substrate, a humidity sensor having a small size and a quick response can be produced in a simple process with a low cost. In this description, the humidity sensing body formed in the form of the film is referred to as a humidity sensing film.
Manganese oxide does not need to be manganese oxide as the starting material, and those which can provide manganese oxide by decomposition, such as manganese carbonate, manganese acetate and manganese nitrate can be used as well. Similarly, lead oxide does not need to be lead oxide as the starting material, and those which can provide lead oxide by decomposition, such as lead carbonate, lead acetate and lead nitrate can be used as well. Manganese oxide, lead oxide and a compound of the alkali metal do not ne

REFERENCES:
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patent: 4052691 (1977-10-01), Nagano et al.
patent: 4210894 (1980-07-01), Nitta et al.
patent: 4373391 (1983-02-01), Johnson
patent: 4793175 (1988-12-01), Fedter et al.
patent: 5136274 (1992-08-01), Shimomura et al.
patent: 5206615 (1993-04-01), Fujita et al.

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