JPS5863828A - Measuring device for differential pressure - Google Patents

Abstract

PURPOSE:To permit zero point adjustment with less span errors in static pressure temp. and tightening by the constitution wherein a bellows is used as a pressure sensitive element, a plate-like movable electrode is provided at the free end thereof and stationary electrodes are provided opposite to said electrode. CONSTITUTION:A plate-like movable electrode 12 is fixed to the free end 111 of a bellows 11 orthogonally with the axis of the bellows 11. Stationary electrodes 16, 17 of an annular shape are disposed on the surfaces of insulators 14, 15 by facing said electrode. When high measuring pressure is introduced through an introducing hole 611 into a measuring chamber 61 and low measuring pressure through an introducing hole 711 into a measuring chamber 71, the pressures are transmitted via sealing diaphragms 23, 24 to sealing liquids 4, 5, the pressures of which are converted to forces by the front and rear surfaces of the bellows 11. These forces displace the electrode 12 at the preceding end of the bellows 11, and on account of said change, the electric capacities between the electrodes 12 and 16 and between the electrodes 12 and 17 change. Even when the bellows end elongates or contracts in a radial direction, the average effective area of the bellows hardly changes.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a differential pressure measuring device piece. 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, as a capacitance detection type differential pressure measuring device, one using a stretch diaphragm as a pressure-displacement conversion element has been widely 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 expensive because they must be made of expensive materials that match the linear expansion coefficient of the diaphragm so that the tensile force of the diaphragm is not adversely affected by changes in ambient temperature, etc. Become something.

Next, differential pressure transmitters are often used with large static pressures. In such a case, the large static pressure causes the housing to bulge in the radial direction of the diaphragm, pulling on the diaphragm and causing the diaphragm to stiffen, creating this one-time static pressure span shift. Furthermore, in order to withstand large static pressures, housings and the like are assembled by strongly tightening them with bolts, etc., but this tightening force also affects the diaphragm and adversely affects its characteristics as a span shift.
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Furthermore, in a capacitance detection type differential pressure measuring device, it is common to use the measuring diaphragm as a movable electrode, and to dispose fixed electrodes on opposite sides of the measuring diaphragm to differentially process displacement. It is desirable that the movable electrode be placed precisely in the center between the fixed electrodes.

The present invention solves these problems.

An object of the present invention is to provide a differential pressure measuring device that has less static pressure span errors, temperature span errors, and tightening span errors and is capable of zero point adjustment.

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 capsule unit 11, a movable electrode 12. Sube→)--13, Insulator 14.15
and fixed electrodes 16 and 17. Free end 1 of bellows 11
11 includes a plate-shaped movable electrode 1 perpendicular to the axis of the bellows 11.
2 is fixed. Free end 1 of the bellows of the movable electrode 12
As shown in FIG. 2, a large number of concentric semicircular grooves 122 are arranged in the vicinity of the fixing part 11 to form an over-range flexible part 121. The insulators 14 and 15 have a disk shape and are arranged opposite to each other on both sides of the movable electrode 120, and a ring-shaped spacer 15 is sandwiched around the insulators 14 and 15. The fixed electrode 16117 has a ring shape and is disposed on the surface of the insulator 14.15, facing the movable electrode 12, and is formed by vacuum deposition in this case.

2 is a housing unit, which has a cylindrical housing body 2
1.22, a seal diaphragm 23.24, and ring-shaped seal holders 25 and 26. Housing body 21
．． 22 houses the capsule unit 1 through its concave portions 211 and 221, and is welded 27 at its outer peripheral edge so as to be integral with each other. The outer surface portion 212.222 of the housing body 21.22 is formed with concentric corrugated surfaces. Thus, the fixed end 112 of the bellows 11 is fixed by welding 113 to the outer plane portion 212 of the housing body 21. Thus, the outside of the bep-11 and the housing body 21122 insulator 14.15. A chamber 51 is formed by the spacer 13. A sealing diaphragm 25.24 covers the outer surfaces 212, 222 of the housing body 24.22, respectively, and
1.22 and form chambers 2'51 and 241, respectively, and their peripheral edges are fixed to the housing body 21.22 by seal holders 25.26.

32 is a communication hole that communicates the inside of the tongue 11 with the chamber 231. 53 is a communication hole that communicates the chamber 31 and the chamber 241. 4 is the inside of the bellows 11, the communication hole 32 and the chamber 231
5 is a filling liquid such as silicone oil, which fills the chamber 31, the communication hole 53, and the chamber 241.

6.7 are covers that cover the seal diaphragm 23.24 and the seal presser 25.26, respectively, and form a measurement chamber 61.71. 611.7N is an introduction hole for introducing measurement pressure into the measurement chamber 6L71. IS+, 171 is a lead drawn out from the fixed electrode 16.17, and hermetically sealed 162, 172 is provided at the lead-out portion from the housing 2. 8 is a zero point adjustment mechanism, which consists of a screw 81 and a spring 82. Sufu!
J, -81 is the capsule unit 1 as shown in FIG.
They pass through near the outer periphery of the housing body 21 and are screwed to the housing body 21, and in this case, three are used.

The spring 82 is inserted into the screw 81 and presses the capsule unit 1 to the right in the figure.

In the above configuration, for example, the introduction hole 6
When a measurement pressure P higher than 11 is introduced into the measurement chamber 71 and a measurement pressure pt lower than the introduction hole 711 is introduced into the measurement chamber 71, the pressure is applied to the sealed liquid 4 through the seal diaphragm 25.24.
．． 5 will be informed. This pressure is converted into force on the front and back surfaces of bellows 11, and if the effective area of bellows 11 is Ae, then (P
g - Pt,) generates a force of Ae. Bellows I: If we take the spring constant of IN as k, the displacement of the tip of bellows 11 is δ=
(pII-P+,) becomes 8e/. Since the movable electrode 12 is attached to the tip of the bellows 11, PH>
In the case of T'+, the movable electrode 12 moves to the right in the figure, the capacitance between the electrodes 12 and 16 decreases, and the capacitance between the electrodes 12 and 17 increases. Bellows 11 and differential pressure (pn-PL
) 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 a measurement pressure, as in the case where a conventional stretch diaphragm is used as a measurement diaphragm, the nozzle supporting the stretch diaphragm bulges in the radial direction, and as a result, the measurement When the diaphragm is stretched, the measuring diaphragm itself becomes rigid, and the drawback of the stretch diaphragm method, which causes span error, 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 will be affected, and the average effective area of the bellows will hardly change. .

Furthermore, although the bellows 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 part of the bellows are stable. Furthermore, the bellows end part that is fixed to the pace usually has a rather long cylindrical part.
This cylindrical portion also prevents strains in 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 bead end. Furthermore, since the mounting uses a bead that is essentially resistant to strain in its parts, it is possible to obtain a device that is less susceptible to span errors due to static pressure.

For the same reason, tightening with bolts or the like provides resistance against span shift.

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

In the present invention, even if the housing and the bellows are made of different materials, the deformation of the housing will not be transmitted to the bellows 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 Bep- is made of a constant elastic material,
There is no material-related temperature span error, the entire device has an extremely small temperature span error, and it can be installed at low cost.
can be done.

Next, the device needs protection against the case where overpressure is applied as the measurement pressure.

In the present application, when overpressure is applied, the seal diaphragms 25 and 24 contact the housing body 21 and 22, respectively, so that the seal diaphragm 23
, 24. However, in the measurement pressure receiving element p-11, the area of the seal diaphragm is larger than the area of the bellows, so the displacement of the bellows becomes very large in response to overpressure.

On the other hand, the gap between the fixed electrodes 16, 17 and the rotation chamber rj12 is small. Therefore, there is a risk that the movable electrode may be destroyed. For this reason, in the conventional pressure system, Bep- could not be selected as the measuring pressure cable l. In the present application, since the over-range flexible part 121 is provided in the movable electrode 12, the over-range flexible part 121 flexibly deforms and absorbs the displacement of the bep-11, so that there is no risk of the movable electrode being destroyed. is obtained.

Next, in the present application, the movable electrode 12 can be easily placed in the center of the fixed electrodes 16 and 17 by turning the screw 81 of the zero adjuster #I￥8 in a state where no measurement pressure is applied. , the capacitances of the movable electrode 12-fixed electrode 16 and the movable electrode 12-fixed electrode 17 can be made exactly equal, and accurate zero adjustment can be easily performed.

As a result, (1) the sealed liquid is placed on both sides of the movable electrode 120, and the respective capacitances between the movable electrode 12 and the fixed electrodes 16 and 17 are not unbalanced due to the influence of ambient temperature, etc.; Since the movable electrode 12 can be placed accurately in the center of the electrodes 16 and 17, the necessary measurement displacement can be accurately taken in both the left and right directions of the figure of the movable electrode 12.

(2) Movable electrode 12 - fixed electrode 16 and movable electrode 12
- Stray capacitances of the fixed electrodes 17 are equal, and constant characteristics can be obtained.

(3) In the displacement detection part, the zero point can be adjusted accurately in advance, so the leads 161, 171
The electric circuit part that processes the capacitance signal extracted from the
(not shown), the zero adjustment and sub-7M adjustment do not have the disadvantage of interfering with each other due to the circuit design.

(4) Since the movable electrode 12 can be placed accurately in the center, zero shift due to changes in ambient temperature, etc. is small.

and other benefits.

As described above, according to the present invention, it is possible to realize a differential pressure measuring device with small static pressure span error, temperature span error, and tightening span error and zero point adjustment.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the configuration of one embodiment of the present invention, FIG. 2, and FIG.
The figure is an explanatory diagram of the main part of FIG. 1. 1... Capsule unit, 11... BeR-1N1.
...Free end, 112...Fixed end, 12...Movable electrode, 121...Overrange flexible part, 122...Groove, 15...Spacer, 14.15...Insulator, 1
6.47...Fixed electrode, 2...Housing, 21.
22...Housing body, 211, 221...Recess, 212, 222...External affairs surface, 25.24...
Seal diaphragm, 251, 241 ... chamber, 5
2.55... Communication hole, 4.5... Filled liquid, 6.7.
・・Cover, 61.71 River measurement room, 611,612・
...Introduction hole, 8...Electric point adjustment mechanism, 81...Scree, 82...Spring. Figure 1 Figure 2 Figure 2

Claims (1)

[Claims] a plate-shaped movable electrode having an overrangeable part formed by a bellow and a groove fixed to the free end of the bellow perpendicularly to the axis of the bellow and provided near the fixed part with the bellow; A capsule unit consisting of a plate-shaped insulator disposed facing the movable electrode through a ring-shaped spacer, and a fixed electrode provided on the surface of the insulator facing the movable electrode.) and a housing body in which the capsule unit is disposed in a chamber provided therein, a housing body having a fixed end of the bellows fixed thereon and a concentric wavy surface formed on the outer surface thereof, and a peripheral surface thereof covering the wavy surface. and a seal diaphragm fixed to the corrugated surface and backed up by the corrugated surface during overload, the housing unit 1. ．． a zero point adjustment mechanism comprising a screen for attaching the capsule unit to the housing unit and a spring disposed between the housing unit and the capsule body to oppose the fastening force of the screen, and the seal; A differential pressure measuring device comprising a cover that covers a diaphragm and configures the seal diaphragm and a measurement chamber.