JP2540970B2 - Differential pressure detector - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention includes a detection unit that outputs a signal corresponding to a differential pressure to be measured, and a detection diaphragm that is provided outside the detection unit and that protects the detection unit against each introduced pressure that causes a differential pressure. The present invention relates to a differential pressure detecting device improved so as to suppress zero-point fluctuation and stress generated in a protective diaphragm at times. It should be noted that this differential pressure detection device becomes a pressure detection device for gauge pressure or absolute pressure because one of the introduction pressures is atmospheric pressure or vacuum.

[Prior art]

A conventional device will be described with reference to FIG. 4, which is a cross-sectional view. In FIG. 4, the conventional device is roughly divided into a detection unit 20 and a protection unit 30, which are each pressure guiding tube.
Connected via 6,7. The detection unit 20 converts the differential pressure to be measured into an electric signal and outputs the electric signal, and the protection unit 30 protects the detection unit 20 against the introduced pressure, which will be described later in detail. Since the configuration of the detection unit 20 is well known, its description is 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 part 30 mainly comprises the main bodies 31 and 32, the protection diaphragm 3, the seal diaphragms 4 and 5, the O-ring 8 and the cover 9. Here, the members having the same names of the main body 31, 32 and the seal diaphragms 4, 5 are the same,
There are two O-rings 8 and two covers 9. Main bodies 31 and 32 are respectively arranged on the left and right sides with the protective diaphragm 3 interposed therebetween, and are joined to each other at their outer circumferences or peripheral portions. In addition, the same recesses 11, 21 and holes 1 are provided in the main bodies 31, 32, respectively.
4,24 and holes 45,55 are formed. 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 is opened near the outer periphery of the recess 11 on the one hand and is guided on the other. 6 pressure tube
Through to communicate with a pressure guiding space (not shown) of the detection unit 20. The right side surface of the main body 31 is formed in a corrugated cross section, and the 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 attached to the right side of the main body 31 on the outer peripheral edge of the seal diaphragm 4 via an O-ring 8. The above is substantially the same for the left main body 32. A space 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 are filled with silicone oil (filled liquid) as a pressure transmitting fluid. The operation of this conventional device is as follows. Differential pressure flow meters, for example, when the respective introduction pressures (including static pressure) inside the orifice are received by the seal diaphragms 4 and 5, respectively, the respective introduction pressures are the space in contact with the seal diaphragm 4, the hole 14 and the recess. 11, a space through the hole 45 to one of the pressure guiding space of the detecting portion 20 and the seal diaphragm 5
It is transmitted to the other pressure guiding space of the detection unit 20 through 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 has extremely large spring constants (rigid), and the protective diaphragm 3 has the above spring constants. Takes two intermediate values. The detection unit 20 converts the differential pressure based on each introduction pressure into an electric signal by a known method, for example, a capacitance method, and outputs the electric signal. The above is the case where the normal pressure introduction operation is performed. However, if only the right seal diaphragm 4 receives pressure due to an erroneous operation, if there is no protective portion 30,
The detection unit 20 may be damaged by a large one-sided pressure. 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. In FIG. 4, assuming that only the seal diaphragm 4 receives pressure, this pressure is applied to the hole 14 and the recess 11 via the filled liquid.
On the other hand, the recess on the left side through the protection diaphragm 3
21, transmitted through the hole 24 to inflate the seal diaphragm 5. On the other hand, it is transmitted to the pressure guiding space on the right side of the detecting portion 20 via the hole 45. However, this transmission pressure is controlled 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.

[Problems to be Solved by the Invention]

As described above, in the conventional technique, if the protective diaphragm 6 is made to be as soft as possible and, in other words, to be largely displaced by a small pressure, the one-sided pressure transmitted to the detection unit 20 can be suppressed. Moreover, at this time, the protective diaphragm 6 must be protected from damage by not increasing the stress generated in itself. Therefore, conventionally, a method of stacking a plurality of diaphragms may be used as the protective diaphragm. However, in this method, due to the surface friction between the diaphragms adjacent to each other, when the acting one-sided pressure is removed, it does not completely return to the initial position, that is, residual displacement occurs, and as a result, zero point fluctuation occurs. There is. An object of the present invention is to provide a differential pressure detecting device which solves the above problems of the conventional technique and improves so as to suppress the zero point fluctuation and the stress generated in the protective diaphragm.

[Means for Solving the Problems]

In order to solve this problem, the differential pressure detection device according to the present invention includes a detection unit that outputs a signal corresponding to the differential pressure to be measured, and each introduced pressure that is externally provided to the detection unit and that causes the differential pressure. A protective diaphragm for protecting the detecting part with respect to the detecting diaphragm, wherein the protective diaphragm has one disk-shaped central diaphragm; and a central part laminated on both sides of the central diaphragm. A side diaphragm having a circular hole and having the same diameter, thickness, and material as the central diaphragm and having a ratio of the diameter of the hole to the diameter of the operating portion in the range of 0.1 to 0.4.

[Action]

The circular hole drilled in the center of the side diaphragm eliminates any friction that may occur due to radial displacement during displacement in the center between the central diaphragm and the side diaphragm. Further, by setting the ratio of the diameter of the hole to the diameter of the working portion of the side diaphragm in the range of 0.1 to 0.4, the center portion of the central diaphragm and the circumference of the working portion, and the circumference of the center hole of the side diaphragm. The maximum value of each stress generated on the circumference of the operating portion can be suppressed.

【Example】

An embodiment of the differential pressure detecting device according to the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view of a protective diaphragm in the first embodiment, and FIG. 2 is a front view of the same. In FIG. 1, the protective diaphragm 60 comprises a central diaphragm 61 and side diaphragms 62 arranged adjacent to each side thereof. Both the central diaphragm 61 and the diaphragms 62 on each side are flat discs having the same diameter,
While the central diaphragm 61 has no hole in the center,
Each side diaphragm 62 has a hole 62a at the center. Therefore, the presence of the hole 62a eliminates the friction that may occur due to the radial deviation at the center between the central diaphragm 61 and the side diaphragm 62 adjacent to the central diaphragm 61, and eliminates the friction between the surfaces. Friction is reduced. As a result, the protective diaphragm 60 returns almost completely to the initial position when the partial pressure acting on it is removed, and as a result, the zero point fluctuation is suppressed. By the way, the protective diaphragm 60 is structurally a three-layer structure, but is operationally equivalent to a two-layer structure. That is, it is the central diaphragm 61 and either side diaphragm 62 that are displaced when a differential pressure is applied. The stresses generated in the central diaphragm and side diaphragms will be analyzed in detail below. The location where the maximum stress occurs in each diaphragm and its stress direction are either the radial direction at the center for the central diaphragm or the radial direction on the circumference of the working part, and the location of the central hole for the side diaphragm. It is either in the circumferential direction on the circumference or in the radial direction on the circumference of the working portion. Now, based on the formula regarding the stress when the disk-shaped member is subjected to the pressure perpendicular to its surface and the assumption that the displacements of the central and side diaphragms are the same, Is derived as follows. Where h: common plate thickness of the center and side diaphragms a: radius of the operating part b: radius of the circular hole of the side diaphragm ν: Poisson's ratio of each diaphragm E: Young's modulus of each diaphragm P: differential pressure acting , Each stress σ1, corresponding to the above ,,,
σ2, σ3, σ4 are σ1 = 3 (1 + ν) {a ² (Y2-Y1-X1) + b ² [(b / a)
² + ^4ln (a / b)] ^{X1} P / 8h 2 (Y2} -Y1) ...... (1) σ2 = 3 {a 2 (X1 + Y1-Y2) + b 2 [(b / ^a) 2 -2] X1} P ^{/ 4h 2 (Y2-Y1)} ...... (2) σ3 = 3a 2 [{(1 + 3ν) +4 (1 + ν) (A + ln (a / b)) + 2 (1-ν)} (b / a) 2 + ( 1-ν) B (a / b) ² ] X1 ・ P / 8h ² (Y2-Y1) ……
(3) σ4 = 3a ² {3 + ν + 4A (1 + ν) (b / a) ² − (1-ν) [2 (b / a) ² + B]} X1 ・ P / 8h ² (Y2-Y1) ...... (4 ) ^{However, X1 = (a 2 -b 2} ) 2 / 64D Y1 = ^{[- a 4 + 6a 2 b 2} -3b 4 -12b 4 ln (a / b) -2b 6 / a 2 ] / 64D Y2 = - [ ^{a 4 -9b 4 + 8a 2 b} 2 + 8A (a 2 b 2 -b 4) +4 (a 4 B -2b 4) ln (a / b) ] ^{/ 64D D = E, 3/} 12 (1-ν 2) A = −a ² {(1-ν) (2 + a ² / b ² ) + [(1 + 3ν) +4 (1 + ν) ln (a / b] b ² / a ² } / 4 [(1-ν} a ² + (1 + ν) b ² ] B = −b ² {(1 + ν) [1−4ln (a / b) b ² / a ² ] + (1−ν) b ² / a ² } / [(1-ν) a ² + (1 + ν) b ² ] Now, let b / a = ε and rearrange equations (1) to (4) to obtain the following, where ε is the ratio of the circular hole diameter to the working portion diameter. , following this is referred to hole diameter ^{ratio. σ1 = (a / h)} 2 · P · F1 (ε) ...... (5) σ2 = (A / h) ² · P · F2 (ε) …… (6) σ3 = (a / h) ² · P · F3 (ε) …… (7) σ4 = (a / h) ² · P · F4 (Ε) (8) Fi (ε): i = 1,2,3,4 is a function determined by ε, that is, the hole diameter ratio of the side diaphragm, where the horizontal axis shows the hole diameter ratio of the side diaphragm. ε and the vertical axis of each function Fi (ε): i = 1,2,3,4 are shown in Fig. 3. In Fig. 3, when ε is in the range of 0.1 to 0.4, The maximum value of each function Fi (ε) can be suppressed to a certain allowable value or less, which is F3 (ε) at ε = 0.1 and ε = 0.4, as is clear from FIG. Note that, to be a little supplementary, the above-mentioned maximum value becomes the minimum when ε = 0.13 (corresponding to the point M ₁ ) and ε =
With 0.31 (corresponding to point M ₂ ), the values are F2 (0.1
3) and F2 (0.31). In addition, within the range of each point M ₁ and M ₂ ,
The values are almost the same with only a slight difference in%. That is, F2
(0.22) ≈F2 (0.13) ≈F2 (0.31) ≈F3 (0.13) ≈F4
(0.13). In practice, the range is limited to the points N ₁ and N _{2 in} the figure in consideration of formulas, assumptions, and manufacturing errors. The points N ₁ and N ₂ correspond to ε = 0.1 and 0.4. Next, the stress value at ε = 0.1 or 0.4 in the embodiment is numerically compared with the stress value of the conventional one-piece protective diaphragm. The displacement with respect to the unit pressure difference, that is, the value Kb in the embodiment of the spring constant of the protective diaphragm, and the value K in the conventional example are Vb in the embodiment in the differential pressure P and V in the conventional example in the differential pressure P. When the displacement, Kb = Vb / P = π (1-ν 2) a 6 ^{[1 + (- 1 + 3ε 2} -3ε 4 + ε 6) X1 / (Y2-Y1) ] ^{/ 16Eh 3 K = V / P} = π (1-ν ² ) a ⁶ / 16Et ³ However, t is the plate thickness of the conventional one-piece protective diaphragm. As a matter of course, the spring constants of the embodiment and the conventional example must be the same, so Kb = K. Accordingly, ^{[1 + (- 1 + 3ε 2} -3ε 4 + ε 6) X1 / (Y2 -Y1) ] ^{/ h 3 = 1 / t 3} ...... (9) Further, the maximum stress σ of the protective diaphragm in the prior art,
Radial stress on the working diameter, σ = 3 (a / t) ² P / 4 (10) Eliminating t from equations (9) and (10), ε = 0.1 or 0.4
When σ is calculated, it becomes the maximum stress of the protective diaphragm in the conventional example to be obtained. E = 20
000Kg / mm ² and ν = 0.3. In conclusion, the calculation result is as follows. Ε in the example
The stress value at = 0.1 is about 87% of the stress value in the conventional example with the same spring constant, and the stress value at ε = 0.4 is about 82% of the stress value in the conventional example. Can be suppressed considerably.

【The invention's effect】

According to the embodiment of the present invention, the protective diaphragm is almost completely returned to the initial position when the partial pressure acting on the protective diaphragm is removed, as a result, the zero point fluctuation is suppressed, and the maximum stress generated is increased. Has an excellent effect of being reduced by about 13 to 18% of the conventional value.

[Brief description of drawings]

FIG. 1 is a side sectional view of a protective diaphragm in an embodiment according to the present invention, FIG. 2 is a front view thereof, FIG. 3 is a diagram of a function Fi (ε) relating to the stress of the protective diaphragm, and FIG. It is sectional drawing of an example. Code Description 60: Protective diaphragm, 61: Central diaphragm, 62: Side diaphragm, 62a: Hole.

Claims (1)

(57) [Claims] 1. A detection unit that outputs a signal according to a differential pressure to be measured, and a protective diaphragm that is provided outside the detection unit and protects the detection unit against each introduced pressure that causes the differential pressure. In the detection device, the protective diaphragm includes one disk-shaped central diaphragm; laminated on each side of both sides of the central diaphragm, having a circular hole in the center, and having the same diameter and the same diameter as the central diaphragm. A side diaphragm having the same thickness and a disk shape, and the ratio of the diameter of the hole to the diameter of the working portion is in the range of 0.1 to 0.4;
A differential pressure detection device comprising: