JP2765333B2 - Pressure measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure measuring device,
More specifically, it relates to an improvement in the surface configuration of the seal diaphragm.

[0002]

2. Description of the Related Art FIG. 2 is a sectional view of a conventional pressure measuring device. This conventional device mainly includes a detection unit 20 and a protection unit 30, which are connected via pressure guiding tubes 16 and 17. The detecting unit 20 converts the differential pressure to be measured into an electric signal and outputs the electric signal. The protection unit 30 protects the detection unit 20 against the introduction pressure as described later.

There is a pressure measuring device in which the detecting unit 20 is provided inside the protecting unit 30. However, as shown in FIG. 2, a pressure measuring device in which the detecting unit 20 is provided outside the protecting unit 30 is used. When the temperature of the measurement fluid is high, the effect of the temperature does not reach the detection unit 20.

[0004] The protection section 30 is mainly composed of main bodies 31, 32,
The protective diaphragm 13, the seal diaphragm 10, the O-ring 18, the cover 19, and the pressure guiding tube 23. Here, the main bodies 31 and 32 are disposed on the left and right sides of the drawing with the protective diaphragm 13 interposed therebetween, and are joined to each other at their outer circumferences or peripheral edges. Two O-rings 18, a cover 19, a pressure guiding tube 23, and two seal diaphragms 10 are provided.

In the main bodies 31, 32, concave portions 11, 21, holes 14, 24, and holes 45, 55 are formed symmetrically. The recess 11 is formed in a coaxial mortar shape on the left side surface of the main body 31, the hole 14 penetrates the main body 31 along its axis, the hole 45 opens on the one hand in the vicinity of the outer periphery of the recess 11, and on the other hand conducts. It penetrates through the pressure tube 16 and communicates with a pressure guiding space (not shown) of the detection unit 20. The right side surface of the main body 31 has a corrugated cross section, and the seal diaphragm 10 having substantially the same shape as the corrugation forms a space 10A between the right side surface of the main body 31 and is fixed at the periphery thereof. On the right side of the main body 31, the outer periphery of the seal diaphragm 10 is
A cover 19 is attached via a ring 18, and a pressure guiding tube 23 is connected to the cover 19.

[0006] The left main body 32 has substantially the same configuration as the above, and the space 10 in contact with the seal diaphragm 10 is provided.
The space defined by A, the holes 14 and 24, the recesses 11 and 21 and the holes 45 and 55 is filled with silicone oil (filled liquid) as a pressure transmitting medium.

In such a pressure measuring device, under certain conditions, some of the hydrogen atoms in the measurement fluid permeate through the seal diaphragm 10 and penetrate into the silicone oil side as the pressure transmitting medium, and The gas may accumulate inside and hinder accurate pressure measurement. In a serious case, a problem may occur that the pressure measurement itself is disabled.

[0008] The mechanism of the penetration and retention of the hydrogen gas into the silicone oil is presumed as follows. ^{M → M 2+ + 2e - ...} 2H + + 2e - → 2H ... 2H → H 2 ... That is, for example, is more of the metal of the seal diaphragm cover 19 of a metal 10 and impulse lines 23 is less noble (a large ionization tendency) First, as shown in the equation, the metal (M) of the cover 19 and the pressure guiding tube 23 elutes into the measurement fluid and emits electrons.

Next, the reaction that takes place is mainly based on the formula.

Therefore, if a reaction of the formula occurs on the seal diaphragm 10 side, most of the hydrogen atoms adsorbed on the surface thereof become molecular hydrogen based on the formula and become hydrogen gas. This hydrogen gas cannot pass through the seal diaphragm 10 due to the size of the molecule. However, some hydrogen atoms diffuse in the seal diaphragm 10 at the stage of the equation, that is, in the state of hydrogen atoms, and penetrate and penetrate to the silicone oil side, and then become hydrogen gas and enter the inside of the detection unit. Will accumulate.

Hitherto, in order to prevent hydrogen permeation through the seal diaphragm, it has been proposed to coat gold (Au) on the surface of the seal diaphragm 10 on the side of the fluid to be measured by plating or the like (Japanese Utility Model Application Laid-Open No. 62-86528). ).

[0012]

Problems to be Solved by the Invention
No. 8, the permeation of hydrogen through the seal diaphragm is prevented to some extent by the Au coating, but the following problems occur.

[0013] The metal constituting the vicinity of the diaphragm, which is more electrically noble than mainly stainless steel, Hastelloy, etc.,
That is, by coating Au having a small ionization tendency on the seal diaphragm, for example, an electric circuit due to the electric difference is formed between Au and the cover 19, and the metal dissolves in the measurement fluid as described above. To emit electrons. That is, the above reaction occurs. Next, hydrogen is adsorbed on the Au coating film surface according to the formula.

The Au coating film has the effect of preventing the diffusion and permeation of the adsorbed hydrogen. However, in practice, the coating thickness is reduced from the viewpoint of cost and the pressure responsiveness of the seal diaphragm. There is also a limit, and it is difficult to reliably prevent hydrogen permeation.

In addition, the Au plating film always has a problem of a pinhole in the film. Even when a very small portion of the Au plating film directly contacts the seal diaphragm and the measurement fluid due to the pinhole of the Au plating film, as described above. A local battery is formed by the electric circuit, and the seal diaphragm itself causes local corrosion. In particular, the thickness of the seal diaphragm
Normally, the thickness is about 0.1 mm, and a hole may be formed in the seal diaphragm itself due to corrosion, which may make measurement impossible. By forming a thick Au plating film,
Although it is possible to prevent the formation of pinholes, considering the performance of the transmitter, the thickness of the Au diaphragm is limited because the seal diaphragm thickness is limited, and it is extremely difficult to completely eliminate pinholes. Difficult.

The present invention solves the above-mentioned conventional problems and reliably prevents the permeation of hydrogen through the seal diaphragm.
It is an object of the present invention to provide a pressure measuring device capable of always performing accurate pressure measurement by protecting a seal diaphragm.

[0017]

According to a first aspect of the present invention, there is provided a pressure measuring apparatus provided with a seal diaphragm for isolating a fluid whose pressure is to be measured and a medium for transmitting pressure to a pressure detecting section. A hydrogen permeation preventing metal layer, an intermediate metal layer, and an insulating layer are sequentially laminated and coated on the surface of the seal diaphragm on the measurement fluid side such that the insulation layer is on the measurement fluid contact side, and the intermediate metal layer is It has a higher ionization tendency than the metal constituting the hydrogen permeation preventing metal layer, and has a linear expansion coefficient between the linear expansion coefficient of the metal constituting the hydrogen permeation preventing metal layer and the linear expansion coefficient of the material constituting the insulating layer. Characterized by comprising a metal having

According to a second aspect of the present invention, in the pressure measuring device according to the first aspect, the hydrogen permeation preventing metal layer is made of gold or tungsten.

In a third aspect of the present invention, the intermediate metal layer is made of titanium, tungsten, chromium, molybdenum, niobium, tantalum, zirconium or nickel. .

According to a fourth aspect of the present invention, there is provided a pressure measuring device according to any one of the first to third aspects, wherein the insulating layer is made of ceramics.

According to a fifth aspect of the present invention, there is provided a pressure measuring device as set forth in any one of the first to third aspects, wherein the insulating layer is made of S
iC, Al ₂ O ₃ , AlN, SiO ₂ , BN, ZrO ₂
Or, it is characterized by being made of Si ₃ N ₄ .

[0022]

In the pressure measuring device according to the present invention, the permeation of hydrogen to the seal diaphragm is prevented by the hydrogen permeation preventing metal layer.

On the other hand, the outermost insulating layer ensures corrosion resistance and prevents an electrochemical reaction on the surface on the side of the measurement fluid.

By providing an intermediate metal layer between the insulating layer and the hydrogen permeation preventing metal layer, the following operation and effect can be obtained.

Since the intermediate metal layer is made of a metal having a higher ionization tendency than the constituent metal of the hydrogen permeation preventing metal layer, the potential difference from the diaphragm main body is reduced by the intermediate metal layer. That is, (potential difference between diaphragm main body and hydrogen permeation preventing metal layer)> (potential difference between diaphragm main body and intermediate metal layer). Thereby, galvanic corrosion due to formation of a local battery is reduced.

The intermediate metal layer is formed of a metal having a linear expansion coefficient between the linear expansion coefficient of the metal constituting the hydrogen permeation preventing metal layer and the linear expansion coefficient of the insulating layer forming material. For this reason, stress due to the difference in linear expansion coefficient between the hydrogen permeation preventing metal layer and the insulating layer is reduced, and the adhesion of the coating layer is improved.

In the present invention, the hydrogen permeation preventing metal layer is preferably made of gold (Au) or tungsten (W), and the intermediate metal layer is made of titanium (Ti), W, chromium (Cr), molybdenum (W). Mo), niobium (Nb), tantalum (Ta), zirconium or nickel (Ni), and the insulating layer is made of ceramics, especially S
iC, Al ₂ O ₃ , AlN, SiO ₂ , BN, ZrO ₂
Alternatively, it is preferable to be made of Si ₃ N ₄ . The thickness of each layer is determined by the combination of materials or the environmental conditions used within a range that does not impair the response characteristics of the diaphragm.

[0028]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an enlarged sectional view of a seal diaphragm portion (a portion corresponding to I in FIG. 2) according to an embodiment of the pressure measuring device of the present invention.

This pressure measuring device has the same configuration as the conventional pressure measuring device shown in FIG. 2 except that a specific three-layer coating layer is formed on the seal diaphragm.

Reference numeral 32 denotes a diaphragm main body, 10 denotes a seal diaphragm, 10A denotes a pressure transmitting medium (silicone oil) sealed portion, and 30A denotes a measurement fluid retaining portion. A hydrogen permeation preventing metal layer 1, an intermediate metal layer 2, and an insulating layer 3 are sequentially laminated and coated on the surface of the seal diaphragm 10 on the measurement fluid side such that the insulation layer 3 is on the measurement fluid contact side.

The metal constituting the hydrogen permeation preventing metal layer 1 is not particularly limited as long as hydrogen does not easily diffuse or does not diffuse, and examples thereof include Au and W. Preferably, Au is suitable.

The material constituting the insulating layer 3 is preferably a non-conductive ceramic. In particular, SiC, Al ₂ O ₃ , AlN, SiO ₂ , S
i ₃ N ₄ , BN, ZrO _{2 and the} like are preferred.

The metal constituting the intermediate metal layer 2 is electrically lower than the metal constituting the hydrogen permeation preventing metal layer 1,
And has a linear expansion coefficient between the linear expansion coefficient of the metal forming the hydrogen permeation preventing metal layer 1 and the linear expansion coefficient of the material forming the insulating layer 3.
For example, when the hydrogen permeation preventing metal layer 1 is formed of Au, the intermediate metal layer 2 is made of Ti, W, Cr, Ni, Zr, or the like.
It is preferable to use Ta, Nb, Mo, or the like.

The linear expansion coefficient of general ceramics that can be used as the insulating layer 3, the linear expansion coefficient of Au suitable as the hydrogen permeation preventing metal layer 1, and the linear expansion coefficient of the metal suitable for the intermediate metal layer 2 are shown in Table 1 below. It is as follows.

[0035]

[Table 1]

The intermediate metal layer materials shown in Table 1 are all electrically lower than Au.

In the present invention, the metal layer for preventing hydrogen permeation is A
u plating, vapor deposition, sputtering, CVD, ion implantation, ion plating, etc., the intermediate metal layer is formed by vapor deposition, sputtering, CVD, ion implantation, ion plating, etc., and the insulating layer is vapor deposition, sputtering, CV
D, ion implantation, ion plating or the like is preferable.

The seal diaphragm 10 is generally made of stainless steel, Hastelloy, Monel, tantalum or the like.

Hereinafter, the present invention will be described more specifically with reference to specific examples.

EXAMPLE 1 As shown in FIG. 1, Au was formed to a thickness of 3 μm as a hydrogen permeation preventing metal layer, Ti was formed to a thickness of 0.5 μm as an intermediate metal layer, and an insulating layer was formed on the surface of the seal diaphragm. A hydrogen permeation acceleration test was performed on an SiC (silicon carbide) formed to a thickness of 0.8 μm (No. 1) under accelerated test conditions, and the output drift of the pressure measurement device reached 0.5%. The results were shown in Table 2.

For comparison, a seal diaphragm coated with only Au to a thickness of 4.3 μm (No. 2)
The same test was carried out for the sample having no coating (No. 3), and the results are shown in Table 2.

[0042]

[Table 2]

From Table 2, the following is clear. In other words, the use of only the Au coating prevents hydrogen permeation as compared with the case of no coating, but has a limited effect. In contrast, according to the present invention, A
With u, Ti, and SiC coatings, there is no abnormality even after 3000 Hr, which is twice the conventional product, and the effect of the present invention is clear.

[0044]

As described above in detail, according to the pressure measuring device of the present invention, the hydrogen permeation preventing metal layer, the intermediate metal layer and the insulating layer reliably prevent the permeation of hydrogen and also prevent galvanic corrosion. Is done. Moreover, the coating film has excellent corrosion resistance, adhesion, and durability.

Therefore, according to the present invention, the intrusion of hydrogen gas into the pressure transmitting medium is reliably prevented for a long time, and accurate pressure measurement is guaranteed.

Further, according to the configuration of the present invention, the thickness of the hydrogen permeation preventing metal layer made of an expensive metal such as Au can be reduced, which is extremely advantageous in terms of cost.

In particular, according to the pressure measuring devices of the second to sixth aspects, more excellent effects can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged sectional view of an essential part for explaining a pressure measuring device according to an embodiment of the present invention.

FIG. 2 is a sectional view of a pressure measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal layer preventing hydrogen permeation 2 Intermediate metal layer 3 Insulating layer 10 Seal diaphragm

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kimihiro Nakamura 1 Fujimachi, Hino City, Tokyo Inside Fuji Electric Co., Ltd. (72) Inventor Masao Saito 2-2-1 Nagasaka, Yokosuka City, Kanagawa Prefecture Fuji Electric Co., Ltd. (56) References JP-A-4-348243 (JP, A) JP-A-62-286528 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01L 13/00

Claims (5)

(57) [Claims] 1. A pressure measuring apparatus provided with a seal diaphragm for isolating a fluid whose pressure is to be measured and a medium for transmitting pressure to a pressure detecting section, wherein a surface of the seal diaphragm on a measurement fluid side has hydrogen permeation. An anti-metal layer, an intermediate metal layer and an insulating layer are sequentially laminated and coated such that the insulating layer is on the measurement fluid contact side, wherein the intermediate metal layer is more electrically conductive than the metal constituting the hydrogen permeation preventing metal layer. Pressure measurement characterized by comprising a metal having a coefficient of linear expansion intermediate between the coefficient of linear expansion of the metal constituting the hydrogen permeation preventing metal layer and the material constituting the insulating layer. apparatus. 2. The pressure measuring device according to claim 1, wherein the hydrogen permeation preventing metal layer is made of gold or tungsten. 3. The device according to claim 1, wherein
A pressure measuring device, wherein the intermediate metal layer is made of titanium, tungsten, chromium, molybdenum, niobium, tantalum, zirconium or nickel. 4. The pressure measuring device according to claim 1, wherein the insulating layer is made of ceramics. 5. The device according to claim 1, wherein the insulating layer is made of SiC, Al ₂ O ₃ , Al.
N, SiO _2, BN, pressure measuring device characterized by consisting of ZrO ₂ or Si ₃ N _4.