JPS62168031A - differential pressure transmitter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to a differential pressure transmitter for detecting differential pressure in a process control system, etc., and particularly relates to an overpressure protection mechanism.

(b) Conventional technology In general, a differential pressure transmitter that detects differential pressure by utilizing the distortion of a spring member such as a semiconductor has flanges (flanges) on both sides of the body a, as shown in FIGS. 3 and 4. (omitted in Figure 3) to form a high pressure introduction chamber C and a low pressure introduction chamber d, an overpressure protection chamber e and a pressure detection chamber f are formed in the body a, and a protection means g is formed in the protection chamber e. , a pressure sensor h equipped with a semiconductor piezoresistive element is provided in each of the detection chambers, and a seal diaphragm i is provided in each introduction chamber c, d, and from this seal diaphragm i through a communication path j, a protection chamber and a detection chamber are provided. The sealing liquid k is filled over an area f. In this differential pressure transmitter, the pressure introduced into each introduction chamber C1d is transmitted through a seal diaphragm i and a sealed liquid k to a pressure sensor h.
When a pressure difference occurs again, the resistance value of the pressure sensor h changes, and this resistance change is used as an electrical signal to lead wire! It is designed to detect the differential pressure.

(c) Problems to be Solved by the Invention In the differential pressure transmitter described above, the protection means g is formed by forming two protection chambers e provided with bellows m in the one shown in FIG. The outer chamber side of the bellows m and the inner chamber side of one bellows m are communicated with each other, and the top plate n of the bellows m is displaced due to the pressure difference. When this pressure difference exceeds a certain level, the top plate closes the communication path j. , the pressure sensor h is configured so that a differential pressure of more than a certain level does not act on the pressure sensor h.

In addition, the protection means g in FIG. 4 includes a center diaphragm 0 disposed in a protection chamber e, and when the center diaphragm 0 is displaced by a pressure difference and this pressure difference exceeds a certain level, the seal diaphragm i is moved from the body a. The pressure sensor h is configured to come into contact with the pressure sensor h, stop the movement of the sealed liquid, and prevent pressure above a certain level from acting on the pressure sensor h.

However, in any of the protection means g, since the bellows m or the center diaphragm 0 starts to move at the same time as the differential pressure is generated, the nonlinearity and hysteresis caused by the movement of the bellows m or the center diaphragm 0 affect the input/output characteristics of the pressure sensor h. This was causing deterioration. Also,
Non-linearity and hysteresis in the movement of the seal diaphragm i shown in FIG. 4 also caused deterioration of the input/output characteristics of the pressure sensor h.

(d) Means and operation for solving the problems In the present invention, a first pressure introduction chamber and a second pressure introduction chamber are formed on both sides of the housing, and a pressure detection chamber and an overpressure first introduction chamber are formed on both sides of the housing. A protection chamber and a second protection chamber are formed, the reintroduction chamber is provided with a seal diaphragm, each introduction chamber is divided into an introduction side and a detection side, and the detection chamber is provided with a spring member made of a brittle material. A pressure sensor is provided to divide the detection chamber into two pressure receiving sides, a bellows having a top plate is provided in both of the protection chambers, and each protection chamber is partitioned into an inner chamber side and an outer chamber side; 1st
The detection side of the introduction chamber, the outer chamber side of the first protection chamber, and the pressure receiving side of one of the detection chambers are the detection side of the second introduction chamber, the outer chamber side of the second protection chamber, and the pressure receiving side of one of the detection chambers. are in communication with each other via communication passages, and the outer chamber side of the first introduction chamber and the inner chamber side of the second introduction chamber are connected to the outer chamber side of the second introduction chamber and the outer chamber side of the first introduction chamber. The bellows are communicated with the chamber side through communication passages, and the top plate of each bellows is pressed against the housing with a predetermined force under pressure from each introduction chamber.

Therefore, while the pressure in each introduction chamber acts on the pressure sensor via the seal diaphragm and the filled liquid, if the differential pressure is within the measurement range, the bellows is pressed against the housing and does not displace, so the internal and external seals If the liquid does not move and the differential pressure exceeds a predetermined pressure, the top plate of the bellows will be displaced, and this displacement will start the movement of the filled liquid.Then, the seal diaphragm will come into contact with the housing and prevent the movement of the filled liquid, reducing the pressure. This prevents excessive differential pressure from being applied to the sensor.

(e) Examples Hereinafter, one embodiment of the present invention will be described based on the drawings.

As shown in FIG. 1, reference numeral 1 denotes a differential pressure transmitter, which detects differential pressure in a process control system or the like.

The housing 2 of the differential pressure transmitter 1 has a body 2a in the center and flanges (not shown) attached to both sides, and a first pressure introduction chamber 3a between the body 2a and the flange.
and a second entrance chamber 3b are formed, through which high and low process pressures, etc. are introduced.

In the center of the body 2a, a pressure detection chamber 4 is formed in the upper part, and a first overpressure protection chamber 5a and a second protection chamber 5b are formed in the lower part. This detection chamber 4 has a pressure sensor 6.
The pressure sensor 6 is made up of a spring member, a semiconductor device made of a semiconductor, a resistance element, and a detection chamber 4.
is divided into two pressure receiving sides.

Further, each protection chamber 5a, 5b is provided with a bellows 7a, 7b, and the bellows 7a, 7b is connected to a bellows part 8a, 8b.
top plates 9a and 9b are connected to each other, and each protective chamber 5a and 5
b is divided into an outer chamber side and an inner chamber side. Further, the bellows 7a, 7b are configured such that a compressive force is applied to the bellows parts 8a, 8b, etc., and the top plates 9a, 9b are pressed against the body 2a on the side of the introduction chambers 3a, 3b with a predetermined pressure. There is.

A seal diaphragm 10a is provided in each of the introduction chambers 3a and 3b.
, 10b are provided, and each introduction chamber 3a, 3b is divided into a pressure introduction side and a pressure detection side.

Further, the detection side of the first and second introduction chambers 3a, 3b and the outer chamber side of the first and second protection chambers 5a, 5b are the same as the outer chamber side of the first and second protection chambers 5a, 5b and the detection chamber. The pressure-receiving side of No. 4 is communicated with the pressure receiving side through communication passages 11a, llb and 12a, 12b, respectively, so as to allow free flow.

Further, the outer chamber side of the first protection chamber 5a and the inner chamber side of the second protection chamber 5b are connected to each other, and the outer chamber side of the second protection chamber 5b and the outer chamber side of the first protection chamber 5a are connected to a communication path 13a, respectively. 13b for free circulation.

Communication path 11 between the introduction chambers 3a, 3b and the protection chambers 5a, 5b
The protective chamber side openings 14a and 14b in a and Ilb are formed with narrow grooves, and the top plates 9a and 9b of the bellows 7a and 7b leave the narrow grooves of the openings 14a and l4b, and the body 2
It is pressed by a. In addition, an incompressible filled liquid 1 is applied from the seal diaphragms 10a and 10b of each introduction chamber 3a and 3b to the protection chambers 5a and 5b and the pressure sensor 6 of the detection chamber 4.
5a and 15b are filled, and the pressure in the introduction chambers 3a and 3b is transmitted to the pressure sensor 6.

Note that 16 is a lead wire connected to the pressure sensor 6, and 17 is a lead wire connected to the pressure sensor 6.
is a hermetic seal that covers this lead wire 16 within the body 2a.

Next, the differential pressure detection operation of this differential pressure transmitter 1 will be explained.

First, the pressure introduced into each introduction chamber 3a, 3b is applied to the sealed liquid 15a, 15b from the seal diaphragm 10a, 10b.
At the same time, it acts on each bellows 7a, 7b through the pressure sensor 6. And this first protection room 5a
The pressure of the first introduction chamber 3a acts on the bellows 7a from the outside, and the pressure of the second introduction chamber 3a acts on the bellows 7b of the second protection chamber 5b from the outside.
The pressure in the introduction chamber 3 is applied from the inside by the pressure in the first introduction chamber 3a.

In this state, when a difference occurs in the pressure between the two introduction chambers 3a and 3b, this pressure difference acts on the pressure sensor 6, the resistance value changes, and this resistance change is used as an electrical signal to lead '4316.
to detect the differential pressure. On this occasion,
Differential pressure will also act on each bellows 7a, 7b from the inside and outside, but since the top plates 9a, 9b are pressed against the body 2a with a predetermined force F, until F< (Pa-Pi)XA. The top plates 9a and 9b will not be displaced. Furthermore, P.O.
is the pressure on the outer chamber side, pi is the pressure on the inner chamber side, A is the bellows 7
This is the effective area of a and 7b. Therefore, until the top plates 9a, 9b are displaced, the openings L4a, 14 of the communication path 11a, Ilb
b is a state of narrow grooves. Since the bellows is not displaced, the sealed liquids 15a and 15b do not move.

The stationary state of the filled liquids 15a and 15b is shown in FIG.
-C, and a measurement range is set between BC and B. When xA, points B and C in Figure 2 are reached, the top plates 9a and 9b begin to displace, and the filled liquids 15a and 15b begin to move.Then, when the differential pressure becomes larger, points E and 0 in Figure 2 are reached. point, the seal diaphragms 10a, 10b come into contact with the body 2a, the movement of the sealed liquids 15a, 15b is stopped, and excessive pressure is prevented from acting on the pressure sensor 6.Therefore, within the measurement range, Since the movement of the filled liquids 15a, 15b is very small, the seal diaphragms 10a, 10
The distance between b and the body 2a can be set narrowly, and the volume change due to the differential pressure between the seal diaphragms 10a and 10b is large, but non-linear.

In this embodiment, the pressure sensor 6 uses a semiconductor piezoresistive element, but the spring member may be made of a brittle material such as single crystal silicon, quartz, quartz glass, or ceramic.

Further, the top plates 9a and 9b of the bellows 7a and 7b may be pressed against the body 2a by other tension means or compression means, and further,
If differential pressure acts, it is not necessary to provide narrow grooves in the openings 14a and 14b.

(f) Effects of the Invention As described above, according to the differential pressure transmitter of the present invention, a bellows is provided in the protective chamber communicating with each introduction chamber, and the top plate of the bellows is pressed against the housing with a predetermined force to make a differential pressure transmitter. Because the pressure is applied, when the differential pressure is within the measurement range, the bellows does not displace and the sealed liquid remains stationary and only transmits pressure, which improves the linearity of the differential pressure applied to the pressure sensor. Since the condition is good and hysteresis of the bellows does not occur, the input/output characteristics of the pressure sensor can be detected straightforwardly.

Additionally, when the sealed liquid expands and contracts due to temperature changes, static pressure, etc., the bulge of the seal diaphragm changes.
The operating point changes and the volume change rate changes, but
The volume change rate of the pressure sensor is extremely small, and span changes due to temperature, static pressure, etc. can be prevented.

Furthermore, since there is no movement of the filled liquid within the measurement range, the amount of filled liquid can be reduced, and increases and decreases caused by expansion and contraction of the filled liquid due to static pressure and temperature can be reduced, reducing static pressure errors and Temperature errors (zero point changes) can be virtually eliminated.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1 and 2 show an embodiment of the present invention.
The figure is a sectional view of the differential pressure transmitter, Figure 2 is a change diagram showing the amount of movement of the sealed liquid with respect to changes in differential pressure, and Figures 3 and 4 are:
FIG. 3 is a cross-sectional view showing a conventional differential pressure transmitter. 1: Differential pressure transmitter, 2: Housing, 3a/3b:
Introduction chamber, 4: Detection chamber, 5a/5b: Protection chamber, 6: Pressure sensor, 7a/7b:
Bellows, 9a/9b: Top plate, 10a-10b: Seal diaphragm, 11a/llb/12a/1
2b, 13a, 13b: Communication path, 15a, 15b
: Filled liquid.

Claims (1)

[Claims] (1) A first pressure introduction chamber and a second pressure introduction chamber are formed on both sides in the housing, and a pressure detection chamber and a first protection chamber and a second protection chamber for overpressure are formed; A seal diaphragm is provided in both introduction chambers to divide each introduction chamber into an introduction side and a detection side, and a pressure sensor equipped with a spring member made of a brittle material is provided in the detection chamber, and the detection chamber is divided into two pressure receiving sides. A bellows with a top plate is provided in both protection chambers to divide each protection chamber into an inner chamber side and an outer chamber side, and a detection side of the first introduction chamber and an outer side of the first protection chamber. The chamber side and one pressure receiving side of the detection chamber are communicated with each other via communication passages, and the detection side of the second introduction chamber, the outer chamber side of the second protection chamber, and one pressure receiving side of the detection chamber are communicated with each other via communication passages. , the outer chamber side of the first introduction chamber and the inner chamber side of the second introduction chamber are connected to the outer chamber side of the second introduction chamber and the first introduction chamber.
The introduction chambers are communicated with the outer chamber side through communication passages, and the top plate of each bellows is pressed against the housing with a predetermined force under pressure from each introduction chamber, so that a differential pressure is generated. A differential pressure transmitter characterized in that when the pressure exceeds this predetermined pressure, the top plate moves to fully open the communication path.