JPS6024428A - Pressure sensor - Google Patents

Abstract

PURPOSE:To constitute a stable pressure sensor with good reproducibility, by providing the second electrode plate so as to face an electrode plate, which is fixed to a central projection part of an elastic body, forming a capacity between both electrodes, and reducing the fatigue caused by the repeating use of the elastic body. CONSTITUTION:A first electrode plate 31 is fixed to a projection part 2, which is provided at the center of a thin part 21 of an elastic body 20. A second electrode plate 32 is provided so as to face the first electrode plate. A thin dielectric 33 for preventing short circuit is inserted between the two plates. When the pressure change of a fluid is transmitted through an opening part 34, the projection part 22 is moved accordingly, the interval between the first and second electrode plates is changed, and as a result the capacity is changed. In this constitution, the entire device becomes very thin, and the moving distance of the projection part 22 is small. Therefore, fatigue caused by the repeating use of the elastic body 20 is reduced, and the stable pressure sensor with good reproducibility can be constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure sensor whose capacity changes depending on pressure.

FIG. 1 is a block diagram of a crystal oscillator, in which 11 is a variable capacitor, 12 is a crystal resonator, 1a is a feedback amplifier, and the crystal oscillator is formed as a whole.

It is generally well known that changing the variable capacitor 11 changes the oscillation frequency of the crystal oscillator. This pressure sensor converts changes in pressure into changes in capacitance, and uses this change in capacitance to change the excavation frequency of the crystal oscillator to measure pressure.

Pressure sensors that use variable capacitance have already been announced, but the elastic body becomes fatigued due to repeated use.
There was a fear that reproducibility would deteriorate.

The present invention provides a more stable pressure sensor with good reproducibility and reduced fatigue due to repeated use of the elastic body. In addition, electrodes are provided that face the capacitor in a direction perpendicular to the direction in which the elastic body expands and contracts, thereby simplifying the structure and making it thinner than conventional ones.

FIG. 2 shows an elastic body 20 of the present invention in which a projection 22 is provided at the center of a thin film portion 2I and a thick portion 23 is integrally formed around the periphery.

FIG. 3(a) is a perspective view of a pressure sensor using the elastic body 20 shown in FIG. 2, which is an embodiment of the pressure sensor, and FIG. 3(b) is a sectional view taken along line A-A. (However, the third
In Figure (a), the dielectric 33 is power saving). A first electrode plate 31 is fixed to the protrusion 22 of the elastic body. This first
A second electrode plate 32 is arranged opposite to the electrode plate.

In between, a thin dielectric material 33 such as Teflon is inserted to also serve as short circuit prevention 1 between both electrodes.

When the pressure change of the fluid is transmitted through the opening 34, the thin film portion 21 of the elastic body 20 expands and contracts in response to the change in the protrusion 22.
By moving, the first electrode plate 31 and the second electrode plate 32
The spacing between them changes, resulting in a change in capacitance. Also 3
0 is an air circulation part.

A feature of this pressure sensor is that it can be made very thin overall. Except for the tubular part of the opening, the third
The length L of the casing portion 36 in FIG. 3(b) can be made to be approximately 6a+m. Instead, if the amount of change in capacitance is increased, the area becomes larger.

In this pressure sensor, the thickness and external dimensions of the thin film part 21 are designed so that the moving distance of the projection part 22 is 2 mm with a predetermined pressure change, and as a result, the electrode spacing changes from 2 to 3 mm by 0 to 3 mo+. shall be. Assuming that the electrode plate has a diameter of 15 and a Teflon sheet of 0.2...m is inserted between them, the change in capacitance is from about 1 pF to 8 pF. If this amount of capacitance change is obtained, it is sufficient for a normal pressure horn sensor, and the frequency change of the crystal oscillator is 10M.
Hz frequency becomes 4 kHz. Therefore, the movement distance of the protrusion should be 2 degrees depending on the change in the pressure to be measured.
Determine the thickness and external dimensions of the thin film part.

FIG. 4 shows another embodiment in which silicone rubber is used as the elastic body, and adhesive does not stick to the silicone rubber. To fix the electrode plate, the protrusion 22 is made into a cylindrical shape as shown in the cross-sectional view of FIG. insert,
An electrode plate is fixed onto this with adhesive or solder. 42
is a lead wire drawn out from the first electrode plate 31 and the second electrode plate 32.

FIG. 5 shows another embodiment in which a thick part 53 is provided around the thin film part 52 of the elastic body 51, and furthermore, a thick part 53 is provided on the outer periphery of the thin film part 52 and is thicker than the casing part which also serves to hold the elastic body. 54 is provided.

By doing this, the influence of expansion and contraction of the thin film portion 52 is prevented from reaching the thick portion 54 on the side of the housing as much as possible. That is, when the thick part 53 is not present, the expansion and contraction of the thin film part 52 extends to the holding casing part full+the thick part 54. However, by increasing the thickness of the thick part 54 on the side of the housing, the effects of deformation of the holding part due to expansion and contraction of the thin film part can be minimized. By further providing a thick portion 53,
The influence of expansion and contraction of the thin film portion 52 is absorbed by the thick wall portion 53 and is prevented from reaching the thick wall portion 54 on the side of the holding housing. By doing so, reproducibility with repeated use becomes better. The elastic body can be molded into any shape, such as a circle or a rectangle, and has good reproducibility. Of course, the thick portion may not be formed as shown in the drawings of this embodiment, and the thickness may gradually increase from the center of the elastic body toward the outside.

In the present invention, silicone rubber is used as an example of the elastic body, but other elastic bodies may be used. Furthermore, although a crystal resonator is taken as an example of the piezoelectric body, an oscillator using other materials such as lithium tantalate, piezoelectric ceramic, etc. may also be used.

[Brief explanation of drawings]

Figure 1 is a block diagram of a crystal oscillator. FIG. 2 is a perspective view showing the elastic body. FIG. 3(a) is a perspective view showing the pressure sensor of the present invention. FIGS. 3(b), 4, and 5 are cross-sectional views of the pressure sensor according to the present invention. 20.51...Elastic body 22...Protrusion 31...First electrode plate 32...Second electrode plate 36.36゛... ...Housing portion 33...Dielectric material

Claims (3)

[Claims] (1) The elastic body has a protrusion in the center, a first electrode plate is provided on the protrusion approximately parallel to the main surface of the elastic body, and a second electrode plate is provided opposite to the first electrode plate on the elastic body. A pressure sensor, characterized in that the fourth electrode and the second electrode form a capacitance that is fixed to a housing part together with the body. (2) The pressure sensor according to claim 1, characterized in that a dielectric material is inserted between the first electrode plate and the second electrode plate 7 forming the capacitance. (3) The pressure sensor according to claim 1, wherein the thickness of the elastic body increases from the protrusion toward the housing.