JP3488758B2 - Pressure transmitter and method of assembling pressure transmitter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure transmitter and a method for assembling the pressure transmitter. More specifically, the present invention relates to a pressure detector for converting a deformation of a diaphragm due to a pressure difference between a pressure receiving surface and a rear surface thereof into an electric signal. The present invention relates to a pressure transmitter and a method for assembling the pressure transmitter in which a unit and a signal processing unit that performs processing such as amplification on an electric signal detected by the pressure detection unit are housed in the same case.

[0002]

2. Description of the Related Art Conventional pressure transmitters (pressure transducers) of this type
Is configured, for example, as shown in FIG. In FIG. 8, 5l is a metal introducing member having a connecting portion 51b formed of a male screw that is connected to an object to be measured such as a gas tank, and the central shaft portion of the introducing member 51 is
A pressure introducing passage 5la for introducing the fluid to be measured is provided.

At one end of the introducing member 5l opposite to the connecting portion 51b, one end of a flexure element 52 having rigidity integral with the metal diaphragm 52a is airtightly fixed by welding or the like. A pressure receiving chamber 52b is formed between the inner surface and the end surface of the introducing member 5l to store the fluid to be measured introduced through the pressure introducing passage 5la. A strain gauge SG that converts deformation of the diaphragm 52a due to a pressure difference between the pressure receiving surface and the back surface into an electric signal is attached to the back surface side of the diaphragm 52a opposite to the pressure receiving surface.

A gauge lead connected to a gauge tab of the strain gauge SG is connected to the substrate 53 arranged so as to face the diaphragm 52a. This board 5
An airtight terminal 54 arranged so as to face 3 is airtightly fixed to the other end (upper end in FIG. 8) of the flexure element 52 by resistance welding. The conductive pin 54a implanted in the airtight terminal 54 includes a conductive pattern of the substrate 53 on the lower surface side in FIG. 1, an amplifier on the upper surface side, a bridge balance adjusting circuit,
Signal and power supply / reception is controlled in a state where airtightness is maintained with the circuit elements of the signal processing unit 55 such as.

The signal processing section 55 includes an amplifier mounted on the substrate 55a and other circuit elements constituting the circuit. Of these, 55b is a fine adjustment for balance adjustment of the bridge circuit. Is a variable resistor for. The signal processing unit 55 is circuit-connected to a waterproof connector 56 that supplies power and relays a detection signal.

A short cylindrical member 57a and a flat plate ring member 57 are provided between the other end of the strain generating body 52 and the waterproof connector 56 so as to mainly surround the signal processing section 55.
The first case 57 including the b and the long cylindrical member 57c.
And a long cylindrical second case 58 are provided.

In the first case 57, the three members 57a to 57c are integrally welded in advance in a hermetically sealed manner as shown in FIG. 8, but different from the second case 58. Make it on the body. The member 57 of the first case 57
After the wiring work from the strain gauge SG to the airtight terminal 4 is completed, a and the other end of the flexure element 52 are airtightly joined by welding the outer periphery thereof.

The member 57c of the first case 57 and one end of the second case 58 are joined to each other by welding the outer periphery of the joining portion after rough adjustment is completed in the balance adjustment work of the bridge circuit. After that, the fine adjustment variable resistor 55b is rotationally adjusted by using a tool such as a driver through the adjustment hole 57d formed in the member 57c of the first case 57 to adjust the balance of the bridge circuit. , Fine adjustment and then blind lid 5
Seal with 9. After completing all such operations, the transparent heat-shrinkable tube 60 is attached to the outer periphery of the second case 58 and the first case 57 (strictly speaking, the member 57c).

[0009]

However, the above-mentioned conventional pressure transmitter has the first drawback that it is susceptible to high frequency radio noise. That is, with respect to the conventional transmitter shown in FIG. 8, a characteristic test of the zero point variation amount when the frequency of the applied electric field is changed in the range of 0 to 200 MHz with the applied electric field strength being constant, in other words, the pressure transmission. Compatibility as the ability of the device to withstand radio interference (Immu
As a result of conducting a nity to interference) test, it was found that as shown in FIG. 9, it was significantly affected in the frequency region of 10 MHz to 60 MHz.

Further, in FIG. 10, a radio frequency / constant electric field test was conducted in order to see the change in the zero point fluctuation amount when the electric field strength and the frequency of the applied electric field were changed stepwise for the same pressure transmitter. The results show that the zero level fluctuates more as the electric field strength increases, and also in this case, 27 MHz and 40 MHz are greatly affected. In such an environment where a strong radio wave is received, the zero point shifts, and the resolution is lowered due to high frequency radio wave noise, so that pressure detection cannot be performed with high accuracy and high resolution.

That is, the pressure transmitter as shown in FIG.
It cannot be used in places that are easily affected by radio waves, such as broadcasting stations, radio bases, and places where CB radios are installed, and high precision, high stability, and high resolution are required. For example, gas insulated switchgear ( There is a big problem that it cannot be used as a pressure transmitter for "GIS" (abbreviated as "GIS"). In addition, the above-mentioned conventional example has a drawback that the number of assembling steps is large and the manufacturing cost is increased accordingly.

Further, FIG. 8 shows a signal processing unit 55.
Since the space where is provided is formed only by the first case 57, the second case 58, and the connector 56, the portion of the waterproof connector 56 during long-term use,
There is a risk that the outside air may enter through the gap between the adjustment hole 59d and the blind lid 59, etc., and the circuit elements forming the signal processing unit 55 may be deteriorated by moisture, oxygen, etc. contained in the atmosphere. is there.

Further, in the above-mentioned conventional example, since the variable resistor 55b is used for the balance adjustment of the bridge circuit, the variation of the contact resistance value of the contact portion, the variation of the resistance value due to the variation of the contact position, The resistance value is liable to change due to wear of the contact portion, and there is a drawback that the contact position of the contact portion is easily changed particularly when the resistance value is attached to an object to be measured accompanied by vibration. Further, although the above-mentioned conventional example is derived from its structure, it requires a large number of assembling steps, and for that reason, it is easy to assemble the components of the signal processing unit 55 to the board and to perform the wiring process. It's hard to say.

The present invention has been made in view of the above-mentioned circumstances. The first object of the present invention is that even if the present invention is used in an environment exposed to strong radio waves, it is not affected by the radio waves, and zero fluctuations occur. It is an object of the present invention to provide a pressure transmitter and a method for assembling the pressure transmitter that can convert the pressure to be measured into an electric signal with high resolution. A second object of the present invention is to rationalize the assembling process to simplify the process, significantly improve the electromagnetic compatibility due to the assembling order, and reduce the manufacturing cost. Another object of the present invention is to provide a method of assembling a pressure transmitter that can achieve the above.

A third object of the present invention is to improve the airtightness of the signal processing section and the strain gauge in the space where the signal processing section and the strain gauge are disposed, and to configure the strain gauge and the signal processing section by the invasion of the outside air. It is an object of the present invention to provide a pressure transmitter capable of preventing deterioration of performance due to deterioration of insulation of elements or oxidation.
A fourth object of the present invention is to provide a method of assembling a pressure transmitter that can accurately adjust the balance of a bridge circuit and stably maintain the balanced state for a long period of time. .

[0016]

In order to achieve the above first and third objects, the pressure transmitter according to the present invention prevents the diaphragm from being deformed due to the pressure difference between the pressure receiving surface and the back surface thereof. In the pressure transmitter which detects using a strain gauge attached to the and converts it into an electric signal and appropriately amplifies the electric signal in the signal processing section and outputs it through the connector section , an introducing member having a pressure introducing path, and pressure
It is airtightly fixed by welding etc. so as to block the inner end of the introduction path.
Surrounding the diaphragm part and the diaphragm part
The end is airtightly fixed to the introduction member by welding or the like, and the other end
To the airtight terminal by welding etc.
A metal inner case that forms a tightly held reference pressure chamber.
The metal inner case and the signal processing circuit , and a shield body is brazed or soldered in the middle.
A metallic outer <br/> case interior is hermetically fixed to is kept airtight Ri, hermetically by welding or the like to the other end of the outer casing
And anchored connector portion, anda high frequency wave noise filter circuit configured to include the anchored feedthrough capacitor hermetically to said shield body, the radio noise be used in an environment subjected to strong wave It is characterized in that it is configured to be cut off to obtain an electric signal corresponding to the pressure received by the diaphragm.

In order to more reliably achieve the first object, a high frequency radio noise filter circuit for a pressure transmitter according to the present invention is provided with a feedthrough capacitor airtightly fixed to the shield body, and this feedthrough capacitor. It is composed of a ferrite core that is placed close to and connected to the power supply / signal line and the signal processing unit, and cuts off high frequency radio noise mixed from the power / signal line. However, the configuration is such that the signal is not transmitted to the signal processing unit.

Further, in order to achieve the above first, second and third objects, the method of assembling the pressure transmitter according to the present invention is characterized in that the diaphragm is deformed by the pressure difference between the pressure receiving surface and the back surface thereof. A pressure detection unit that converts into an electric signal using a strain gauge attached to the pressure sensor and a signal processing unit that performs amplification processing etc. on the detection signal detected by this pressure detection unit are integrally housed in the same case. In the transmitter assembling method, a pressure detecting / signal processing unit assembling step of forming the pressure detecting / signal processing unit by attaching the signal processing unit to the pressure detecting unit, and at least the pressure detecting unit,
In a metal hollow case for housing the signal processing unit, a shield body for isolating the signal processing unit and the connector unit is airtightly fixed by brazing or soldering, and a shield case unit is provided. Following the shield case unit assembling step of forming and the shield case unit assembling step, the shield case unit is attached to the pressure detecting / signal processing unit by hermetically fixing one end of the case to the rigid portion of the pressure detecting section by welding. Attaching the shield case, and subsequently to this shield case attaching step, attach the connector section to the shield case unit by welding the connector section for relaying the power supply / output signal to the other end of the case in an airtight manner by welding. And a connector part attaching step.

Further, in the method of assembling the pressure transmitter according to the present invention, in order to more reliably achieve the second object, the high frequency radio noise filter circuit is constructed in the shield case unit assembling step or the steps before it. The feedthrough capacitor, which is one element, is hermetically fixed to the shield body, and the power supply and output terminal pins are inserted into the bead type ferrite core, which is one element that constitutes the high frequency radio noise filter circuit. -The output terminal pins are fixed to the substrate of the signal processing unit side, and the power supply / output terminal pins are inserted into the through holes of the feedthrough capacitor when the shield case attaching step is performed. It is a feature.

In order to achieve the third and fourth objects, the pressure transmitter assembling method according to the present invention is formed by the strain gauge after the pressure detecting / signal processing unit assembling step. In order to roughly balance the Wheatstone bridge circuit, an appropriate fixed resistor is selected and connected to the signal processing unit to perform rough adjustment, and after the shield case unit mounting step, the bridge circuit is finely balanced. In order to make fine adjustments by selecting and connecting an appropriate fixed resistance through the adjustment hole formed in the shield body, a blind lid is screwed into the adjustment hole and sealed airtight with a sealant. It is characterized by stopping.

[0021]

When the pressure transmitter having the above-mentioned structure is used in an environment where a strong electric wave is received, the high-frequency electric wave noise mixed in the power source / signal line is blocked and is prevented from being transmitted to the signal processing unit. Therefore, the shield body is arranged so as to cut off between the signal processing section and the connector section, and the strain gauge is sealed inside the inner case made of metal, and
The inner portion of the outer casing to seal the signal processing unit, outside air intrusion
Of strain gauges and circuit elements that make up the signal processing unit
It is possible to reliably prevent performance deterioration due to insulation deterioration and oxidation.
In addition to preventing it from being directly affected by radio waves, a high frequency radio noise filter circuit including a feedthrough capacitor fixed to the shield body is provided to block high frequency radio noise mixed in the power supply / signal line, The noise is prevented from being transmitted to the processing unit.

Further, in the method of assembling the pressure transmitter including the above steps, in order to reduce the number of assembling steps, the pressure detecting / signal processing unit assembling step, the shield case unit assembling step, and the shield case attaching step are performed. The connector mounting process is roughly divided into four units for assembly. Among these, in the shield case unit assembling process, the shield body is airtightly fixed in the case by brazing or welding to ensure the electrical connection and mechanical connection between the two.

This is because the pressure detection and
If you try to connect the shield body and the case by brazing or soldering after connecting the signal processing unit and the both together, the temperature at the time of joining will be too high and the circuit element or the board will be burned or This is because it will have an adverse effect. For this reason, when avoiding high-temperature work such as brazing and using a conductive adhesive, the shielding effect is weakened, the sealing property is poor, and the inert gas cannot be replaced, and the expensive conductive adhesive is used. There is a new problem that the material cost increases due to the use of.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the pressure transmitter and its assembling method according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a vertical cross-sectional view showing the cross-sectional structure of one embodiment of the pressure transmitter according to the present invention.

FIGS. 2 and 3 are views for explaining the method of assembling the pressure transmitter according to the present invention for each assembling step. Of these, FIG. 2 shows the shield case unit assembling step ( FIG. 6A is a vertical cross-sectional view for explaining A) and the pressure detection / signal processing unit assembly step (B) shown in the lower stage thereof, and also for explaining the state before shifting to the shield case attachment step shown in the next figure. FIG. 3 is a vertical cross-sectional view for explaining the shield case attaching step (C), the connector section assembling step (D), and the connector section attaching step, respectively.

In FIG. 1, reference numeral 1 denotes a metal introducing member having a connecting portion 1b made of a male screw which is connected to a portion to be measured such as a gas insulated switchgear (GIS), and a central axis of the introducing member 1. A pressure introducing passage 1a for introducing the fluid pressure to be measured is formed in the portion. Joining part 1 of introducing member 1
At the end opposite to b, a cylindrical portion 2 having rigidity and integral with the metal diaphragm 2a is airtightly fixed by welding or the like, and a pressure is applied between the inner surface of the diaphragm 2a and the end surface of the introducing member 1. A pressure receiving chamber 2b is formed in which the fluid to be measured introduced through the introduction passage 1a is stored.

A strain gauge SG for converting a deformation of the diaphragm 2a due to a pressure difference between the pressure receiving surface and the back surface into an electric signal is bonded to the back surface side of the diaphragm 2a forming a part of the pressure receiving chamber 2b, which is opposite to the pressure receiving surface. , Evaporation, sputtering,
It is attached by welding or other means.

In the strain gauge SG, a meandering gauge element made of Ni-Cr alloy or the like is attached to a gauge base made of phenol resin, polyimide resin or the like. Further, at least four strain gauges SG are attached to the back surface of the diaphragm 2a, and these four strain gauges are connected so as to form a Wheatstone bridge circuit as described later.

An inner cylinder 3 that covers the cylindrical portion 2 having the diaphragm 2a at regular intervals is concentrically arranged on the outer periphery thereof, and one end edge (lower end edge in FIG. 1) of the inner cylinder 3 is arranged.
Is hermetically fixed to the introduction member 1 by welding or the like, and the airtight terminal 4 is fitted to the opening at the other end (upper edge in FIG. 1). The peripheral edge of the metallic lid member 4a forming the airtight terminal 4 is airtightly fixed to the upper end of the inner cylinder 3 by welding or the like. The inner cylinder 3 and the airtight terminal 4 form a reference pressure chamber on the back surface side of the diaphragm 2a.

A plurality of pin terminals 4c forming the airtight terminal 4 are pierced and supported by an insulating sealing material 4b, and a gauge lead is provided between one end of each pin terminal 4c and the gauge electrode of the strain gauge SG. It is connected. The other end of the pin terminal 4c is fitted into a through hole formed in the mounting board 5 and fixed to the mounting board 5 by soldering.

An amplifier board 6 is fixed on the mounting board 5, and the amplifier board 6 has a Wheatstone bridge circuit including a strain gauge SG such as an adjusting resistor, a hybrid IC, a transistor, etc. as described above. An electric circuit section 7 is provided as a signal processing section for performing processing such as amplification, waveform shaping, and calculation of the bridge output, including a balance adjustment resistor and a sensitivity adjustment resistor. A fine adjustment board 8 is fixed to the other end (upper end in FIG. 1) of the amplifier board 6.

The fine adjustment substrate 8 has a fixed resistor R1 for fine adjustment having a resistance value determined as described later.
A small adjusting resistor terminal 9 for inserting 5, R16, R17 is provided, and the small adjusting resistor terminal 9 and fixed resistors R15, R
Since 16 and R17 are firmly fixed by soldering, there is no disconnection or contact failure even when subjected to vibration. The adjusting blind lid 10 as a blind lid has an adjusting hole formed in the shield body 11 and is provided with fixed resistors R15 to R17 for fine adjustment.
Is fixed to the small adjusting resistor terminal 9, then closed, and the periphery thereof is hermetically sealed with an adhesive (sealant) or the like.

A through capacitor 12 with a hole is hermetically fitted and fixed to the shield body 11 in a hermetically sealed manner, and a bead type ferrite core 13 is provided on the fine adjustment substrate 8. And ferrite core 13
A power source / output terminal 14 as a pin-shaped power source / output terminal pin is provided, which penetrates through and has one end (lower end) thereof fixed to the fine adjustment substrate 8 through.

An outer cylinder 15 is provided so as to fit on the outer peripheral surface of the shield body 11, and one end (lower end) of the outer cylinder 15 is provided.
Is attached to the stepped portion of and is airtightly fixed by welding, and the connector mounting plate 16 is fixed to the other end (upper end) by soldering or the like. A waterproof receptacle 17 as a connector portion is attached to the central opening of the connector attaching plate 16 by a screw means with a rubber packing 17d interposed. Connection terminal 1 of this waterproof receptacle 17
Cable 17b is provided between 7a and the power supply / output terminal 14.
Are connected via a metal connection socket 17c.

Next, a method of assembling the pressure transmitter having such a structure will be described. First, the pressure detecting portion including the introducing member 1, the cylindrical portion 2 (diaphragm 2a), the inner cylinder 3, the airtight terminal 4 and the like is joined by welding as described above.
Prior to this welding work, it is assumed that the strain gauge SG is attached to the diaphragm and the gauge lead is connected.

Next, the signal processing unit is assembled. That is, the pin terminal 4c of the airtight terminal 4 is inserted into the pin hole formed in the mounting substrate 5.
Insert and solder to fix. Then, one end of the amplifier substrate 6 to which circuit elements such as adjustment resistors, hybrid ICs, transistors, etc. are attached is attached to the attachment substrate 5, and the fine adjustment substrate 8 is attached to the other end of the amplifier substrate 6. At this time, the power source / output terminal 14 in which the ferrite core 13 is inserted is attached to the fine adjustment substrate 8 and is electrically connected by soldering.

In the state of being assembled in this way,
That is, what is shown in the lower stage (B) of FIG. 2 is referred to as a pressure detection / signal processing unit here, and such a work process is
It will be referred to as a pressure detection / signal processing unit assembly process. Next, the shield body 11 to which the through capacitor 12 with a hole, which is a constituent element of the high frequency radio noise filter circuit is attached, is fitted into the outer cylinder 15 as a case, and airtightly fixed by brazing or soldering. To do. The thus assembled state, that is, the one shown in the upper part (A) of FIG. 2 is referred to as a shield case unit here, and such an operation process is referred to as a shield unit assembly process.

Next, the shield case unit shown in the upper part of FIG. 2 is fitted and assembled in the pressure detection / signal processing unit shown in the lower part of FIG. That is, one end (lower end) of the outer cylinder 15 is hermetically fixed to the introduction member 1 as a rigid body portion of the pressure detection portion by welding. This work process
Here, it will be referred to as a shielded case attaching process, and such a process stage is shown in the lower stage (C) of FIG.

Next, the connector unit is assembled.
The male screw portion of the waterproof receptacle 17 is inserted through the through hole formed in the center of the connector mounting plate 16 with the rubber packing 17d interposed between the one surface (the upper surface in FIG. 3) side and the other side of the connector mounting plate 16. Nut (17) from the surface (lower side)
Screw e together to attach the waterproof receptacle 17 to the connector mounting plate 16. Then, one end of the cable 17b is soldered to the connection terminal 17a, and the connection socket 17c is attached to the other end of the cable 17b by soldering.

The thus assembled structure is as follows:
What is shown in the upper part (D) of FIG. 3 is referred to as a connector portion or a connector unit here, and such a working process is referred to as a connector portion assembling process. Next, the outer periphery of the connector mounting plate 16 of this connector portion and the other end of the outer cylinder 15 are fixed by welding. However, prior to this coupling work, the connection socket 17c is inserted into the power supply / output terminal 14 for electrical connection. The product assembled in this manner is a completed product of the pressure transmitter, and the work at this stage will be referred to as a connector part mounting step here.

Assembling the pressure transmitter by the above assembling process has the following advantages. First, in the shield unit assembly process, the shield body 11 is attached to the outer cylinder 1
5 is airtightly fixed to the inside of the outer cylinder 15 by brazing or soldering, so that there is an advantage that the electrical connection and the mechanical connection (airtight connection) between the both can be ensured.

The reason is that, for example, by changing the above steps,
The shield body 11 is first attached to the pressure detection / signal processing unit, and then the shield body 11 is inserted into the outer cylinder 15 together with the pressure detection / signal processing unit to braze the shield body 11 to the inner cylinder portion of the outer cylinder 15. Alternatively, when joining by soldering, the temperature at the time of joining by brazing or the like is too high, and the circuit element or the board is burned or adversely affected.

Therefore, when a high-temperature work such as brazing is avoided and a conductive adhesive is used, the shield effect becomes weaker, the hermeticity is poor, and the inert gas cannot be replaced. For this reason, the shield body 11 and the outer cylinder 15 are airtightly fixed by brazing or the like prior to the pressure detection / signal processing unit assembly process.

Further, the feedthrough capacitor 1 is attached to the shield body 11.
2 is inserted in advance and fixed by soldering, while the power supply / output terminal 14 with the bead type ferrite core 13 inserted is set up on the fine adjustment substrate 8 on the signal processing section side. Therefore, when the shield case unit is assembled to the pressure detection / signal processing unit, the power supply / output terminal 14 is fitted into the fitting hole of the feedthrough capacitor 12, and electrical connection is immediately made, and at the same time, the feedthrough capacitor 12 is connected. , The ferrite core 13, and the power supply / output terminal 14 are electrically coupled to form a high frequency radio noise filter circuit, and extremely efficient assembly is performed.

If the electrical coupling work as described above is performed by another method within the narrow space inside the outer cylinder 15, the workability is poor and must be performed by a skilled worker. It can be said that this is a rational assembling method, as can be seen by comparison with the possibility of poor contact or electrical coupling with low vibration resistance. next,
A high-frequency radio noise filter circuit, which is a main part of the pressure transmitter according to the present invention, will be described mainly with reference to FIG. 4 and further with reference to FIG.

In FIG. 4, 12 is a feedthrough capacitor,
A through hole is formed in the central portion, and the central portion, which is one end of the through hole, is electrically contacted while being inserted into the pin-shaped power supply / output terminal 14. The outer peripheral surface, which is the other end of the feedthrough capacitor 12, is in electrical contact with a metallic shield body 11 that is a good conductor, and is further fixed to the shield body 11 by brazing or soldering. It is also electrically connected to the manufactured outer cylinder 15 and is in a state of being grounded. (Further, it is also connected to the introduction member 1, the connector mounting plate 16, etc., which are each made of metal).

One end of the feedthrough capacitor 12 is electrically connected via the power supply / output terminal 14 to one end of a bead type ferrite core 13 inserted through the central portion by the power supply / output terminal 14. And the ferrite core 13
The other end is connected to, for example, an amplifier of the electric circuit 7 as a signal processing unit via a conductive pattern or the like arranged on the fine adjustment substrate 8.

[0048] In the high frequency wave noise filter circuit shown in FIG. 4 made of such a configuration, i _N: noise current i _'N: noise current entering the amplifier (amp) i _C: current flowing through the feedthrough capacitor i _L: Ferrite Current k flowing through the core: coefficient (j × 2π) f: frequency C: capacitance L: inductance, the impedance Zc of the feedthrough capacitor 12 has a relationship of Zc = 1 / k · f · C.

That is, when the frequency f of the radio wave entering the current / signal line becomes higher, the impedance Zc of the feedthrough capacitor 12 becomes smaller and the current i _C flowing through the feedthrough capacitor 12 becomes larger. As a result, the ferrite core 1
The noise current i _N passing through 3 and entering the electric circuit section (signal processing section) becomes sufficiently small.

On the other hand, when the frequency of the radio wave entering the current / signal line increases, the impedance Z _L of the ferrite core 13 increases and the current i _L flowing through the ferrite core decreases, as can be seen from the above relational expression. since the noise current i _'N entering the electric circuit 7 through the ferrite core 13 is sufficiently small. That is,
According to the high frequency radio noise filter circuit configured as described above, the high frequency radio noise current is cut.

The results of an immunity test (electromagnetic compatibility test) on the product of the present invention are shown in FIGS. 6 and 7. Since FIG. 6 corresponds to FIG. 9 described above and FIG. 7 corresponds to FIG. 10 described above, the difference can be clearly seen by comparing both corresponding figures. According to the present invention, when the frequency sweep is performed in the range of 1 MHz to 200 MHz, the zero point fluctuation amount is 1 m.
V / scale is within 1 scale.

Further, FIG. 7 shows changes in the zero point fluctuation amount when the radio frequency and the electric field strength thereof are gradually changed for the same product of the present invention. You can see that it has not changed. From the test results of FIGS. 6 and 7, it is apparent that the high frequency radio noise filter circuit according to the present invention reliably removes high frequency radio noise.

Next, an embodiment of the bridge balance adjusting circuit of the Wheatstone bridge circuit included in the pressure detecting portion of the pressure transmitter according to the present invention will be described with reference to FIG. Figure 5
It is a circuit diagram which shows the structure of one Example of the bridge balance adjustment circuit. In FIG. 5, the Wheatstone bridge circuit includes four resistors R1 and R2 such as strain gauges.
, R3, R4.

The unbalanced component of this Wheatstone bridge circuit is determined by seven fixed resistors R11, R12, R13, R14 and R1.
A resistor having an appropriate resistance value close to the resistance value obtained by a predetermined calculation is selected from 5, R16 and R17 and adjusted.
Bridge power supply input b of Wheatstone bridge circuit,
A voltage having a large bridge resistance value is applied from the bridge power source E between d. A sensitivity adjusting resistor R21 is connected in series to the supply path of the bridge power source E, and a sensitivity adjusting resistor R22 is connected in parallel with the sensitivity adjusting resistor R21.

The seven fixed resistors (actually, the number is not limited to seven) for adjusting the unbalanced component can be roughly classified into a coarse adjusting resistor and a fine adjusting resistor according to their functions. That is, the coarse adjustment resistors are the four fixed resistors R11, R12, R13 and R14 as the first resistor group. The fine adjustment resistors are a fine adjustment series resistor R15 as a second fixed resistor and two fixed resistors R16 and R17 as a third fixed resistor, and the fixed resistor R15 is It is for sensitivity adjustment of fine adjustment (that is, for sensitivity desensitization). In this configuration,
The final adjustment is the fixed resistor R16 as the third fixed resistor.
And R17.

Now, the structure of the bridge balance adjusting circuit will be described in more detail with reference to FIG. The Wheatstone bridge circuit is composed of, for example, four resistors including a strain gauge on at least one side thereof. Positive of the bridge power supply E of this Wheatstone bridge circuit
The positive and negative electrodes of the bridge power supply E are respectively connected to the negative input terminals b and d, and an output due to the imbalance of the Wheatstone bridge circuit appears between the output terminals a and c.

In other words, this Wheatstone bridge circuit has a series circuit of resistors R1 and R2 forming the first two sides between the positive and negative input terminals b and d of the bridge power source E, The series circuit of the resistors R3 and R4 forming the second two sides is connected. In the case of the embodiment of FIG.
Fixed resistors R12 and R14 are apparently inserted in parallel to the resistor R4 on one side of the resistors R3 and R4 forming the second two sides, and to the resistor R3 on the other side. The fixed resistors R11 and R13 are connected to each other, but substantially, the fixed resistors R11 and R14 are equal to being open because their resistance value is ∞.

Here, the fixed resistors R11 to R14 are
It will be referred to as a first fixed resistor group. And the second
One end of the second fixed resistor R15 is connected to the connection point of the resistors R3 and R4 forming the two sides of the above, that is, one output end c. In addition, one of two connection points between the second two sides formed by the resistors R3 and R4 and the first two sides formed by the resistors R1 and R2, that is, one of the bridge power source input terminals b and d. A third fixed resistor R16 is connected between the connection point b and the other end of the second fixed resistor R15, and the other connection point d and the second fixed resistor R15 are connected. A fourth fixed resistor R17 is connected between the other end of R15 and R15.

The fixed resistor R as the first resistor group
Although 11 to R14 have been described as the coarse adjustment resistors, if further divided functionally, the fixed resistors R11 and R12 are coarse adjustment resistors, and the fixed resistors R13 and R14 are It can be said that it is a fixed resistor for intermediate adjustment.

The fixed resistor R1 for these rough adjustments
In principle, both R1 and R12 are not connected at the same time, but only one is connected depending on the unbalanced state of the Wheatstone bridge circuit.
When 1 × R3> R2 × R4, the fixed resistor R11 is connected in parallel to the resistor R3, and conversely R
When 1 × R3 <R2 × R4, the fixed resistor R12 is connected in parallel to the resistor R4.

In principle, the fixed resistors R13 and R14 for intermediate adjustment are not connected at the same time in principle. As a result of the rough adjustment, the fixed resistors R11 and R12 connected in the circuit are included. Also, depending on which of the products of the resistance values of the fixed resistors on each side of the Wheatstone bridge circuit is larger, only one of them is connected.

For example, as a fixed resistor for rough adjustment, R12
Is connected in parallel with the resistor R4, the product of the resistors R1 and R3 is larger than the product of the combined resistance R2 of the resistor R2 and the resistor R4 and the fixed resistor R12. (R4 // R12). In this case, the fixed resistor R13 is connected in parallel to the resistor R3, and when the product value has the opposite relationship, the fixed resistor R14 is connected in parallel to the resistor R4.

Here, an example of the adjustment procedure of FIG. 5 will be described below. The adjustment procedure for adjusting the unbalance of the Wheatstone bridge circuit is roughly classified into the following two. I. The resistance of each side of the bridge is measured and theoretically calculated and corrected. B. The unbalance amount is measured and the adjustment resistance value is added to a predetermined side to gradually decrease the unbalance amount.

In each of these adjustments, a predetermined number of resistors having different resistance values for coarse adjustment (including intermediate adjustment) and fine adjustment are prepared in advance, and as described above, , Select an appropriate one from these resistance values and proceed with the adjustment in sequence. In order to balance the Wheatstone bridge circuit in a circuit including a Wheatstone bridge circuit composed of strain gauges and a bridge power supply E, first, a + coarse adjustment fixed resistor R11 or a −coarse adjustment fixed resistor R12 is used for adjustment. .

Next, as the intermediate adjustment, adjustment is performed by the + intermediate adjustment fixed resistor R13 or the −intermediate adjustment fixed resistor R14. Here, the intermediate adjustment requires a higher resistance value than the coarse adjustment. Next, fine adjustment is performed, but for the + fine adjustment fixed resistor R16 or the − fine adjustment fixed resistor R17,
A higher resistance value is required. However, due to the action of the fine adjustment series resistor R15, the intermediate adjustment resistor R13 (R
Adjustment is possible with a standard resistance value similar to 14).

With such a circuit configuration, strict balance adjustment of the Wheatstone bridge circuit becomes possible without using a variable resistor. Further, since it is the balance adjustment using the fixed resistor, it has excellent vibration resistance and high stability in terms of aging. Further, since the fine adjustment can be performed with a lower resistance value, the fixed resistor can be easily obtained, the adjustment range can be expanded, and the fine adjustment can be performed with high accuracy.

Next, the operation of the pressure transmitter of FIG. 1 having such a configuration will be described. This pressure transmitter guides the fluid to be measured (gas) to the pressure introducing passage 1a in a state where the coupling portion 1b of the introducing member 1 is attached to the gas pressure monitoring output portion of the gas insulated switchgear.

Then, since the gas pressure is applied to the pressure receiving surface of the diaphragm 2a, the diaphragm 2a undergoes a deformation (deflection) corresponding to the gas pressure, and the strain gauges SG (R1 to R4 in FIG. 5) apply pressures. Shows the change in resistance value corresponding to. Therefore, the electric signal (voltage) corresponding to the gas pressure is output from the output end of the Wheatstone bridge circuit assembled by the four strain gauges SG to the electric circuit unit 7, so that the electric circuit unit 7 appropriately amplifies the signal. , Waveform shaping,
After being subjected to processing such as calculation, a detection signal corresponding to the fluid pressure (gas) to be measured is derived to the outside through the power / output terminal 14, the cable 17b, the connection terminal 17a, and the like in order.

Before starting such pressure detection work,
It goes without saying that the balance adjustment work of the Wheatstone bridge circuit as described above is performed. Incidentally, appropriate fixed resistors R11 to R14 for coarse adjustment, the sensitivity adjustment resistors R21 and R22, and the zero temperature special compensation resistor are the resistance value and the temperature coefficient of resistance calculated through the above procedure. Of the fixed resistors (R15 to R17) for fine adjustment are attached to the small adjustment resistor terminal 9 with the resistance value obtained by a predetermined procedure. Then, when the balance adjustment work is completed, the work opening formed in the shield body 11 is closed by the adjustment blind lid 10 and airtightly sealed with an adhesive.

According to the pressure transmitter configured and operating as described above, the fixed resistors R11 to R17 for coarse adjustment, intermediate adjustment, and fine adjustment, which form the balance adjustment circuit of the Wheatstone bridge circuit, are variable. Since it is a fixed resistor without a movable part (sliding part) such as a resistor and is firmly fixed to the amplifier substrate 6 and the small adjusting resistor terminal 9 by soldering, the resistance value may change due to vibration. Since the resistance value does not change due to wear even if it is used for a long period of time, high equilibrium stability is maintained for a long period of time.

The present invention is not limited to the above-mentioned embodiments, and various modifications can be made without departing from the scope of the invention. For example, in the above-described embodiment, the example in which the present invention is applied to the pressure transmitter has been described, but the present invention is also applicable to strain gauge type transducers such as pressure transducers and acceleration transducers.

[0072]

As is clear from the above description in detail, according to the present invention, even when used in an environment exposed to a strong electric wave, it is not affected by the electric wave noise,
In other words, it is possible to provide a pressure transmitter and a method for assembling the pressure transmitter, which has a very small zero point variation and is capable of converting a measured pressure into an electric signal with a high resolution, and particularly obtaining an amplified electric signal. Further according to the invention, a strain gauge
The metal inner case, airtight terminals, and
It is airtightly fixed and sealed by welding etc.
Gold to surround the upper and inner cases and the signal processing unit.
Weld between the outer case made of metal, the shield body and the introduction member.
It becomes airtightly fixed by contact, brazing, etc.
The metal outer case and the connector so that it surrounds the shield.
Since it is airtightly fixed and sealed with the connector, temporarily connect
Even if outside air enters from the
In addition, even if a small amount of outside air invades from the shield
Is also blocked by the airtight terminal, so outside air reaches the strain gauge.
Strain gauges and signals due to the entry of outside air
Performance due to insulation deterioration and oxidation of the circuit elements that make up the processing unit
Can be prevented and, for example, as described above,
The internal space and the seal formed by the dense terminal and the inner case.
Internal space formed by the sleeve and metal outer case
Is highly airtight, so it can hold an inert gas.
To reduce insulation and oxidation of strain gauges and circuit elements.
A pressure transmitter that can more reliably prevent performance deterioration due to
Can be provided.

Further, according to the present invention, the pressure transmission which rationalizes the assembling process and simplifies the process, significantly improves the electromagnetic compatibility due to the assembling order, and can also reduce the manufacturing cost. A method of assembling the container can be provided.

[0074] the of et, according to the present invention, it is possible to provide a Wheatstone balancing of the bridge circuit across the accurately performed and long-term stable and method of assembling a pressure transmitter capable of retaining its equilibrium state .

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a pressure transmitter showing an embodiment of a pressure transmitter and a method for assembling the pressure transmitter according to the present invention.

FIG. 2 is a vertical sectional view showing an assembling procedure of the embodiment.

FIG. 3 is a vertical cross-sectional view showing an assembly procedure performed subsequently to the assembly procedure shown in FIG. 2 of the embodiment.

FIG. 4 is a circuit diagram showing a configuration of an embodiment of a high frequency radio noise filter circuit which is a main part of the present invention.

5 is a circuit diagram showing a configuration example of a bridge balance adjustment circuit of the Wheatstone bridge circuit of the pressure transmitter shown in FIG.

6 is an example of data of a frequency sweep test of the immunity (electromagnetic compatibility) test of the pressure transmitter shown in FIG.

7 is an example of data of a radio frequency / constant electric field test of the immunity (electromagnetic compatibility) test of the pressure transmitter shown in FIG.

FIG. 8 is a vertical cross-sectional view for explaining the configuration and assembling method of a conventional pressure transmitter.

9 is an example of data of a frequency sweep test corresponding to FIG. 6 of the conventional pressure transmitter shown in FIG.

10 is an example of data of a radio frequency constant / electric field test corresponding to FIG. 7 of the conventional pressure transmitter shown in FIG.

[Explanation of symbols]

1 Introduction member 2 cylindrical part 2a diaphragm 2b Pressure receiving chamber 3 inner cylinder SG strain gauge 4 Airtight terminal 5 Mounting board 6 amplifier board 7 Electric circuit section 8 Fine adjustment resistor terminal 9 Small adjustment resistor terminals 10 Blind lid for adjustment 11 shield body 12 feedthrough capacitor 13 Ferrite core 14 Power supply / output terminal 15 Outer cylinder 16 Connector mounting plate 17 Waterproof Receptacle 17a connection terminal 17b cable 17c connection socket 17d rubber packing R1, R2, R3, R4 resistor (strain gauge) R11, R12, R13, R14 Fixed resistor for coarse adjustment R15 Series resistor for fine adjustment R16, R17 Fine adjustment fixed resistor R21, R22 Sensitivity adjustment resistor E-bridge power supply

Front page continuation (72) Inventor Sakae Arakawa 3-5 Chofugaoka, Chofu-shi, Tokyo 1 Kyowa Denki Co., Ltd. (56) Reference JP-A-6-129926 (JP, A) Sankaihei 2- 89320 (JP, U) Actual development Sho 61-50240 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01L 9/04 H01Q 17/00 H05K 9/00

Claims (5)

(57) [Claims] 1. A connector which detects deformation of a diaphragm due to a pressure difference between a pressure receiving surface and a back surface thereof by using a strain gauge attached to the diaphragm, converts the electric signal into an electric signal, and appropriately amplifies the electric signal by a signal processing unit. In a pressure transmitter that outputs through a section, an introducing member having a pressure introducing passage and an airtight member such as welding so as to close the inner end of the pressure introducing passage.
And anchored diaphragm portion, surrounds the diaphragm portion, soluble one end to said introduction member
It is fixed airtightly by contact, etc. and the other end is welded to the airtight terminal.
Reference pressure that is more airtightly fixed and keeps the inside airtight
A metal inner case that forms the force chamber, and surrounds the metal inner case and the signal processing circuit ,
The shield body is airtight by brazing or soldering in the middle
Through internal fixed is secured a metallic outer casing held airtight, and <br/> connector secured airtightly by welding or the like to the other end of said outer casing, hermetically to said shield body A high-frequency radio noise filter circuit configured to include a capacitor, and even when used in an environment where strong radio waves are received, the radio noise is blocked and an electric signal corresponding to the pressure received by the diaphragm can be obtained. A pressure transmitter having the above-mentioned configuration. 2. A high frequency radio noise filter circuit comprises a feedthrough capacitor airtightly fixed to the shield body, and a ferrite core arranged and connected in proximity to the feedthrough capacitor. The high-frequency radio noise mixed from the power supply / signal line is blocked by inserting a circuit between the signal processing unit and the signal processing unit, and is not transmitted to the signal processing unit. Pressure transmitter. 3. A pressure detector for converting a deformation of the diaphragm due to a pressure difference between the pressure receiving surface and the back surface thereof into an electric signal by using a strain gauge attached to the diaphragm, and an amplified detection signal detected by the pressure detector. In a method of assembling a pressure transmitter in which a signal processing unit that performs processing and the like is integrally housed in the same case, the signal processing unit is attached to the pressure detection unit to detect pressure.
A pressure detecting / signal processing unit assembling step for forming a signal processing unit; and a signal processing section and a connector section in a metal hollow case for accommodating at least the pressure detecting section and the signal processing section. A shield case unit assembling step of forming a shield case unit by airtightly fixing the shield body that separates the space by brazing or soldering, and following this shield case unit assembling step, the case is attached to the rigid portion of the pressure detecting section. Of the shield case unit to attach the shield case unit to the pressure detection / signal processing unit by fixing one end of the case airtightly by welding, and following this shield case installation process, connect the connector part that relays the power supply / output signal to the case The connector part is attached to the other end of the And the connector mounting step of mounting the shield case unit, the assembly method of the pressure transmitter, characterized in that it consists of. 4. A shield capacitor, which is one element constituting a high-frequency radio noise filter circuit, is hermetically fixed to the shield body in the shield case unit assembling step or a step before the shield case unit. The power supply / output terminal pin is inserted into the bead type ferrite core which is one element to configure
The output terminal pin is fixed to the substrate of the signal processing unit side, and the power supply / output terminal pin is inserted into the through hole of the feedthrough capacitor when the shield case attaching step is performed. The method for assembling the pressure transmitter according to claim 3. 5. After the pressure detecting / signal processing unit assembling step, an appropriate fixed resistor is selected and connected to the signal processing unit in order to roughly balance the Wheatstone bridge circuit formed by the strain gauge. Coarse adjustment, and after the shield case unit mounting step, in order to finely balance the bridge circuit, an appropriate fixed resistor is selected and connected through an adjustment hole formed in the shield body. 4. A method of assembling a pressure transmitter according to claim 3, wherein the blind lid is screwed into the adjusting hole and hermetically sealed with a sealing agent.