JPS5814974B2 - 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 attached to a main body case 2 that houses a pressure-sensitive element 1 that converts pressure into an electrical signal, and to both opening sides of the main body case 2 that communicate with both sides of the pressure-sensitive element 10. and pressure receiving flanges 4a, 4b having pressure inlets 3a, 3b for detected pressures Pa, Pb.

Diaphragms 5a and 5b are attached between the main body case and the pressure-receiving flange 4at4b, respectively, and each closed space formed by the diaphragms 5a and 5b and the pressure-sensitive element 1 is filled with a pressure transmission medium such as silicone oil. 6a
, 6b are sealed in a liquid-tight manner.

The output end of the pressure sensitive element 1 is connected to a preamplifier and various control circuits (not shown) via a cable γ.

Additionally, there is an overload inside the main body case 2 to prevent the pressure sensitive element 1 from being distorted and unable to return to its original state or being damaged when pressure exceeding its elastic limit is applied from one side of the pressure sensitive element 1. A pressure prevention mechanism 10 is provided.

This mechanism 10 includes a bellows 11 whose inner and outer surfaces are in contact with the meat pressure transmission media 6a and 6b, a valve 12 that is interlocked with the bellows 11 and prevents movement of one of the pressure transmission media 5-a, and an operation for controlling the valve 12. It is composed of a piece 13.

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

O-rings 12A are provided at both ends of this valve 120. 12B are attached respectively.

For example, when a pressure exceeding the elastic limit of the element 1 is applied to the element 1, the O-rings 12A and 12B come into close contact with the main body case 2 in response to the expansion and contraction of the bellows 11 to prevent the pressure transmission medium 6a from moving. It is something to do.

Further, the operating piece 13 has two fulcrums 16a and 16b pressed by a spring 15, and the bellows 1
It rotates clockwise or counterclockwise via the valve 12 and root spring 14 in response to the expansion and contraction of the valve 1.

With this configuration, the bellows 11
When the pressure applied to the element 10 is within the elastic limit, that is, within the detection tolerance, no operation occurs; however, when one of the detected pressures Pa, Pb exceeds the pressure of the spring 15 and the repulsive force of the leaf spring 14, i.e. When the element 10 exceeds its elastic limit, it expands and contracts, and the valve 12 and leaf spring 14 operate in response to this movement.

Now, if one of the detected pressures pb is applied exceeding the elastic limit of the pressure sensitive element 1, the operating piece 13 is moved from the fulcrum 16 against the repulsive force of the leaf spring 14 and the pressing force of the spring 15.
Rotate clockwise around b to move the valve 12 to the right in the figure and bring it into close contact with the main body case 2.

As a result, the pressure transmission medium 6a is completely separated at the valve 120 portion, and movement of the medium 6a between the diaphragm 5a and the valve 12 and between 12 and the pressure sensitive element 1 is prevented.

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

However, it actually has the following drawbacks.

For example, when an excessive pressure Pa is applied, the O-ring 12A comes into contact with the side wall of the main body case 2 and prevents the movement of the pressure transmission medium 6a, as shown in FIG. 2A. When the force is applied, the valve 12 further moves to the left in the figure as shown in FIG. 2B, and the O-ring 12 is substantially
A is deflected and a change in volume occurs.

In other words, a change in volume occurs by the area V shown in A in the same figure,
For this reason, an excessive pressure may be further applied to the element 1, or even a negative pressure may be generated, and it cannot be said that overpressure is prevented optimally.

Furthermore, the provision of such an overpressure prevention mechanism 10 complicates the structure, making it difficult to adjust each member and increasing the size of the entire device.

Accordingly, the pressure transmission medium 6a is susceptible to expansion due to temperature changes in the signal taken out from the pressure sensitive element 1.
, 6b not only increase, but also because the valve 12 or the operating piece 13 of the mechanism 10 is placed in one of the media 6a, the amounts of 6a and 6b cannot be made equal, and therefore the total amount Alternatively, the detection accuracy is likely to be affected by non-uniform expansion of the media 6a, 6b due to the difference between the two.

Moreover, 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 viewpoint of reliability, the diaphragms 5a and 5b are attached by welding, but since this is done after the element 1 is attached due to the structure, there is no influence on the element 1 such as heat radiation, vibration, shock, or dust caused by the process. It is difficult to prevent this.

Furthermore, since the element 1 is directly attached to the main body case 2, the output temperature error of the element 1 increases due to the difference in their temperature expansion coefficients, or stress due to the deformation of the main body case 2 under static pressure is applied directly to the element 1. In addition, the static pressure error will increase.

The present invention has been made to address the above-mentioned drawbacks, and provides a differential pressure detection device that can prevent overpressure, prevent temperature and static pressure errors, and simplify the manufacturing system.

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

First, the general configuration will be explained.

30 is a cylindrical main body case with a through hole 31 in its center.
However, there are two introduction holes 32a and 32b in the upper part, respectively.
An opening 33 communicating with the through hole 31 is provided.

An overpressure prevention mechanism 34 is housed in the through hole 31, and a pressure sensitive element 35 arranged parallel to the overpressure prevention mechanism 34 is housed in the upper opening 33.

Further, both ends of the through hole 310 are provided with a diaphragm 36a,
36b, and the upper opening 33 is sealed by a seal cap 37.

Furthermore, pressure media 38a and 38b are sealed in these through holes 31 and upper opening 33.

This pressure transmission medium 38at38b is the overpressure prevention mechanism 3.
4. They are separated from each other by a pressure sensitive element 35.

Also, holes 39a are provided outside the diaphragms 36a and 36b to introduce detected pressures Pa and Pb.

Pressure receiving flanges 40a and 40b having 39b are arranged side by side, and these flanges 40a and 40b are attached to the main body case 30 in a liquid-tight manner.

Now, next is the mounting structure of the pressure sensitive element 35 and the overpressure prevention mechanism 34.
The configuration and mounting structure will be explained.

First, the pressure sensitive element 35 will be explained.
is attached to one side of an annular holding disk 41 made of the same material.

Further, this holding disk 41 is joined to a cylindrical metal stress absorbing shaft 43 whose coefficient of linear expansion is extremely close to that of the holding disk 41.

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

The shaft 43 and the element output signal extraction pin 44 are attached to the metal body 42 in a hermetic structure using glass or the like.

Further, a printed wiring board 45 for external connection is attached on top of the element output signal output pin 44.

In this way, by insulating the element signal output pin 44 and shaft 43 from the metal body 42 using an insulating material such as glass, the insulation between the metal body 42 and the element 35 is perfect.

One side of the element 35 configured in this way is located toward the opening 33, and the other side is located on the inlet 32b side. Therefore, both sides of this element 350 are provided with the pressure transmission medium 38a.
, 38b are in contact with the liquid.

By the way, since the element 350 is attached to the holding disk 41 having the same coefficient of linear expansion, no unnecessary stress is applied to the element 35 due to temperature changes or the like.

Furthermore, since it is attached to the stress-absorbing shaft 43 whose coefficient of linear expansion is approximately the same as that of the holding disk 41, the mechanical stress generated in the main body case 30 when the metal body 42 is housed is not applied to the element 35.

Further, since the metal body 42 housing this element 35 can be temporarily attached with the diaphragm 36at36b by welding, the device position of the metal body 42 and the internal volume of the seal cap 37 can be adjusted depending on the characteristics of the diaphragms 36a and 36b after welding. Since the balance of the internal volume of the case 30 can be changed, output errors due to temperature expansion and output errors due to static pressure can be prevented.

Next, an overpressure prevention mechanism 3 acts to protect the element 35 when a pressure exceeding the elastic limit of the element 350 is applied.
4 will be explained.

This mechanism 34 is located in the through hole 31 of the main body turf 300.
It is attached movably in a direction orthogonal to the diaphragms 36a and 36b.

Further, this mechanism 34 has bellows 65a on both sides thereof.

The connecting member 34a has a connecting member 34a to which a bellows 65b is attached, and this connecting member 34a has holes 34b, 34b formed inside each bellows 65a, 65b so that a medium 38a, 38b different from the outside thereof is supplied. .

That is, different media 38a, 38b are in contact with the inner and outer surfaces of the bellows 65a, 65b, respectively.

Further, support shafts 51a, 51b are attached to the bellows 65a, 65b, and are connected to the movement of the bellows, and screw portions are provided at both ends of the support shafts 51a, 51b.

This support shaft 51a. 51b includes control valves 54a and 54, respectively.
b are screwed together.

The control valves 54a, 54b are connected to the support shafts 51a, 51b.
are screwed together, and each end face has an O-ring 56a.
, 56b are attached.

Projections 57at57b are located in portions facing the O-rings 56a, 56b, and the O-rings 56a, 56b are moved by the respective projecting portions 57a, 57a, 56b in response to the movement of the support shafts 51a, 51b.

57b.

These O-rings 56a, 56b and the protrusion 57a.

Distance with 5yb11. (2) can be easily adjusted by screwing the valve 54a754b into the threaded portion of the support shafts 51a, 51b.

This interval 11, 12 is a basic condition for regulating the amount of movement of the media 38a, 38b, that is, the applied pressure.

Also, the diaphragm 36a of the control valves 54a, 54b
Spring bodies 58a and 58b for displacement adjustment are provided on the t36b side, respectively.
are attached by nuts 60a, 60b.

These spring bodies ssa and s8b are for controlling the movement of the valves 54a and 54b, and their ends are attached to the holders 61a and 61b.
It is attached to the main body case 30 with screws 62 via.

Further, as shown in FIG. 4, the spring bodies 58a and 58b are formed in a circular shape and have a plurality of holes 63 for providing elastic force, and furthermore, the above-mentioned screws 62 are provided on the outer periphery of the spring bodies 58a and 58b.
Elongated holes 64 for attachment into which can be inserted are formed at three locations.

The bellows 65a, 65b attached in this manner are configured to have their inner and outer surfaces in contact with the media 38a, 38b, respectively, and to expand and contract as the media 38a, 38b move.

Also, the bellows 65a and 65b allow the through hole 3 to
1 is divided into the introduction hole 32a side and 32b side.

Further, the introduction holes 32a and 32b are blocked by an element 35.

The diaphragms 36a, 36b have flanges 40a, 4
For example, it is welded to a portion of the main body case 300 that protrudes from 0b and has a small diameter.

Now, in the device configured as described above, the pressures Pa and Pb within the detection range are respectively connected to the pressure receiving flanges 40a.

When applied through the holes 39a and 39b of the diaphragm 40b, the pressure is applied to the diaphragms 36a and 36b according to the husband's pressure Pa and Pb.
is displaced, and the pressure transmission medium 38a.

38b moves.

Due to the movement of the media 38a and 38b, the pressure sensitive element 35
A pressure difference of (pa-pb) is generated on both sides, and the pressure difference (Pa-Pb) is converted into an electrical signal.

The output is then supplied to various control systems and detected as differential pressure.

Furthermore, due to the movement of the media 38a, 38b, the bellows 65a,
65b also expands and contracts, supporting shafts 51a, 51b and valves 54a, 54.
b moves but does not close media 38a, 38b if the applied pressure is within the detection range.

By the way, when a pressure exceeding the elastic limit of the pressure sensitive element 350 is applied, the overpressure prevention mechanism 3 is activated as described below.
4 acts to protect the element 35.

For example, it is assumed that the detected pressure Pa exceeds the elastic limit of the element 350.

That is, when the pressure pa is supplied, the bellows 5 is activated via the diaphragm 36a and the pressure transmission medium 38a.
5a receives pressure on the outer surface, and 65b receives pressure on the inner surface, and moves to the left in the figure.

Accordingly, the support shafts 51a, 51b, the control valve 54a
t54b moves to the left, and the O-ring 56a of the valve 54a comes into close contact with the protrusion 57a.

Here, the pressure medium 38a is between the diaphragm 36a and the O-ring 56a and between the O-ring 56a and the bellows 65.
The outer surface of the bellows 65b, the inner surface of the bellows 65b, and the element 35 are sealed.

Therefore, movement of the medium 38a is stopped.

Furthermore, even if more excessive pressure is applied and the O-ring 56a is crushed, the bellows 65b becomes a pressure displacement body for protecting the element after overpressure is prevented, and the bellows 65b moves and the element 3
5 is configured to minimize pressure changes.

Also, in this state, there is a temperature change, and the outer surfaces of the O-ring 56a and the bellows 65a, the inner surface of the bellows 65b, and the element 3
The bellows 6sb moves even when the pressure transmission medium 38a sealed with both the bellows 6sb moves and prevents changes in pressure applied to the element 35 to a minimum.

In this embodiment, the pressure applied to the element 35 can be set by adjusting the distance 11 between the O-ring 56a attached to the valve 54a and the protrusion 57a. The pressure applied to the element 35 can be set by adjusting the distance 12 between the attached O-ring 56b and the protrusion 57b.

In this way, in the case of excessive pressure Pa>Pb, the bellows 65
The bellows 65b acts as a pressure displacement elastic body for preventing excessive pressure, and the bellows 65b functions as a pressure displacement elastic body for preventing excessive pressure.

On the other hand, in the case of overpressure Pa<pb, the bellows 65b acts as a pressure displacement elastic body to prevent overpressure, and the bellows 65a functions as a protective pressure displacement elastic body after overpressure prevention, resulting in a highly reliable overpressure prevention effect. .

In addition, the main body case 30 is formed into a circular shape, and the element 35 is housed in the opening 33 and separated from the through hole 31 in which the overpressure prevention mechanism 34 is housed, so the space factor is good and the pressure transmission medium 38a .

The total amount of the media 38b can be reduced, and since they are formed almost symmetrically, each medium 38a can be formed with extremely high accuracy.

The amount of 38b can be adjusted.

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

Further, according to the conventional example shown in FIG. 1, the diaphragm 5b is attached by welding or the like after the element 1 is installed in the main body case 2, but according to this embodiment, the diaphragm 5b is attached by welding or the like. After installation, attach the element 35 to the main case 3.
Since it can be installed at zero, it can be installed under extremely good conditions.

In other words, the element 3
5 can be installed.

In addition, since the element 35 is attached to the main body case 30 via the stress absorbing member of the holding disk 41 and the stress absorbing shaft 43 having similar coefficients of linear expansion, the element 35 is It is hardly affected by expansion or contraction, and is also not affected by stress caused by distortion of the main body case 30 caused by static pressure or distortion generated when attaching members housed in the main body case 30.

Therefore, output fluctuations due to changes in temperature and static pressure can be almost eliminated.

In addition, the diaphragms 35a and 35b have flanges 40at.
40b, and is attached to the part of the main body case 30 that has a small diameter, so even if the main body case 30 becomes larger, the standard spacing between high and low pressure piping of a differential pressure type flowmeter used in a measuring instrument, that is, the flange 40a, can be maintained. , 40b hole 39a,
Not only is it possible to fully satisfy the standard spacing of 54 m for 39b, but it is also possible to reduce the effects of heat and residual stress during attachment.

Further, regulating valves 54a, 54b and a support shaft 51a.

Since it is configured by screwing together with 51b, O-ring 56at
The distance l between 56b and the protrusions 57a and 57b is the support shaft 51.
Adjustment can be made simply by screwing the control valves 54a and 54b into the at51b, and can be done without applying unnecessary stress to the bellows 65a and 65b.

Further, since long holes 64 for attachment are formed in the spring bodies 58a and 58b, respectively, the spring bodies 58a.

Slightly loosen the screw 62 that fastens 58b.

The spring bodies 58a, 58b rotate without any problem.

Therefore, by screwing the control valves 54a and 54b, the interval 1
1, the valves 54a, 54b and the spring body 58a
, 58b can be adjusted while being integrated, making the adjustment operation easy.

Although circular members are used as the spring bodies 58a and 58b, an M-shaped member 58b' may be used as shown in FIG. 5, and any shape may be used as long as it has this external elastic force. It's not something I'm particular about.

In order to hold this M-shaped spring body 58b', it is removed) 60
Oak) 60b' may be used in place of b.

Next, another embodiment will be described with reference to FIG.

Incidentally, the same reference numerals are given to the parts that are substantially the same as those in the above embodiment, and detailed explanation thereof will be omitted.

That is, the device of this embodiment is provided with a damping throttle in at least one pressure transmission medium, such as the medium 38b.

The gasket 66 is in close contact with the valve 54b to prevent the medium 38b from flowing.

67 is the medium 38b on the diaphragm 36b side and the bellows 6
This is a guide hole for communicating with the medium 38b on the 5b side, and a throttle shaft 68 that can be screwed in by external operation is inserted into this hole 67.

The shaft 68 is tapered and has a slightly smaller diameter than the guide hole 67.

70 is an O-ring, 71 is a shaft, and 68 is a screw for preventing removal.

By threading this shaft 68 and changing the clearance Y between the shirt g68 and the guide hole 67,
The resistance experienced by the medium 38b during movement can be varied.

Incidentally, the amount of movement of the medium 38b relative to the full-scale pressure of the normal element 35 is extremely small, and the change in volume due to pressure is also small.

Therefore, the damping effect is related to the product of the resistance and the change in volume, and if the change in volume is small, the damping effect will almost disappear for the same resistance.

However, this structure has a bellows 65a. 65b responds to pressure changes and its volume changes are large, so a good damping effect can be achieved.

In other words, the first-order lag time constant that determines the damping effect is T
=RXC, and since R is proportional to the length of the shaft and the closed area and the cross-sectional area of the shaft and the closed area, assuming that the numerator is constant, it becomes TαC/cross-sectional area.

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 present invention, since the volume change C is large, the time constant T cannot be changed suddenly. It is easy to adjust and provides sufficiently high accuracy.

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 description, a bellows has been used as the pressure displacement elastic body, but a pressure displacement elastic body other than the bellows, such as a diaphragm, may also be used.

Since the present invention is configured in this way, even after one pressure displacement elastic body blocks the movement of the pressure transmission medium, the other elastic body absorbs the slight movement of the sealed medium on the pressure sensitive element side. I can do it.

Therefore, even if a change in volume of the medium occurs due to a change in temperature or the like when the medium is closed, the change can be absorbed, and excessive pressure will not be applied to the element.

Furthermore, the following effects are also achieved.

(2) Reliability is improved by directly blocking the medium on the side to which excessive pressure is applied.

2. Since the overpressure prevention mechanisms are arranged evenly, the amounts of both enclosed media can be equalized, and the influence of temperature changes can be minimized.

3. Since each bellows and control valve are arranged in each medium, individual adjustment is possible and overpressure prevention can be performed with high precision.

4. Assembly is easy because each bellows is arranged in a straight line.

5. The overpressure prevention mechanism and pressure-sensitive element are placed separately, so
The respective attachments become easier, and the stress generated when attaching the overpressure prevention mechanism is not transmitted to the pressure-sensitive element.

6. Since the structure can be made symmetrical as a whole, manufacturing and assembly are easy, and maintenance can be performed easily.

[Brief explanation of drawings]

Fig. 1 is a sectional view for explaining a conventional differential pressure detection device, Fig. 2 a and b are sectional views each extracting and enlarging a portion of Fig. 1, and Fig. 3 is an embodiment of the present invention. 4 is an exploded perspective view extracting and enlarging a part of FIG. 3; FIG. 5 is an exploded perspective view for explaining a modification of FIG. 4; The figure is a partially cutaway sectional view for explaining another embodiment. In the figure, 30 is the main case, 31 is the through hole, 33 is the opening,
34 is an overpressure prevention mechanism, 35 is a pressure sensitive element, 36a, 36b
is a diaphragm, 38a and 38b are pressure transmission media, and 40
at40b is a pressure receiving flange, and 65ap65b is a bellows.

Claims (1)

[Claims] 1. A main body case, a pressure sensitive element housed within the case and converting pressure into an electrical signal, and a pressure sensitive element arranged in a straight line parallel to this element so as to divide the inside of the main body case by this element. Two pressure displacement elastic bodies are arranged facing each other and respond to the pressure to be measured, and a pressure transmission medium is housed in each of the divided main body cases and sealed with a diaphragm that is displaced by the pressure to be detected. and a pair of control valves that are arranged in the medium and respond to each of the elastic bodies to separate the respective medium into the pressure sensitive element side and the diaphragm side, and a pressure above the detection range is applied. When the control valve responds to one of the elastic bodies, the medium is separated into the diaphragm side and the element side to prevent the medium from moving, and the other elastic body separates the medium from the sealed medium on the element side. A differential pressure detection device characterized by absorbing minute movements. 2. The differential pressure detection device according to claim 1, wherein the pressure sensing element is arranged parallel to the moving direction of the elastic body. 3. The differential pressure detection device according to claim 1, wherein the pressure sensitive element is attached to the main body case via a stress absorbing member. 4. The differential pressure detection device according to claim 1, wherein the diaphragm is attached to a portion of the main body case that projects in the direction of movement of the elastic body. 5. The differential pressure detection device according to claim 1, wherein the main body case is provided with an aperture for controlling the movement of at least one of the media. 6. The differential pressure detection device according to claim 1, wherein the internal volume can be adjusted even after the diaphragm is welded to the main body case.