JPH03223639A - Differential-pressure detecting device - Google Patents

Abstract

PURPOSE:To make it possible to measure pressure difference highly accurately in a broad temperature range by providing a receiving surface at a facing position that is separated from a diaphragm at a specified distance at the inner surface of a sealing diaphragm. CONSTITUTION:A corrugated receiving surface 12a which is formed on the right end surface of a main body 12 is provided so that a distance to a sealing diaphragm 4 is a specified distance and the surface can be moved in parallel in the leftward direction. Namely, the specified distance is selected so that the sealing diaphragm is sufficiently moved in a region wherein pressure/capacity characteristics are linear even under the expansion and contraction of sealed liquid due to temperature change. Thus, the inner surface of the sealing diaphragm 4 faces the corresponding receiving surface 12a at a certain distance. Therefore, the operation is carried out in the region wherein the pressure/capacity characteristics, i.e. the changing rates between the pressure and the capacity, are linear even if the sealed liquid is expanded and contracted by the temperature change. As a result, the actually acting differential pressure has the linear relationship with the differential pressure to be measured, and a detecting part can output the signal which is in proportion to the differential pressure to be measured.

Description

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

The present invention includes a detection section that outputs a signal according to the differential pressure to be measured, a seal diaphragm that is installed externally to the detection section and receives each introduction pressure related to the differential pressure, and a seal diaphragm that protects the detection section from excessive pressure. The present invention relates to a differential pressure detection device that is equipped with a protective diaphragm that can measure differential pressure with high precision over a particularly wide temperature range.

[Conventional technology]

The conventional device will be explained with reference to FIG. 4, which is a sectional view of this device. In FIG. 4, the conventional device is roughly divided into a detection section 2o and a protection section 3o, which are connected via pressure impulse pipes 6 and 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 2o 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 2o is installed outside the protection section 3o is to prevent This is to prevent the influence of temperature from reaching the detection section 2o. Now, the protection part 30 mainly consists of each main body 31, 32, a protection diaphragm 3, each seal diaphragm 45.0 ring 8, and a cover 9. Here, each main body 3L32 and each seal diaphragm 4, 5 are the same members, and there are two O-rings 8 and two covers 9. Main bodies 31 and 32 are respectively disposed on the left and right sides with the protective diaphragm 3 in between, and are joined to each other at their respective outer peripheries or peripheral edges. Further, each main body 3L32 has the same recessed portions 11.
21, reply 14.24 and reply 45, 55 are formed. More specifically, the main body 31 on the right side will be described as follows. The recess 11 is formed coaxially with the left side of the main body 31 in a forest shape, the hole 14 passes through the main body 31 along its axis, and the hole 45 opens near the center of the recess II of the hole I4. , and on the other hand, it passes through the pressure guide pipe 6 and communicates with a pressure guide space (not shown) of the detection unit 20 . The right side of the main body 31 has a wave-shaped cross section, and a seal diaphragm 4 having substantially the same shape as the wave is fixed at its periphery with a space between it and the right side of the main body 31. Main body 31
A cover 9 is attached to the outer peripheral edge of the seal diaphragm 4 on the right side of the seal diaphragm 4 via an O-ring 8. The above is substantially the same for the left main body 32. The spaces in contact with each seal diaphragm 45, the recesses 14 and 24, the recesses 11 and 21, and the recesses 4,
Each of the spaces consisting of 5.55 mm 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 respectively received by the seal diaphragm 4.5, the respective introduced pressures are applied to the spaces and holes 14.5 in contact with the seal diaphragm 4, respectively. Recessed portion 11. Detection unit 20 through hole 45
, and the space in contact with the seal diaphragm 5, the hole 24° and the recess 21. The pressure is transmitted through the hole 55 to the other pressure guiding space of the detection unit 20 . In addition, each seal diaphragm 4, 5 has an extremely small spring constant (soft <).
The detecting diaphragm (not shown) of the detecting section has an extremely large spring constant (stiffness<), and the protective diaphragm 3 has a spring constant 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 the case when the pressure introduction cycle 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. 4, if only the seal diaphragm 4 receives pressure, this pressure is transmitted to the hole 14 through the sealed liquid. Recess 1
1 on the one hand through the protective diaphragm 3 into the left-hand recess 21. It is transmitted through the hole 24 and inflates 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 seal diaphragm 4 coming into contact with the corrugated surface on the right side of the opposing body 31, so there is no risk of the sensor being destroyed and the protective function has worked. It turns out.

Problem to be Solved by the Invention I In the conventional technology as explained above, each seal diaphragm 4, 5 is charged with each pressure P1°P2 (PI
>P2) is activated, the replies 14, 45 and 24.
Each pressure Psl transmitted to the detection unit 20 via 55,
Ps2 changes by each pressure transmission loss LL, L2 of each seal diaphragm 4.5. Now, the rate of change of pressure with respect to capacity for each seal diaphragm 4 and 5 is Kl, respectively, and 2, and the initial pressure (value obtained by dividing the initial force in the axial direction by the area) is Jl and J2, respectively, and the movement of the filled liquid. If the quantity is ■, Ll = KI V + J1, L2 =
- Since 2 V + J2, Psi-PI -KI V-JI Ps2 = P2 + 2 V-J2 Therefore, Psi-Ps2 = (PI - P2) - (Kl + 2 V-J2
) V-(Jl-J2)...(1
) Now, the change in capacity Vi related to the protective diaphragm 3,
Since both capacitance changes Vp related to a measurement diaphragm (not shown) of the detection unit 20 are proportional to (Psi-Ps2), they can be expressed as follows with Cm and Cp being constants. Psi −Ps2= C+a Vn+ = Cp Vp
Also, since V = V + a + Vp, Psi
−Ps2=CV・”(2)
Here, CmCm Cp / (CRI + CI))
2 If we eliminate V from (1) and (2), we get Psi-Ps
2-((PL-P2)-(Jl-J2))/
(1+ (Kl 102) C)=A (Pi −
P2) -B...(3) Here, A=1
/ (1+ (2 to Kl +)C), B=(Jl −
J2 ) / (1 + (2 to Kl +) C) By the way, in the conventional example, when measuring differential pressure at high or low temperatures, the operating range of the seal diaphragm deviates from the linear range due to swelling and contraction of the filled liquid. There is a risk of partial deviation. FIG. 5 is a pressure/capacity characteristic diagram of a conventional seal diaphragm, in which the horizontal axis represents pressure P and the vertical axis represents capacity V. In FIG. 5, A indicates the operating range of the seal diaphragm at room temperature, B indicates the operating range at high temperature, and C indicates the operating range at low temperature. B and C move from A due to swelling and contraction of the sealed liquid due to a temperature change from room temperature, and some of B and C include nonlinear characteristic portions. This shows that 2 is not a constant for Kl in equation (3), and (Psi-Ps2) is (
The relationship is no longer linear with respect to (PI-P2), and (P s
This means that measurements based on l - P s2) will result in errors. It is an object of the present invention to provide a differential pressure detection device that solves the above-mentioned problems of the conventional technology and is capable of measuring differential pressure with high accuracy over a wide temperature range. [Means for Solving 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 externally installed in the detection section. In an apparatus comprising a seal diaphragm that receives each introduction pressure related to the differential pressure, a protection diaphragm that protects the detection section from excessive pressure, and a sealed liquid that fills the internal space, the inner surface of each of the seal diaphragms is At least at the center thereof, there are receiving surfaces located opposite each other at a distance such that the seal diaphragm can operate in a linear region of its pressure/capacitance characteristics under swelling and contraction of the sealed liquid due to temperature changes.

[For use]

Since the inner surface of each seal diaphragm and the corresponding receiving surface face each other at a certain distance, the operation of each seal diaphragm under expansion and contraction of the filled liquid due to temperature changes depends on its pressure and capacity characteristics. It takes place in a linear area. As a result, the differential pressure actually acting on the detection section has a linear relationship with the differential pressure to be measured, and the detection section can output a signal proportional to the differential pressure to be measured.

【Example】

A first embodiment of the differential pressure detection device according to the present invention will be described with reference to FIG. 1, which is a sectional view of the main parts thereof. The difference between the first embodiment and the conventional example shown in FIG. 4 is the positional relationship of each end face portion of the main body with respect to the seal diaphragm. In FIG. 1, the main body constituting the protection part is typically shown in cross section of the end face of the main body 12 on the right side, and the illustration of the main body on the left side is omitted. Note that the main body 12 corresponds to the main body 31 in the conventional example shown in FIG. In FIG. 1, the distance between the wave-shaped receiving surface 12a formed on the right end surface of the main body 12 and the seal diaphragm 4 is 0.3.
It is carved in parallel to the left from the position in the conventional example so that the distance is 0.5 mm. In other words, the above-mentioned distance of 0.3 to 0.5 mm allows each seal diaphragm to operate in a region where its pressure/capacitance characteristics are linear even when the sealed liquid expands or contracts due to temperature changes. It was selected so that it was sufficient for The operation of the seal diaphragm 4 is such that its inner surface (the left side in the figure) and the corresponding receiving surface 12a face each other at the above-mentioned distance, so that even when the sealed liquid expands or contracts due to temperature changes, , the pressure/capacitance characteristics, that is, the rate of change of pressure with respect to capacity, occur in a linear region as will be described later. That is, Kl in equation (3) is completely constant. As a result, the detection section 20 has a linear relationship between the differential pressure actually acting thereon and the differential pressure to be measured, and can output a signal proportional to the differential pressure to be measured. FIG. 3 is a pressure/capacity characteristic diagram of the seal diaphragm in the first embodiment, which is common to the second embodiment described below. In FIG. 3, since the range of movement of the seal diaphragm is expanded, the linear range is also expanded. As a result, the operating ranges B and C of the seal diaphragm at high and low temperatures are both within linear ranges with respect to the operating range A at room temperature. This shows that highly accurate differential pressure measurement is possible over a wide temperature range. FIG. 2 is a sectional view of the end face of the right main body 22 in the second embodiment. The main body 22 of this second embodiment differs from the main body 12 of the first embodiment in that a receiving surface 22 formed on the end surface
A has a concave waveform. Receiving surface 2
The distance between the seal diaphragm 2a and the seal diaphragm 4 is maximum at the center, and on average is the same as the value in the first embodiment, ranging from 0.3 to
0.5 saliva. The operation of the second embodiment is the same as that of the first embodiment, and its pressure/capacity characteristics are commonly shown in FIG. 3, which has already been described.

【Effect of the invention】

As explained above, in this invention, since the inner surface of each seal diaphragm and the corresponding receiving surface face each other at a certain distance, swelling of the sealed liquid due to temperature changes,
Under contraction, each seal diaphragm operates in a region where its pressure/capacitance characteristics are linear, and as a result, the sensing section has a linear relationship between the differential pressure actually acting on it and the differential pressure to be measured. , it is possible to output a signal proportional to the differential pressure to be measured. Therefore, according to the present invention, it is possible to measure differential pressure with high precision over a wider temperature range than with conventional techniques, and this invention has the advantage of being easily obtained by changing the shape of the main body member to which the seal diaphragm is welded or by additional processing. It has a positive effect.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a main part of a first embodiment according to the present invention, FIG. 2 is a cross-sectional view of a main part of a second embodiment, and FIG.
4 is a sectional view of the conventional example, and FIG. 5 is a pressure/capacity characteristic diagram of the seal diaphragm of the conventional example. Symbol explanation 3: Protective diaphragm, 4: Seal diaphragm, Figure 2, Figure 3, Figure East, Figure 5, Hyakko 4.

Claims (1)

[Claims] 1) A detection unit that outputs a signal according to the differential pressure to be measured;
In a device comprising: a seal diaphragm that is installed externally to the detection section and receives each introduction pressure related to the differential pressure; a protection diaphragm that protects the detection section from excessive pressure; and a sealed liquid that fills the internal space. facing at least the center of the inner surface of each of the seal diaphragms at a distance such that the seal diaphragm can operate in a linear region of its pressure/capacitance characteristics under expansion and contraction of the sealed liquid due to temperature changes; A differential pressure detection device characterized by comprising a receiving surface that is positioned.