JPS58167936A - Differential pressure transmitter - Google Patents

Abstract

PURPOSE:To protect a pressure sensor from an excessively large differential pressure by such an arrangement wherein a by-pass is caused to open when a differential pressure exceeds a certain limit, and fluid at both sides of the pressure sensor is caused to interflow. CONSTITUTION:When an opening inside the body 1 of a bypass 20 is caused to open to the right of an O ring 12 by a differential pressure exceeding a certain limit, fluid entering through an inlet 15 at the right hand side flows toward an inlet 16, and by this flow, the pressure of fluid at the right hand side falls, and on the contrary, the pressure of fluid at the left hand side rises, and the difference between the pressure of fluid at the left side and that of fluid at the right side of a movable element 11 equilibrates with the righting moment of bellows 13, 14 at such a position at which the O ring 12 causes the opening inside the body of the bypass 20 to slightly open to the right of the movable element 11, and even if the pressure of fluid at the right hand side rises further, the position of the movable element 11 is hardly varied, and consequently undue force will never be applied to the bellows 13, 14.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a medical protection device when an over-range differential pressure is applied to a differential pressure transmitter.

Conventionally, in differential pressure transmitters, in order to protect the pressure sensor when an over-range differential pressure is applied, when the differential pressure reaches a certain value, the seal diaphragm hits the body of the differential pressure transmitter and prevents the pressure sensor from exceeding the pressure range. Methods such as making it impossible to displace or blocking the passage of the sealed liquid are used. However, even with this arrangement, if overrange is applied, distortion may occur in the diaphragm or body, causing problems in measurement such as deviation of the zero point.

The present invention aims to solve the above-mentioned problems, and is designed to not only protect the pressure sensor from over-range pressure, but also protect differential pressure transmitter components such as the diaphragm and body from over-range pressure. The present invention provides a pressure transmitter.

In order to clarify the purpose and effect of the present invention, a conventional example will first be described. Different conventional examples are shown in FIG. 1 and FIG. 2, respectively. FIG. 1 shows a conventional example using a capacitive pressure sensor. 1 is a body with a small chamber in the center, which is partitioned into left and right sides by a flat diaphragm 2. Electrode plates 3.4 are provided on both sides of the small chamber, respectively, and face the seal diaphragm to form a capacitor, and this capacitor serves as a pressure sensor. Numerals 5 and 6 are seal diaphragms, and the inner surface of each diaphragm communicates with the small chamber.

The small chamber is filled with a sealed liquid and transmits the displacement of the seal diaphragm to the flat diaphragm 2. A measuring pressure acts on the outer surface of each sealing diaphragm 5,6. When the difference between the pressures acting on the outer surfaces of the left and right seal diaphragms 5 and 6 reaches a value, the inner surface of the seal diaphragm on the side with the higher operating pressure hits the body 1, and even if the pressure difference becomes larger than that, The sealing diaphragm can no longer be displaced, so that the planar diaphragm 2 forming the pressure sensor is protected from excessive pressure differences.

However, at this time, considering the side of the seal diaphragm that is pressed against the body 1, the seal diaphragm is provided with a corrugate (concentric waveform), and the surface of the body 1 that the seal diaphragm contacts is fitted with the corrugate. However, there are limits to processing and assembly accuracy, so the corrugations of the seal diaphragm and the corrugations of the body do not perfectly match, and the seal When the diaphragm is pressed against the body, local contact occurs and local deformation that exceeds the elastic limit occurs.As a result, after the overrange pressure difference disappears, the equilibrium position of the left and right seal diaphragms shifts and the zero point is lost. A phenomenon occurs in which the sensitivity changes due to distortion or changes in the rigidity of the seal diaphragm. Also body 1
However, since it is not composed of a single block but multiple parts that are stacked and joined together with a diaphragm in between, the excessive differential pressure will cause the connections to shift and the zero point will shift. may occur. The example shown in Fig. 2 has a configuration in which the displacement of the spool 7 connected between the left and right seal diaphragms 5 and 6 is taken out of the body l by a lever 8, and when an excessive differential pressure acts, the spool of the seal diaphragm is attached. The seat surface is pressed against the O-ring 9 or 10 to prevent the sealed liquid between the seal diaphragm and the body from escaping toward the seal diaphragm on the opposite side, and to prevent the sealed liquid between the body and the seal diaphragm from escaping towards the seal diaphragm on the opposite side. This is designed to prevent the seal diaphragm from coming into contact with the body 1 by confining the body 1, which prevents the seal diaphragm from deforming as shown in Figure 1, but causes an unbalanced excessive force to act on the body 1. This is unavoidable, and since the bodies are stacked, it is unavoidable that the unbalanced acting force on the left and right causes distortion in the connection and causes zero point movement. The present invention attempts to solve such problems.

The present invention will be explained below with reference to Examples.

FIG. 3 and FIG. 4 show an embodiment of the present invention.
The figure shows an equilibrium state, and FIG. 4 shows a state when an over-range differential pressure is applied. 1 is a cylindrical body, into which a moving body 11 is fitted. An O-ring 12 is fitted around the outer periphery of the movable body 11 to provide an airtight connection with the body 1, and the movable body 11 moves left and right like a piston due to the pressure difference between the left and right sides. '13.14 is a bellows that supports the moving body. 15.16 is the inlet of the fluid whose pressure is to be measured;
These fluids also enter the inside of the bellows 13.14 through passages 17.18 provided in the body l, and enter the bellows 13.14.
The body 1 is provided with bypasses 19 and 20 which communicate with the fluid inlets 15 and 16 and open into the cylindrical inner surface of the body. The opening positions of the cylindrical inner surface of the bypasses 19 and 20 are closer to the fluid inlets 15 and 1, respectively, than the equilibrium position of the moving body 11 (FIG. 3).
It's on the side closer to 6. Reference numeral 21 denotes a pressure sensor attached to the center of the moving body 11, which generates an output in response to the pressure difference between the fluid on its left and right sides. Let's now consider a case where the fluid pressure on the right side increases and the difference between the left and right fluid pressures exceeds the set value. At this time, the movable body 11 is moved to the left, and the O-ring 12 is opened on the inner surface of the body 1 of the bypass 20. over to the left. This state is shown in FIG. 0 ring bypass 20
If you go beyond the inner surface opening of the body 1 to the left side, there is a fluid inlet port 15.
The fluid that enters through the bypass 20 flows toward the lower pressure fluid inlet 16. As a result, the fluid pressure on the right side of the movable body 11 decreases, the fluid pressure on the left side increases, and the differential pressure stops increasing, and the movable body 11 is moved so that the O-ring 12 is about to cross the inner surface opening of the body l of the bypass 20 to the left. Stop at the right place. When the fluid pressure on the left side rises, the movable body 11 is moved to the right, and when the pressure difference exceeds the limit, the O-ring 12 crosses the inner opening of the body 1 of the The movable body 11 stops at that position by the same action as at that position.

FIG. 5 shows another embodiment of the present invention in which the bellows 13 and 14 in the above embodiment are replaced with coil springs 13' and 14', and the operating principle is exactly the same as in the above embodiment.

Returning to Figure 4, if the differential pressure exceeds the limit
When the inner opening of the body 1 of O-ring 12 opens on the right side of the O-ring 12, the fluid pressure on the right side is higher than the fluid pressure on the left side, so the fluid that enters from the fluid inlet port 15 on the right side flows toward the inlet port 16. , the fluid pressure decreases due to the action of this flow chair, etc., and conversely, the fluid pressure on the left side increases. In balance with the restoring force of the bellows 13 and 14 in the position where the right side of the bellows 11 is slightly opened, even if the fluid pressure on the right side further increases, the movable body 11 moves slightly to the left to increase the degree of opening of the bypass 20. , the position of the moving body 11 hardly changes, and no unreasonable force is applied to the bellows 13 and 14. Furthermore, the pressure difference between the left and right sides within the body hardly changes and never exceeds a preset pressure difference.

The differential pressure transmitter of the present invention has the above-mentioned configuration, and when the differential pressure exceeds the limit, the bypass opens and communicates the fluid on both sides of the pressure sensor, preventing the differential pressure from increasing further and preventing the pressure sensor from becoming excessive. In addition to being protected from excessive pressure differences, the components of the differential pressure transmitter will not be exposed to excessive pressure differences, and distortions that may interfere with subsequent measurements, etc., can be avoided.

[Brief explanation of the drawing]

Figures 1 and 2 are longitudinal sectional side views of different conventional examples, Figure 3 is a longitudinal sectional side view of an embodiment of the present invention in an equilibrium state, and Figure 4 is the limit differential pressure of the embodiment. Fig. 5 is a longitudinal side view of another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Body, 11... Moving body, 12... 0 ring, 13.14... Bellows, 15.16... Fluid inlet, 19.20... Bypass, 21... pressure sensor. Agent Patent Attorney Kosuke

Claims (1)

[Claims] A movable body is fitted airtightly and slidably into a cylinder of a body having a cylindrical inner surface, and the pressure of the fluid to be measured is applied to both sides of the movable body, and openings are provided near both ends of the cylindrical inner surface. A bypass is provided which leads to the measurement fluid inlet on each side of the body, and the moving body is supported by an elastic body to give the moving body a restoring force to the center position, and a preset limit differential pressure is maintained. A differential pressure transmitter characterized in that the movable body at the bottom crosses an opening on the inner cylindrical body of the body of the bypass provided on the low-pressure side and connects the bypass to the high-pressure side.