JPH08136381A - Pressure sensor - Google Patents

Abstract

PURPOSE: To provide a pressure sensor with a small count of parts in a simple constitution which does not require high assembling accuracy in the manufacturing process and is not easily influenced by a temperature change, by connecting a piezoelectric vibration plate obtained by baking a piezoelectric ceramic on a metallic thin plate to an oscillation circuit so that the piezoelectric vibration plate itself constitutes a part of the oscillation circuit. CONSTITUTION: A piezoelectric vibration plate 5 obtained by baking a piezoelectric ceramic 4 on a metallic thin plate is placed on the upper surface of a recessed housing 3. At the same time, the piezoelectric vibration plate 5 is securely caulked to a pressure container 6 airtightly welded to a flange 2 of the housing by a bracket 8 via a spacer 7 in this pressure sensor. The piezoelectric vibration plate 5 is connected to an oscillation circuit 9 so that the plate 5 itself constitutes a part, of the oscillation circuit. The pressure is detected by measuring the oscillation frequency of the oscillation circuit 9 determined by the resonant frequency of the piezoelectric vibration plate 5 which changes in accordance with the pressure within the pressure container.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure detecting device which is attached to a pressure fluid circuit of, for example, an air conditioner or a refrigerator and detects the fluid pressure of the pressure fluid circuit. The present invention relates to a simple pressure detection device.

[0002]

2. Description of the Related Art Conventionally, as this type of pressure detecting device,
A capacitance type pressure detecting device shown in FIG. 1 of Japanese Patent Laid-Open No. 174575/1994 is proposed, and its configuration is shown in FIG.
It was as shown in The structure of this capacitance type pressure detecting device will be briefly described below with reference to FIG.
Is a metal housing that does not deform or bend even if pressure is introduced into the inside, and a pressure introduction port 1 is opened at the lower end of the housing 3 and a pressure introduction chamber 10 is provided above it. Has been. On the upper side of the pressure introducing chamber 10 inside the housing 3, a flexible thin metal film 11 is attached to the shoulder portion of the housing 3 by means such as welding around the entire circumference.

Numeral 17 is a pressure detection in which the outer peripheral portion of the diaphragm 12 and the indicating member 13 having a plate thickness thicker than the diaphragm 12 are joined by a low melting point glass 14 so as to maintain a minute gap between the electrodes. Of the pressure detector, electrodes 15 and 16 are formed on the respective surfaces of the diaphragm 12 and the supporting member 13 facing each other by printing or the like, and a capacitor having a capacitance between the electrodes 15 and 16 is formed. It is something that is done.

In this apparatus, the pressure introduced from the pressure introducing port 1 into the pressure introducing chamber 10 displaces the diaphragm 12 via the thin metal plate 11, and the diaphragm 12 is displaced.
An electrostatic capacitance is output according to the flexural displacement of the. Although not shown, this output is connected to an electronic circuit to output an electric signal corresponding to the pressure.

[0005]

However, the conventional capacitance type pressure detecting device has the diaphragm 12
A low melting point glass 14 is formed on the outer peripheral portion of the indicating member 13 which is thicker than the diaphragm 12 so that a minute interval between electrodes is maintained.
A structure in which electrodes 15 and 16 are formed by printing or the like on the respective surfaces facing each other to form a capacitor having a capacitance between the electrodes 15 and 16 Therefore, the number of parts is large, and the size of the gap between the electrode 15 of the diaphragm 12 and the electrode 16 of the indicating member 13 has an important meaning in determining the electrostatic capacitance between them, and this dimensional accuracy is important for detecting pressure. Since it affects the accuracy of the manufacturing process, a high-precision processing and assembling technology such as bonding with the low melting point glass 14 is required in the manufacturing process, which raises the manufacturing cost.

In principle, a capacitor is formed and its capacitance is detected. However, since the capacitance of a capacitor is easily affected by temperature changes, various detection errors caused by it are minimized. Ingenuity is needed.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a piezoelectric vibrating plate 5 formed by firing a piezoelectric ceramic 4 on a thin metal plate is itself an oscillation circuit. By connecting to the transmitting circuit 9 to form a part, it is possible to obtain a pressure detection device that has a small number of parts and a simple configuration, does not require high precision in processing and assembly in the manufacturing process, and is not easily affected by temperature changes. It is an object.

That is, in the pressure detecting device of the present invention, the piezoelectric ceramic 4 is fired on the thin metal plate on the upper surface of the concave housing 3 having the pressure inlet 1 at the center of the lower surface and the flange 2 formed on the outer peripheral portion of the upper surface. The piezoelectric vibrating plate 5 is placed, and the outer peripheral portion of the piezoelectric vibrating plate 5 is airtightly welded to the flange 2 of the housing and attached to the pressure container 6, and the outer periphery is provided via the spacer 7 on the upper surface of the pressure container 6. The piezoelectric vibration plate 5 is connected to an oscillation circuit 9 so as to form a part of an oscillation circuit, and the piezoelectric vibration plate 5 responds to the pressure applied in the pressure container. The pressure can be detected by measuring the oscillation frequency of the oscillation circuit 9 which is determined by the resonance frequency of the piezoelectric diaphragm 5 which changes as a result.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a pressure detecting device of the present invention.
The pressure vessel 6 is provided with a pressure introduction port 1 at the center of the lower surface and has a concave housing 3 formed with a pressure introduction chamber 10 and a collar 2 at the upper side, and a piezoelectric vibrating plate formed by firing a piezoelectric ceramic 4 on a thin metal plate. 5, and both are adhered to each other by airtight welding at the outer peripheral portion thereof. The pressure vessel 6 is caulked and fixed by a bracket 8 made of metal or resin via a spacer 7.

The oscillation circuit 9 is connected to the piezoelectric vibrating plate 5, the piezoelectric vibrating plate 5 constitutes a part of the oscillation circuit, and the oscillation frequency of the transmitting circuit 9 is the piezoelectric vibrating plate 5. It depends on the resonance frequency of.

[0010]

The operation of the present invention configured as described above will be described. The pressure fluid introduced from the pressure inlet 1 into the pressure vessel 6 exerts pressure on the piezoelectric vibrating plate 5 as shown in FIG. The resonance frequency of the piezoelectric diaphragm 5 changes according to the pressure. The piezoelectric vibrating plate 5 is connected to a transmitting circuit 9 which forms a part of the piezoelectric vibrating plate 5, and the transmitting frequency of the transmitting circuit 9 is determined by the resonance frequency of the piezoelectric vibrating plate 5. The oscillation frequency of the oscillation circuit changes according to the pressure exerted on the piezoelectric diaphragm 5 by the pressure fluid guided from the pressure vessel 6 to the oscillation frequency, and this oscillation frequency is measured by another frequency measurement circuit (not shown). As a result, the pressure of the pressure fluid introduced from the pressure inlet 1 into the pressure vessel 6 can be detected.

Table 1 shows data obtained by actually measuring the change in the transmission frequency of the transmission circuit 9 when the pressure of the pressure fluid is changed using the present invention.

[0012]

[Table 1]

Further, FIG. 2 is a graph thereof, and also from this experimental result, according to the present invention, the pressure inlet 1 to the pressure vessel 6 are
It can be seen that the pressure of the pressure fluid introduced therein can be detected.

[0013]

In the pressure detecting device of the present invention, the piezoelectric vibrating plate 5 itself, which is formed by firing the piezoelectric ceramic 4 on the thin metal plate, constitutes a part of the oscillation circuit 9, and therefore the pressure container The pressure can be detected by measuring the oscillation frequency of the oscillation circuit 9 which is determined by the resonance frequency of the piezoelectric diaphragm 5 which changes according to the pressure applied inside. Further, according to the present invention, since the number of parts is small and the structure is simple, and high precision of working and assembling is not required even in the manufacturing process, it is possible to obtain a pressure detecting device which is inexpensive and is not easily affected by temperature change.

[Brief description of drawings]

FIG. 1 is a sectional view of a pressure detection device of the present invention.

FIG. 2 is a graph showing the relationship between frequency and pressure characteristics in the pressure detection device of the present invention.

FIG. 3 is a sectional view of a conventional pressure detection device.

[Explanation of symbols]

1 Pressure inlet. 2 Tsuba. 3 housing. Four
Piezoelectric ceramic. 5 Piezoelectric diaphragm. 6 Pressure vessel. 7 Spacer.
8 brackets. 9 Transmitter circuit. 10 Pressure inlet. 11 Thin metal plate. 12 diaphragm. 13 Indicator member. 14 Low melting glass. 15 electrodes. 16 electrodes.

Claims (1)

[Claims] 1. A piezoelectric vibrating plate 5 formed by firing a piezoelectric ceramic 4 on a thin metal plate on the upper surface of a concave housing 3 having a pressure inlet 1 at the center of the lower surface and a collar 2 on the outer peripheral portion of the upper surface.
And a pressure vessel 6 in which the outer peripheral portion of the piezoelectric vibrating plate 5 is airtightly welded to the flange 2 of the housing and attached.
A pressure detecting device in which an outer peripheral portion is caulked and fixed by a bracket 8 via a spacer 7 on an upper surface of the pressure container 6, wherein the piezoelectric vibrating plate 5 itself constitutes a part of an oscillation circuit. The pressure can be detected by measuring the oscillation frequency of the oscillation circuit 9 which is connected to the pressure vessel and which is determined by the resonance frequency of the piezoelectric diaphragm 5 which changes according to the pressure applied to the pressure vessel. Pressure detector.