JPS5814973B2 - Differential pressure detection device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a differential pressure detection device using a pressure sensitive element.

As shown in FIG. 1, this type of device is equipped with a main body case 2 that houses a pressure-sensitive element 1 that converts pressure into an electrical signal, and a main body turf 20 that is attached to both opening sides that communicate with both sides of the pressure-sensitive element 10. , pressure receiving flanges 4a, 4b having pressure inlets 3a, 3b for detected pressures Pa, Pb.

Diaphragms 5a and 5b are stuck between the main body case 2 and the pressure-receiving flanges 4a and 4b, respectively. Pressure transmission media 6a, 6b are sealed in a liquid-tight manner.

A cable I sends the output signal of the pressure sensitive element 1 to a preamplifier and various control circuits (not shown).

Further, an overpressure prevention mechanism 10 is installed inside the main body case 72 in order to prevent damage to the pressure sensitive element 1 due to pressure exceeding the elastic limit.

This overpressure prevention mechanism 10 has a meat pressure transmission medium 6a on the inner and outer surfaces.
Bellows 11 in contact with t6b, this bellows 1
1 and an operating piece 13 that controls the valve 12.

The valve 12 and the operating piece 13 are located within the pressure transmission medium 6a, and are connected by a leaf spring 14.

Each of the valves 12 has a 01
Ng 12A.

12B are attached to both ends.

Further, the operating piece 13 has two fulcrums 16a and 16b pressed by a spring 15, and the bellows 11 when overpressured
It rotates clockwise or counterclockwise via the valve 12 and leaf spring 14 in accordance with the expansion and contraction of the valve.

Further, the valve 12 is designed to prevent the pressure transmission medium 6a from moving when, for example, a pressure exceeding its elastic limit is applied to the pressure sensitive element 1.

Incidentally, in the differential pressure detection device as described above, the bellows 11 of the pressurization prevention mechanism 10 does not operate at any pressure within the elastic limit of the pressure sensitive element 10, that is, within the detection tolerance, but when one of the detected pressures Pa.

When pb exceeds the pressing force of the spring 15 and the repulsion length of the leaf spring 14, that is, the elastic limit of the pressure sensitive element 10 is exceeded, an expansion and contraction operation is performed, and in response to this movement, the valve 12 and the leaf spring 14 also operate. .

Now, if one of the detected pressures pb is applied exceeding the elastic limit of the pressure sensitive element 10, the repulsive force of the leaf spring 14 and the spring 1
The operating piece 13 rotates clockwise about the fulcrum 16b against the pressing force 5, and the valve 12 moves rightward in the figure and comes into close contact with the main body case 2.

As a result, the pressure transmission medium 6a is completely separated by the valve 12, and movement of the pressure transmission medium 6a between the diaphragm 5a and the valve 12 and between the valve 12 and the pressure sensitive element 1 is prevented.

As a result, the movement of the pressure transmission medium 6b on the opposite side of the pressure sensitive element 10 is also indirectly prevented, and no further pressure increase in the detected pressure pb is applied to the pressure sensitive element 1.

Therefore, the pressure sensitive element 1 can be protected from excessive pressure.

However, the differential pressure detection device having the overpressure prevention mechanism 10 as shown in FIG. 1 has the following drawbacks.

For example, when excessive pressure Pa is applied, O ring 12A
As shown in FIG. 2A, the valve 12 comes into contact with the side wall of the main body case 2 to prevent the movement of the pressure transmission medium 6a, but when a larger pressure Pa is applied, the valve 12 moves as shown in FIG.
As shown in the figure, the O-ring 12A moves to the left in the figure, and as a result, the O-ring 12A is pushed by the valve 12 and flattened, causing a substantial change in volume.

In other words, the volume changes by the area V shown in A in the same figure,
For this reason, an excessive pressure may be applied to the pressure sensitive element 1, or even a negative pressure may be generated, and therefore it cannot be said to be an optimal means for preventing overpressure.

Furthermore, the overpressure prevention mechanism 10 has a complicated structure, and it is difficult to adjust each member, making the entire device large.

As a result, the amount of the pressure transmission media 6a and 6b that are susceptible to expansion due to temperature changes is large (not only that, but the valve 12 or the operating piece 13 of the overpressure prevention mechanism 10 is located inside one of the pressure transmission media 6a). Therefore, the amount of meat pressure transmission medium 6a>6b cannot be made equal, and therefore,
Non-uniform medium 5a due to its total amount or the difference between the two
.

6b is susceptible to expansion, resulting in a decrease in detection accuracy.

Further, since the pressure sensitive element 1 is arranged parallel to the diaphragms 5a and 5b and is installed on the mounting surface A side of the overpressure prevention mechanism 10, the structure becomes complicated and an increase in size is unavoidable.

In addition, from the standpoint of reliability, the diaphragms 5a and 5b are attached by welding, but due to their structure, they are attached after the pressure-sensitive element 1 is attached, so the pressure-sensitive elements such as heat dissipation, vibration, shock, or dust generated during processing may be difficult to handle. It is difficult to prevent the effect on the element 1.

Furthermore, since the pressure-sensitive element 1 is directly attached to the main body case 2, the output temperature error of the pressure-sensitive element 1 increases due to the difference in their temperature expansion coefficients, or the main body case 2 deforms under static pressure. This has the disadvantage that the stress caused by this is directly applied to the pressure sensitive element 1, resulting in an increase in static pressure error.

The present invention has been made in order to eliminate the above-mentioned drawbacks, and is capable of properly protecting a pressure-sensitive element from thermal changes in the medium caused by excessive pressure or temperature changes, and adjusting the pressure prevention mechanism. The purpose of the present invention is to provide a differential pressure detection device that improves accuracy by making it possible to improve accuracy and further eliminates static pressure errors.

An embodiment of the present invention will be described below with reference to FIG.

In the same figure, 30 is a main body case, and a through hole 31 whose diameter increases in a stepwise manner is formed approximately along the central axis of the main body case.
And two medium introduction passages 32 are provided on one side of the through hole 31.
An opening 33 is provided which communicates via a, 32b.

An overpressure prevention mechanism 34 is accommodated in this through hole 31 .

Further, both ends of the through hole 310 are sealed by a diaphragm 36at36b whose end portions are welded to the main body case 30, and the opening 33 is sealed by a seal cap 37.

A pressure transmission medium 38a is provided inside these through holes 31 and openings 33.

38b is enclosed.

This pressure transmission medium 38a. 38b are separated by an overpressure prevention mechanism 34 and a pressure sensitive element 35, respectively.

In addition, diaphragms 36a are provided on both sides of the main case 300.
, 36b, the pressure receiving flange 4 has pressure introduction ports 39a and 39b for introducing detected pressures Pa and Pb so as to cover the pressures Pa and Pb.
0a and 40b are mounted in a liquid-tight manner.

Next, the mounting structure of the pressure-sensitive element 35, the structure of the overpressure prevention mechanism 34, and its mounting structure will be explained.First, the pressure-sensitive element 35 will be explained. It is attached liquid-tightly to close the opening.

The holding disk 41 is made of the same material as the pressure sensitive element 35.

Further, this holding disk 41 is joined to an annular metal stress absorbing shaft 43 having a coefficient of linear expansion very similar to that of the disk 41.

For example, the material of the stress absorbing shaft 43 is a Ni--Fe alloy or the like when using the semiconductor pressure-sensitive element 35 such as silicone.

The stress absorbing shaft 43 and the signal output pin 44 of the pressure sensitive element 35 are hermetically sealed to the metal body 42 with glass or the like.

Further, a printed wiring board 45 for external connection is attached to the signal output pin 44.

In this way, the signal extraction pin 44 and the stress absorption shaft 4
3 insulates the metal body 42 using an insulating material such as glass, thereby perfecting the insulation between the metal body 42 and the pressure sensitive element 35.

Since the pressure-sensitive element 35 is attached to the holding disk 41 which has approximately the same coefficient of linear expansion as the pressure-sensitive element 35, unnecessary stress due to temperature changes etc. is not applied to the element 35, and furthermore, the holding disk 41 is linearly connected to the holding disk 41. Since the pressure-sensitive element 3 is attached to the stress-absorbing shaft 43 having a substantially equal expansion coefficient, the mechanical stress generated in the main body case 30 when the metal body 42 is stored is absorbed by the pressure-sensitive element 3.
It never joins 5.

Further, since the metal body 42 housing the pressure sensitive element 35 can be covered after welding the diaphragms 36a and 36b, the installation position of the metal body 42 and the attachment of the seal cap 37 can be adjusted depending on the characteristics of the diaphragms 36at36b after welding. Since the balance of the internal volume of the main body case 30 can be changed depending on the position, output errors due to temperature expansion and output errors due to static pressure can be prevented6.
Note that the pressure-sensitive element 35 configured as described above is arranged so that one side is located on the opening 33 side and the other side is located on the medium introduction passage 32b side, so that the pressure-transmitting medium 38a is placed on both sides of the pressure-sensitive element 350, respectively. .

38b is in contact with the liquid.

Next, the overpressure prevention mechanism 34 that protects the pressure sensitive element 35 from excessive pressure will be explained.

This overpressure prevention mechanism 34 is provided within the through hole 31 of the main body turf 300 so as to be movable in a direction perpendicular to the diaphragms 36a, 36b.

That is, this overpressure prevention mechanism 34 has a support shaft 50 extended on both sides of a piston section 470 to which the O-ring 46 is mounted, and threaded sections 51a and 51b (51b is not shown) provided at the ends thereof.

The threaded portions 51a and 51b include the threaded portions 51at51b.
With a larger diameter, the O-rings 56a and 56b are attached to the support shaft 50.
A control valve 54at54b provided on the side is screwed together.

The O-rings 56a and 56b are attached to the main body case 30.
A protruding body 57a formed by directly or screwed into the main body case 30
t57b, and as the support shaft 50 moves, the protrusions 57a and 57bKa come into contact with each other.

The distance 11 between the O-rings 56a, 56b and the protrusion 57at57b can be easily adjusted by threading the regulating valves 54a, 54b into the threaded portions 51a, 51b of the support shaft 50.

This interval 11 is a pressure transmission medium 38a. This is a basic condition that regulates the amount of movement of 38b, that is, the applied pressure.

Furthermore, a protruding body with a threaded portion is provided on the opposite side of the support shaft 50 of the control valves 54a, 54b, and displacement adjusting spring bodies 58a, 58b are attached to nuts 60a, 60b, respectively.
It is attached by.

The spring bodies 58a, 58b restrict the movement of the control valves 54at54b, and are attached to the main body case 30 by screws 62 via holders 61a, 61b.

As shown in FIG. 4, the spring bodies 58a and 58b are formed into a circular shape with a plurality of holes 63 for providing elastic force, and further have elongated mounting holes 64 on the outer periphery into which the screws 62 can be inserted.
is pierced in three places.

On the other hand, the piston portion 47 is surrounded by a cylinder chamber 52, to which one end of a bellows 65 that responds to the medium 38at38b is attached.

The cylinder chamber 52 and the piston portion 47 have a gap 12, which is less than half of the gap 11.

This piston portion 41 is connected to a spring body 58a via a support shaft 50,
58b, and starts moving when the distance between the bellows 65 and the cylinder chamber 52 is reduced.

The bellows 65 thus assembled has its inner and outer surfaces in contact with the pressure transmission medium 38at38b, respectively, and expands and contracts as the mediums 38a and 38b move.

Next, the operation of the differential pressure detection device configured as above will be explained.

First, when the pressures Pa and Pb are zero, as shown in FIG. 5A, the right distance 12 and the left distance 12 formed by the piston portion 47 and the cylinder chamber 52 are approximately equal.

In this state, the pressures Pa and Pb within the detection range are the pressure inlets 39a and 3 of the pressure receiving flanges 40a and 40b, respectively.
9b, each detected pressure P
The diaphragm 36at36b is displaced in accordance with a and Pb, and as a result, the pressure transmission medium 38a>38b moves.

Due to the movement of the media 38a and 38b, a pressure difference of (Pa-Pb) is generated on both sides of the pressure-sensitive element 350, and the pressure difference (P
a-Pb) is converted into an electrical signal.

Although not shown, this electrical signal is sent to various control systems via signal lines and detected as a differential pressure.

In addition, in response to the pressure of Pa>Pb, the pressure transmission medium 38a,
38b moves, the bellows 65 of the overpressure prevention mechanism 34
is extended, the right side interval 12 is reduced, and at the same time the support shaft 50 is
and the control valves 54at54b also move, but since the applied detected pressures Pa and Pb are within the detection range, the amount of movement is not enough to close the gap 11, and therefore the pressure transmission media 38a and 38b are It is not closed by the control valves 54a, 54b.

Next, a case where the detected pressures Pa and Pb exceed the elastic limit of the pressure sensitive element 35 will be described.

It is assumed that the gold wave detection pressure has a relationship of Pa>pb, and the pressure Pa exceeds the elastic limit of the pressure sensitive element 350.

Therefore, when such pressure Pa is applied, the bellows X65 of the overpressure prevention mechanism 34 moves to the left in the figure via the diaphragm 36a and the pressure transmission medium 38a,
Accordingly, the right inner surface of the cylinder chamber 52 comes into close contact with the right surface of the piston portion 47.

If the bellows 65 moves further in this state. Spring body 58
a, the control valve 54a and the support shaft 50 move leftward, and the OJ ring 56a of the control valve 54a comes into close contact with the protrusion 57a as shown in FIG. 5B.

Furthermore, when the detected pressure Pa increases, the O-ring 56a is crushed by the pressure Pa;
Since the movement of the medium 38a is prevented by 6a,
The support shaft 50 moves to the left via the control valve 54a and presses the piston portion 47 to the left.

As a result, the right surface of the piston portion 4γ is separated from the right inner surface of the cylinder chamber 52, and a gap 12 is formed between the right surface of the piston portion 47 and the right inner surface of the cylinder chamber 52, as shown in FIG. 5C.

The medium 38a corresponding to the volume change caused by the flattening of the O-ring 56a is supplied into the cylinder chamber 520 formed by this interval 12.

Then, by stopping the movement of the support shaft 50, etc., the pressure transmission medium 38a is transferred to the diaphragm 36a and the control valve 54.
a, the control valve 54a, the pressure sensitive element 35, the bellows 65
etc. and the piston portion 47, respectively.

Therefore, the overpressure prevention mechanism 34 prevents excessive pressure Pa (however,
When Pa)Pb) is applied, it moves by (distance 11 between the control valve 54a and the protruding body 57a) + (distance 12 between the right surface of the piston part 47 and the right inner surface of the cylinder chamber 52), and conversely, Pa<Pb When pressure is applied, it moves by (distance 11 between control valve 54b and protrusion 57b) + (distance 12 between left surface of piston portion 47 and left inner surface of cylinder chamber 52).

Therefore, since the present device is configured as described above, a similar effect can be obtained.

(1) If there is a temperature change in the state shown in Figure 5C,
A volume change occurs in the pressure transmission medium 38a sealed by the control valve 54a, the pressure sensitive element 35, the bellows 65, the piston part 47, etc., but the movement of the piston part 47 is completely sealed at the position shown in FIG. 5C. On the other hand, since there is a gap 12 between the right surface of the piston portion 47 and the right inner surface of the cylinder chamber 52, the bellows 65 further extends to the left in response to the volume change increased by the thermal expansion of the medium 38a. attitude(.

Furthermore, to be more specific, the bellows 65 originally has a pressure P
The medium 38a is stretched to the left as a increases, but under the pressure condition shown in FIG. 5B, the medium 38a is
Since the movement of the bellows 65 is blocked, the movement of the bellows 65 is also blocked at this point.

However, if the medium 38a undergoes thermal expansion due to a temperature change, the volume within the bellows 65 increases, and the bellows 65 moves to the left in response to the volume increase.

Then, the medium 38a in the chamber formed by the interval 12 flows out of the chamber and is absorbed by the increase in the internal volume of the bellows due to the movement of the bellows 65.

Therefore, no further excessive pressure is applied to the pressure sensitive element 35.

■Also, since the main body case 30 is formed into a circular shape, and the pressure sensitive element 35 is housed in the opening 33, and is separated from the through hole 31 in which the overpressure prevention mechanism 34 is housed, the space factor is improved ( , the total amount of pressure transmission media 38a, 38b can be reduced.

Furthermore, since they are formed almost symmetrically, the amount of each pressure transmission medium 38a, 38b can be adjusted with great precision.

Furthermore, a pressure transmission medium 38a. Temperature errors due to thermal expansion and thermal contraction of 38b can be reduced.

■ Is the pressure sensitive element 35 the diaphragm 36a? Since it can be installed in the main body case 30 after attaching 36b, it can be installed under extremely good conditions.

That is, it is possible to install the pressure sensitive element 35 in a process that is separate from the process of adjusting the overpressure prevention mechanism 34 and the process of welding the diaphragms 36a and 36b.

■Also, since the pressure-sensitive element 35 is attached to the main body case 30 via the holding disk 41 and the stress-absorbing shirt g43, which have similar linear expansion coefficients, the pressure-sensitive element 35 is attached to the main body case 30.
It is hardly affected by expansion or contraction due to temperature changes (and may also be affected by stress due to distortion of the main body case 30 that occurs under static pressure or distortion that occurs when attaching members stored in the main body case 30). It disappears.

Therefore, it is possible to almost eliminate output fluctuations due to changes in temperature and static pressure.

■Also, the diaphragms 36a and 36b are attached to the flange 40a.
, the main body case 30 protrudes inside 40b and has a small diameter.
Since it is attached to the main body case 30, even if the main body case 30 becomes larger, the standard spacing between the high and low pressure piping of a differential pressure flowmeter used in a measuring instrument, that is, the pressure introduction holes 39a and 39 of the flanges 40a and 40b, can be maintained.
Not only can the standard spacing 54tt of b be fully satisfied, but also the effects of heat and residual stress during attachment can be reduced.

(2) Further, since the control valves 54a, 54b and the support shaft 50 are screwed together, an O-ring 56a is required.

The distance 11 between 56b and the protrusions 57a and 57b corresponds to the support shaft 50.
The adjustment can be made simply by screwing the adjustment valves 54a and 54b forward, and can be done without applying unnecessary stress to the bellows 65.

Also, screws 62 that tighten the spring bodies 58a and 58b
If you loosen them a little, the spring bodies 58a and ssb will rotate without any trouble.

Therefore, the control valve 54a. When adjusting the interval 11 by screwing the valve 54b, the adjustment valves 54a, 54b and the spring body 58a
It can be adjusted while being integrated with t58b, making the adjustment operation easy.

Although the description has been made using circular members as the spring bodies 58a and 58b, it is also possible to use an M-shaped member 58t/ as shown in FIG. It's not something I'm particular about.

Narrow down to hold this M-shaped spring body 58b'
In addition to 0b, 60b' may also be used.

Next, FIG. 7 shows another embodiment of the device of the present invention.

Note that the same parts as in FIG. 3 are given the same reference numerals, and detailed explanation thereof will be omitted.

That is, the device shown in FIG. 6 is one in which a damping throttle is provided in at least one pressure transmission medium, for example 38b.

66 is a gasket attached to the control valve 54b,
This is in close contact with the protrusion 57b and prevents the flow of the pressure transmission medium 38b.

67a is a guide hole for communicating the pressure transmission medium 38b on the diaphragm 36b side and the medium 38b on the bellows 65 side.

This hole 67a communicates with the bellows side through a hole 67b open to the outside, and a throttle shaft 68 that can be screwed in by external operation is inserted into this hole 67b from the outside.

This shaft 68 is tapered and has a slightly smaller diameter than the diameter of the hole 67b.

70 is an O-ring, and 71 is a screw for preventing the shaft 68 from being pulled out.

The shaft 68 and the hole 67b are screwed together.
By changing the clearance Y between the medium 38b and the medium 38b, it is possible to change the resistance that the medium 38b receives when moving.

In this structure, the bellows 65 responds to changes in pressure, and its volume changes widely, so a good damping effect can be achieved.

In other words, the first-order lag time constant that determines the damping effect is
Since T=R-C, and R is proportional to the length formed by the closed areas of the shaft and the cross-sectional area formed by the closed areas of the shaft, it becomes ToC/cross-sectional area assuming that the numerator is constant.

Therefore, if the volume change C is small, the cross-sectional area must also be made small, and the time constant T will change suddenly, making adjustment difficult. However, according to the device of the present invention, since the volume change C is large, the time constant T Since there is no sudden change, adjustment is easy and a sufficiently high accuracy can be obtained.

There are no particular restrictions on the installation location of the aperture shaft.
Alternatively, it may be provided within both media 38a and 38b.

In the above embodiment, a bellows is used as the pressure displacement elastic body, but a pressure displacement elastic body other than the bellows, such as a diaphragm, may be used.

As described in detail above, the device of the present invention is configured so that the elastic body can absorb slight movements of the medium even after its movement is prevented by the overpressure prevention mechanism. Even if the change occurs, the change is absorbed and no excessive pressure is applied to the pressure-sensitive element (therefore, excessive pressure can be prevented with a sufficiently high accuracy, and the pressure-sensitive element is removed from the main body case by the pressure-absorbing member). Since it is floating, temperature errors during static pressure can also be prevented.

Furthermore, since the control valve and the support shaft can be screwed together, the distance 1 between the O-ring and the protruding body can be adjusted by simply screwing the control valve against the support shaft, and the bellows Don't add unnecessary applications (you can do that).

In addition, the spring body can be fastened with a screw, so if this screw is loosened a little, the spring body will rotate without any trouble.

Therefore, when adjusting the interval 11 by screwing the control valve, the control valve and the spring body can be adjusted together, making the adjustment operation easy.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a conventional differential pressure detection device, Fig. 2 a and b are partially extracted and enlarged views of Fig. 1, and Fig. 3 is an implementation of the differential pressure detection device according to the present invention. 4 is an exploded perspective view showing an enlarged view of the spring body in FIG. 3; FIG. 5 is a diagram showing the operating state of the pressure prevention mechanism as pressure increases;
FIG. 6 is an exploded perspective view illustrating another example of the apparatus shown in FIG. 4, and FIG. 7 is a partially cutaway sectional view illustrating another embodiment of the present device. 30...Body case, 31...Through hole, 33...Opening, 34...Overpressure prevention mechanism, 35...Feeling Pressure element, 36at36b...
...Diaphragm, 37...Seal cap, 38a, 28b...Pressure transmission medium, 40a
, 40b...pressure receiving flange, 41...
Holding disk, 43... Metal stress absorbing shaft, 50... Support shaft, 54a, 54b...
Control valve, 58at58b... Spring body, 65...
...Bellows.

Claims (1)

[Claims] 1. A main body case having a through hole formed therein, and both ends of the through hole being sealed by a diaphragm that receives the pressure to be detected; A cylinder device comprising a pressure displacement elastic body having one end attached to the main body case side, and a piston portion attached to the other end of the pressure displacement elastic body and movable in a liquid-tight manner. , a control valve that is arranged at a predetermined distance from a surface of the main body case that is perpendicular to the support shaft, and that the ends of the support shaft are screwed together. an overpressure prevention mechanism having;
a spring body located inside the diaphragm provided at both ends of the through hole and fixed to the main body case, supporting the control valve of the overpressure prevention mechanism and responding to the detected pressure; a pressure sensitive element that is in contact with the two medium introduction passages extending from the through hole on both sides and is attached to the main body case via a stress absorbing member; A differential pressure detection device comprising a diaphragm, a pressure displacement elastic body, and a pressure transmission medium sealed so as to be divided into two parts by a pressure sensing element. 2. The differential pressure detection device according to claim 1, wherein the stress absorbing member is a member having a coefficient of linear expansion substantially equal to that of the pressure sensitive element. 3. The differential pressure detection device according to claim 1, wherein the pressure sensitive element is arranged substantially parallel to the through hole of the main body case.