JPS60231129A - Pressure converter - Google Patents

Abstract

PURPOSE:To protect a strain gauge from humidity, by isolating both sides of a diaphragm from the outside by a partition wall and bringing the back pressure side of the diaphragm into communication with the open air by a capillary tube like curved communication pipe sealed with a liquid on the way thereof. CONSTITUTION:A front chamber A, wherein a diaphragm 1 is communicated with a strain generation plate 5 having a strain gauge 7 attached thereto by a transmission rod 6, and the back pressure side B of the strain generation plate 5 are isolated from the outside by a casing 2 and the fixing screw member 12 threaded with said casing 2. A cable 13 is inserted through the piercing bore provided to the cable gland screw 15 threaded with the fixed screw member 12 through a rubber bush 14 in an air-tight manner. The cable 13 has capillary tubes 16a-16c and the end parts of said tubes are connected by connection tubes 18a, 18b while silicone oil Si isinjected into the intermediate part of the tube 16b and the atmospheric pressure of a back pressure chamber B is made equal to atmospheric pressure and insulated from the open air. By this method, the strain gauge is isolated from humidity in the open air and the lowering in insulating property is prevented and reliability can be held over a long period of time.

Description

Detailed Description of the Invention (,) Technical Field The present invention relates to a pressure transducer, and more particularly, to a pressure transducer that deforms in response to pressure from an object to be measured, or a pressure transducer that deforms in response to pressure from a measurement object, or a pressure transducer that deforms in response to pressure from a measurement object, or a pressure transducer that deforms in response to pressure from a measurement object. A strain gauge is attached to the deformable strain plate, and a sealed chamber is formed by covering the pressure receiving diaphragm or the strain plate with a casing member so as to isolate at least the side of the strain plate to which the strain gauge is attached from the outside. The present invention also relates to a pressure transducer in which a cable, one end of which is connected to the strain gauge, is led out in an airtight manner from four cable outlets bored in the casing member.

(b) Prior Art In general, a pressure transducer using a strain gauge is based on the resistance value of a strain gauge attached to the plate surface of a diaphragm or a strain plate connected to the diaphragm via a transmission rod, as described above. Pressure is detected by electrically detecting changes. However, the resistance change of this strain gauge is very small and is subtly affected by the environment, such as the surrounding temperature and humidity. Among these, the change in resistance value due to the influence of temperature can be corrected to some extent by inserting a resistance element for temperature compensation into a Wheatstone bridge circuit formed by a strain gauge, for example. However, strain gauges tend to absorb moisture, resulting in a decrease in insulation, which not only introduces large errors into detected values, but also makes them unusable.

Therefore, various moisture-proofing measures have been conventionally applied to strain gauges. The simplest solution is
There is a method of applying a moisture-proofing agent such as grease, wax, or epoxy resin over a strain gauge attached to a diaphragm or strain plate with an adhesive or the like.

However, although this method has a short-term moisture-proofing effect, it cannot be said to be sufficient as a long-term moisture-proofing effect.

On the other hand, in order to isolate the strain gauge from the outside world, a differential pressure transducer is generally used in which a casing member surrounds a strain plate to which the strain gauge is attached.

FIG. 5 is a central vertical sectional view showing the configuration of the conventional differential pressure type pressure transducer.

In the figure, reference numerals 1a and 1b are flexible disk-shaped diaphragms, which respectively close one end side of casings 2 and 3, which are cylindrical rigid bodies. The openings at the other ends of these casings 2 and 3 are screwed together to form a sealed chamber 4 therein. Reference numeral 5 designates a beam-shaped strain plate whose both ends are fixed to the inner circumferential surface of the casing 2, and whose center portion is a highly rigid strain plate installed between the center portion of the diaphragm 1a and the center portion of the diaphragm 1b. It is fixed to the transmission rod 6. Reference numeral 7 denotes a strain gauge attached to the plate surface of the strain plate 5, and the detection output of the strain gauge 7 is transmitted to the outside of the sealed chamber 4 by a cable 8 that is hermetically inserted into the side wall of the casing 3. derived.

In this differential pressure type pressure transducer, the diaphragm 1a deforms when it receives pressure from the object to be measured, and the force caused by the deformation causes the strain plate 5 to bend via the transmission rod 6. As a result, the resistance value of the strain gauge 7 attached to the strain plate 5 changes, and a voltage signal corresponding to the change in resistance value is led out via the cable 8.

Here, when a temperature change occurs around this pressure transducer, the sealed chamber 4 expands or contracts due to the change in internal pressure, causing a volume change, but the volume change at this time equally spreads between the two diaphragms la and lb. As a result, the strain plate 5 deforms depending only on the pressure of the object to be measured without being affected by temperature changes. Of course, since the strain gauge 7 is completely isolated from the outside world by the casings 2 and 3, its moisture proofing is complete.

However, this differential pressure type has the disadvantage that it not only has a complicated structure and is unnecessarily expensive, but also that it is difficult to adjust the balance of the diaphragms la and lb.

On the other hand, when only one diaphragm is used to simplify the structure, the back pressure of the diaphragm greatly influences the detected pressure value. As a measure to correct this back pressure of the diaphragm, a method of attaching a thin tube as shown in FIG. 6 can be considered.

That is, FIG. 6 is a schematic diagram showing a reference example for explaining the thought process of the present invention.

In FIG. 6, the surface side of the diaphragm 1 to which the strain gauge 7 is attached (non-pressure receiving surface side) is covered with a casing member 9 so as to be isolated from the outside to form a sealed chamber, and one part of the casing 9 A long thin tube 10 is pulled out along with a cable (not shown) for leading the detection output of the strain gauge 7 to the outside through the opening, and a droplet is sealed in an appropriate position in the thin tube 10. With this configuration, it becomes possible to correct the back pressure and to some extent prevent deterioration of the strain gauge 7 due to moisture absorption.

However, in this latter case, if the capillary tube that corrects the back pressure of the diaphragm 1 is too short, droplets will be discharged from the capillary tube 10 into or outside the casing 9 due to temperature changes, and the moisture from the outside will be absorbed into the casing 9. This will cause the strain gauge 7 to deteriorate. Furthermore, if the thin tube 10 is made long in order to avoid such problems, it will not only be a nuisance in handling, but also have the disadvantage of causing a breakage accident if the thin tube is made of a fragile material.

(c) Purpose The present invention was devised in view of the above-mentioned problems of the conventional pressure transducer, and it is possible to correct the back pressure of the diaphragm with a simple structure, and without applying moisture-proofing treatment to the strain gauge as in the conventional method. The object of the present invention is to provide a pressure transducer that completely isolates a strain gauge from the outside world, completely prevents deterioration of insulation, and maintains long-term reliability.

(e) Structure The present invention has a strain gauge attached to a diaphragm that deforms in response to the pressure of the object to be measured, or a strain plate that deforms in response to the force generated by the deformation of this diaphragm via a transmission rod. A sealed chamber is formed by enclosing at least the side of the strain gauge on the side of the ramie board with a casing member so as to isolate it from the outside, and a cable connected to the strain gauge is pierced through the casing member. In a pressure transducer that is airtightly led out from a provided cable outlet.

One open end faces the sealed chamber and the other open end faces the outside, and the middle part is bent or twisted as appropriate to create a capillary-shaped conduit from inside the sealed chamber to the outside through the casing member. A nonvolatile liquid droplet is provided so as to penetrate through the conductive path, and is injected into a predetermined position in the middle of the conductive path, which can block the conductive path and can move in response to changes in the pressure inside the conductive path. This aims to fully achieve the above objectives.

Hereinafter, the present invention will be explained in detail based on one embodiment.

FIG. 1 is a central vertical cross-sectional view showing the configuration of an embodiment of the present invention, and members that can be considered to be the same as those in the conventional example described above are given the same reference numerals.

In the figure, reference numeral 1 denotes a diaphragm that deforms upon receiving pressure from the object to be measured, and closes one end of a casing 2 made of a cylindrical rigid body. Reference numeral 5 denotes a beam-shaped strain plate that is fitted into the casing 2 from the other end of the casing 2 and fixed to the casing 2 so that its plate surface is parallel to the plate surface of the diaphragm 1. A strain gauge 7 is attached to each plate surface. Reference numeral 6 denotes a transmission rod installed at the center of the diaphragm 1 and the strain plate 5 so as to be perpendicular to the respective plate surfaces, and converts the pressure from the measurement object received by the diaphragm 1 into force to transfer the pressure to the strain plate. 5. 11 is fitted from the open end side of the casing 2, and connects both ends of the strain plate 5 to the casing 2.
This is a fixing ring that is press-fixed to the stepped portion 2a of. 12
is a fixing screw member as a casing member having a frustoconical outer shape, and a threaded portion 1'2a on the outer periphery of one end is screwed into a threaded portion 2b on the inner periphery of the other end of the casing 2, and the fixing ring 11 is Holds down. This fixing screw member 12 has a thinner half on one end side to form a concave space, and the proximal end of the cable 13 is inserted into the cable outlet 12c bored in the center of the shaft. There is. This cable 13 includes a lead wire for extracting the detection signal output of the strain gauge 7 to the outside, a capillary tube for adjusting the internal pressure of the sealed chamber 4 formed by the casing 2 and the fixing screw member 12, etc. (Details (described later).

A rubber bushing 14 is fitted from the other end of the fixing screw member 12 and tightly contacts the outer periphery of the cable 13 and the inner wall of the fixing screw member 12 to keep the cable outlet 12c airtight. It is pressed by a cable gland screwdriver 5 screwed onto the fixing screw member 12.

FIG. 2 is a longitudinal sectional view showing an enlarged main part of the cable 13 shown in FIG. 1.

In the figure, the lead wires from the strain gauge 7 are omitted. 16a, 16b, and 16c are linear capillary tubes (hereinafter simply referred to as tubes) that are three capillary tubes with a minute diameter covered by the cable 13.
Both ends of each tube 16a, 16b, 16c are opened to the sealed chamber 4 and the outside world 17, respectively. Three tubes 16 are opened to the side of the sealed chamber 4.
a.

Among 16b and 16c, tube 16b and tube 16
The openings c are connected by a U-shaped connecting tube 18a. Further, among the tubes 16a, 16b, and 16c opened to the outside world 17 side, tubes 16a and 16
The openings b are connected by a connecting tube 18b which also has a U-shape. The three tubes 16a, 16b, 16c connected in this way have one end connected to the sealed chamber 4.
It essentially functions as a single tube that is open inward and the other end is open to the outside world 17.

Here, the method of connecting the three tubes using the connecting tubes 18a and 18b may be other than the above. Si is
Droplets of silicone oil (hereinafter simply referred to as silicone) are injected into the tubes 16a to 16c, typically the connecting tube 18a.

Injected before connection of 18b.

FIG. 3 shows a cross section of the cable 13 in more detail. Around the core material 19 at the center of the cable 13, there are the three tubes 16a to 16c described above and four lead wires 21a and 2 covered with an insulating coating 20, respectively.
lb, 21c.

21d are arranged. This core material 19 is connected to these tubes 16a to 16c and lead wires 21a to 21d.
Among these lead wires 21a to 21d, for example, lead wires 21a and 2
1d is for supplying a bias voltage (so-called bridge voltage) to the strain gauge 7, and a lead wire 21
c and 21d are for transmitting the output of the strain gauge 7 to an external measuring device or the like. These tubes 16a
-16c and the lead wires 21a to 21d are covered with a shield braided member 22 on the outside to prevent interference from the surroundings, and further protected on the outside with a sheath 23 made of chloroprene or the like. This sheath 23 prevents the tube 16a from being damaged by external pressure and friction applied to the cable 13.
16c and the lead wires 21a to 21d.

The operation of the embodiment configured as described above will be explained with reference to FIGS. 1 and 2.

First, when the ambient temperature of the pressure transducer rises, the sealed chamber 4
The internal pressure of increases. This increased pressure presses the surrounding wall surface, enters the tube 16a opened in the sealed chamber 4, and tries to push out the silicon Si injected into the tube 16 toward the outside world 17. do. On the other hand, since outside air is flowing in from the tube 16c opened toward the outside world 17, the silicon Si is moved within the tube 16 to a position where the pressure inside the sealed chamber 4 and the pressure of the outside world 17 are balanced. becomes. When the ambient temperature of the pressure transducer decreases, on the contrary, the internal pressure within the sealed chamber 4 decreases, so that the silicon Si within the tube 16 is moved toward the sealed chamber 4 side.

Next, when the diaphragm 1 receives pressure from the object to be measured, the internal pressure (back pressure) in the sealed chamber 4 increases in the same way as in the case of temperature rise described above, so the silicon S1 in the tube 16 also moves. However, it stops at a position balanced with the pressure applied from the outside world 17 side. Therefore, diaphragm 1 is
The strain plate 5 is displaced and deformed only by the pressure received from the object to be measured.

Next, the relationship between the shape of the tube 16 and temperature change will be explained based on the schematic diagram shown in FIG. 4.

However, to simplify the explanation, the tube 16 is drawn in a straight line.

Between the volume V+ of gas in the sealed chamber 4 at temperature T1 and the volume V2 of this gas at temperature T2, there is a
If the internal pressure of is the same as that of the outside world 17, the relationship V+/T+=V2'/T2 (1) holds true. The length of the tube 16 is 2Q, its cross-sectional area is a,
Assuming that silicon Si is at a distance Q from the opening of the tube 16 when the temperature is T+, when the temperature changes from T1 to T2, the volume change of the gas is.

V2-V+ =V+ ・(T2/TI-1) (2
) Therefore, in order to prevent silicon Si from jumping out of the tube 16, it is necessary to form the tube 16 so as to satisfy the relationship IV+.(T2/T+ -IN<a-Q (3)). However, in this case, the influence of pressure from the object to be measured on the diaphragm 1 is not considered.

In this way, it can be seen that if the operating temperature range of the pressure transducer changes from T+ by ±ΔT=±(T2−T+), it is sufficient to use the tube 16 having a length of 2Q that satisfies equation (3). Therefore, such a tube I6 is shown in FIGS.
As shown in FIG. 3, three tubes 16a to 16c are connected by connecting tubes 18a and 18b, and the intermediate portions of the tubes are arranged in the cable 13 as if folded back and bent, so that the tubes are covered. The actual length of the wrapped cable 13 is 2Q, which is 1/3 of the conventional length.
/3.

As described above, in this embodiment, the surface of the strain plate 5 connected to the diaphragm l via the transmission rod 6, to which the strain gauge 7 is attached, is covered by the casing 2 and the fixed screw member 12, and Since it is completely isolated from the strain gauge 17, there is no need to worry about the strain gauge 7 being exposed to moisture in the outside world 17, and therefore there is no risk of insulation deterioration or corrosion due to condensation, etc., so it can provide highly reliable pressure with stable characteristics over a long period of time. A converter can be provided. Moreover, the internal pressure of the sealed chamber 4 formed by the casing 2 and the fixing screw member 12 is configured to be always equal to the pressure of the outside world 17 due to the tube 16 and silicon Si within the tube 16, and the temperature around the pressure transducer is Even if there is a change in the diaphragm l due to pressure from the object to be measured or a change in atmospheric pressure, the sealed chamber 4
Since the internal pressure is always maintained equal to atmospheric pressure, the pressure from the object to be measured can always be accurately transmitted to the strain plate 5. Therefore, it is possible to transmit small pressures without the complexity of conventional differential pressure types. A low capacity pressure transducer that can detect with high accuracy can be obtained.

In addition, the three tubes 168 to 16C are connected to the cable 13
After arranging the lead wires 21a to 21d in parallel inside the tube, a predetermined one of each opening is connected to the connecting tube 1.
8a and 18b to form substantially one tube 16, the tube 16 is easy to process and the length of the cable 13 is also straight.
It can be set to 1/3. Further, the silicon Si in the tube 16 can be injected with a syringe needle or the like, but in this case, the tubes 16a to 16c are connected to the connecting tube 1.
If silicon Si is injected from an arbitrary opening before connection by 8a and 18b, positioning of silicon Si can be more easily performed.

It should be noted that the present invention is not limited to the embodiments described above, and it goes without saying that various modifications can be made within the scope of the invention.

For example, pressure transducers are usually used only in high temperature ranges or low temperature ranges, and in such cases, if the pressure transducer is used only in high temperature ranges, the tube 16
The length of the tube 16 can be further shortened by injecting droplets of Si toward the opening on the side of the sealed chamber 4, and injecting silicon Si toward the opening on the outside world 17 side in the case of a low-temperature type. be able to.

Further, as the conduction path, it is not necessary to use the capillary tube 16, but a capillary-like pore formed in a wall of the fixing screw member 12 or the like in a spiral shape, for example, may be used.

Further, the number of capillary tubes 16 is not limited to three, but may be any number. For example, one tube 16 is spirally wound around the core material 19 or the shield braided member 22, and one opening is closed to the sealed chamber 4. The other opening may be configured to open to the outside world 17, and if configured in this way,
The tube 16 can be made longer without making the cable 13 longer.

Furthermore, other liquids than silicon may be used as the droplets, as long as they are inert, nonvolatile, and have a relatively strong adhesive force within the conductive path.

(e) Effects As detailed above, according to the present invention, the back pressure of the diaphragm can be corrected with a simple structure, and the strain gauge can be isolated from the outside world without applying moisture-proofing treatment to the strain gauge as in the conventional case. Thus, it is possible to provide a pressure transducer that can completely prevent insulation deterioration and maintain long-term reliability.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view showing the configuration of an embodiment of the present invention, and FIG.
The figure is an enlarged vertical sectional view showing the structure of the conduction path which is the main part of the present invention, and FIG. cross section,
FIG. 4 is a schematic diagram for explaining the operation of the same embodiment, FIG. 5 is a vertical cross-sectional view showing the configuration of a conventional differential pressure type pressure transducer, and FIG. 6 is for explaining the thought process of the present invention. FIG. 3 is a schematic diagram showing a reference example for l...diaphragm, 2...casing, 4...sealed chamber, 5...distortion plate. 6...Transmission rod, 7...Strain gauge, 12...Fixing screw member. 13... Cable, 14... Rubber bushing, 15... Cable gland screw. 16.16a-16c... Capillary tube, 17... External world, 18a, 18b... Connection tube, Si...
...Silicone oil droplets. Figure 1 Figure 2 Figure 3 Figure 4

Claims (6)

[Claims] (1) A strain gauge is attached to a diaphragm that deforms in response to pressure from a measurement object, or a strain plate that deforms by receiving force generated by the deformation of this diaphragm via a transmission rod, and A sealed chamber is formed by enclosing at least the side to which the strain gauge is attached with a casing member so as to isolate it from the outside, and a cable connected to the strain gauge is connected to a cable lead provided in the casing member. In a pressure transducer that is airtightly led out from the outlet, a capillary-shaped conduit is formed by having one open end facing the sealed chamber and the other open end facing the outside, and the intermediate portion being bent or twisted as appropriate. provided so as to penetrate from the inside of the sealed chamber to the outside via the casing member,
the conductor 1 at a predetermined position in the middle of the conductive path;
! IN qk + bta-y +-shi+, + -z
Lecture 2y, ah 7? % l-1-1tm 77%
A pressure transducer characterized by injecting nonvolatile droplets that can move in response to pressure changes. (2) The pressure transducer according to claim 1, wherein the conductive path is formed by a capillary tube. (3) The capillary tube is comprised of a plurality of straight capillary tubes and a plurality of connecting tubes that sequentially communicate the capillary tubes at both ends thereof to form substantially one capillary tube.
Pressure transducer as described in section. (4) The pressure transducer according to claim 1, wherein the capillary tube is integrated with the cable. (5) The pressure transducer according to claim 1, wherein the conduction path is a pore bored in the casing member. (6) The pressure transducer according to claim 1, wherein the nonvolatile droplets are silicone oil droplets.