JPH07128170A - Differential pressure detector - Google Patents

Abstract

PURPOSE:To lower output errors which are attributed to a gap generated at a contact part between a protective diaphragm and a main body due to a welding and will be caused by changes in ambient temperature and variations in introduction pressure. CONSTITUTION:When a protective diaphragm 3 having a concentric circular groove 3a and individual main bodies 31 and 32 are welded together on the outer circumference, a protective diaphragm 3 with a larger heat expansion modulus expands larger thermally than the bodes 31 and 32 radially and the heat expansion component causes a groove 3a to deform. That is, the heat expansion component is absorbed by the groove 3a. As a result, a bending stress left in the protective diaphragm 3 after the welding is lowered eventually minimizing a gap generated at a contact part between the protective diaphragm 3 and the bodies 31 and 32. This enables the lowering of output errors which are attributed to the gap and will be caused by changes in ambient temperature and variations in introduction pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detecting device comprising a differential pressure detecting portion, a protective portion having a protective diaphragm, and a main body with a seal diaphragm pressure receiving portion, and a difference in thermal expansion coefficient between the protective diaphragm and the main body and welding. Due to non-uniformity and unevenness along the outer circumference of the protective diaphragm of the part, a gap is created at the contact part between the protective diaphragm and the main body after welding, and this gap causes changes in the ambient temperature and fluctuations in the introduced pressure. The present invention relates to a differential pressure detecting device improved so as to reduce an output error.

[0002]

2. Description of the Related Art FIG. 5 is a sectional view of a conventional example.
Will be described with reference to. In FIG. 5, the conventional example is roughly divided into a detection unit 20 and a protection unit 30, which are connected via pressure guiding pipes 6 and 7. The detection unit 20 converts the differential pressure to be measured by the capacitance method into an electric signal and outputs the electric signal.
Although the details of 30 will be described later, the detection unit 20 is protected against the introduced pressure. Since the configuration of the detection unit 20 is well known, description thereof will be omitted. Although there is another conventional device in which the detection unit 20 is internally provided in the protection unit 30, the purpose of the configuration in which the detection unit 20 is externally provided in the protection unit 30 is that when the measurement fluid has a high temperature. This is to prevent the influence of temperature from affecting the detection unit 20.

Now, the protection section 30 is mainly composed of the main bodies 31, 32.
, Protective diaphragm 3, each seal diaphragm 4,
5, an O-ring 8 and a pressure introducing process cover (hereinafter referred to as a cover) 9. Where each body 31,32
Further, the members having the same names of the seal diaphragms 4 and 5 are the same, and the O-ring 8 and the cover 9 are each two. The main bodies 31 and 32 are respectively arranged on the left and right with the protective diaphragm 3 sandwiched therebetween, and are joined to each other at their outer circumferences or peripheral portions.

Further, the same recesses 11 and 21, holes 14 and 24, and holes 45 and 55 are formed in the main bodies 31 and 32, respectively. More specifically, the main body 31 on the right side is described as follows. The recess 11 is formed on the left side surface of the main body 31 in the shape of a mortar that is coaxial therewith, the hole 14 penetrates the main body 31 along its axis, and the hole 45 opens on the one hand in the vicinity of the center of the recess 11 of the hole 14, and on the other hand Then, it penetrates the pressure guiding pipe 6 and communicates with a pressure guiding space (not shown) of the detection unit 20. A cross section of the right side surface of the main body 31 is formed in a corrugated shape, and a seal diaphragm 4 having substantially the same shape as the corrugated shape is fixed to the right side surface of the main body 31 at a peripheral edge thereof with a space. A cover 9 is provided on the right side of the main body 31 on the outer peripheral edge of the seal diaphragm 4 via an O-ring 8.
Is attached. The above is substantially the same for the left main body 32. Then, the space that is in contact with the seal diaphragms 4 and 5, 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 fluid. To be done.

The operation of this conventional example is as follows. When a differential pressure flow meter, for example, each introduction pressure (including static pressure) on both sides of the orifice is received by each seal diaphragm 4 and 5, each introduction pressure is applied to the space and the hole 14 in contact with the seal diaphragm 4. Then, through the recess 11 and the hole 45, into the pressure-inducing space on one side of the detection unit 20, and also the seal diaphragm 5
Is transmitted to the other pressure guiding space of the detection unit 20 through the space in contact with the hole 24, the recess 21, and the hole 55. The seal diaphragms 4 and 5 have extremely small spring constants (soft), the detection diaphragm (not shown) of the detection unit 20 has extremely large spring constant (rigid), and the protective diaphragm 3 has the spring constant. Takes an intermediate value between the above two. In the detection unit 20,
The differential pressure based on each introduced pressure is converted into an electric signal by a well-known capacitance type and is output. The above is the case where the normal pressure introduction operation is performed.

However, if only the right seal diaphragm 4 receives a pressure due to an erroneous operation, if the protective portion 30 is not provided, the detection portion 20 may receive a large one-sided pressure and the sensor may be destroyed. Even if only one of the pressures is received by the seal diaphragm due to an erroneous operation in introducing each pressure on both sides of the orifice, the protection unit 30 protects the detection unit 20 by the following operation. Now, assuming that only the seal diaphragm 4 receives pressure, this pressure is
On the other hand, the sealing diaphragm 5 is inflated by being transmitted from the hole 14 and the concave portion 11 through the filled liquid and the protective diaphragm 3 through the concave portion 21 and the hole 24 on the left side. On the other hand, the hole 45
Is transmitted to the pressure guiding space on the right side of the detection unit 20 via. However, this transmission pressure is limited to a certain value or less by the contact of the seal diaphragm 4 with the corrugated surface on the right side of the opposing main body 31, so that there is no danger of the sensor being damaged and the protection function has been activated. Become.

By the way, the differential pressure detecting unit 20 of the conventional example detects the differential pressure based on the electrostatic capacitance formed between the measurement diaphragm and the silicon plate electrodes on each side, which is not shown. It Now, one introduction pressure is P1, the other introduction pressure is P2 (greater than P1), and the corresponding one capacitance value is C1,
If the other capacitance value is C2, C1 = εA / (d−Δd) C2 = εA / (d + Δd) where ε: permittivity of filled liquid, A: effective area of electrode,
d is the average gap amount between the measurement diaphragm and the electrode when pressure is not introduced, and Δd is the displacement amount of the measurement diaphragm when pressure is introduced. It is possible to know the differential pressure by obtaining an F value approximately expressed by the following equation through a well-known electronic circuit.

F = (C1−C2) / (C1 + C2) ≈Δd / d = k (P2−P1)

[0009]

In the conventional example, as shown in FIG.
As shown in detail in the side cross-sectional view of the main part of FIG. 3, the protective diaphragm 3 and each of the main bodies 31 and 32 are fixed to each other by Tig welding or plasma welding at the outer circumference of the joint. The part indicated by dots in the figure is the welded part, which is slightly offset to the right. Since the protective diaphragm 3 is a member that receives repeated pressure, it is made of stainless steel (type code:
A spring material such as SUS301CP) is used, and stainless steel SUS316 is used for each body 31, 32 in consideration of corrosion resistance and weldability. Where stainless steel SUS3
The thermal expansion coefficients of 01CP and stainless steel SUS316 are 16.9 × 10 ^-6 / ° C and 16.0 × 10 ^-6 / ° C, respectively.

Due to the difference in the coefficient of thermal expansion between the protective diaphragm 3 and each of the main bodies 31 and 32, and the unevenness and unevenness of the welded portion along the outer periphery of the protective diaphragm 3, the protective diaphragm 3 and each of the protective diaphragm 3 are not welded after welding. A gap is formed at the contact portion with the main bodies 31 and 32 as shown by the mechanism described below. That is, since the protective diaphragm 3 is not evenly heated on both sides and the thermal expansion due to heating is different from that of the main bodies 31 and 32, bending stress based on the residual thermal stress is generated in the protective diaphragm 3 after welding. A gap is created in the contact area between the two. If there is a change in ambient temperature or fluctuation in the introduced pressure, each main body 31, 32 and the cover 9
The tightening force of the bolts that fasten and fix the and changes, and the gap between the contact parts changes. This change in the gap causes displacement of the protective diaphragm 3 and further causes an output error.

The problem to be solved by the present invention is to solve the above-mentioned problems of the prior art, to make a difference in the thermal expansion coefficient between the protective diaphragm and the main body, and to make the welded portion uneven along the outer periphery of the protective diaphragm. Since a gap is created in the contact part between the protective diaphragm and the main body after welding due to the characteristics and bias, the difference improved to reduce the output error caused by the change in ambient temperature and the change in the introduced pressure due to this gap. It is to provide a pressure detection device.

[0012]

A differential pressure detecting device according to a first aspect of the present invention comprises a differential pressure detecting portion for detecting a differential pressure of each introduction pressure transmitted through a filled liquid, and a disc-shaped protective diaphragm. Protective part that has a main body with pressure receiving part that is sandwiched from both sides and welded together at the sandwiched outer peripheral part, and a protective part that protects the differential pressure detection part from each introduction pressure, and pressure introduction that is fastened and fixed by sandwiching this protective part from both sides In the device consisting of the process cover for use, the one with the larger coefficient of thermal expansion of the protective diaphragm and the main body
It has a concentric annular groove in its peripheral portion.

[0013]

In the differential pressure detecting device according to the first aspect, when the protective diaphragm and the main body are welded together at the outer periphery of the joint,
Due to the welding heat, the member with the larger thermal expansion coefficient
It expands more than the other side in the radial direction, but the part affected by this thermal expansion is up to the groove part, and the thermal expansion is accommodated by the deformation of this annular groove,
The effect does not reach the central part. As a result, the bending stress generated in the central portion of the protective diaphragm after welding can be reduced, and the deformation (gap) of the protective diaphragm can be reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the differential pressure detecting device according to the present invention will be described below with reference to the drawings. 1 is a side sectional view of a main part of the first embodiment, FIG. 2 is a side sectional view of a protective diaphragm of the first embodiment, and FIG. Here, in the first embodiment, it is assumed that the thermal expansion coefficient of the protective diaphragm 3 is larger than that of each of the main bodies 31 and 32. As the order of explanation, the shape of the protective diaphragm 3 will be described.
In FIG. 2, the protective diaphragm 3 of the first embodiment has concentric annular grooves 3a formed on both side surfaces thereof. In addition,
The groove 3a has a U-shaped cross section, but may have any other general V-shaped or semi-circular shape. Well, Figure 1
Returning to, the outer periphery of the joint between the protective diaphragm 3 and each of the main bodies 31 and 32 on both sides is welded to form a welded portion as shown by dots.

Therefore, the protective diaphragm 3 and the main bodies 31, 3 are
When 2 and 2 are welded together on the outer periphery of the joint, the welding heat generated by the 2 protects the protective diaphragm 3 with the larger coefficient of thermal expansion.
Is thermally expanded in the radial direction to a greater extent than each of the main bodies 31 and 32, and this thermal expansion causes deformation of the groove 3a, that is, the annular groove.
Absorbed by 3a. As a result, it is possible to reduce the bending stress remaining in the protective diaphragm 3 after welding, and it is possible to reduce the gap generated at the contact portion between the protective diaphragm 3 and each of the main bodies 31 and 32. Therefore, even if the protective diaphragm 3 has a coefficient of thermal expansion larger than that of each of the main bodies 31 and 32, and even if the welded portion has unevenness or unevenness along the outer circumference of the protective diaphragm 3, the It is possible to reduce the occurrence of a gap in the contact portion with each of the main bodies 31 and 32, and it is possible to reduce an output error caused by a change in ambient temperature or a change in introduced pressure due to the gap. It can be said that the position of the groove 3a should be as close to the welded portion as possible in order to absorb the thermal expansion. However, as shown in Fig. 1, even if the groove 3a is within the contact area between the protective diaphragm 3 and each of the main bodies 31 and 32, the groove 3a is displaced from the contact area toward the center side as shown by the broken line. However, there is only a slight difference in the degree of absorption.

FIG. 3 is a side sectional view of an essential part of the second embodiment. In FIG. 3, the second embodiment is different from the first embodiment in that the thermal expansion coefficient of each of the main bodies 31 and 32 is different from that of the protective diaphragm 3.
Is larger than that, and the annular groove is not formed on the protective diaphragm 3 side, but is formed on the main body 31, 32 side as annular grooves 31a, 32a, respectively. Grooves 31a, 32a of each body 31, 32 in the second embodiment
The action of is basically the same as the groove 3a of the protective diaphragm 3 in the first embodiment. Ie protective diaphragm
When 3 and each of the main bodies 31 and 32 are welded together at the outer periphery of the joint, due to the welding heat, each of the main bodies 31 and 32, which has a larger coefficient of thermal expansion, has a greater thermal expansion in the radial direction than the protective diaphragm 3. However, this thermal expansion causes deformation of the grooves 31a and 32a, that is, is absorbed by the grooves 31a and 32a. As a result, the gap can be reduced, and the same effect as the first embodiment,
That is, the effect of reducing the output error caused by the change of the ambient temperature and the change of the introduced pressure can be enhanced.

[0017]

In the differential pressure detecting device according to the first aspect of the present invention, when the protective diaphragm and the main body are welded together at the outer periphery of the joint, the member having a larger coefficient of thermal expansion is radially moved by the welding heat. However, the part that is affected by this thermal expansion is up to the groove part, and this annular groove deforms to accommodate the thermal expansion, and even the central part Not affected. as a result,
The bending stress generated in the central portion of the protective diaphragm after welding can be reduced, and the deformation (gap) of the protective diaphragm can be reduced. Therefore, even if there is a difference in the coefficient of thermal expansion between the protective diaphragm and the main body, or if the welded portion has unevenness or unevenness along the outer circumference of the protective diaphragm, the contact portion between the protective diaphragm and the main body after welding It is possible to reduce the occurrence of a gap in the space, and it is possible to reduce an output error caused by a change in the ambient temperature or a change in the introduced pressure due to the space.

[Brief description of drawings]

FIG. 1 is a side sectional view of an essential part of a first embodiment according to the present invention.

FIG. 2 is a side sectional view and (b) is a front view of the protective diaphragm of the first embodiment.

FIG. 3 is a side sectional view of an essential part of the second embodiment of the same.

FIG. 4 is a side sectional view of a main part in a conventional example.

FIG. 5 is a side sectional view of a conventional example.

[Explanation of symbols]

 3 Protective Diaphragm 3a Groove 20 Detecting Part 30 Protecting Part 31, 32 Main Body 31a, 32a Groove

Claims (1)

[Claims] 1. A pressure difference detecting section for detecting a pressure difference between respective introduction pressures transmitted through a filled liquid, and a pressure receiving section welded together with a disc-shaped protective diaphragm sandwiched from both sides. In a device comprising a protective unit having a main body with a protective unit for protecting the differential pressure detecting unit from each introduction pressure, and a pressure introducing process cover fastened and fixed so as to sandwich the protective unit from both sides,
A differential pressure detecting device, wherein one of the protective diaphragm and the main body, which has a larger coefficient of thermal expansion, has a concentric annular groove at its peripheral edge.