JPS60237336A - Differential pressure transmitter - Google Patents

Abstract

PURPOSE:To enhance measuring accuracy by preventing plastic deformation by excessive force and the generation of hysteresis, by constituting the title transmitter so that a barrier diaphragm is formed into a protruded shape and arranging the same in the pressure receiving side surface of a main body so as to hold a gap from said side surface. CONSTITUTION:A high pressure side barrier diaphragm 1A and a low pressure side barrier diaphragm 1B, both of which are respectively formed into a corrugated disc, are arranged to the pressure receiving side surfaces 3a, 3b of a main body 2 formed in a split state in such a state that the peripheral edge parts of both diaphragms are welded. High pressure and low pressure are respectively applied to the outer side surfaces of said diaphragms 1A, 1B by the fluid flowed in from the holes 6a, 6b between both side covers 5 secured to the main body 2 by bolts and the main body 2. In due regard to the movement amounts of the barrier diaphragms 1A, 1B, both diaphragms are formed into a protruded shape by draw molding and separated from the pressure receiving side surfaces 3a, 3b in a free state prior to liquid sealing. By this method, the generation of hysteresis by excessive pressure is prevented.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a differential pressure transmitter that measures the pressure difference between two points, which is a process variable. It is designed so that it can be expanded.

[Prior art]

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

Differential pressure transmitters used for this type of pressure measurement generally apply each measurement pressure to barrier diaphragms on the high-pressure side and low-pressure side, and separate the sealed circuit to prevent movement of the sealed liquid due to the pressure difference at that time. The structure is such that strain in the semiconductor pressure sensor is extracted as an electrical output.

However, in this type of differential pressure transmitter, even if a barrier diaphragm with appropriate dimensions, strength, materials, etc. in accordance with the measurement specifications of the Prussse is selected and used, the system is susceptible to excessive pressure. , can reach the semiconductor pressure sensor and damage it, making subsequent measurements impossible.

Therefore, in general, the gap between the back chamber of the barrier diaphragm, that is, the pressure-receiving side of the body body, and the barrier diaphragm is set small, and the pressure-receiving side is formed in the same waveform as the barrier diaphragm to create an overpressure film retention mechanism. When pressure is applied, the barrier diaphragm is seated on the pressure-receiving side to prevent pressure from being transmitted to the interior of the body, thereby preventing damage to the semiconductor pressure sensor.

By the way, as shown in FIG. 1, a conventional barrier diaphragm 1 is formed by drawing, and after its peripheral edge 1a is fixed to the pressure-receiving side surface 3 of the body main body 2 in a state where it is bent,
When a predetermined amount of the internal sealing liquid 4 is sealed in the body main body 2, it is forcibly displaced into a convex shape as shown by the chain line, and a back side chamber is formed between the internal sealing liquid 4 and the pressure-receiving side surface 3. Therefore, even when the differential pressure input is zero, the barrier diaphragm 1 is at point A (the point where the stress δ is not zero) in the strain-stress diagram in Figure 2, and from this state the measured pressure changes from the high pressure side or the low pressure side. When it is added, it is displaced around the point A. This displacement is considered to be within the elastic range of the material of the barrier diaphragm 1, but if excessive pressure is applied and the displacement is large within the range of X, it will enter the plastic range, causing hysteresis in the output of the differential pressure transmitter and reducing measurement accuracy. There was a drawback. Furthermore, since point A is close to the plastic region, the measurement range is also narrow.

[Summary of the invention]

The present invention has been made in view of the above-mentioned points, and by arranging a barrier diaphragm on a pressure-receiving side surface while maintaining a gap from the side surface, and increasing the permissible displacement amount of the barrier diaphragm, υ can be prevented due to excessive pressure. The present invention provides a differential pressure transmitter that prevents the occurrence of hysteresis, expands the measurement range, and improves measurement accuracy.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

〔Example〕

FIG. 3 is a sectional view showing an embodiment of a differential pressure transmitter according to the present invention. In the same figure, a body main body 2 that is divided into parts is shown.
A high-pressure side barrier diaphragm 1A and a low-pressure side barrier diaphragm 1B each formed in the shape of a corrugated disc are disposed on each of the pressure-receiving sides 3m and 3b, with their peripheral edges welded together. Each of the pressure-receiving side surfaces 3m and 3b is formed in the same waveform as the barrier diaphragm LA and IB, respectively. On the outer surface of each of the barrier diaphragms IA and IB,
A hole 5 m between the body body 2 and the covers 5 on both sides fixed to the body body 2 by bolts (not shown).

High pressure and low pressure are applied by the fluid flowing in from 6b. In addition, each barrier diaphragm IA, I
An appropriate interval is provided between B and the pressure-receiving side surfaces 3m and 3b, forming back chambers 7m and 7b.

A sensor capsule 9 is disposed in the upper part of the main body 2 via a neck member 8.
A well-known semiconductor pressure sensor 10 is mounted on a sensor stand 11 in a sensor chamber 9 therein. A body interior chamber 14 is formed in the center of the body main body 2 .

The body interior chamber 14 is partitioned by a center diaphragm 15 into two left and right chambers 114b, each of which has a communication passage 16 with the back chambers 7m and 7b.
1T and to the enclosed circuit 18,19. These enclosed circuits 18, 19 are separated by the semiconductor pressure sensor 10. and,
An internal sealing liquid 4 such as silicone oil is sealed between each of the back side chambers 7a, Tb and the high pressure side and low pressure side of the semiconductor pressure sensor 10 via the communication path 16.17 and the sealed circuit 18.19. has been done. Note that 23 is a liquid sealing hole.

In the differential pressure transmitter configured in this way, when high pressure and low pressure from the process are respectively applied to each barrier diaphragm IA and IB, the barrier diaphragms IA and IB
is depressed, and the internal liquid 4 moves by the amount of compression, and the semiconductor pressure sensor 10 detects the difference in the amount of movement of the internal liquid 4 due to the pressure difference on both sides.
The differential pressure is measured by detecting this and transmitting it as an electrical signal.

By the way, each barrier diaphragm IA, IB is attached to the pressure-receiving side surfaces 3m, 3b in a bottomed state, and is then forcibly displaced in a shim-like manner by the pumping up of the internal sealing liquid 4 and separated from the pressure-receiving side surfaces 3a, 3b. As mentioned above, the elastic range is small and there is a risk of plastic deformation even under slight excessive pressure. Therefore, in the present invention, the barrier diaphragms 1A and IB are drawn into a convex shape as shown in FIG. 4, taking into account the amount of movement of the barrier diaphragms 1A and IB.
This feature prevents the occurrence of hysteresis due to excessive pressure and makes it possible to expand the measurement range.

In other words, if the barrier diaphragms IA and IB are formed in a convex shape and are mounted apart from the pressure-receiving sides 3a and 3b, only a small amount of forced displacement is required due to the sealing of the internal sealing liquid 4, and the allowable displacement amount can be increased accordingly. The point A shown in FIG. 2 can be moved to any position to bring it closer to zero.

Therefore, even if a large excessive pressure is applied, the displacement occurs within the elastic range (range of Y) and does not reach the plastic range. In addition, conventionally, the state where the bottom landed on the pressure-receiving side (the state where the stress δ was zero)
Since it is displaced by the pumping up of the sealing liquid 4, only half of the elastic range can be used, which has the disadvantage that the measurement range is narrow. On the other hand, if it is formed into a convex shape in advance as in the present invention, if it is displaced in the direction of the pressure-receiving side 3m (3b), it can be further displaced even if the stress δ passes through the point of zero, so the elastic region can be used effectively and the measurement range can be expanded. In this case, the displacement of the barrier diaphragms IA and IB in the opposite direction (towards the pressure-receiving side) is applied as a contractile force until the barrier diaphragms face parallel to the pressure-receiving side and no longer have a convex bulge, and then deform into a concave shape. Although it becomes a tensile force, the bottoming position is set midway through the process, before reaching the plastic region.

FIG. 5 is a sectional view of a main part showing a state of a barrier diaphragm before liquid sealing, showing another embodiment of the present invention. In this embodiment, the barrier diaphragm 1A is made into a flat plate and curved into a convex shape, and the peripheral edge 11 of the barrier diaphragm 1A is welded and fixed to the pressure receiving side surface 31 formed on the flat surface. It has been displaced.

Even in such a configuration, the barrier diaphragm 1A is in the free state before liquid sealing, except for the peripheral edge 1a, and the pressure-receiving side surface 3 is
Since it is far from a, it is clear that the allowable displacement amount can be increased accordingly, and the same effect as in the above embodiment can be obtained.

Although the present invention has been described regarding a differential pressure transmitter using a semiconductor pressure sensor, the present invention is not limited to this, and the center diaphragm 1
Needless to say, the present invention can be applied to capacitance type and inductance type type devices that directly detect the displacement of 5, and can also be applied to pressure needles.

〔Effect of the invention〕

As described above, the differential pressure transmitter according to the present invention has a barrier diaphragm formed in a convex shape, and M
Since it is arranged with a gap from the il1 surface, the allowable displacement is large, which prevents plastic deformation due to excessive pressure, prevents the occurrence of hysteresis, expands the measurement range, and improves measurement accuracy. can. In addition, the structure of the barrier diaphragm is simple, making it easy to manufacture and attach to the body within seconds.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a main part to explain the installation of a conventional barrier diaphragm, Fig. 2 is a diagram showing the relationship between strain and stress, and Fig. 3 is a diagram of a differential pressure transmitter according to the present invention. FIG. 4 is a side view showing the natural state of the barrier diaphragm, and FIG. 5 is a sectional view showing a main part of another embodiment of the present invention. 1, IA, IB... barrier diaphragm, 211
--Body main body, 3.3m, 3b @...Pressure receiving side, 4...Fist sealing liquid, 10...Semiconductor pressure sensor. Patent applicant Yamatake Honeywell Co., Ltd.

Claims (1)

[Claims] A barrier diaphragm is disposed on each pressure-receiving side of the body body, and an internal liquid is sealed in the body body,
Applying a measurement pressure to each of the barrier diaphragms,
The differential pressure transmitter for detecting the differential pressure is characterized in that the barrier diaphragm is disposed on a pressure-receiving side surface of the body main body before liquid sealing with a gap maintained between the pressure-receiving side surface and the side surface. . e) The differential pressure transmitter according to claim 1, characterized in that the pressure-receiving side surface is formed as a flat surface, and the barrier diaphragm is pre-curved in a direction away from the pressure-receiving side surface.