JPH08201202A - Balanced-bridge adjusting circuit of strain guide converter - Google Patents

Abstract

PURPOSE: To provide a balanced-bridge adjusting circuit of a strain gauge converter capable of easily, quickly and accurately carrying out the adjustment of the balanced-bridge by utilizing a conventional fixed resistor and of stably maintaining the balanced condition for a long time. CONSTITUTION: A bridge circuit consists of four resistors R1-R4 like as, for example, in a strain gauge. Plus and minus electrodes of a bridge power source E are connected to plus and minus input terminals (b, d). When the bridge circuit is in an unbalanced condition, one of fixed resistors R11, R12 for rough adjustment is connected to one of the resisters R3, R4 in parallel. Then, one of fixed resisters R13, R14 for intermediate adjustment is connected thereto in the same manner. Lastly, a serial resister R15 for fine adjustment is selectively connected thereto and fixed resisters R16, R17 for fine adjustment are selectively connected thereto under condition that the fixed resisters for adjustment are connected thereto. It is, thereby, possible to easily, quickly and accurately carry out the adjustment of balance of the bridge circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bridge balance adjusting circuit for a strain gauge type transducer.

[0002]

2. Description of the Related Art Conventionally, a bridge balance adjusting circuit of a strain gauge type converter is generally composed of a circuit as shown in FIG. The circuit example shown in FIG. 8 is a case where the variable resistor VR1 is used to adjust the unbalance of the four resistors R1, R2, R3 and R4 forming the Wheatstone bridge circuit. The resistor R25 is a resistor that reduces the sensitivity of the variable resistor VR1. The Wheatstone bridge circuit
It is excited by the bridge power supply E.

FIG. 9 shows an example in which a plurality of stages of fixed resistors R31 to R37 are used to adjust the imbalance of the four resistors R1, R2, R3 and R4 constituting the Wheatstone bridge circuit. Shows. In this circuit, the numerical value or symbol in parentheses shown together with the symbol of each resistor represents the resistance value. The symbol ∞ is equivalent to no resistor connection. Thus, resistors R31, R34 and R36 are essentially not connected to the circuit. Among these resistors, the resistance value of the resistor R37, particularly 10.83 MΩ, is an extremely high resistance value.

The advantages of the balance adjustment circuit using the variable resistor shown in FIG. 8 (hereinafter, also referred to as "variable resistance balance adjustment circuit") are as follows. 1) Easy to adjust. The disadvantages include the following. 11) It is difficult to make fine adjustments. 12) Poor stability (against temperature, vibration, time, etc.). 13) The installation space tends to be large.

A balance adjustment circuit using the fixed resistor shown in FIG. 9 (hereinafter, also referred to as "fixed resistance balance adjustment circuit").
The advantages of the are as follows. 2) High stability. The disadvantages include the following. 14) Requires an extremely high resistance resistor with low manufacturability.

The two types of balanced adjustment circuits for the Wheatstone bridge circuit have the advantages and disadvantages described above, respectively. The balance adjustment circuit in a realistic product may be generally selected from either one while compensating for the disadvantages as much as possible, based on the characteristics required in the corresponding product. For example, in a product having a sufficient mounting space, a variable resistance balance adjustment circuit is configured by using a highly stable multi-rotation potentiometer as a variable resistor. With this configuration, the above disadvantages 11) will be suppressed and the advantages 1) will be utilized.

Further, in a product which has no space or is subject to vibration, a fixed resistance balance adjusting circuit is constructed. The balance adjustment in this case is performed by preparing resistors having various resistance values in advance and selecting a resistor having an appropriate resistance value from these resistors.

[0008]

However, in some products, the space for mounting the adjusting resistor is limited,
In addition, there are some that are required to have long-term stability despite being subjected to vibration. In such products, it is necessary to meet the demand for higher stability of bridge balance characteristics. With respect to this type of product, the requirements required in the examples shown in FIGS. 8 and 9 cannot be sufficiently satisfied.

In this case, if a fixed resistance balance adjustment circuit is actually adopted, it is necessary to prepare various kinds of resistors including a resistor having an ultrahigh resistance value and multiply the adjustment man-hours for a long time. Lost. In particular, it is generally difficult to obtain a small-sized, high-accuracy, low-priced resistor having a large resistance value on the order of MΩ, and it is not practical at this time. INDUSTRIAL APPLICABILITY The present invention makes it possible to easily and accurately adjust the balance of a bridge using a general fixed resistor whose number is as small as possible, and to adjust the bridge balance of a strain gauge type transducer that can maintain a stable balanced state for a long period of time. The purpose is to provide a circuit.

[0010]

In order to achieve the above object, the bridge balance adjusting circuit of the strain gauge type converter of the present invention comprises a first two connected in series between the positive and negative input terminals of the bridge power supply. In the bridge balance adjusting circuit of the strain gauge type converter for adjusting the balance of the Wheatstone bridge circuit, which is composed of a side and a second side that is also connected in series between the positive and negative input terminals, the Wheatstone bridge A first fixed resistor group connected in parallel with at least one of the second two sides of the circuit;
A second fixed resistor whose one end is connected to the connection point between the sides,
A third fixed resistor connected between one of the two connecting points between the second two sides and the first two sides and the other end of the second fixed resistor. And a connection point of the other of the two connection points between the second two sides and the first two sides,
A fourth fixed resistor connected between the other end of the second fixed resistor and the other end of the second fixed resistor, and when performing balanced adjustment of the Wheatstone bridge circuit, coarse adjustment is performed by the first fixed resistor group. And fine adjustment can be performed by the second to fourth fixed resistors.

Further, in order to achieve the above object, the bridge balance adjusting circuit of the strain gauge type converter of the present invention comprises a first two connected in series between the positive and negative input terminals of the bridge power supply.
In the bridge balance adjusting circuit of the strain gauge type converter for adjusting the balance of the Wheatstone bridge circuit, which is composed of a side and a second side that is also connected in series between the positive and negative input terminals, the Wheatstone bridge A first side of the circuit and a first side of the second side connected in parallel with at least one of the two sides connected adjacent to each other; 1 fixed resistor group, and a second connection point having one end connected to the connection point between the second two sides.
Of the fixed resistor, one of the two connection points between the second two sides and the first two sides, and the other end of the second fixed resistor. A third fixed resistor, the other connecting point of the two connecting points between the second two sides and the first two sides, and the other end of the second fixed resistor. And a fourth fixed resistor connected to the first fixed resistor group when performing the balance adjustment of the Wheatstone bridge circuit, and performing the coarse adjustment with the first fixed resistor group. It is characterized in that it can be finely adjusted by.

The first fixed resistor group and the second to fourth fixed resistors according to the present invention are resistors having standard resistance values set at predetermined numerical intervals. It has a feature. Further, the bridge balance adjusting circuit according to the present invention is used for a pressure transmitter which is required to have stability for a long period of time.

[0013]

The bridge balance adjusting circuit of the strain gauge type converter having the above-described structure adjusts the unbalance of the Wheatstone bridge circuit composed of four resistors by the first resistor group to the coarse adjustment or the intermediate adjustment. By performing the fine adjustment with the second, third and / or fourth fixed resistors, the Wheatstone bridge circuit can be easily, quickly and accurately balanced and subjected to vibration. Even under such an environment, the equilibrium state can be stably maintained for a long period of time.

The second fixed resistor acts as a resistor that slows down the action of the third and fourth fixed resistors, and the third fixed resistor and the third fixed resistor are slower than the first fixed resistor. Since it has the effect of making the sensitivity more insensitive, it is not necessary to use resistors of ultra-high resistance as the third and fourth fixed resistors.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a bridge balance adjusting circuit for a strain gauge type converter according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing a configuration of an embodiment of a bridge balance adjusting circuit of a strain gauge type converter of the present invention.

<Circuit Configuration Example> In FIG. 1, the Wheatstone bridge circuit is composed of four resistors R1, R2, R3 and R4 such as strain gauges. The unbalanced component of this Wheatstone bridge circuit is selected from seven fixed resistors R11, R12, R13, R14, R15, R16, and R17 that have an appropriate resistance value close to the resistance value obtained by a predetermined calculation. Select and adjust. A bridge power supply E applies a bridge voltage between the bridge power supply input terminals b and d of the Wheatstone bridge circuit.

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 of fixed resistors 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 the function. That is, the coarse adjustment resistors are the four fixed resistors R as the first resistor group.
11, R12, R13 and R14.

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. R15 is for fine adjustment sensitivity adjustment (that is, for desensitization). In this configuration, the final adjustment is made by fixed resistors R16 and R17 as the third fixed resistor.
Here, the configuration of the bridge balance adjusting circuit of the strain gauge type converter according to the present invention will be described 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. Bridge power supply E of this Wheatstone bridge circuit
The positive and negative input ends of the bridge power supply E are connected to the positive and negative input ends b and d, respectively, and the output due to the imbalance of the Wheatstone bridge circuit appears between the output ends a and c.

In other words, this Wheatstone bridge circuit has, between the positive and negative input terminals b and d of the bridge power supply E, a series circuit of resistors R1 and R2 forming the first two sides, The series circuit of the resistors R3 and R4 forming the second two sides is connected.

In the case of the embodiment shown in FIG. 1, fixed resistors R12 and R14 are apparently inserted in parallel with the resistor R4 on one side of the resistors R3 and R4 forming the second two sides. , A fixed resistor R11 for the resistor R3 on the other side
And R13 are to be connected, but in effect, the fixed resistors R11 and R14 are equivalent to being open because their resistance value is ∞. Here, the fixed resistors R11 to R14 are referred to as a first fixed resistor group.

Then, the resistors R3 and R forming the second two sides
One end of the second fixed resistor R15 is connected to the connection point of 4, that is, one output end c. Also, resistors R3 and R
Two connection points between the second two sides formed by 4 and the first two sides formed by the resistors R1 and R2, that is, one of the connection points b and d of the bridge power supply inputs b and d. A third fixed resistor R16 is connected between the other end of the second fixed resistor R15 and the other connection point d and the other end of the second fixed resistor R15. A fourth fixed resistor R17 is connected between them.

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.

Then, a fixed resistor R1 for these coarse adjustments is used.
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, and as a result of the rough adjustment, the fixed resistors R11 or 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, if R12 is connected in parallel to the resistor R4 as a fixed resistor for coarse adjustment, the product of the resistors R1 and R3 is the combined resistance R2 of the resistors R2 and R4 and the fixed resistor R12.
If the product is larger than (R4 // R12), the fixed resistor R13 is connected in parallel to the resistor R3. If the product has the opposite relationship, the fixed resistor R14 is used as the resistor. The circuit will be connected in parallel with R4.

<Example of Adjustment Procedure> Here, an example of the adjustment procedure of FIG. 1 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 corrected theoretically. 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 equipped with a Wheatstone bridge circuit consisting of strain gauges and a bridge power supply E, first, a + coarse adjustment fixed resistor R11 or a − coarse adjustment fixed resistor R
Adjust with 12.

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).
The specific procedure is illustrated below.

Coarse adjustment of the first stage In the theoretical procedure of b), the resistance value of each side of the Wheatstone bridge circuit of FIG. 1 is calculated as R1 = 499.2623.
Assume .OMEGA., R2 = R3 = R4 = R500 .OMEGA .. The resistance value R12 (or R11) in FIGS. 1 and 2 required to maintain the balance of the Wheatstone bridge circuit under this condition is obtained. In this case, R1 and R3 (499.
2623Ω × 500Ω) <R2 · R4 (500Ω × 50
Since it is 0 Ω), the one coarse adjustment fixed resistor R12 is connected in parallel to the resistor R4.

The resistance value R1 of the resistor R1 is set to the reference resistance value (5
00Ω) and a virtual resistance value Rx of parallel connection, the following relational expression holds. However, the symbol // represents a parallel connection.

R1 = 500 // Rx R1 × R3≈R2 (R4 // R12) (1) R12≈Rx From the relational expression (1), Rx = 338.391 KΩ is obtained.
R11 = R13 = R14 = ∞ (no connection).

However, since it is unrealistic to prepare the fixed resistor R12 having a resistance value of 6 digits of the effective value each time, in the coarse adjustment of the first stage, the optimum resistance value is selected from the predetermined standard resistance values. Select. In the case of this embodiment, R12 = 316K
Ω is selected and R11 is not connected (open). By connecting this resistance value R12, the coarse adjustment of the first stage is performed.

Second-stage coarse adjustment resistance value R4 and R12 connected in parallel (combined resistance) r4
Is r4 = R4 // R12 = 500Ω // 316KΩ = 499.2
It becomes 10Ω.

R4 = 499.210Ω <R1 = 499.
From the relationship of 2623Ω, it is clear that R1.R3> R2. (R4 // R12), so that the resistor R13 is connected in parallel to the resistor R3 as the second stage coarse adjustment. The combined resistance value r3 of the side including the resistor R3 can be obtained from the following relational expression.

R1 (R3 // R13) = R2 (R4 // R12) (2) r3 = R3 // R13 = (R4 // R12) R2 / R1 = 499.210 × 500 / 499.2623 = 499.9476 [Ω] The resistance value of R13 obtained from the above equation is 4.77 MΩ. Therefore, for balance adjustment of the Wheatstone bridge circuit composed of the resistors R1 to R3 and r4, R13 =
4.77 MΩ is required. The resistor R14 is not connected (R14 = ∞). From this relationship, in the second-stage coarse adjustment, R13 =
Select an intermediate adjustment resistor R13 having a resistance value of 3.3 MΩ and connect it in parallel with the resistor R3. In this case, fixed resistor R14
Is not connected.・ Fine adjustment: The resistance value of the parallel connection of R3 and R13 is r3 = R3 // R
13 = 500 // 3.3 MΩ = 499.924539Ω. For balance adjustment of the Wheatstone bridge circuit of R1 to R2, r4 and r3, Ry = 10.83M in FIG.
Ω is required. Since this fixed resistor having a very high resistance value is difficult to obtain, it is adjusted by the resistors R15, R16 and R17 shown in FIG.

FIG. 4 is a rewritten version of the adjusted resistance values set above based on FIGS. 1, 2 and 3. The resistance value of these resistors R15, R16 and R17 is R15 = 3.3 in consideration of the adjustment range, standardized resistance value and the like.
MΩ and R16 (or R17) = 1 MΩ, and R17 (or R16) is used as an adjustment resistor. The resistance value of the adjustment resistor R17 is determined by, for example, Y-Δ conversion.

Based on FIG. 5, the following relational expression is obtained.

Rx = {R17 (R15 + R16) + R15.R16} / R16 (3) ry = {R17 (R15 + R16) + R15.R16} / R17 ... (4) rz = {R17 (R15 + R16) + R15.R16} / R15 (5) Further, the relational expression (6) is obtained from the equilibrium condition of the Wheatstone bridge circuit.

R1 (r3 // ry) = R2 (r4 // rx) (6) The relational expression (6) is sequentially converted as follows.

R1 {(1 / r4) + (1 / rx)} = R2 {(1 / r3) + (1 / ry)} (7) (R1 / r4)-(R2 / r3) = ( R2 / Ry)-(R1 / Rx) = {(R2 / R17)-(R1 / R16)} / {R17 (R15 + R16) + R15 / R16} (8) From the above relational expression, R17 The resistance value of is calculated.

-4.7257E-5 = {(500.R17)-(499.2623E
6)} /{(4.3 E6 ・ R17 + 3.3 E12)} −47.257 ＝ {(500 ・ R17−499.2623E6)} / {(4.3 ・ R17 +
3.3 E6) R17 (500 + 4.3 x 47.257) = 499.2623 E6 -47.257
× 3.3E6 R17 = 343.31387E6 / 703.20553 = 0.488 E6 The resistance value of R17 is R17 = 488 KΩ, and R17 = 510 KΩ is finally selected from the predetermined standard resistance values.
The adjustment is completed by the above-described first-stage coarse adjustment, second-stage coarse adjustment (intermediate adjustment), and fine adjustment.

However, the number of adjustment stages varies depending on the unbalanced state (degree) of the Wheatstone bridge circuit. Also,
The above adjustment is a theoretical adjustment procedure B, and a simple adjustment procedure B may be adopted in some cases. For example, the following procedure.

(1) While monitoring the unbalanced amount of the Wheatstone bridge, a resistor having a predetermined resistance value is temporarily connected to one of the R3 and R4 bridge sides, and the first stage is checked while observing the amount of change in the unbalanced amount. Coarse adjustment of. That is, the resistance value of the resistor R12 in FIG. 2 is determined.

(2) The unbalance amount after the resistance value R12 is connected is monitored to check whether the unbalance amount is less than a predetermined value. Depending on the size of the unbalanced amount checked, perform further rough adjustment,
Decide whether to make fine adjustments or not.

(3) In the case of this embodiment, further adjustment is performed to determine the resistance value of the coarse adjustment resistor R13 of the second stage.

(4) The necessity of further adjustment work is determined.

(5) In the case of this embodiment, fine adjustment is further performed to selectively set the resistors R16 and R17.

When comparing FIG. 1 and FIG. 9 in specific numerical values, the resistance value of the fine adjustment resistance is approximately one digit (1 MΩ: 1
0.83 MΩ). This value is merely an example, and a resistor having a higher value may be required as a resistance value for fine adjustment in an unbalanced state of the Wheatstone bridge or a state of coarse adjustment. With such a circuit configuration, strict balance adjustment of the Wheatstone bridge circuit becomes possible without using a variable resistor.

Since the balance adjustment is performed by using the fixed resistor, the vibration resistance is excellent and the high stability can be obtained in terms of the change over time. In addition, since fine adjustment can be performed with a lower resistance value, a low-priced fixed resistor can be easily obtained, the adjustment range can be expanded, and high-precision fine adjustment can be performed.

<Application Example> FIG. 6 shows a pressure transducer (or pressure transmitter) which is a kind of strain gauge type transducer of the present invention.
It is sectional drawing of the Example applied to the bridge balance adjustment circuit of the Wheatstone bridge circuit comprised by the strain gauge. In FIG. 1, reference numeral 1 denotes a metal introducing member having a connecting portion 1b made of a male screw that is connected to a measured portion such as a gas insulated switchgear (GIS). A pressure introducing passage 1a is formed therethrough for introducing the measured fluid pressure.

At the end portion of the introduction member 1 opposite to the connecting portion 1b, a cylindrical portion 2 having a rigidity integral with the metal diaphragm 2a is airtightly fixed by welding or the like, and is introduced to the inner surface of the diaphragm 2a. Between the end faces of the member 1, a pressure receiving chamber 2b is formed in which the fluid to be measured introduced via the pressure introducing 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, vapor-deposited on 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. It is attached by sputtering, welding, or other means.

In the strain gauge SG, a meandering gauge element made of Ni-Cr alloy or the like is attached on a gauge base made of phenol resin, polyimide resin or the like. At least four strain gauges SG are attached to the back surface of the diaphragm 2a, and the four strain gauges correspond to, for example, R1 to R4 in FIG.

On the outer peripheral surface of the diaphragm 2a, an inner cylinder 3 which covers the diaphragm 2a at regular intervals is concentrically arranged, and one end edge of the inner cylinder 3 is hermetically fixed to the introduction member 1 by welding or the like. At the same time, the airtight terminal 4 is fitted in the other end opening. The peripheral edge of the metallic lid member 4a forming the airtight terminal 4 is airtightly fixed to 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. The plurality of pin terminals 4c forming the airtight terminal 4 are pierced and supported by the insulating sealing material 4b, and the pin terminals 4c and the gauge electrodes of the strain gauge SG are connected by gauge leads.

The upper ends of the pin terminals 4c are fitted into through holes 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 balancing resistor such as an adjusting resistor, a hybrid IC, a transistor, etc., which is composed of a strain gauge SG as described above. An electric circuit unit 7 for amplifying the bridge output, shaping the waveform, and performing operations such as calculation is provided, including an adjustment resistor and a sensitivity adjustment resistor.

The other end of the amplifier board 6 (upper end in FIG. 6)
The fine adjustment substrate 8 is fixed to the. The fine adjustment board 8 is provided with a small adjustment resistance terminal 9 into which the fine adjustment fixed resistors R15, R16, and R17 having the resistance value determined in the above-described manner are inserted. The fixed resistors R15, R16, and R17 are firmly fixed by soldering, and therefore, even if subjected to vibration, disconnection or poor contact does not occur. In addition, the adjustment blind lid 10 has an opening formed in the shield body 11 and has fixed resistors R15 to R15 for fine adjustment described above.
After fixing 17 to the small adjusting resistor terminal 9, close it,
The periphery thereof is hermetically sealed with an adhesive or the like.

The shield body 11 includes a feedthrough capacitor 12
Is tightly fitted and fixed, and the fine adjustment substrate 8 is provided with a ferrite bead core 13, which penetrates the feedthrough capacitor 12 and the ferrite bead core 13, and one end (lower end) thereof penetrates the fine adjustment substrate 8. A fixed pin-shaped power supply / output terminal 14 is provided. An outer cylinder 15 is provided so as to be fitted to the outer peripheral surface of the shield body 11, one end (lower end) of which is fitted into the step portion of the introducing member 1 and is airtightly fixed by welding, and the other end (upper end) thereof. The connector mounting plate 16 is fixed by welding or the like.

A waterproof receptacle 17 is attached to the central portion of the connector mounting plate 16 by screw means.
The connection terminal 17a of the waterproof receptacle 17 and the power supply / output terminal 14 are connected to each other via a cable 17b and a connection pipe 17c made of metal. The pressure converter having such a structure is configured such that, for example, the fluid to be measured (gas) is introduced into the pressure introduction path in a state where the coupling portion 1b of the introduction member 1 is attached to the gas pressure monitoring output portion of the gas insulated switchgear. Lead to 1a.

Then, since the gas pressure is applied to the pressure receiving surface of the diaphragm 2a, the diaphragm 2a is deformed (deflected) corresponding to the gas pressure, and the strain gauges SG (R1 to R4 in FIG. 1) are pressed. 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. By the way, the appropriate ones of the 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. Is selected and soldered to the amplifier substrate 6, but the fixed resistors for fine adjustment (R15 to R17) having the resistance value obtained by the above procedure are mounted on the small adjustment resistor terminal 9. 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 hermetically sealed with an adhesive.

According to the pressure conversion configured and acting 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 Moving part (sliding part) such as
Since it is a fixed resistor that is not attached and is firmly fixed to the amplifier substrate 6 and the small adjustment resistor terminal 9 by soldering, the resistance value changes due to vibration, and even if it is used for a long period of time, it will be worn out. Since the resistance value never changes, high equilibrium stability is maintained for a long period of time.

The present invention is not limited to the above-mentioned embodiments, but various modifications can be made without departing from the scope of the invention. For example, as shown in FIG. 7, the position on the circuit where the fixed resistors R12 and R14 for coarse adjustment are connected is not limited to being connected in parallel with at least one of the second two sides, that is, , The resistor R forming the second two sides
The configuration is not limited to parallel connection to either one of the sides 3 and R4, but is configured to be connected in parallel to the resistor R2 forming one side of the resistors R1 and R2 forming the first two sides. You may.

Further, in FIG. 7, the two resistors R1 and R2 forming the first two sides are replaced with each other,
It is completely free to replace the two resistors R3 and R4 forming the second two sides with each other.

Further, the strain gauge type transducer to which the bridge balance adjusting circuit according to the present invention is applied is not limited to the above-mentioned pressure transducer (pressure transmitter), but an acceleration transducer, a torque transducer, a wall surface. Regardless of name, earth pressure gauge, load converter, inclinometer, displacement converter, etc., the strain-generating part receives a physical quantity or mechanical quantity, and the strain generated in the strain-generating part is converted into an electric quantity by a strain gauge. Needless to say, all strain gauge type transducers configured to form a Wheatstone bridge circuit by the strain gauges are included.

The fixed resistors forming the first fixed resistor group are always plural (for example, R, as in the above-described embodiment).
11 to R14) It is not necessary, and in extreme cases, only one may be necessary.

[0064]

As described in detail above, according to the present invention, firstly, in order to adjust the balance of the Wheatstone bridge circuit, a variable resistor is not used, and all standard fixed resistors are used. All of them are configured to be firmly fixed and connected to the board member by soldering or other means, so even if applied to the balance adjustment circuit of the Wheatstone bridge circuit in the strain gauge type converter installed in the part subject to vibration, There is no factor such as a change in the resistance value due to such inadvertent rotation and a change in the resistance value due to abrasion of the sliding portion due to repeated balance adjustment, and an accurate balanced state can be maintained for a long period of time.

Second, as a fixed resistor for balance adjustment,
Coarse adjustment and intermediate adjustment can be performed by the first fixed resistor group for coarse adjustment. After the coarsely adjusted unbalanced output is attenuated by the second fixed resistor, the third and fourth fixed resistors are Since the fine adjustment is performed by the resistor, the resistance value of the third and / or fourth fixed resistors can be a resistance value of a relatively standard intermediate adjustment resistor, and therefore the cost is low. Thus, the time required for balance adjustment can be shortened, and a small size fixed resistor is sufficient. Therefore, the strain gauge type converter itself can be downsized and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a bridge balance adjustment circuit of a strain gauge type converter of the present invention.

FIG. 2 is a circuit diagram for explaining an adjustment procedure of the bridge balance adjustment circuit of FIG.

FIG. 3 is a circuit diagram for explaining an adjustment procedure of the bridge balance adjustment circuit of FIG.

FIG. 4 is a circuit diagram for explaining an adjustment procedure of the bridge balance adjustment circuit of FIG.

5 is a circuit diagram for explaining Y-Δ conversion in FIG.

6 is a cross-sectional view for explaining the configuration of a pressure converter using the bridge balance adjustment circuit of FIG.

FIG. 7 is a circuit diagram showing a configuration of another embodiment of the bridge balance adjustment circuit of the strain gauge type converter of the present invention.

FIG. 8 is a diagram showing an example of a bridge balance adjustment circuit of a conventional strain gauge type converter.

FIG. 9 is a diagram showing another example of the bridge balance adjustment circuit of the strain gauge converter.

[Explanation of symbols]

 R1, R2, R3, R4 Resistors (strain gauges) R11, R12, R13, R14 Coarse adjustment fixed resistor R15 Fine adjustment series resistor R16, R17 Fine adjustment fixed resistor R21, R22 Sensitivity adjustment resistor E bridge Power supply 1 Introduction member 2 Cylindrical part 2a Diaphragm 2b Pressure chamber 3 Inner cylinder SG Strain gauge 4 Airtight terminal 5 Mounting board 6 Amplifier board 7 Electric circuit section 8 Fine adjustment board 9 Small adjustment resistance terminal 10 Adjustment blind lid 11 Shield 12 Feedthrough capacitor 13 Ferrite bead core 14 Power supply / output terminal 15 Outer cylinder 16 Connector mounting plate 17 Waterproof receptacle 17a Connection terminal 17b Cable 17c Connection pipe

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroki Okuda 3-5 Chofugaoka, Chofu City, Tokyo 1 Kyowa Denki Co., Ltd.

Claims (4)

[Claims] 1. A bridge power supply comprising a first two sides connected in series between positive and negative input terminals and a second two sides connected in series between the positive and negative input terminals as well. In a bridge balance adjustment circuit of a strain gauge type converter for adjusting the balance of a Wheatstone bridge circuit, a first fixed resistor connected in parallel with at least one of the second two sides of the Wheatstone bridge circuit. A group of devices, a second fixed resistor whose one end is connected to a connection point between the second two sides, and two connection points between the second two sides and the first two sides. A third fixed resistor connected between one connection point and the other end of the second fixed resistor, and two between the second two sides and the first two sides. A fourth fixed resistor connected between the other connection point of the connection points and the other end of the second fixed resistor. Has the door, in performing the balancing of the Wheatstone bridge circuit performs rough adjustment in the first fixed resistor group, the second
~ A bridge balance adjusting circuit for a strain gauge type converter, characterized in that it is configured so that fine adjustment can be performed with a fourth fixed resistor. 2. A bridge power supply is composed of a first two sides connected in series between the positive and negative input terminals, and a second two sides connected in series between the positive and negative input terminals as well. In a bridge balance adjustment circuit of a strain gauge type converter for adjusting the balance of a Wheatstone bridge circuit, one side of the first two sides and one side of the second side of the Wheatstone bridge circuit. And a first fixed resistor group connected in parallel with at least one of two sides connected adjacent to each other, and a second point having one end connected to a connection point between the second two sides. Connected between one of the two connection points between the second fixed side and the second fixed side, and the other end of the second fixed side. A third fixed resistor, and two connection points between the second two sides and the first two sides. A fourth fixed resistor connected between the other connection point and the other end of the second fixed resistor, wherein the first fixed resistor is used when balancing the Wheatstone bridge circuit. Rough adjustment is performed with a resistor group, and the second
~ A bridge balance adjusting circuit for a strain gauge type converter, characterized in that it is configured so that fine adjustment can be performed with a fourth fixed resistor. 3. The first fixed resistor group and the second fixed resistor group
~ The fourth fixed resistor is a resistor having a standard resistance value set at a predetermined numerical interval, and the bridge balance adjusting circuit of the strain gauge type converter according to claim 1 or 2, wherein . 4. The bridge balance adjusting circuit for a strain gauge type converter according to claim 1, wherein the bridge balance adjusting circuit is used in a pressure transmitter which is required to have stability for a long period of time. .