JPS6261898B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a differential pressure measuring device. More specifically, the present invention relates to a capacitance detection type differential pressure measuring device that applies measuring pressures to the inside and outside of the bellows and detects displacement of the free end of the bellows as a change in capacitance.

In recent years, capacitive detection type differential pressure measuring devices include:
Those using a stretch diaphragm as a pressure-displacement conversion element are often used.

In such devices, a constant tensile force must always be applied to the diaphragm. For this reason, the capsule body that fixes the diaphragm and the housing that fixes the capsule are made of expensive materials that match the coefficient of linear expansion of the diaphragm so that the tensile force of the diaphragm is not adversely affected by changes in ambient temperature, etc. It has to be used and is expensive.

Next, differential pressure transmitters are often used with large static pressures. In such cases, the large static pressure causes the housing to bulge in the radial direction of the diaphragm, pulling on the diaphragm and stiffening the diaphragm, thereby creating a static pressure span shift. Further, in order to withstand large static pressure, the housing and the like are assembled by strongly tightening bolts, etc., but this tightening force also affects the diaphragm and adversely affects the characteristics as a span shift.

Next, when large static pressure or overpressure is applied,
There is a possibility that the housing is displaced and a static pressure zero shift or an overpressure zero shift occurs, or a static pressure or overpressure zero shift occurs due to residual deformation at that time.

The present invention solves these problems.

SUMMARY OF THE INVENTION An object of the present invention is to provide a differential pressure measuring device that has small static pressure span errors, temperature span errors, and tightening span errors, and is free from static pressure or overpressure zero shift.

FIG. 1 is an explanatory diagram of the configuration of an embodiment of the present invention.

In the figure, 1 is a capsule unit, which includes a bellows 11, a movable electrode 12, a spacer 13, and an insulator 1.
4 and 15 and fixed electrodes 16 and 17. A plate-shaped movable electrode 12 is fixed to the free end 111 of the bellows 11 so as to be perpendicular to the axis of the bellows 11 . As shown in FIG. 2, near the part where the movable electrode 12 is fixed to the free end 111 of the bellows, there is a concentric semicircular groove 1.
22 are provided, and the over-range flexible portion 12
1 is configured. The insulators 14 and 15 have a disk shape and are arranged opposite to each other on both sides of the movable electrode 12, and a ring-shaped spacer 13 is sandwiched between the insulators 14 and 15 at the periphery thereof. Fixed electrode 16,1
7 has a ring shape and faces the movable electrode 12,
It is arranged on the surfaces of the insulators 14 and 15, and in this case is formed by vacuum evaporation. Reference numeral 18 denotes a substantially disk-shaped support body which is welded and fixed 181 to the fixed end 112 of the bellows and supports the insulator 14. Reference numeral 2 denotes a housing unit, which is composed of cylindrical housing bodies 21, 22, seal diaphragms 23, 24, and ring-shaped seal holders 25, 26. The housing bodies 21 and 22 house the capsule unit 1 in a chamber 220 formed by the recesses 211 and 221, and are welded 27 at their outer peripheral edges so as to be integral with each other. Concentric corrugated surfaces are formed on the outer surfaces 212, 222 of the housing bodies 21, 22. The capsule unit 1 does not touch the recesses 211 and 221, and the tip of the fixed end 112 of the bellows 11 is welded 11 at the outer flat part 212 of the housing body 21.
3 is fixed. Therefore, the outside of the bellows 11 and the housing bodies 21, 22, the insulators 14, 15,
A chamber 31 is formed by the spacer 13. The seal diaphragms 23 and 24 are connected to the housing body 2.
1 and 22, respectively, and covers the housing bodies 21 and 22 and the chamber 23, respectively.
1,241, and its peripheral edge is the seal presser 2.
5 and 26 are fixed to the housing bodies 21 and 22. 32 is the inside of the bellows 11 and the chamber 231
This is a communication hole that communicates with the 33 is room 31 and room 24
This is a communication hole that communicates with 1. 4 is a sealed liquid such as silicone oil that fills the inside of the bellows 11, the communication hole 32, and the chamber 231, and 5 is a sealed liquid such as silicone oil that fills the chamber 31, the communication hole 33, and the chamber 241. 6,7
are covers that cover the seal diaphragms 23, 24 and the seal pressers 25, 26, respectively, and form measurement chambers 61, 71. Reference numerals 611 and 711 are introduction holes for introducing measurement pressure into the measurement chambers 61 and 71. 1
61, 171 are leads drawn out from the fixed electrodes 16, 17, and at the outlet from the housing 2, hermetic seals 162,
172.

In the above configuration, for example, when a measurement pressure P _H higher than that of the introduction hole 611 is introduced into the measurement chamber 61 and a measurement pressure P _L lower than that of the introduction hole 711 is introduced into the measurement chamber 71, the pressure is
3, 24 to the filling liquid 4, 5. This pressure is converted into force on the front and back surfaces of the bellows 11, and if the effective area of the bellows 11 is Ae, then (P _H - P _L )
Generates the power of Ae. The spring constant of bellows 11 is k
Then, the displacement of the tip of the bellows 11 is δ=(P _H −
P _L )Ae/k. Since the movable electrode 12 is attached to the tip of the bellows 11, when P _H > P _L , the movable electrode 12 moves to the right in the figure, and the electrode 12
The capacitance between electrodes 12 and 16 decreases, and the capacitance between electrodes 12 and 17 increases. Bellows 11 and differential pressure (P
The relationship _(H - P _L ) is linear as long as the displacement is small, and a highly accurate pressure→displacement characteristic can be obtained.

Therefore, when a large static pressure is applied as the measuring pressure, as in the case of using a conventional stretching diaphragm as the measuring diaphragm, the housing supporting the stretching diaphragm expands radially, resulting in The disadvantage of the stretch diaphragm method, in which the measuring diaphragm itself becomes stiff by stretching the diaphragm and causes span errors, does not occur.

That is, since the bellows 11 is used as a pressure receiving element, even if the bellows end expands and contracts in the radial direction, only the portion near the bellows end is affected, and the average effective area of the bellows hardly changes. Further, although a bellow is theoretically considered to be a thin-walled cylinder, in a thin-walled cylinder, the length in the axial direction over which the deformation of the end of the cylinder affects the inside of the cylinder is short, and the dimensions of the main portion of the bellow are stable. Furthermore, the bellows end portion that is fixed to the base usually has a slightly elongated cylindrical portion, which also prevents the strain of the base from being transmitted to the bellows.

In short, even if the housing is distorted in the radial direction due to large static pressure, the distortion is absorbed by the cylindrical portion of the bellows end. Furthermore, since a bellows is used which inherently has a property of being resistant to distortion in the mounting portion, it is possible to obtain a device that is less prone to span errors due to static pressure.

For the same reason, it is possible to obtain a structure that is resistant to span shift caused by tightening bolts or the like.

Furthermore, in the case of the stretch diaphragm type,
If there is a material difference between the housing and the diaphragm, the tension in the diaphragm changes due to temperature changes, resulting in a large span change. Therefore, for example, if a constant elastic material is used as the diaphragm, the housing must also be made of the same material, which is expensive.

In the present application, even if the housing and the bellows are made of different materials, the deformation of the housing is not transmitted to the bellows body portion as described above, so the material can be freely selected and inexpensive materials can be used. Therefore, there is no temperature span error factor due to differences in linear expansion coefficients.

Therefore, for example, if the bellows are made of a constant modulus material, there will be no temperature span error due to the material, and the entire device will have an extremely small temperature span error, and can be made inexpensive.

Next, the device needs protection against overpressure being applied as the measurement pressure.

In the present application, when overpressure is applied, the seal diaphragms 23 and 24 close to the housing body 2.
1 and 22, respectively, to protect the seal diaphragms 23 and 24 from overpressure. However, in the bellows 11 serving as the measurement pressure receiving element, the area of the seal diaphragm is larger than the area of the bellows, so the displacement of the bellows becomes as large as an elbow in response to overpressure. On the other hand, fixed electrode 1
The gap between 6, 17 and the movable electrode 12 is small. Therefore, the movable electrode may be destroyed. For this reason, bellows could not be selected as the measurement pressure receiving element in the past. In the present application, the movable electrode 12 has an over-range flexible portion 12.
1 is provided, the over-range flexible portion 121 is flexibly deformed to absorb the displacement of the bellows 11, and the movable electrode can be prevented from being destroyed.

Next, if we consider the case where an overpressure P _H of several 100 kg/cm ² is applied from the left side of the diagram in FIG. It becomes a thick disk that receives from one side, and is deformed so that the central part protrudes as shown in Fig. 3. This deformation is caused by several overpressures.
When it reaches 100Kg/cm ² , the displacement becomes large and cannot be said to be small compared to the measured displacement of the bellows 12. Further, this deformation of the housing 21 is also transmitted to the insulator 14, and the insulator 14 deforms into a donut-shaped disk whose periphery is supported by the force applied to the inner periphery.
At that time, misalignment may occur between the insulator 14 and the housing outer surface 212 or between the contact surface between the insulator 14 and the spacer 13, resulting in a zero shift in which the zero point does not return to its original state even after the excessive pressure is released. be.

In contrast, in the present application, the capsule unit 1 has a recess 21 in the housing unit 2.
1,221, and the housing 2 is floating only at the tip of the fixed end 112 of the bellows 11.
1, and since the insulator 14 is integrally fixed to the fixed end 112 of the bellows 11 via the support 18, zero shift will not occur even if the central part of the outer surface part 212 is displaced. There is no.

When excessive pressure P _L is applied from the right side of the diagram in FIG.
Since there is a gap therebetween, the displacement of the outer surface 222 does not affect it.

Therefore, in the present application, the capsule unit 1 is arranged in a floating state in a chamber 220 provided inside the housing unit 2, that is,
Since the capsule unit 1 is insulated from the housing unit 2, static pressure span errors, temperature span errors, tightening span errors, etc. can be reduced.

As described above, according to the present invention, it is possible to realize a differential pressure measuring device with small static pressure span errors, temperature span errors, and tightening span errors, and without the risk of static pressure or overpressure zero shift.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of one embodiment of the present invention, and FIG.
The figure is an explanatory diagram of the main part of FIG. 1, and FIG. 3 is an explanatory diagram of the main part configuration of the conventional example. 1... Capsule unit, 11... Bellow, 111
...Free end, 112...Fixed end, 12...Movable electrode, 1
21... Overrange flexible part, 122... Groove, 13
...Spacer, 14,15...Insulator, 16,17
...Fixed electrode, 18...Support, 2...Housing unit, 21, 22...Housing body, 220...
Chamber, 211, 221... Recess, 212, 222... Outer plane, 23, 24... Seal diaphragm, 23
1,241...Chamber, 31...Chamber, 32,33...Communication hole, 4,5...Filled liquid, 6,7...Cover, 61,7
1...Measurement chamber, 611, 711...Introduction hole.

Claims (1)

[Claims] 1. A bellow, a plate-shaped movable electrode fixed to the free end of the bellow perpendicularly to the axis of the bellow, and having an overrange flexible part formed by a groove provided near the fixed part with the bellow; A plate-shaped insulator disposed facing each movable electrode via a ring-shaped spacer, a fixed electrode provided on the surface of the insulator facing the movable electrode, and a fixed end of the bellows. a capsule unit consisting of a support that is fixed and supports the insulator; the capsule unit is disposed internally without contacting a chamber provided inside the capsule unit; the fixed end of the bellows is fixed and is concentric with the outer surface A housing unit comprising: a housing body having a wavy surface formed thereon; and a seal diaphragm that covers the wavy surface and has a peripheral surface fixed to the wavy surface and is backed up by the wavy surface during overload; A differential pressure measuring device comprising a cover that covers a seal diaphragm and configures a measurement chamber with the seal diaphragm.