JPH0322572B2 - - 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. according to the measurement specifications of the process is selected and used, it may sometimes be subjected to excessive pressure. The overpressure of the lever can reach the semiconductor sensor and damage it, making further measurements impossible. Therefore, various devices for protecting sensors from this excessive pressure have been proposed and attached to differential pressure transmitters. As a differential pressure transmitter having such a structure, there is one proposed, for example, in Japanese Patent Application Laid-Open No. 56-87372.

However, in differential pressure transmitters equipped with conventional overpressure protection devices, even under normal measurement pressure ranges in which overpressure does not act, the internal liquid moves not only in the direction of the sensor but also in the direction of displacing the center diaphragm, causing the barrier Since the pressure on the diaphragm is not directly transmitted to the sensor, not only is the voltage efficiency low and responsiveness is poor, but the center diaphragm is not held in place by anything within the inner chamber, and the peripheral portion is held in a freely swingable manner. This has the drawback that hysteresis due to repeated displacement is large and measurement accuracy is reduced.

The present invention was made in view of the above points, and the central partition wall in the body is divided into two parts, one on the high pressure side and one on the low pressure side.
A pressure-receiving element is disposed in a pressure-receiving chamber formed between the two parts, and a mover fixed to a movable end of the center of the pressure-receiving element is engaged in a center through-hole of the central partition so as to be movable in the axial direction. By configuring leaf springs to be elastically adjustable on both sides of the central partition so that they are elastically deformed via the pressure-receiving element and slider when excessive pressure is applied, and the pressure-receiving diaphragm being seated on the body side, the measurement range can be increased. The present invention provides a differential pressure transmitter that improves transmission efficiency, responsiveness, measurement accuracy, and overpressure protection function by regulating the movement of internally sealed liquid within the chamber. Embodiments of the present invention will be described in detail below with reference to the drawings.

1 to 4 show an embodiment of the differential pressure transmitter according to the present invention, FIG. 1 is a sectional view thereof, FIG. 2 is a front view and side view of a leaf spring, and FIG. 3 is an example of applying excessive pressure. FIG. 4 is a cross-sectional view of the differential pressure transmitter at this time, and is a relationship diagram between the pressure applied to the pressure receiving diaphragm and the pressure applied to the sensor. In the figure, a differential pressure transmitter 1 includes a body 2 integrally formed with a cylindrical part and a disc part that closes openings at both ends of the body 2, and a sealed sensor chamber 3 is integrally formed above the body 2. There is. A barrier diaphragm 4 on the high-pressure side and a barrier diaphragm 5 on the low-pressure side, which are formed in the shape of a disk with a corrugated cross-section, are located on the side surfaces of both side disk portions of the body 2, and between these and the side surfaces of the body 2, which have approximately the same shape. The peripheral edge is fixed with a gap provided. 6 and 7 are covers respectively connected to both sides of the body 2 with bolts,
Pressure receiving chambers 8 and 9 between barrier diaphragms 4 and 5
It is provided with holes 10 and 11 that open toward the inside, and the holes 10 and 11 communicate with the high pressure side and the low pressure side of the process fluid conduit, respectively. In addition, the gap behind the barrier diaphragms 4 and 5 and the inner chamber of the body 2 are communicated with each other by liquid passages 12 and 13, and the inner chamber of the sensor chamber 3 and the inner chamber of the body 2 are also connected through liquid passages. 14 and 15 communicate with each other.

In the inner chamber of the body 2, an inner chamber 17 on the high pressure side and an inner chamber 18 on the bottom pressure side are separated by a central partition wall 16 whose outer periphery is welded to the body 2. It is divided into two parts, a side and a low pressure side, and a pressure receiving chamber 19 is formed between them. On the other hand, inside the sensor chamber 3, a semiconductor sensor 21 connected to a terminal 20 is mounted and fixed on substrates 22, and the liquid passage 14 opening to the high pressure side inner chamber 17 in the body 2 is connected to the sensor chamber 3. It is opened to the high pressure side of 21. Further, the liquid passage 15 that opens to the low pressure side inner chamber 18 in the body 2 is opened to the low pressure side of the sensor 21.

Reference numeral 23 designates a center diaphragm which is formed in the shape of a disk with a corrugated cross section and serves as a pressure receiving element that separates two chambers in the pressure receiving chamber 19, and has a peripheral fixed end fixed to the central partition wall 16. A mover 24 with a disc-shaped flange is fixed to the center portion, which is the movable end. The shaft portion of the mover 24 is connected to the central partition wall 1
It is engaged in a communicating hole 25 bored through the center of the central partition wall 16 so as to be movable in the axial direction, and the end surface of the shaft portion is positioned almost on the same plane as the outer surface of the central partition wall 16 when no load is applied. is set to . Further, on both sides of the central partition wall 16, a pair of leaf springs 26 and 27 made of an elastic material and formed in an arcuate cross shape when viewed from the side are provided with elastic force by four set screws 28, respectively, as shown in FIG. It is fixed and adjustable, and its elasticity restricts movement of the mover 24 in the axial direction.

The gaps between the barrier diaphragms 4 and 5 and the body 2 of the differential pressure transmitter 1 configured as described above, the liquid passages 12 and 13, the inner chambers 17 and 18, the communication hole 25, the two pressure receiving chambers 19, and the liquid passage 14. , 15 and sensor 2
An internal sealing liquid 29 such as silicone oil is sealed in the high pressure side and the low pressure side of 1. The rigidity of each diaphragm 4, 5, 23 and the spring pressure of leaf springs 26, 27 are set as follows. That is, within a predetermined measuring pressure range, the center diaphragm 23 does not bend, and the plate springs 26 and 27 are pressed against the central partition wall 16 to restrict the movement of the slider 24 in the axial direction. A gap is formed between 5 and the body 2. For example, when an excessive pressure equal to or higher than a predetermined pressure is applied to the barrier diaphragm 4 on the high pressure side, the center diaphragm 23 is bent, the slider 24 pushes the leaf spring 27 on the low pressure side to elastically deform it, and then the barrier diaphragm 4 on the high pressure side The diaphragm 4 seats on the body 2 and stops the movement of the sealing liquid 29.

The operation of the differential pressure transmitter configured as above will be explained. In FIG. 1, high pressure is applied to the high-pressure side diaphragm 4 that communicates with the high-pressure side of the process pipe through holes 10, and low pressure is applied to the low-pressure side diaphragm 5 that communicates with the low-pressure side through holes 11. be done. In this case, the leaf springs 26 and 27 are pressed against the central partition wall 16, and the sealing liquid 29 moves toward the sensor 21 by applying pressure to the barrier diaphragms 4 and 5. At this time, the pressure difference between the high-pressure side and the low-pressure side of the sensor 21 due to the movement of the internal sealing liquid 29 causes the sensor 21 to detect this pressure difference, convert it into an electrical signal, and send it out.This is input and calculated. Then, the flow rate, liquid level, etc. can be measured.

For example, when excessive pressure exceeding a predetermined pressure occurs on the high pressure side and is applied to the barrier diaphragm 4 on the high pressure side, the sealing liquid 29 in the chamber 17 moves toward the pressure receiving chamber 19 as shown in FIG. The center diaphragm 23 is bent, the mover 24 moves in the axial direction, and the low-pressure side leaf spring 27 is elastically deformed.
The barrier diaphragm 4 on the high pressure side is seated on the body 2 and stops the movement of the internal sealing liquid 29. Therefore, excessive pressure does not act on the sensor 21, and it can be protected. It operates in exactly the same way when excessive pressure occurs on the low pressure side.

Figure 4 is a pressure relationship diagram with the horizontal axis representing the differential pressure ΔP on the barrier diaphragm and the vertical axis representing the acting pressure _P on the sensor. It shows the point at which the device started operation, and point P ₂ shows the point at which this operation ended. As is clear in the figure, when excessive pressure is applied beyond the measurement range up to point _P1 , the pressure P on the sensor increases slightly, but it does not destroy the sensor, and after the protective device is activated. That is, after the barrier diaphragms 4 and 5 are seated, the pressure will not rise above this level. Even if the pressure changes within the measurement range, the leaf springs 26, 2
7, the center diaphragm 23, and the slider 24 are stationary, and the inner liquid 29 moves only toward the sensor 21, so errors caused by mechanical hysteresis can be eliminated, and a pressure correctly proportional to the measured pressure can be applied to the sensor. In addition, the response to changes in the measured differential pressure ΔP is extremely good.

Furthermore, the leaf springs 26 and 27 are configured such that their spring pressure can be adjusted by rotating the upper screw 28 back and forth, and the adjustment is made for each transmitter. This is the leaf spring 2 that restricts the movement of the mover 24.
Even if the spring pressure in step 4 is determined according to the measurement range, there will be differences for each transmission due to manufacturing errors of each part and machine variations, so this is adjusted. Variations can be easily absorbed.

As is clear from the above description, according to the present invention, in a differential pressure transmitter, the central partition wall in the body is divided into two parts, a high pressure side and a low pressure side, and a pressure receiving element is disposed in a pressure receiving chamber formed between the high pressure side and the low pressure side. A movable element fixed to the movable end of the center of the pressure receiving element is engaged in a through hole in the center of the center partition so as to be movable in the axial direction, and leaf springs are fixed to both sides of the center partition so that their elasticity can be adjusted freely. When excessive pressure is applied, the pressure-receiving element and the slider are elastically deformed, and the pressure-receiving diaphragm is seated on the body side. Within the measurement range, the plate spring restricts the movement of the slider and the movement of the slider inside the body is reduced. Since the movement of each member is restricted and the movement of the sealed liquid in directions other than the sensor direction is eliminated, the transmission efficiency is high and the responsiveness to changes in fluid pressure is extremely good. In addition, within the measurement range, not only the periphery but also the center of the pressure-receiving element is held, so errors caused by mechanical hysteresis can be suppressed, and extremely accurate pressure proportional to fluid pressure can be measured. The measurement accuracy can be significantly improved. Furthermore, since the spring pressure of the leaf spring can be adjusted, manufacturing errors and variations in function of parts can be easily absorbed, and the overpressure protection function is improved.

[Brief explanation of the drawing]

1 to 4 show an embodiment of the differential pressure transmitter according to the present invention, FIG. 1 is a cross-sectional view thereof, FIG. 2 is a front view and a cross-sectional view of a leaf spring, and FIG. 3 is an example of applying excessive pressure. FIG. 4 is a cross-sectional view of the differential pressure transmitter at this time, and is a relationship diagram between the pressure applied to the pressure receiving diaphragm and the pressure acting on the sensor. 1... Differential pressure transmitter, 2... Body, 4, 5...
Barrier diaphragm, 14, 15...liquid passage, 1
6... Central bulkhead, 17, 18... Inner chamber, 19...
Pressure receiving chamber, 21...sensor, 23...center diaphragm, 24...mover, 25...communication hole, 2
6, 27...plate spring, 28...set screw.

Claims (1)

[Claims] 1 A body having two liquid-filled chambers separated by a central partition wall and communicating through a liquid passage between the high-pressure side and the low-pressure side of the sensor, and pressure-receiving diaphragms arranged on both pressure-receiving surfaces of this body, respectively. In the differential pressure transmitter, the central partition wall is divided into two parts, a high pressure side and a low pressure side, and a pressure receiving chamber is formed therebetween, a peripheral fixed end is fixed to the central partition side, and a central movable end is fixed to the central partition wall side. A pressure-receiving element fixed to a moving element in a communication hole penetrating the central partition in the direction of displacement is disposed in the pressure-receiving chamber, and within a normal measurement pressure range, the movement of the moving element is elastically restricted. A plate spring that is elastically deformed by being pushed by the slider when an excessive pressure is applied to the body is fixed to both sides of the central partition wall so that the elasticity of the pressure receiving diaphragm can be adjusted. A differential pressure transmitter characterized in that it is set to be seated on.