JPH02231539A - Differential pressure detecting device - Google Patents

Abstract

PURPOSE:To properly display a protecting function even at high temperatures by giving a protection diaphragm, which protects a detection part, a larger coefficient of thermal expansion than a member which is joined integrally with the outer peripheral parts of a left and a right side. CONSTITUTION:The detecting device consists of a detection part 20 and a protection part 30, which are connected through conduit pipes 6 and 7. The detection part 20 converts differential pressure to be measured into an electric signal and outputs the signal. The protection part 30 is provided with the protection diaphragm 3 for protecting the detection part 20. The projection diaphragm 3 has the larger coefficient of thermal expansion than main bodies 31 and 32 and when the main bodies 31 and 32 are made of martensite stainless steel, the protection diaphragm 3 is made of austenite stainless steel. Thus, the protecting function of the protection diaphragm is properly displayed even at high temperatures.

Description

[Detailed description of the invention] [Industrial application field]

The present invention provides a detection unit that includes a detection unit that outputs a signal according to a differential pressure to be measured, and a protective diaphragm that is installed externally to the detection unit and protects the detection unit from each introduced pressure that causes a pressure difference. The present invention relates to a differential pressure detection device, and particularly to a differential pressure detection device improved to suppress zero point fluctuation. Note that this differential pressure detection device can be used as a pressure detection device for gauge pressure or absolute pressure because one of the introduced pressures is atmospheric pressure or vacuum.

[Conventional technology]

The conventional device will be explained with reference to the sectional view of this drawing. In FIG. 1, the conventional device can be roughly divided into a detection section 20 and a protection section 30, which are connected via a pressure impulse pipe 6.7. The detection section 20 converts the differential pressure to be measured into an electrical signal and outputs it, and the protection section 30 protects the detection section 20 against the introduced pressure, which will be described in detail later. Since the configuration of this detection unit 20 is well known, its explanation will be omitted. Although there is another conventional device in which the detection section 20 is installed inside the protection section 30, the purpose of the configuration in which the detection section 20 is installed outside the protection section 30 is to prevent This is to prevent the detection unit 20 from being affected by temperature. Now, the protection part 30 mainly consists of a main body 31, 32, a protection diaphragm 33, seal diaphragms 4, 5, an O-ring 8, and a cover 9. Here, the main body 31.32
The members of each of the seal diaphragms 4.5 and 4.5 having the same name are the same, and there are two O-rings 8 and two covers 9. Main bodies 31 and 32 are disposed on the left and right sides with the protective diaphragm 33 in between, and are joined to each other at their outer peripheries or peripheral edges. Also, the main bodies 31 and 32 have the same recesses 11 and 2, respectively.
1, holes 14.24 and 45.55 are formed. More specifically, the zero body 31 on the right side will be described as a representative example as follows. The recess 11 is formed coaxially with the left side of the main body 31 in the shape of a pot, the hole 14 passes through the main body 31 along its axis, the hole 45 opens near the outer periphery of the recess 11 on one side, and the hole 45 opens near the outer periphery of the recess 11 on the other. It passes through the pressure guide pipe 6 and communicates with a pressure guide space (not shown) of the detection section 20 . The right side surface of the zero body 31 has a wave-shaped cross section, and a seal diaphragm 4 having a shape substantially the same as the wave shape is fixed at its periphery with a space between it and the right side surface of the zero body 3I. A cover 9 is attached to the outer peripheral edge of the seal diaphragm 4 on the right side of the zero body 31 via an O-ring 8. The above is substantially the same for the zero body 32 on the left side. Spaces in contact with the seal diaphragms 4, 5, holes 14, 24, recesses 11, 21, and holes 45.5
Each of the spaces 5 is filled with silicone oil (filling liquid) as a pressure transmitting fluid. The operation of this conventional device is as follows. differential pressure flowmeter,
For example, each inlet pressure (including static pressure) on each side of the orifice
are received by the seal diaphragms 4 and 5, respectively, and the introduced pressure passes through the space in contact with the seal diaphragm 4, the hole 14, the recess 11, and the hole 45, respectively, and is detected by the detection unit 20.
The pressure is transmitted to the other pressure guiding space of the detection unit 20 through the space in contact with the seal diaphragm 5, the hole 24, the recess 21, and the hole 55. In addition, the seal diaphragm 4.5 has an extremely small spring constant (soft),
The detection diaphragm (not shown) of the detection section has an extremely large spring constant (rigid <), and the protection diaphragm 33 has a spring constant that is intermediate between the above two values. In the detection unit 20, the differential pressure based on each introduced pressure is converted into an electrical signal by a well-known method, for example, a capacitance method, and is output. The above is a case where the pressure introduction operation is performed normally. However, due to an incorrect operation, the right seal diaphragm 4
If only the protective part 30 is not present, then
The detection unit 20 may receive a large one-sided pressure and the sensor may be destroyed. Even if there is an error in introducing each pressure on both sides of the orifice and only one pressure is received by the seal diaphragm, the protection part 30 protects the detection part 20 by the following operation. In FIG. 1, if only the seal diaphragm 4 receives pressure, this pressure will be 7L 14 ,
The air is transmitted from the recess 11 via the protective diaphragm 33 to the recess 21 and hole 24 on the left side, inflating the seal diaphragm 5. On the other hand, it is transmitted through the hole 45 to the pressure guiding space on the right side of the detection unit 20 . However, this transmitted pressure is limited to a certain value or less by the contact between the seal diaphragm 4 and the right corrugated surface of the opposing zero body 31, so there is no risk of the sensor being destroyed and the protective function has worked. become.

[Problem to be solved by the invention]

However, in the conventional device as described above, the following problem occurs at high temperatures. In other words, the filled liquid expands,
Almost all of this expansion is caused by each seal diaphragm 485
In other words, the volume of this space expands. Therefore, if the above-mentioned one-sided pressure acts in this state, the protective function of the protective diaphragm 3 will be inhibited. In addition, if the coefficient of thermal expansion of the protective diaphragm 3 is the same or smaller than that of the main body 31. 32 in the radial direction, a radial stress is generated in the protective diaphragm 3, which stress contributes to the above-mentioned impairment of the protective function. The reason why the radial stress generated in the protective diaphragm 3 inhibits the protective function is as follows. Now, if σ is the stress in the radial direction, P is the one-sided pressure, and W is the displacement of the protective diaphragm, then W-=P/(C+Kσ)...(1)
Here, C is Young's modulus, Poisson's ratio, and plate thickness of the protective diaphragm. A constant determined by the diameter, K is also the thickness of the plate. It is a constant determined by the diameter. Therefore, as the stress σ increases, the displacement W decreases.
In other words, the protective diaphragm will operate more stiffly, and this stiffness means a reduction in the protective function. An object of the present invention is to provide a differential pressure detection device that solves the above-mentioned problems of the conventional technology and that properly exhibits its protective function even at high temperatures.

[Means to solve the problem]

In order to solve this problem, the differential pressure detection device according to the present invention includes a detection section that outputs a signal according to the differential pressure to be measured, and a detection section that is installed externally to this detection section and responds to the introduction pressure that produces the differential pressure. and a protective diaphragm for protecting the detection section, wherein the protective diaphragm has a coefficient of thermal expansion larger than a member integrally joined at its outer peripheral portion on each of the left and right sides.

[For use]

Since the protective diaphragm has a larger coefficient of thermal expansion than the members integrally joined at its outer periphery on each side of the protective diaphragm, at high temperatures the protective diaphragm is stretched by this due to the difference in thermal expansion of the members. As a result, the protective diaphragm has a larger displacement when subjected to one-sided pressure; in other words, it operates more softly, and its protective function is properly exerted.

【Example】

An embodiment of the differential pressure detection device according to the present invention will be described with reference to FIG. 1, which is a side sectional view. Note that FIG. 1 is the same as the side sectional view of the conventional device described above. It is assumed that the protective diaphragm 3 in FIG. 1 has a coefficient of thermal expansion greater than that of the main body 31,32. For example, when the material of the main bodies 31 and 32 is SUS430, which is a type of martensitic stainless steel, the material of the protective diaphragm 3 is selected to be SUS301, which is a type of austenitic stainless steel. By the way, the thermal expansion coefficient of SUS430 is 10.4 x 10-6/”C,
S[IS301 is 16.9X10-6/"C. At that time, if the protective diaphragm 3 has a stress change Δσ in the radial direction due to the temperature change ΔT, then Δσ−EΔT・Δα/(1−ν) ...(2) Here, E: Young's modulus of the protective diaphragm, ν: Boisson's ratio, △α: difference in thermal expansion coefficient between the main body and the protective diaphragm (Δα<0). ΔT>0, Δα O, Δσ<0, that is, decreases. Therefore, according to equation (1), the protective diaphragm increases its displacement W for the same one-sided pressure P, in other words, it operates more softly. means that the protective function of the protective diaphragm is properly demonstrated at high temperatures.

【Effect of the invention】

Therefore, according to the present invention, compared to the conventional technology,
It has excellent effects in that it properly exhibits its protective function even at high temperatures, and can be achieved at low cost due to its simple structure.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view commonly showing the configurations of an embodiment according to the present invention and a conventional example. Code explanation

Claims (1)

[Claims] 1) A detection unit that outputs a signal according to the differential pressure to be measured;
In the device, the protection diaphragm is provided externally to the detection part and protects the detection part from the introduction pressure that causes the pressure difference, and the protection diaphragm is integrally formed on the outer periphery on each side of the detection part. A differential pressure detection device characterized by having a coefficient of thermal expansion larger than that of a member to be joined to the device.