JPH09229796A - Capacitance-type pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitance-type pressure sensor whose configuration is simple, which is not affected by a temperature change, and whose measuring accuracy is high. SOLUTION: The capacitance-type pressure sensor is provided with a diaphragm 24 to which the pressure of a fluid is applied, a first electrode 22 which is formed on the rear surface of the diaphragm 24 so as to be a plane, a base board 28 as an insulator which is formed by keeping a constant interval from the diaphragm 24, and a second electrode 26 which is formed on the surface of the base board 26 and which is formed so as to face the first electrode 22 in the same manner. The thickness in the peripheral edge part of the diaphragm 24 is formed to be thicker than the thickness in the central part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic capacitance type pressure sensor that guides fluid pressure to a diaphragm, detects its distortion as a change in electrostatic capacitance, and electrically obtains a pressure value.

[0002]

2. Description of the Related Art Conventionally, capacitance type pressure sensors are generally
As shown in FIG. 2, the diaphragm 4 is made of a non-conductive disc-shaped thin plate such as ceramics, and the disc-shaped first electrode 2 is formed in the central portion on the back surface side. And a base substrate 8 on which the second electrode 6 is formed. The gap between the first electrode 2 and the second electrode 6 is set to a constant gap of about 10 to several tens of μm by the sealing agent 9 made of glass frit provided on the peripheral portions of the diaphragm 4 and the base substrate 8. Is held. Both the diaphragm 4 and the base substrate 8 are airtightly bonded to each other with the above-mentioned interval therebetween.

As shown in FIG. 2, this capacitance type pressure sensor is housed in a metal case 10, and a diaphragm 4 faces the measurement pressure introducing hole 11 side of the metal case 10 and the diaphragm is provided. The periphery of 4 is supported by the backup ring 12. Furthermore, the measurement pressure introducing hole 1
An O-ring 14 that seals 1 in an airtight state is provided inside the backup ring 12. Metal case 10
The metal cap member 16 is caulked and fixed to the opening so that the internal sensor does not rattle and the O-ring 14 is securely airtight.

[0004]

In the case of the above-mentioned conventional technique, the O-ring 14 in contact with the diaphragm 4 of the sensor expands and contracts due to a change in ambient temperature, causing the diaphragm 4 to be distorted and changing the capacitance. However, there is a problem that a measurement error occurs.

The present invention has been made in view of the above-mentioned problems of the prior art, and it is an object of the present invention to provide a capacitance type pressure sensor having a simple configuration, which is not affected by temperature changes and has high measurement accuracy. To aim.

[0006]

The present invention is directed to ceramics such as alumina or zirconia to which a fluid pressure is applied,
A diaphragm made of an insulator such as silicon or quartz, a first electrode formed on the back surface of this diaphragm by planar printing or vacuum deposition, and alumina or zirconia provided facing the diaphragm at a constant interval. An insulating base substrate, and a second electrode formed on the surface of the base substrate and facing the first electrode in the same manner as above. It is a capacitance type pressure sensor formed thicker than the thickness.

Further, it has a cylindrical metal case and a pressure introducing portion provided at one end of the case.
The capacitance type pressure sensor is housed in this case, the diaphragm is located facing the pressure introducing portion, and the airtight O-ring is in contact with the peripheral edge portion of the diaphragm, and the peripheral edge of the pressure introducing portion. The portion, the inner side of the diaphragm and the outer space thereof are sealed. Further, the peripheral portion of the diaphragm is convex toward the surface to which the pressure is applied and is formed thick over the entire circumference.

According to the capacitance type pressure sensor of the present invention, even if the force from the O-ring acts on the peripheral portion of the diaphragm, the portion in contact with the O-ring is formed thicker than the central portion, The diaphragm is prevented from being distorted so that the force from the O-ring does not appear as a change in the distance between the first and second electrodes.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. A capacitance type pressure sensor 2 of this embodiment is shown in FIG.
Reference numeral 0 has a circular diaphragm 24 made of alumina to which a fluid pressure is applied. This diaphragm 24
For example, the thickness is formed to be about 0.2 to 0.6 mm. On the back surface of the diaphragm 24, the first electrode 22 formed in a circular shape in plan view is provided. First electrode 22
Are those formed by printing with a conductive paste such as gold, silver, or silver palladium, or those formed by vacuum evaporation. Further, a circular base substrate 28 made of alumina is provided so as to face the diaphragm 24 at a constant interval. The second electrode 2 formed on the surface of the base substrate 28 so as to face the first electrode 22 by a similar method.
6 are provided.

The distance between the first electrode 22 and the second electrode 26 is
By the sealing agent 29 made of glass frit provided on the peripheral portions of the diaphragm 24 and the base substrate 28,
It is held at regular intervals of about several tens of μm. The peripheral edge portion of the diaphragm 24 and the base substrate 28 are joined to each other in an airtight state with the above-mentioned interval. This sealing agent 2
In FIG. 9, in order to form the diaphragm 24 and the base substrate 28 at a constant interval, for example, ceramic beads having a predetermined size are mixed therein. Also,
As shown in FIG. 1, the sealing portion with the sealing agent 29 has an inner sealing portion 29a and is formed so that the interval between the reference capacitance electrodes 27 does not change.

Further, the peripheral portion of the diaphragm 24 is a thick portion 24a formed thicker than the thickness of the central portion. As shown in FIG. 1, the capacitance type pressure sensor 20 is housed in a metal cylindrical case 30 and has a measurement pressure introducing hole 31 which is a pressure introducing portion of the metal case 30.
The diaphragm 24 faces the side. Diaphragm 24
The thick-walled portion 24a of the peripheral edge portion is supported by the backup ring 32, and the O-ring 34 that seals the measurement pressure introducing hole 31 in an airtight state is in contact therewith. A metallic cap member 36 is attached to the opening of the metallic case 30 to prevent the internal sensor 20 from rattling.
The ring 34 is crimped and fixed to the case 30 so as to ensure the airtight state of the ring 34.

The thick-walled portion 24a of the diaphragm 24 has only to be formed in a portion where the O-ring 34 is located and in which the sealing material 29 is provided, and is an outer peripheral edge which does not face the first electrode 22. It may be in a range that does not affect pressure measurement. Further, the diaphragm 24 may have a concave lens shape with a thick peripheral portion and a thin central portion.

In the method of assembling the electrostatic capacitance type pressure sensor of this embodiment, the first and second electrodes 22 and 26 are formed on the diaphragm 24 and the base substrate 28 by printing, vacuum deposition or the like. Then, the diaphragm 24 and the base substrate 28 are made to face each other, and the sealing agent 2 is interposed via the sealing agent 29.
9 is heat-melted and sealed. After that, the sensor 20 is inserted into the case 30. At the time of insertion, the backup ring 32 and the O-ring 34 are previously inserted into the case 30, and the diaphragm 24 of the sensor 20 is inserted into the measurement pressure introducing hole 31.
Insert it on the O-ring 34 side. Then, the cap member 36 is attached to the case 30, and the diaphragm 24 of the sensor 20 is pressed against the O-ring 34 in an airtight state.
The cap member 36 is securely fixed by caulking the peripheral edge of the opening of 0.

The capacitance type pressure sensor 20 of this embodiment
According to this, the thick portion 24a is formed in the peripheral portion of the diaphragm 24, and the strength of the portion contacting the O-ring 34 is high,
There is no influence of thermal strain of the O-ring 34, and a measurement error due to a temperature change does not occur.

The capacitance type pressure sensor of the present invention is
The thickness of the peripheral portion of the diaphragm is not limited to the above-described embodiment, and may be continuous or stepwise. Further, by forming the thick portion even near the portion where the reference capacitance electrode is formed, it is possible to reduce changes and errors in the reference capacitance due to pressure.

[0016]

According to the capacitance type pressure sensor of the present invention, the peripheral portion of the diaphragm is formed thicker than the central portion, distortion is less likely to occur due to an external force, and an external member due to temperature change or the like. It does not cause measurement error due to force from.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a state in which a capacitance type pressure sensor according to a first embodiment of the present invention is attached to a case.

FIG. 2 is a vertical cross-sectional view showing a state in which a conventional capacitive pressure sensor is attached to a case.

[Explanation of symbols]

 2,22 First electrode 4,24 Diaphragm 6,26 Second electrode 8,28 Base substrate 10,30 Case 14,34 O-ring 20 Capacitive pressure sensor 24a Thick portion

Claims (3)

[Claims] 1. A base substrate made of an insulator, which is provided with a diaphragm to which a fluid pressure is applied, a first electrode which is formed flat on the back surface of the diaphragm, and which faces the diaphragm at a constant interval. And a second electrode that is formed on the surface of the base substrate and is similarly provided so as to face the first electrode, and the thickness of the peripheral portion of the diaphragm is made thicker than the thickness of the central portion. Capacitance type pressure sensor. 2. A cylindrical case, and a pressure introducing section provided at one end of the case, wherein the capacitance type pressure sensor is housed in the case, and the pressure introducing section is provided. The diaphragm is positioned facing to, and an airtight O-ring is in contact with the peripheral edge of the diaphragm to seal the peripheral edge of the pressure introducing portion, the inside of the diaphragm and the outer space thereof. The capacitance type pressure sensor according to claim 1. 3. The capacitance according to claim 1, wherein a peripheral portion of the diaphragm is formed so as to be convex on a surface side to which pressure is applied and has a large thickness over the entire circumference. Type pressure sensor.