Fluororesin thin film diaphragm pressure sensor and method of fabricating the same

Abstract

A method of manufacturing a highly corrosion-resistant diaphragm pressure sensor capable of obviating the effects of temperature drift that arises when a pressure-travel coefficient changes with temperature of a fluid whose pressure is sensed. The diaphragm pressure sensor includes a pressure sensing element (10, 20) having a pressure receiving part with a deposition electrode formed on each of the opposing faces of sapphire or alumina ceramic diaphragms which are arranged in opposing relation, and a welding portion (10A, 20A) on a part of each of the surfaces of the diaphragms; and a fluororesin base (41, 61) for securing the pressure sensing element at the welding portion of the pressure sensing element. The pressure sensing element is coated with a fluororesin thin film having a cross-linked structure, and the pressure sensing element and the fluororesin base are welded together via the fluororesin thin film having a cross-linked structure.

Description

[0001] This is a divisional application of Ser. No. 11 / 243,978, filed Oct. 6, 2005.BACKGROUND OF THE INVENTION [0002] The present invention is directed to a diaphragm pressure sensor and a method of fabricating the same, and in particular to a diaphragm pressure sensor for sensing a fluid pressure in, for example, a container for chemicals, a pipe for chemicals or the like, and a method of fabricating the same. [0003] Conventional pressure sensors for sensing a fluid pressure in a container for chemicals, a pipe for chemicals or the like, are generally provided with a diaphragm which acts as a pressure-sensing means, whereby deflection of the diaphragm in response to an applied pressure is translated into an electric signal, to thereby sense a pressure. [0004] Japanese Patent Application No. 2002-130442 discloses an example of such a diaphragm pressure sensor in the invention titled “Electrical capacitance diaphragm pressure sensor”. [0005] Such a diaphragm pressure sensor comprises...

AI Technical Summary

Benefits of technology

The present invention provides a diaphragm pressure sensor with excellent corrosion resistance and mechanical strength. The sensor uses a fluororesin thin film with a crosslinked structure as the pressure-sensing element, which is secured to a fluororesin base using electron beams. The sensor can measure the pressure of a fluid by detecting changes in capacitance caused by variations in the distance between the deposition electrodes on the diaphragms. The use of a fluororesin thin film with a crosslinked structure as the pressure-sensing element eliminates the need for an adhesive and ensures accurate measurements. The entire diaphragm pressure sensor can be made of fluororesin, further enhancing its corrosion resistance and mechanical strength.

Problems solved by technology

In a conventional diaphragm pressure sensor such as that described above, a pressure transfer coefficient varies according to a temperature of a fluid whose pressure is to be measured, and instability such as temperature drift and the like is thereby caused, and as a result, measurement accuracy is significantly compromised.

It is known that a leading cause of temperature drift in a diaphragm pressure sensor is a thermal expansion / contraction coefficient of a diaphragm material.

However, both a sapphire, which is a crystallization of alumina, and an alumina ceramic, which is made of a sintered body of alumina, gradually erode when they come into contact with a strong acid fluid such as a highly concentrated fluoric acid solution or nitrate solution, and therefore, they are not desirable in terms of corrosion resistance.

However, improvement measures such as those described above still cannot solve the following problems:

(1) A fluororesin per se significantly expands and shrinks with temperature, which causes stress strain on a diaphragm and temperature drift in a diaphragm pressure sensor.

(2) When a fluororesin is simply applied to the surface of a diaphragm to form a fluororesin coating, such a coating cannot be tightly secured to the diaphragm, and easily peels.

However, a relatively great thickness of a fluororesin diaphragm, and lack of uniform thickness of an adhesive over a diaphragm, sometimes prevents a pressure from being thoroughly communicated between the fluororesin diaphragm and the diaphragm made of a sapphire plate, a ceramic plate or the like.

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