JPS5836997Y2 - Differential pressure transmitter with temperature compensation - Google Patents

Description

[Detailed description of the invention] This invention is a differential pressure transmitter that detects the difference in pressure applied to both ends of the body as an electrical signal. This paper relates to a temperature-compensated differential pressure transmitter equipped with a temperature-compensating diaphragm so that the change in temperature is small.

In a differential pressure transmitter in which both the pressure receiving diaphragm and the temperature compensation diaphragm are used in contact with a corrosive liquid, corrosion-resistant materials are used for both the pressure receiving diaphragm and the temperature compensation diaphragm.

Corrosion-resistant materials such as tantalum have low springiness (low elastic properties) and have a narrow range of elastic deformation.
It has the disadvantage of causing plastic deformation if excessive input is applied.

First, a conventional differential pressure transmitter with a temperature compensation diaphragm was
Let me explain with reference to the diagram.

In FIG. 1, reference numeral 11 denotes a relatively thick disc-shaped body, and pressure receiving diaphragms 12a and 12b are disposed opposite both end surfaces of the body 11.

The outer periphery of these pressure receiving diaphragms 12a, 12b is attached to the periphery of the end face of the body 11 with a seal ring 13a,
13b and fixed by, for example, welding.

The pressure receiving diaphragms 12a and 12b have a plate ring shape, and disks 14a and 14b are disposed at the center of the pressure diaphragms 12a and 12b, respectively, facing both end surfaces of the body 11.

A seal ring 15 is attached to the inner periphery of the pressure receiving diaphragm 12a, 12b on the periphery of the outer end surface of the teeth 14a, 14b.
A and 15B are held down and fixed by welding.

The center portions of the disks 14a and 14b are connected to each other by a connecting shaft 16 within the body.

Therefore, the through hole 17 through which the connecting shaft 16 is inserted is formed in the body 1.
1 and its axial center position.

A means for detecting the displacement of the connecting shaft 16 as an electrical signal is provided within the body 11.

Therefore, a space is formed in the center of the interior of the body 11 to accommodate means for extracting this electrical signal.

In this example, the displacement of the connecting shaft 16 is detected as a change in capacitance, and a plate-shaped movable electrode 18 is fixed to the intermediate portion of the connecting shaft 16.

Fixed electrodes 19 are arranged opposite to both end surfaces of the movable electrode 18, respectively.
a, 19b are fixed within the body.

An insulating support 21 is fixed between the outer peripheral edges of the opposing surfaces of the fixed electrodes 19 a and 19 b.

The movable electrode 18 is connected to the insulating support 21 by a central leaf spring 22, which serves as a return spring.

In order to strengthen the springiness of the center leaf spring 22, the movable electrode 18
A ring-shaped deep groove 23 is formed on the circumferential surface of the ring, and a central plate spring 22 is connected to the bottom of the groove.

In reality, a disk-shaped central plate spring 22 was used, a convex part was formed at the center of the two movable electrodes 18, and the convex part was brought into contact with the central plate spring to connect and fix these three parts. things are used.

The movable electrode 18 passes through the center plate spring 22 and further connects to the body 11.
a fixed electrode 19a electrically connected to the external terminal 24 of the
19b are respectively connected to terminals 25a and 25b.

The capacitance between the movable electrode 18 and the fixed electrodes 19a and 19b is taken out between the terminal 24 and the terminals 25a and 25b.

The interior of the body 11 is filled with a sealing liquid 26.

Temperature compensating diaphragms 27 a and 27 are provided on the outside of the disks 14 a and 14 b, respectively, facing the disks 14 a and 14 b.
b are arranged respectively, and the periphery of the disk 14
a, 14b.

In this example, the seal rings 15 a , 15 b and the pressure receiving diaphragms 12 a , 12 b are welded together.

The spaces between the disks 14a, 14b and the temperature compensation diaphragms 27a, 27b are mutually connected to each other through the interior of the body 11 and liquid passages 28a, 28b formed in the disks 14a, 14b, respectively. It is communicated.

The volume of the sealing liquid 26 changes as the ambient temperature changes.

Now, in a state where the temperature compensating diaphragms 27a, 27b are not provided, and therefore the liquid flow registers 28a, 28b are not formed, the pressure receiving diaphragms 21a, 2
Assume that the pressure inside the body 11 changes by ΔP as the volume of the sealing liquid 26 inside 1b changes.

If there is a difference ΔS in the effective areas of the pressure receiving diaphragms 12 a and 12 b, a force of Δf−ΔP×ΔS is generated.

Let P be the measurement span and S be the effective area. The zero point fluctuation occurs.

Pressure receiving diaphragm 12a. As a practical matter, it is difficult to make the effective areas of 12b exactly the same.

Therefore, such a zero point fluctuation occurs.

By the way, in the case where the temperature compensation diaphragms 27a and 27b are provided, for example, when the sealing liquid 26 expands due to temperature, the temperature compensation diaphragms 27a and 27b are displaced outward, increasing the internal volume of the body. The change in internal pressure ΔP becomes smaller.

As a result, the force generated based on the difference in the effective areas of the pressure receiving diaphragms becomes smaller than in the case where no temperature compensation diaphragm is provided, and the zero point fluctuation becomes smaller accordingly.

Depending on the purpose of use, the differential pressure transmitter may have pressure receiving diaphragms 12a, 12b,
Special materials are used as the temperature-compensating diaphragms 27a, 27b, which are particularly corrosion-resistant, such as tantalum, for example.

In the case of tantalum, it has poor spring properties and undergoes plastic deformation due to excessive input or significant expansion of the sealing liquid.

In the case of the pressure-receiving diaphragms 12a and 12b, even if they are plastically deformed, once the excessive input is removed, the center plate spring 22 for return works, so they can return to their original shapes, but the temperature-compensating diaphragms 27a and 27b No such force acts on the disks 14a and 14b, and the disks 14a and 14b remain plastically deformed, and their effectiveness as temperature compensation diaphragms is diminished.

This invention provides a differential pressure transmitter with temperature compensation that can perform sufficient temperature compensation when a special material with corrosion resistance and low springiness is used for the pressure receiving diaphragm and the temperature compensation diaphragm.

Therefore, in this invention, the temperature compensating diaphragm has a double structure, the outer diaphragm is made of the same material as the pressure receiving diaphragm, and the inner diaphragm is made of a material with higher springiness.

For example, FIG. 2 shows a temperature compensating diaphragm 27a, which is the essential part of this invention, and the temperature compensating diaphragm 27a has a double structure consisting of an outer diaphragm 31a and an inner diaphragm 32a, as shown only with respect to the temperature compensating diaphragm 27a.

The outer diaphragm 31a is the pressure receiving diaphragm 21a
The same material, for example the same material, is used, for example corrosion-resistant tantalum.

Inner diaphragm 32 a is outer diaphragm 31 a
For example, it is taken over by stainless steel, which has more springiness than steel.

This outer diaphragm 31a and inner diaphragm 3
2 A may be in close contact with each other, or there may be a space between them.

To make this, for example, the inner diaphragm 32a is first attached to the disk 14a by welding, gluing, brazing, etc. at its peripheral edge, and the outer diaphragm 31, which is integrally formed with the pressure receiving diaphragm 21a, is attached to the outside thereof.
A is fixed to the disk 14a by welding or adhesive using a seal ring 15a.

Of course, the temperature compensation diaphragm 17b side also has the same configuration.

The inner diaphragm 32a is highly springy and prevents excessive input.
It does not undergo plastic deformation due to significant expansion of the sealing liquid, has a restoring force that restores the plastic deformation of the outer diaphragm 31a when excessive input, etc. is removed, and is sufficiently soft to absorb the expansion of the sealing liquid for temperature compensation. have.

Because of this configuration, for example, when the sealing liquid 26 expands, the inner diaphragm 32 of the temperature compensation diaphragm
a swells, and the corrosion-resistant outer diaphragm 31a also swells.

Also, even if excessive input is applied to one side of the differential pressure transmitter, the sealing liquid 2
The temperature compensating diaphragm on the opposite side bulges through 6,
The movement of the sealing liquid can be absorbed by the temperature compensation diaphragm.

In this temperature compensation diaphragm, since the inner diaphragm 32a has high springiness, it does not remain in close contact with the plastically deformed retainer disk, and its temperature compensation and compensation effects against excessive input are sufficiently advanced.

Moreover, it has excellent corrosion resistance, so it can be used for special liquids.

In the above description, the displacement of the connecting shaft 16 is detected as a change in capacitance, but it can also be detected as a change in inductance or resistance in the same manner as used in conventional transmitters of this type.

Similarly, this idea can be applied to force balance equations.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a conventional temperature-compensated differential pressure transmitter, and FIG. 2 is a sectional view showing an example of a temperature-compensating diaphragm, which is the essential part of this invention. 11: Body, 12 a, 12 b: Pressure receiving diaphragm, 14 a, 14 b: Teeth disk, 16: Connection shaft, 2
6: Sealing liquid, 27a. 27b: temperature compensation diaphragm, 28a, 28b: liquid passage, 31a: outer diaphragm, 32a: inner diaphragm.

Claims (1)

[Scope of utility model registration request] Pressure-receiving diaphragms made of a material that is corrosion-resistant and has low springiness are installed at the outer periphery of each of the pressure-receiving diaphragms facing both end surfaces of the body, and a pressure-receiving diaphragm made of a material that is corrosion-resistant and has low springiness is installed at the center of each of the pressure-receiving diaphragms. The disks are tested at their peripheries, and the centers of both disks are connected by a connecting shaft supported by a central leaf spring;
Means for electrically extracting the displacement of the connecting shaft is provided in the body, the body is filled with a sealing liquid, and a spring having the same corrosion resistance as the pressure receiving diaphragm is arranged opposite to the outside of the disk. A temperature-compensating diaphragm made of a material with low elasticity is fixed at a peripheral edge of the temperature-compensating diaphragm, and a liquid passageway is formed in each of the discs to communicate between the temperature-compensating diaphragm, the disc, and the inside of the body.
In a differential pressure transmitter in which the pressure-receiving diaphragm and temperature-compensating diaphragm are used in contact with a corrosive liquid, the temperature-compensating diaphragm is highly resilient, and even if the temperature-compensating diaphragm is plastically deformed due to excessive input, it has the ability to return to its original state. A differential pressure transmitter with temperature compensation, characterized in that an inner diaphragm having flexibility to absorb expansion of the sealing liquid is provided inside the temperature compensation diaphragm.