JPS5956139A - Differential pressure transmitter - Google Patents

Abstract

PURPOSE:To secure a measurement range and to improve linear characteristics and responsibility by arranging a couple of spacers made of material of lower thermal expansion coefficient than a main body in the internal chamber of the body partitioned into two chambers by a center diaphragm. CONSTITUTION:The couple of spacers 30 and 31 made of material of lower thermal expansion coefficient than the main body 22 are arranged in the internal body chamber 28 partitioned into two chambers by the center diaphragm 29 on both sides of the center diaphragm 29 with displacement margins left. When high pressure and low pressure from a process are applied to barrier diaphragms 23 and 24, the barrier diaphragms 23 and 24 are recessed to move sealed-in liquid according to the compression, and their pressures are applied to the high pressure side and low pressure side of the sensor. The sensor detects the pressure difference between both sides and transmits it as an electric signal to measure the differential pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a differential pressure transmitter that measures a pressure difference between two points as a process variable.

For example, when trying to measure the flow rate of fluid in a pipe, an orifice plate is installed in the pipe, the fluid resistance and the pressure difference between the upstream and downstream sides are measured, and the flow rate is calculated based on a predetermined calculation formula. things are being done.

A differential pressure transmitter used for this type of pressure difference measurement applies each measurement pressure to pressure receiving diaphragms on the high pressure side and low pressure side, and the movement of the sealed liquid due to this pressure is detected by a semiconductor sensor installed by partitioning the sealed circuit. The structure is such that the distortion is extracted as an electrical output.

However, in this type of differential pressure transmitter, even if a pressure-receiving diaphragm with appropriate dimensions, strength, and materials is selected and used according to the measurement specifications of the process, it may sometimes receive excessive pressure. Overpressure between the sensor and the sensor can reach the semiconductor sensor and damage it, making subsequent measurements impossible. Therefore, various devices for protecting sensors from this excessive pressure have been proposed and attached to differential pressure transmitters.

FIG. 1 is a sectional view of a conventional differential pressure transmitter equipped with this type of overpressure retaining device. A barrier diaphragm 2 on the high-pressure side and a barrier diaphragm 3 on the low-pressure side, which are formed in a disc shape, are attached to these barrier diaphragms 2 and 3, and covers 4 on both sides bolted to the body 1 and the body High pressure and low pressure are respectively applied by fluids flowing in from holes 5 and 6 between the holes 5 and 1.

On the other hand, in a sensor chamber in the sensor capsule 7 above the body 1, a semiconductor sensor 8 connected to a terminal (not shown) is held by a substrate 9, and a high voltage From the lower pressure side and the upper side, there is a liquid passage 10.
and 11 extend toward the body 1. code 1
2 is a center diaphragm formed in the shape of a corrugated disk, which divides the inner chamber provided at the central joint of the half-split body 1 into a high-pressure side inner chamber 13 and a low-pressure side inner chamber 14. The liquid passages 10 and 11 are fixed to the body 1 as shown in FIG.
are opened into inner chambers 13 and 14, respectively.゛Also,
The gap formed between each of the barrier diaphragms 2, 3 and the body 1 and the inner chamber 13°14 form a liquid passage 15.1.
6 are connected to each other. Silicone oil or the like is provided between the gap between the barrier diaphragm 213 and the body 1 and the high-pressure side and low-pressure side of the sensor 8 via the liquid passage 15.16, the inner chamber 13.14, and the liquid passage 10.11. An internal sealing liquid 17 is sealed.

In the differential pressure transmitter configured as described above, when high pressure and low pressure from the process are respectively applied to the barrier diaphragms 2 and 3, the barrier diaphragms 2 and 3 are depressed and the inner liquid 17 is filled by the amount of compression. The sensor 8 detects the difference in the amount of movement of the sealed liquid 1γ due to the pressure difference on both sides, and transmits this as an electric signal, thereby measuring the differential pressure.

In this case, the center diaphragm 12 is deformed due to the pressure difference on both sides, but it does not sit on the walls of the inner chambers 13 and 14.
``Furthermore, the barrier diaphragm 2.3 does not sit on the body 1 during normal differential pressure measurement.For example, when excessive pressure acts on the high pressure side, the barrier diaphragm 2 on the high pressure side deforms greatly and completely hits the body 1. Since the barrier diaphragm 2 is seated, pressure on the high pressure side is no longer transmitted to the inside.In other words, the barrier diaphragm 2 serves as an overpressure retainer by being seated.

In such a conventional differential pressure estrus device, since the body 1 and the internal liquid 17 have different thermal expansion coefficients, when the temperature environment in which the differential pressure transmitter is placed changes, the body 1 and the internal liquid 17
7 expand and contract at different expansion rates, the amount of liquid in the gap between the barrier diaphragm 2.3 and the body 1 changes greatly.

When the liquid length increases, the pressure at which the overpressure protection device starts operating increases, and when the liquid volume decreases, it operates at a lower pressure. Even if the same sensor is used, the operating pressure changes, so it is difficult to measure. Not only is the range reduced;
There was a drawback that the direct spinning characteristics and responsiveness deteriorated due to the expansion of the liquid. 1 The present invention has been made in consideration of the above-mentioned points, and a pair of spacers made of a material having a lower coefficient of thermal expansion than the body body are placed in the interior of the body, which is divided into two chambers by a center diaphragm. By arranging the diaphragm on both sides while leaving the diaphragm displaced, we provide a differential pressure transmitter that reduces the influence of temperature changes on operating pressure, secures a measurement range, and improves linear characteristics and responsiveness. to do). Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows an embodiment of the differential pressure transmitter according to the present invention. In the figure, the body 22 of the differential pressure transmitter 21 has a high-pressure side back plate 2 with a circular recess that reaches the center in the thickness direction.
2a and the low pressure side backplay fitted into its recess)
22b and each puncture play)
In the side pressure-receiving recessed surfaces of 22a and 22b, there is a gap 25.26 between the high-pressure side barrier diaphragm 23 and the low-pressure side barrier diaphragm 24, which are formed in the shape of a corrugated disk, and the circular pressure-receiving lower surface. The peripheral edge portion is fixed to the body 22 side with the exception of . In addition, each back plate 22a, 22
Although not shown, a cover similar to that shown in FIG. 1 is joined to b, and a barrier diaphragm 23
, 24 are respectively applied with low pressure and high pressure flowing in from the holes in the cover. The gaps 25 and 26 are connected by a bypass 27 having apertures at both ends, and a thin cylindrical body interior chamber 28 is provided at the junction of the back plate 22a and 22b on the bypass 27. .

Reference numeral 29 designates a center diaphragm formed in the shape of a disk with a corrugated cross section, which separates two chambers, a low pressure side chamber and a high pressure side chamber, in the body interior chamber 28. It is welded to the body 22.

Furthermore, inside the body interior chamber 28, a pair of disc-shaped slides 30 and 31, which are made of ceramic having a lower coefficient of thermal expansion than the body 22 and have the same dimensions as the body interior chamber 28, are installed on both backs. It is provided so that each half is engaged with the plates 22a and 22b. The inner surface of the spacer 30.31 is
It is formed in the shape of a corrugated disk having substantially the same shape as the center diaphragm 29, and between this inner surface and the center diaphragm 29, a pressure receiving chamber 32, 33 is formed as a displacement substitute space for the center diaphragm 29.

On the other hand, inside the sensor capsule 34 that is integrally joined to the body 22, a semiconductor sensor and a substrate, which are not shown but are indicated by reference numerals 8 and 9 in FIG. The high pressure side of the sensor is in communication with the pressure receiving chamber 32 on the high pressure side through liquid passages 35 and 36.

The low pressure side of the trench sensor is communicated with the pressure receiving chamber 33 on the low pressure side through liquid passages 37,38. Then, the gap 25°26 behind the barrier diaphragms 23, 24, the bypass 27
．． Pressure receiving chambers 32, 33. and liquid passages 35, 36, 37.
38 is sealed with an internal sealing liquid 41 such as silicone oil injected from liquid filling holes 39 and 40.

The operation of the differential pressure transmitter configured as above will be explained.

When high pressure and low pressure from the process are respectively applied to the barrier diaphragms 23 and 24, the barrier diaphragms 2
3 and 24 are recessed, and the inner liquid moves by the amount of compression thereof, and respective pressures are applied to the high pressure side and the low pressure side of the sensor.

The sensor detects the pressure difference on both sides and transmits it as an electric signal, thereby measuring the pressure difference.

In differential pressure measurement work using a differential pressure transmitter operating in this manner, the environmental temperature varies significantly from 150° to +120°. For example, when the temperature changes from a low temperature to a high temperature, the body 22 expands due to this increase in temperature, and at the same time the internal liquid 41 also expands.
However, when comparing the thermal expansion coefficients of the body 22 and the inner sealing liquid 41, the inner sealing liquid 41 is much larger, so the elbow of the inner sealing liquid 41 in the gap 25.26 behind the barrier diaphragm 23.24 is The barrier diaphragms 23 and 24 will not be seated unless the pressure is higher than that at low temperature, and the operating pressure of the φ device will become higher in order to detect the overpressure of the sensor. However, in this differential pressure transmitter, the eye
Since the spacer 30I31 with a low expansion coefficient is provided in the body inner chamber 28, if the volume of this spacer 30. This can be offset by the low expansion of −30.31 −), and it is possible to reduce the apparent expansion point of the internal sealing liquid 41 to 0. Therefore, it is possible to avoid an increase in the operating pressure of the overpressure protection device η due to an increase in temperature.

The effect of canceling out overexpansion by creating a difference in the thermal expansion coefficient will be further explained in detail based on FIG. It is assumed that a spacer 30 and an internal sealing liquid 41 are contained in the body 22 of. The body expansion coefficient of the body 22 is αA, and the spacer 3
Assuming that α11 is the body expansion coefficient of 0, αt is the body expansion coefficient of the internal liquid 410, VAO is the internal volume of the body 22, and vno is the volume of the spacer 30, the following equation holds true when the temperature rises by t'C. .

Internal volume of body 22 VA 1 = (1+aAl
) VA O spacer 300 i & Vnl = (1
+abt ) Volume of VBO internal sealing liquid 41 Vl+ −(+
-1-cu't) (V person o-vno) In order to prevent the apparent volume change from occurring even if the temperature rises by t'C, the following equation must hold.

VAI = VB I +V11 Substituting the above formula into this, (1+aht)VA O= (1+aat)VB
o ten (1+alt) (VAO-VBO) aAVAG
= dBvBo +aJ(Vpersono −VBO)(ctl
-aA)VAO= (αi-αn) VnOVHOαl
-αA VAOat-co+ Here, if the material of the body 22 is ausbunite stainless steel, the material of the spacer 30 is amber, and the inner sealing liquid 41 is silicone oil, αA = 4.8X t o ”/'aαB = 0.
3X10-5/'0 αt = 94X10'/'C! Therefore, by bringing the volume of the spacer 300 closer to the internal volume of the body 22 and making the ratio 0.952, the apparent change in the upper volume can be reduced to 0. It is clear that the value becomes smaller.

As is clear from the above description, in the differential pressure transmitter according to the present invention, a pair of chambers formed of a material having a coefficient of thermal expansion lower than that of the body main body is provided in the inner chamber of the body which is partitioned into two chambers by the center diaphragm. By placing the spacers on both sides of the center diaphragm, leaving the center diaphragm displaced, even if the environmental temperature changes significantly during measurement, the difference in thermal expansion between the body and the internal liquid is offset by the low expansion of the spacer. Since the operating pressure of the overload protection device can be held constant regardless of changes in the environmental temperature, the measurement range can be expanded compared to conventional methods, and since there is no spurious liquid expansion, linear characteristics can be improved. and improve responsiveness.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional differential pressure transmitter, FIG. 2 is a sectional view of an embodiment of the differential pressure transmitter according to the present invention, and FIG. 3 is an explanatory diagram of the thermal expansion effect. 21... Differential pressure transmitter, 22°°°° body, 23.
24...Barrier diaphragm, 25°26...
Gap, 2T... Bypass, 28... Body interior, 29... Center diaphragm, 30.31...
...Spacer, 35°36I3γ, 38...Liquid passage. Patent applicant: Yamatake Newell Co., Ltd. Agent
Masaki Yamakawa (and 1 other person) Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] An internal body chamber is provided on the bypass that connects the gap between each pressure receiving diaphragm on both sides of the body and the body at the center.
A center diaphragm is provided in the interior of the body to separate two chambers connected to each other by a liquid passage between the high pressure side and the low pressure side of the sensor. 1. A differential pressure transmitter, characterized in that a pair of spacers made of a material are disposed on both sides of the center diaphragm except for the displacement type.