JP2008175659A - Pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure sensor which has a high moisture resistance, and will not sacrifice the output characteristics. <P>SOLUTION: The pressure sensor is composed of a diaphragm formed in its case, a pressure-sensitive element arranged on the surface on the opposite side of the pressure-receiving part of this diaphragm, and a wiring pattern and lead wires for extracting the signal of this pressure-sensitive element. Along with covering the upside of the diaphragm, including the pressure-sensitive element and the wiring pattern with a moisture-proof film having a small steam permeability, resin is arranged in between the diaphragm and the moisture-proof film. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pressure sensor in which a diaphragm is provided with a pressure-sensitive element or a wiring pattern and detects distortion of the diaphragm as an electric signal, and relates to a pressure sensor that is intended to prevent abnormal output of the pressure sensor.

FIG. 3 is a cross-sectional view of a principal part showing a conventional example of a pressure sensor to which the present invention is applied.
In the figure, reference numeral 1 denotes a sensor housing, and in the illustrated example, a diaphragm 1a is integrally formed. Reference numeral 2 denotes a pressure-sensitive element. For example, a thin film of chromium oxide is deposited on the diaphragm by reactive sputtering.

  3 is a wiring pattern connected to the pressure-sensitive element 2, and 4 is a lead wire connected to the wiring pattern 3. 5 is a protective coating agent formed so as to cover the wiring pattern 3 and the diaphragm including the wiring pattern, 6 is a process pressure receiving portion formed in the sensor casing, and 7 is an air introduction portion.

  In the above-described configuration, when pressure is applied to the process pressure receiving surface 6, the diaphragm 1 a is deformed and the pressure sensitive element 2 is distorted. This distortion is converted into an electric signal, amplified by an amplifying means (not shown), and output. The coating agent 5 (resin, grease, etc.) is for protecting the pressure sensitive element 2 and the wiring pattern 3 from contaminants and moisture when exposed to the atmosphere.

By the way, such a conventional pressure sensor has the following problems.
1) The protective coating agent 5 generally has water vapor permeability, and moisture contained in the atmosphere of the air introduction part 7 diffuses into the protective coating agent 5.

  2) When the pressure receiving medium is a cold medium for beverages or water, there is often a sudden change in temperature, and condensation occurs at the interface between the coating agent 5 and the diaphragm 1a. Due to this dew condensation, electrolytic corrosion occurs in the portions of the pressure sensitive element 2, the wiring pattern 3, and the lead wires 4 that are not covered with insulation, causing abnormal output and corrosion on the atmosphere introduction part 7 side of the sensor housing 1.

  In order to prevent the generation of moisture, it is necessary to strengthen the coating. However, if the diaphragm is coated with a hard material such as metal or ceramic, the diaphragm characteristics are affected and normal output cannot be obtained.

Further, if the air introduction part is sealed so that moisture does not enter, the pressure sensor measures on the basis of the atmospheric pressure, so that an error occurs due to atmospheric pressure fluctuation.
Therefore, a relatively soft resin or grease must be used as a coating agent even if it has some water vapor permeability.

The present invention has been made to solve the above-described problems, and an object thereof is to realize a pressure sensor that has high moisture resistance and does not sacrifice output characteristics.
In addition, there exist some which were shown by the following patent document as a prior art of such a pressure sensor.

Japanese Patent Laid-Open No. 9-119855 Japanese Patent Laid-Open No. 11-14302

The present invention has been made to solve the above problems, and in the invention of the pressure sensor according to claim 1,
In a pressure sensor composed of a diaphragm formed in the sensor housing, a pressure sensitive element disposed on the surface opposite to the pressure receiving portion of the diaphragm, and a wiring pattern and a lead wire for taking out a signal of the pressure sensitive element,
The diaphragm including the pressure-sensitive element and the wiring pattern is covered with a moisture-resistant film having a low water vapor transmission rate, and a resin is disposed between the diaphragm and the moisture-resistant film.

In claim 2, in the pressure sensor according to claim 1,
The moisture resistant film is provided with a hole for taking out the lead wire.

In claim 3,
In a pressure sensor composed of a diaphragm formed in the sensor housing, a pressure sensitive element disposed on the surface opposite to the pressure receiving portion of the diaphragm, and a wiring pattern and a lead wire for taking out a signal of the pressure sensitive element,
The diaphragm including the pressure sensitive element and the wiring pattern is covered with a disk-shaped block having a diameter larger than the outer diameter of the diaphragm and having a through hole in the thickness direction, and a surface including the through hole of the block is covered. It is characterized by being airtightly covered with a moisture-resistant film.

In claim 4, in the pressure sensor according to claim 2,
A space having a predetermined height is formed between the diaphragm and the block, and the outer periphery of the block and the diaphragm is hermetically fixed.

In claim 5, in the pressure sensor according to claim 3 or 4,
The block is provided with a hole for taking out a lead wire.

As is apparent from the above description, according to claims 1 to 5 of the present invention, the following effects can be obtained.
According to the first aspect of the present invention, moisture present in the atmospheric pressure introduction portion is blocked by the moisture-resistant film and does not diffuse into the resin, so that no condensation occurs on the pressure sensitive element or the wiring pattern even if there is a sudden temperature change.
In addition, since the pressure-resistant film is thin and soft, it does not adversely affect the diaphragm characteristics.
According to the third aspect of the present invention, the moisture present in the atmospheric pressure introduction portion is blocked by the moisture-resistant film and does not reach the diaphragm, so that no dew condensation occurs on the pressure-sensitive element or the wiring pattern even if there is a sudden temperature change.
In addition, since a space having a predetermined height is provided between the diaphragm and the block, the diaphragm characteristics are not adversely affected.

  FIG. 1 is a sectional view of an essential part of a pressure sensor showing an embodiment of the present invention. In the figure, the same elements as those in the conventional example of FIG. That is, an integrally formed diaphragm 1a is provided at the center of the sensor housing 1, and when pressure is applied to the process pressure receiving portion 6, it is displaced in the direction of the air introduction portion 7 and the surface is distorted. . In the illustrated example, the diaphragm 1a is displayed as an integral body, but the diaphragm may be formed of a separate member and the outer periphery thereof may be fixed to the sensor housing by electron beam welding or the like. Reference numeral 2 denotes a pressure-sensitive element, and a chromium oxide thin film is deposited on a diaphragm by reactive sputtering, for example, as in the conventional example.

A wiring pattern 3 is connected to the pressure sensitive element 2, and an electric signal generated by the distortion is transmitted to the lead wire 4.
In the present invention, the entire diaphragm 1a including the pressure sensitive element 2 and the wiring pattern is covered with a soft moisture-resistant film 8 having a low water vapor transmission rate in order to suppress the intrusion of moisture existing in the atmospheric pressure introduction portion 7. Between the moisture-resistant film 8 and the diaphragm 1a, resin 5a is filled in order not to allow moisture-containing air to enter from the lead wire through hole 8a or the gap 8b in the outer peripheral portion of the moisture-resistant film.

As the moisture-resistant film 8, a Teflon trifluoride (registered trademark) film (PCTFE) or an aluminum-deposited PET film having a thickness of about several tens of microns with respect to a conventionally used coating agent and a water vapor permeability of 1/20 or less. Is used. Further, the moisture resistant film 8 is provided with a hole 8a through which the lead wire 4 is passed with a size that does not impair the moisture permeability.
In the figure, the lead wire 4 is taken out from a through hole formed in the moisture resistant film 8, but may be taken out from a gap 8 b in the outer peripheral portion of the moisture resistant film 8. In that case, the hole 8a is unnecessary.

  According to the above-described configuration, moisture existing in the atmospheric pressure introduction portion 7 is blocked by the moisture-resistant film 8 and does not diffuse into the resin, so that dew condensation occurs on the pressure sensitive element 2 and the wiring pattern 3 even if there is a sudden temperature change. It does not occur. Moreover, since the thickness of the moisture-resistant film 8 is thin and soft, the diaphragm characteristics are not adversely affected.

Next, an embodiment of claim 3 will be described with reference to a cross-sectional view of the main part of FIG.
In the figure, the same elements as those in the conventional example of FIG. That is, an integrally formed diaphragm 1a is provided in the center of the sensor housing 1, and when pressure is applied to the process pressure receiving portion 6, it is displaced in the direction of the air introduction portion 7 and the surface is distorted. .

  In the illustrated example, the diaphragm 1a is displayed as an integral body, but the diaphragm may be formed of a separate member and the outer periphery thereof may be fixed to the sensor housing by electron beam welding or the like. Reference numeral 2 denotes a pressure-sensitive element, and a chromium oxide thin film, for example, is deposited on the diaphragm 1a by reactive sputtering as in the conventional example.

A wiring pattern 3 is connected to the pressure sensitive element 2, and an electric signal generated by the distortion is transmitted to the lead wire 4.
Reference numeral 9 denotes a disk-shaped block having ring-shaped convex portions 10 formed at the edges of both surfaces and having a pressure-guiding hole 5a at the center, and has a diameter slightly larger than the diameter of the diaphragm 1a. And the moisture-proof film 8 is stuck on the whole surface including the pressure guide hole 9a by the adhesive etc. at the convex part by the side of the air introduction surface 7 of the block 9. The material of the block 9 is made of metal or plastic resin.

A seal member (for example, an O-ring (not shown)) is disposed on the convex portion of the block 9 on the side facing the diaphragm 1a. The height including the thickness of the seal member is such that the pressure sensitive element 2, the wiring pattern 3, the lead wire, etc. do not contact the surface of the block 9 when the diaphragm 1a receives pressure and is distorted to the block 9 side. Is formed. The block 9 is fixed to the sensor housing 1 outside the diaphragm 1a with screws (not shown) so that air between the diaphragm 1a and the diaphragm 1a does not leak outside.
Further, a hole for taking out the lead wire 4 to the outside is formed in the vicinity of the edge of the sensor housing 1, and this hole is sealed with a hermetic seal or the like after the lead wire is taken out.

According to the above-described configuration, the inflow of air from the atmosphere introduction unit 7 can be sealed by the block 9 and the moisture resistant film 8. Then, the volume increase due to the thermal expansion of the sealed internal air is prevented by loosening the moisture-proof film 8, thereby preventing measurement errors due to the tension of the film and the increase of the internal pressure.
Similarly, by taking an appropriate clearance between the moisture-proof film 8 and the block 5, it is possible to prevent the moisture-proof film 8 from sticking to the block 9 even if the internal air is thermally contracted.

The above description merely shows a specific preferred embodiment for the purpose of explanation and illustration of the present invention. For example, the convex part of the diaphragm 1a formed in the block 9 does not have to be sufficiently high with a seal member, and the pressure guide hole 9a formed in the block 9 does not necessarily have to be in the center. Further, the convex portion on the air introduction part 7 side may not be required if a predetermined amount of air can be secured.
Therefore, the present invention is not limited to the above-described embodiments, and includes many changes and modifications without departing from the essence thereof.

It is principal part sectional drawing of the pressure sensor which shows one Example of this invention. It is principal part sectional drawing of the pressure sensor which shows another Example. It is principal part sectional drawing of the conventional pressure sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sensor main body 1a Diaphragm 2 Pressure sensitive element 3 Wiring pattern 4 Lead wire 5a, 9a Pressure introducing hole 5 Block 6 Process pressure-receiving surface 7 Air introduction part 8 Moisture-resistant film 8a Lead wire through-hole 8b Clearance 9 Block 10 Convex part

Claims (5)

In a pressure sensor composed of a diaphragm formed in the sensor housing, a pressure sensitive element disposed on the surface opposite to the pressure receiving portion of the diaphragm, and a wiring pattern and a lead wire for taking out a signal of the pressure sensitive element,
A pressure sensor characterized in that the diaphragm including the pressure sensitive element and the wiring pattern is covered with a moisture resistant film having a low water vapor transmission rate, and a resin is disposed between the diaphragm and the moisture resistant film.   The pressure sensor according to claim 1, wherein a hole for taking out the lead wire is provided in the moisture resistant film. In a pressure sensor composed of a diaphragm formed in the sensor housing, a pressure sensitive element disposed on the surface opposite to the pressure receiving portion of the diaphragm, and a wiring pattern and a lead wire for taking out a signal of the pressure sensitive element,
The diaphragm including the pressure sensitive element and the wiring pattern is covered with a disk-shaped block having a diameter larger than the outer diameter of the diaphragm and having a through hole in the thickness direction, and a surface including the through hole of the block is covered. A pressure sensor that is airtightly covered with a moisture-resistant film.   The pressure sensor according to claim 2, wherein a space having a predetermined height is formed between the diaphragm and the block, and an outer periphery of the block and the diaphragm is fixed in an airtight manner.   The pressure sensor according to claim 3 or 4, wherein a hole for taking out a lead wire is provided in the block.

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