JPH0331212B2 - - Google Patents

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 inside the pipe to act as a fluid resistance.
The pressure difference between the upstream side and the downstream side is measured and the flow rate is calculated based on a predetermined calculation formula. 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, material, etc. is selected and used according to the measurement specifications of the process, it may sometimes receive excessive pressure. This overpressure may 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 protection device. A barrier diaphragm 2 on the high-pressure side and a barrier diaphragm 3 on the low-pressure side are installed, and these barrier diaphragms 2 and 3 are provided with covers 4 on both sides bolted to the body 1.
A high pressure and a low pressure are applied by fluids flowing in from holes 5 and 6 between the body 1 and the body 1, respectively.
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 bonded and held to a substrate 9. The low pressure side 8b is connected to the high pressure side and low pressure side of the body via liquid passages 10 and 11. (As an example of the structure, there is Japanese Patent Application Laid-Open No. 56-87372.)
The reason why the sensor 8 has a high pressure side 8a and a low pressure side 8b is because this type of sensor has a directional pressure strength. In other words, since the sensor 8 is bonded to the substrate, it is weak against pressure from the anti-bonding direction (direction from the top to the bottom), but has relatively high breaking strength against pressure from the bonding direction. It is from. What is indicated by the reference numeral 12 is a center diaphragm formed in the shape of a corrugated disk,
It is fixed to the body 1 so that the inner chamber provided at the central joint of the half-split body 1 is separated into a high pressure side inner chamber 13 and a low pressure side inner chamber 14, and each of the liquid passages 10,
11 is opened into inner chambers 13 and 14, respectively. Also, the gaps formed between the barrier eye diaphragms 2, 3 and the body 1 and the inner chamber 13,
14 through liquid passages 15 and 16, respectively. And barrier diaphragm 2,
3 and the liquid passage 15, 1 from the gap between the body 1
6. An internal sealing liquid 17 such as silicone oil is sealed between the high pressure side and the low pressure side of the sensor 8 via the internal chambers 13 and 14 and the liquid passages 10 and 11.

In the differential pressure transmitter configured as 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 compressed by the amount of compression.
moves, and the sensor 8 detects the difference in the amount of movement of the sealed liquid 17 due to the pressure difference between 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 does not come into contact with the walls of the inner chambers 13 and 14. Furthermore, the barrier diaphragms 2 and 3 do not come into contact with the body 1 during normal differential pressure measurement. For example, when excessive pressure acts on the high pressure side, the barrier diamond Flow 2 on the high pressure side deforms greatly and comes into full contact with the body 1, so that the pressure on the high pressure side is no longer transmitted to the inside. That is, by seating the barrier diaphragm 2, it functions to protect against excessive pressure.

In a conventional differential pressure transmitter equipped with such an overpressure protection device, even under the normal measurement pressure range in which no overpressure acts, the internal liquid 17 moves not only in the direction of the sensor 8 but also in the direction in which the center diaphragm 12 is displaced. Since the pressure on the barrier diaphragms 2 and 3 is not directly transmitted to the sensor, not only is the transmission efficiency low, but the response is also poor.
Since the center diaphragm 12 is not held by anything inside the inner chambers 13 and 14, and is only held at its peripheral edge so as to be able to swing freely, the hysteresis due to repeated displacement is large and difficult to measure. The drawback was that accuracy decreased. Also,
This type of differential pressure transmitter usually has a
The breaking strength of the sensor is set to about 5 times the upper limit of the measurement range in consideration of safety against thermal expansion of the internal liquid due to changes in environmental temperature of up to 120°. For this reason, the measurement range of the sensor is also narrowed, resulting in a poor signal-to-noise ratio.

The present invention has been made in view of the above-mentioned points, and includes a spacer which is divided into two chambers by the center diaphragm in the inner chamber, and the lower pressure side of the chamber is provided with a means for communicating the internal liquid, and the spacer is connected to the center diaphragm side. A spring member is disposed to urge the spacer, and is configured to be brought into close contact with the spacer center diaphragm when the differential pressure is below a predetermined pressure, and to compress the spring member when the differential pressure is above a predetermined pressure, and to seat the pressure receiving diaphragm on the body when excessive pressure is applied. As a result, while the differential pressure between the high-pressure side and the low-pressure side is below a predetermined value, the movement of the center diaphragm is restricted by the spacer that is spring-loaded by the spring member, improving pressure transmission efficiency, responsiveness, and measurement accuracy. The present invention provides a differential pressure transmitter that expands the measurement range of the sensor and improves measurement accuracy by making it possible to bring the upper limit of the measurement range closer to the sensor breaking strength. Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a sectional view showing an embodiment of the differential pressure transmitter according to the present invention. In the figure, the body 22 of the differential pressure transmitter 21 is integrally made up of a low-pressure side back plate 22a having a circular recess reaching the center in the thickness direction and a high-pressure side back plate 22b fitted in the recess. Each back plate 2
In the side pressure receiving concave surfaces of 2a and 22b, a low pressure side barrier diaphragm 23 and a high pressure side barrier diaphragm 24 formed in the shape of a corrugated disk are arranged, and a low pressure side barrier diaphragm chamber is formed between the same shaped pressure receiving bottom surface. 2
5 and a high pressure side barrier diaphragm chamber 26 (hereinafter referred to as gaps 25 and 26), the peripheral edge portion is fixed to the body 22 side. Further, although not shown, a cover similar to that shown in FIG. 1 is joined to each back plate 22a, 22b, and the barrier diaphragm 23, 24 is connected to the low pressure of the liquid flowing through the hole in the cover. A high voltage is applied to each. The gaps 25 and 26 are connected by a liquid passage 27 having apertures at both ends, and the back plates 22a and 2 on this liquid passage 27
2b, a body interior chamber 28 is provided with most of it located on the back plate 22a side and a part of it located on the back plate 22b side.

Reference numeral 29 denotes a center diaphragm which is formed into a disk shape with a corrugated cross section and separates two chambers in the body inner chamber 28, an inner chamber 28a on the low pressure side and an inner chamber 28b on the high pressure side. Back plate 22
The inner wall surface of the back plate 22b is formed in the same shape as the center diaphragm 29. An inner chamber 28a on the low pressure side, which is formed between the center diaphragm 29 and the inner wall surface of the back plate 22a and has a slightly larger diameter than the inner chamber 28b on the back plate 22b side, is capable of moving forward and backward with respect to the center diaphragm 29. A spacer 30 and a disc spring 31 as a spring member that urges the spacer 30 toward the center diaphragm 29 are provided. The spacer 30 is formed into a disk shape, and the side surface on the center diaphragm 29 side is formed in the same shape as the center diaphragm 29 so as to be in close contact with the center diaphragm 29. A liquid passage 30a is provided which extends in the shape of a cross. Therefore, the spacer 30 is restricted from moving to the left from the illustrated position by the back plate 22b via the center diaphragm 29. Further, the disc spring 31 is formed in a conical shape with a low head, and when the differential pressure from the high pressure side is less than a predetermined pressure, the spacer 30 overcomes this pressure.
is brought into close contact with the center diaphragm 29, and its spring pressure is set so that it is pressed by the spacer 30 and compressed when the pressure exceeds a predetermined pressure.

On the other hand, inside the sensor capsule 32 which 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 8a of the sensor is communicated with the high pressure side interior chamber of the body interior chamber 28 through the liquid passage 33. Further, the low pressure side of the sensor is communicated with the low pressure side 8b interior of the body interior chamber 28 through a liquid passage 34. Gaps 25, 26 behind the barrier diaphragms 23, 24, liquid passage 27, body interior chamber 28,
In the liquid passages 33 and 34, a liquid sealing hole 35,
Internal sealing liquid 37 such as silico oil injected from 36
The spacer 30 has a plurality of communication holes 38 as communication means for the inner sealing liquid 37.
is drilled.

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 23 and 24 are recessed, and the sealing liquid 37 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 between both sides and transmits it as an electrical signal, thereby measuring the pressure difference. in this case,
As for the pressure from the process, in most cases the pressure applied to the barrier diaphragm 24 on the high pressure side is higher than the pressure applied to the barrier diaphragm 23 on the low pressure side, and this case will be described first. When the differential pressure is 0, the spacer 30 acts as a disc spring 31.
When a differential pressure is applied to the center diaphragm 29 via the high pressure side internal sealing liquid 37,
If this differential pressure is below a predetermined pressure, the spacer 3
0 and the center diaphragm 29 are maintained in close contact. Therefore, during this time, the inner sealing liquid 37 moves only toward the sensor, and a pressure proportional to the differential pressure is applied to the sensor. When the differential pressure from the process exceeds a predetermined pressure, the center diaphragm 29 and the spacer 30 move toward the low pressure side against the elastic force of the disc spring 31, and this pressure causes excessive pressure before it destroys the sensor. In this case, the barrier diaphragm 24 on the high pressure side is seated on the pressure receiving surface of the back plate 22b, so no more pressure is transmitted to the sensor, and the sensor can be protected from excessive pressure.

Next, although it is rare, the pressure on the barrier diaphragm 23 on the low pressure side is higher than the barrier diaphragm 2 on the high pressure side.
There are cases where the pressure is greater than the pressure on 4, so this will be explained. That is, when differential pressure is applied to the low pressure side, the sealing liquid 37 in the gap 25 flows into the liquid passage 27.
and through the communication hole 38 to between the center diaphragm 29 and the spacer 30, and the center diaphragm 29 is displaced to the high pressure side. In this case, the movement of the sealing liquid 37 toward the sensor is the same as in the conventional device shown in FIG. 1, and the transmission efficiency is not necessarily good, but the pressure on the low pressure side is rarely higher than the high pressure side. Moreover, since the sensor itself has a directional pressure resistance strength, there is no problem in practical use as long as the low pressure side 8b is protected against overpressure. Then, when the differential pressure reaches a predetermined pressure before destroying the sensor, the barrier diaphragm 23 on the low pressure side seats on the pressure receiving surface of the back plate 22a, so no more pressure is transmitted to the sensor, and the sensor can be protected from overpressure.

FIG. 3 is a sectional view showing another embodiment of the present invention, and in this embodiment, a bellows 39 is provided in the space between the spacer 30 and the body 22 and fixed to the back plate 22b at the fixed end thereof. However, since the movable end is fixed to the spacer 30 and is the same as the previous embodiment, the same reference will be given and the explanation thereof will be omitted.
By doing so, movement of the sealing liquid 37 between the high pressure side and the low pressure side can be sealed.

In each of the above embodiments, since the spacer 30 and disc spring 31 are provided, the inner chamber on the low pressure side is larger than the inner chamber on the high pressure side, and there is a difference in the amount of liquid between the two chambers. Therefore, if the body 22 and the internal sealing liquid 37 simultaneously expand due to a change in the environmental temperature, this will be transmitted to the sensor due to the large difference in the coefficient of expansion between the metal and silicone oil and the difference in the amount of liquid in both chambers. This affects the differential pressure applied. Therefore, as another embodiment, if the spacer 30 is formed of a material with a low coefficient of thermal expansion, such as ceramic or invar, even if the internal sealing liquid 37 in the low-pressure side inner chamber expands greatly, the low expansion coefficient of the spacer 30 can prevent this expansion. By canceling out the difference with the high pressure side where the liquid amount is small, it is possible to eliminate the influence on the amount of differential pressure transmitted to the sensor.

Further, in each of the above embodiments, an example was shown in which a cross-shaped liquid passage 30a was provided as a communication means for the inner sealing liquid to separate the spacer 30 from the center diaphragm 29. The spacer 3 is formed by plastic processing such as providing a large number of protrusions using a punch-type protrusion forming process.
0 from the center diaphragm 29, processing for forming the liquid passage becomes easy and processing costs can be reduced.

Further, in each of the above embodiments, the communication hole 38 is provided as a communication means for the internal sealing liquid 37 provided in the spacer 30, but the spacer 30 may be made of a porous sintered metal with air permeability, a cellular metal, or It may be formed from a material such as ceramic, which eliminates the need for hole drilling or curved surface processing, which can significantly reduce processing costs, and also allows for smooth flow of the sealing fluid to prevent excessive pressure. The quick response of the protection device can be improved.

As is clear from the above description, according to the present invention, in a differential pressure transmitter, the inner chamber of the body is divided into two chambers by a center diaphragm, and the lower pressure side chamber of the two chambers is provided with a spacer and a spacer provided with a means for communicating the internal sealing liquid. The spacer is placed in close contact with the center diaphragm when the differential pressure is below a predetermined pressure, and the spring member is compressed when the differential pressure is above a predetermined pressure. By configuring the sensor to be seated, not only can the sensor be protected from excessive pressure, but also when the differential pressure is below a predetermined value, the movement of the sensor diaphragm is restricted by the spacer that is sprung by the spring member. Since the pressure is directly transmitted to the sensor, the transmission efficiency can be improved, and since the center diaphragm is stationary, hysteresis can be reduced. In addition, since there is no movement of the sealing liquid in any direction other than the direction of the sensor, pressure response is extremely good and measurement accuracy is improved. Therefore, since it can be easily selected, it can easily correspond to all conditions. moreover,
The upper limit of the measurement range can be brought close to the breaking strength of the sensor, and the measurement range of the sensor can be expanded accordingly, and the S/N ratio can be increased, making it possible to significantly improve measurement accuracy.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional differential pressure transmitter equipped with an overpressure protection device, and FIGS. 2 and 3 show an embodiment of the differential pressure transmitter according to the present invention, and FIG. 2 is a sectional view thereof. , FIG. 3 is a sectional view of a differential pressure transmitter as another embodiment of the present invention. 21, 21A... Differential pressure transmitter, 22... Body, 23, 24... Barrier diaphragm, 25,
26...Gap, 27...Liquid passage, 28...Body interior, 29...Center diaphragm, 30...
Spacer, 31...disc spring, 33, 34...liquid passage, 37...inner sealing liquid, 38...communication hole.

Claims (1)

[Claims] 1 The body internal chamber 28, which communicates with the high and low pressure side barrier diaphragm chambers 26 and 25 provided on both sides of the body, is divided into two chambers by a center diaphragm 29, and one of the divided chambers is connected to the high pressure side of the sensor. 8
a, and the other chamber is connected to the low-pressure side 8b of the sensor, in which a spring member 31 is attached in the direction of the center diaphragm to the chamber that is connected to the low-pressure side barrier diaphragm chamber 25 of the two chambers. 1. A differential pressure transmitter characterized in that a spacer 30 is inserted which is biased and whose movement is restricted at its peripheral edge.