JP3757226B2 - Carrier type 3-wire strain measurement system - Google Patents

Description

  The present invention relates to a carrier-type three-wire strain measurement system that uses an AC power supply voltage as a power supply for a bridge circuit including a resistance strain gauge.

  When measuring strain generated in an object using a resistance-type strain gauge (a strain gauge whose resistance value changes according to the strain), in order to detect a minute resistance value change of the strain gauge attached to the object, A strain gauge is connected to a resistance circuit composed of a plurality of resistors having a fixed resistance value to constitute a bridge circuit (specifically, a Wheatstone bridge circuit). Then, while applying a power supply voltage to the bridge circuit, a signal voltage corresponding to a change in the resistance value of the strain gauge is output from the bridge circuit, and the strain measurement is performed based on the signal voltage.

  In this case, a carrier-type distortion measurement system that uses an AC voltage as the power supply voltage of the bridge circuit is generally known. In this carrier-type strain measurement system, the signal voltage output from the bridge circuit is obtained by amplitude-modulating a carrier wave having the same frequency as the power supply voltage in accordance with a change in the resistance value of the strain gauge. By removing the carrier wave component, a signal component corresponding to the change in resistance value of the strain gauge is obtained.

  On the other hand, a so-called three-wire type is known as a configuration of a bridge circuit including a strain gauge and a method for measuring its output. The three-wire measurement method will be described with reference to FIG. As shown in the figure, the first lead wire a1 is connected to one end of the strain gauge A, and the two lead wires of the second and third lead wires a2 and a3 are connected to the other end. These lead wires a1 to a3 are usually connected to the strain gauge A in advance. The resistance circuit C for constituting the bridge circuit B together with the strain gauge A includes three fixed resistance resistors D2 to D4 connected in series as shown in the figure, and one end of the strain gauge A is The other end is connected to the resistor D2 via the second lead wire a2 while being connected to the resistor D4 via the first lead wire a1. Thereby, the bridge circuit B including the strain gauge A on the first side b1 which is one of the first to fourth sides (four sides) is configured.

  More specifically, the bridge circuit B has a first side b1 composed of a strain gauge A and a first lead wire a1, and a second side adjacent to the first side b1 via the other end of the strain gauge A. b2 includes the second lead wire a2 and the resistor D2. A third side b3 that is the opposite side of the first side b1 and a fourth side b4 that is the opposite side of the second side b2 are configured by resistors D3 and D4, respectively. Further, an intersection point I1 (a connection point between the first lead wire a1 and the resistor D4) between the first side b1 and the fourth side b4, and an intersection point I2 (the resistor D2 with the second side b2 and the third side b3). (A connection point with the resistor D3) is a pair of power input portions I1 and I2 of the bridge circuit B (these are a pair of diagonal points of the bridge circuit B), and a power source is connected between the power input portions I1 and I2. A voltage ein (an AC voltage in a carrier type strain measurement system) is applied. Further, the intersection point O1 (the other end of the strain gauge A) between the first side b1 and the second side b2 and the intersection point O2 (the connection point between the resistor D3 and the resistor D4) between the third side b3 and the fourth side b4. ) Is a pair of output portions O1 and O2 of the bridge circuit B (these are the other pair of diagonal points of the bridge circuit B), and the voltage eout generated between the output portions O1 and O2 is the signal voltage. As obtained. In this case, the potential of the output unit O1 is extracted through the third lead wire.

  In such a three-wire type, the first lead wire a1 and the second lead wire a2 are included in different sides (first side b1, second side b2) of the bridge circuit B, respectively. For this reason, if the length, material, and diameter of the first lead wires a1 and a2 are the same, and the resistance value changes of the first and second lead wires a1 and a2 due to changes in the environmental temperature are substantially the same, The output voltage eout of the bridge circuit B is not affected by the resistance value change of the first and second lead wires a1 and a2. For this reason, the three-wire strain measurement method eliminates the influence of changes in the resistance values of the first and second lead wires a1 and a2 when the lengths of the first lead wires a1 and a2 are relatively long. It is a useful technique that can be used in many strain measurements.

  Incidentally, in the three-wire strain measurement system, the first to third lead wires a1 to a3 are relatively long. In particular, when multipoint strain measurement is performed by attaching a large number of strain gauges to an object, it is possible to switch and connect each strain gauge to a common resistance circuit and configure a bridge circuit in order for each measurement point. Since it is general, the first to third lead wires a1 to a3 corresponding to the respective strain gauges tend to be long. In such a case, in the carrier wave type strain measurement system using an AC power source as the power source of the bridge circuit B, the stray capacitance existing between the lead wires a1 to a3 connected to the strain gauge A is It is generally known that the output voltage eout is affected and becomes a distortion measurement error factor. For example, even when no strain is generated in the strain gauge A, the bridge circuit B is unbalanced (initial unbalance) due to the stray capacitance, and the strain value measured from the output voltage eout of the bridge circuit B is zero. Don't be. Further, the stray capacitance changes depending on the environmental temperature or the like. As a result, the output voltage eout of the bridge circuit B changes even if the strain of the strain gauge is constant. Therefore, in the carrier wave type strain measurement system, it is an important subject to eliminate the influence of the stray capacitance as much as possible.

  In this case, as a technique for eliminating the influence of the stray capacitance, conventionally, for example, one shown in Japanese Patent Publication No. 2-16441 (Patent Document 1) or Japanese Patent Publication No. 2-16962 (Patent Document 2) is known. ing.

  The technique found in Patent Document 1 is to feed back a voltage corresponding to the imaginary component (capacitance component) of the output voltage of the bridge circuit to one of the pair of output portions of the bridge circuit via a constant capacitor. It is intended to eliminate the initial imbalance of the bridge circuit due to stray capacitance. Further, the technique found in Patent Document 2 is based on the imaginary number component (capacitance component) of the output voltage of the bridge circuit, the imaginary number component (capacitance component) and the real number component (resistance component) of the output voltage due to the initial unbalance of the bridge circuit A cancellation signal for canceling is generated and superimposed on the output voltage of the bridge circuit.

However, the techniques found in these Patent Documents 1 and 2 are based on the premise that a capacitance component due to stray capacitance exists only on one side of the bridge circuit. For this reason, even if these techniques are applied to a three-wire carrier type measurement system, it is difficult to sufficiently eliminate the influence of stray capacitance. This is because in the three-wire strain measurement system, as shown in FIG. 9, the first lead wire a1 and the second lead wire a2 are incorporated in the first side b1 and the second side b2 of the bridge circuit B, respectively. Therefore, a capacitance component due to stray capacitance is incorporated at least in the first side a1 and the second side a2. Therefore, it has been difficult to sufficiently eliminate the influence of the stray capacitance in the techniques of Patent Documents 1 and 2 that assume that a capacitive component exists only on one side of the bridge circuit B.
Japanese Patent Publication No. 2-16441 Japanese Patent Publication No. 2-16962

  The present invention has been made in view of such a background, and in a carrier-type three-wire strain measurement system, the stray capacitance between lead wires connected to a strain gauge and the influence of the change are appropriately eliminated, and a high-precision strain is obtained. An object of the present invention is to provide a strain measurement system capable of performing measurement.

  In the strain measurement system of the present invention, a first lead wire connected to one end of a resistance strain gauge and a second lead wire connected to the other end are connected to a resistor circuit composed of a plurality of resistors having fixed resistance values. Thus, the first side is composed of the strain gauge and the first lead wire, and the second side connected to the first side via the other end of the strain gauge is the second lead wire and the fixed resistance. A bridge circuit composed of a resistor having a fixed resistance value, and a third side and a fourth side, which are opposite sides of the first side and the second side, are formed of a resistor having a fixed resistance value. Using the intersection of the first side and the fourth side of the bridge circuit and the intersection of the second side and the third side as a pair of power input units, while applying an AC power supply voltage to the power input unit, the first side And the other end of the strain gauge as an intersection of the second side, Using a third lead wire connected to the other end of the strain gauge separately from the second lead wire, with the intersection of the three sides and the fourth side serving as a pair of output portions, In a carrier-type three-wire strain measurement system that measures and measures strain generated in a strain gauge from the measured signal voltage, the resistor of the second side of the bridge circuit and the resistance of the second lead wire A body is disposed in the vicinity of the strain gauge, and the resistor and the second lead wire are connected in series from the other end of the strain gauge in this order, and the end of the second lead wire opposite to the resistor body The portion is connected to a resistor constituting the third side.

  Although details will be described later, in the carrier-type three-wire strain measurement system, in order to suitably eliminate the influence of the stray capacitance between the first to third lead wires, the first to fourth sides of the bridge circuit Of these, the side where the first lead wire and the second lead wire are incorporated, that is, the capacitance component of the first side and the fourth side (capacitance component equivalently incorporated into these sides by stray capacitance (more specifically, these components) The capacitance components)) expressed as parallel equivalent capacitances may be equal to the resistance value components of the sides.

  Here, according to the present invention, the resistor constituting the second side of the bridge circuit and the resistor of the second lead wires are arranged in the vicinity of the strain gauge. The resistor and the second lead wire are connected in series from the other end of the strain gauge in this order, and the end of the second lead wire on the side opposite to the resistor is connected to the bridge circuit first. It is connected to a resistor that constitutes three sides. More specifically, to be more precise, one end of a resistor that is a component of the second side of the bridge circuit is connected to the other end of the strain gauge, and one end of the second lead wire is connected to the other end of the resistor. The other end of the second lead wire is connected to one end of a resistor constituting the third side of the bridge circuit. In this case, in other words, the second lead wire is connected to the strain gauge via a resistor which is a component on the second side. The end of the second lead wire on the side opposite to the resistor corresponds to the intersection of the second side and the third side of the bridge circuit.

  According to such a connection configuration, the capacitance components of the first side and the fourth side of the bridge circuit can be made substantially equal. In this case, it is preferable that the first to third lead wires have substantially the same length, and the first to third lead wires are aligned with each other (to be bundled). Wiring) is preferred.

  As described above, according to the present invention, the capacitance components of the first side and the fourth side of the bridge circuit in which the first lead wire and the second lead wire are incorporated (capacitance component due to the stray capacitance between the first to third lead wires). ) Can be made substantially equal, it is possible to output from the bridge circuit a signal voltage that is hardly affected by the stray capacitance or the change. Therefore, it is possible to appropriately eliminate the stray capacitance between the lead wires connected to the strain gauge and the influence of the change, and perform accurate strain measurement.

  An embodiment of a carrier-type three-wire strain measurement system of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing the overall configuration of the strain measurement system of the present embodiment. As shown in the figure, the strain measurement system of the present embodiment includes a strain gauge 1 (resistance strain gauge), a bridge box 2, and a measuring instrument 3. The strain gauge 1 and the bridge box 2 are connected via a cable 4, and the bridge box 2 and the measuring instrument 3 are connected via a cable 5.

  The cable 4 has first to third three lead wires 4a, 4b, 4c, which are bundled by a cover tube, a band member or the like (not shown) while being along each other. The first lead wire 4a and the third lead wire 4c are connected to one end 1a and the other end 1b of the strain gauge 1 by soldering in advance. A resistor 6 having a fixed resistance value is connected to the other end 1b of the strain gauge 1 together with the third lead wire 4c in advance by soldering or the like. The second lead wire 4b is connected to the end by soldering or the like. Accordingly, the resistor 6 and the second lead wire 4b are connected in series from the other end 1b of the strain gauge 1 in this order. In this case, the resistor 6 is in the vicinity of the strain gauge 1 (the distance between the strain gauge 1 and the resistor 6 is sufficiently smaller than the lengths of the first to third lead wires 4a, 4b, and 4c. Are placed at the same position). The first to third lead wires 4a, 4b, and 4c have substantially the same length, and the materials and diameters thereof are also the same. Further, the ends of the first to third lead wires 4a, 4b, 4c opposite to the strain gauge 1 are connected to connection terminals 2a, 2b, 2c provided on the bridge box 2, respectively.

  Note that, as the resistor 6, a normal resistance element may be used, but a strain gauge different from the strain gauge 1 may be used.

  The bridge box 2 incorporates a resistance circuit 7 for constituting a bridge circuit (Wheatstone bridge circuit; details will be described later) together with the strain gauge 1 and the resistor 6 and a power supply voltage applied to the bridge circuit. (AC voltage) A pair of power input terminals 2d and 2e for introducing ein from the outside, and a pair of output terminals 2f and 2g for outputting the output (signal voltage) eout of the bridge circuit to the outside Yes.

  In this case, as shown in the figure, the connection terminal 2c for connecting the third lead wire 4c is electrically connected to the output terminal 2f at the same potential inside the bridge box 2. Further, the connection terminal 2b for connecting the second lead wire 4b and the connection terminal 2a for connecting the first lead wire 4a are electrically connected to the power input terminals 2d and 2e in the bridge box 2 at the same potential.

  The resistor circuit 7 includes a pair of resistors 8 and 9 having a fixed resistance value connected in series between the connection terminals 2 b and 2 a, and the middle point of these resistors 8 and 9 is the inside of the switch box 2. Thus, the output terminal 2g is electrically connected to the same potential.

  In addition, the conduction | electrical_connection between the terminals of the above-mentioned bridge box 2, and the conduction | electrical_connection and connection regarding the resistance circuit 7 are made | formed by the circuit pattern of the circuit board which is not shown in figure, for example. The resistance values of the resistors 6, 8, and 9 are the same as the nominal resistance value of the strain gauge 1 (resistance value in a state where the strain gauge 1 is not strained).

  A bridge circuit 10 as shown in FIG. 2 is configured on the circuit configuration by the connection configuration between the strain gauge 1 and the bridge box 2 and the configuration of the bridge box 2 as described above. In this bridge circuit 10, the first side 10a (upper left side in the figure) of the four sides is composed of the strain gauge 1 and the first lead wire 4a, and the other side of the strain gauge 1 is connected to the first side 10a. A second side 10b (upper right side in the figure) connected via the end 1b is composed of the resistor 6 and the second lead wire 4b. The third side 10c (lower right side in the figure) that is the opposite side of the first side 10a and the fourth side 10d (lower left side in the figure) that is the opposite side of the second side 10b are the resistor 8, 9.

  The connection terminal 2a as the intersection of the first side 10a and the fourth side 10d and the connection terminal 2b as the intersection of the second side 10b and the third side 10c are a pair of power input portions I1, The AC power supply voltage ein is applied to the power input portions I1 and I2 via the power input terminals 2e and 2d of the bridge box 2. Furthermore, the other end 1b of the strain gauge 1 as an intersection of the first side 10a and the second side 10b and a midpoint of the resistors 8 and 9 as an intersection of the third side 10c and the fourth side 10d are bridged. The pair of output portions O1 and O2 of the circuit 10 is obtained, and the output (signal voltage) eout of the bridge circuit 10 is taken out from the output portions O1 and O2 via the output terminals 2f and 2g of the bridge box 2. In this case, the potential of the other end 1b of the strain gauge 1 is extracted to the output terminal 2f via the third lead wire 4c and the connection terminal 2c.

  Returning to the description of FIG. 1, the cable 5 is configured by bundling a pair of power supply lines 5a and 5b and a pair of signal lines 5c and 5d by a cover tube, a band member, or the like (not shown). 5a and 5b are connected to power input terminals 2d and 2e of the bridge box 2, respectively, and signal lines 5c and 5d are connected to output terminals 2f and 2g of the bridge box 2, respectively. The cable 5 may be provided separately for the power supply lines 5a and 5b and the signal lines 5c and 5d.

  The measuring instrument 3 includes connection terminals 3a, 3b, 3c, 3d for connecting the ends of the power supply lines 5a, 5b and signal lines 5c, 5d of the cable 5 opposite to the bridge box 2 side, respectively. An AC power supply unit 11 that generates an AC power supply voltage ein having a predetermined frequency (for example, 5 kHz, 10 kHz) to be applied to the bridge circuit 10 between the connection terminals 3a and 3b, and a bridge circuit 10 that is input from the connection terminals 3c and 3d. And a strain measurement processing unit 12 that performs a strain measurement process (a process for obtaining a strain measurement value) from the output eout.

  In this case, the distortion measurement processing unit 12 detects a component (real number component) in phase with the AC power supply voltage ein from the output eout of the bridge circuit 10, and removes a component having the same frequency as the AC power supply voltage ein from the inphase component. The strain measurement value is obtained based on the signal component (signal component corresponding to the change in the resistance value of the strain gauge 1). Since the circuit configuration of such a strain measurement processing unit 12 may be a known one, further description thereof is omitted here.

  In the present embodiment, the bridge box 2 and the measuring device 3 are illustrated as separate components, but they may be configured integrally. In that case, the cable 5 is unnecessary.

  Next, the operation of the strain measurement system of this embodiment will be described. In the present embodiment, the first to third lead wires 4a to 4c extend in parallel with each other as shown in FIG. Therefore, floating between the first lead wire 4a and the third lead wire 4c, and between the second lead wire 4b and the third lead wire 4c, as representatively indicated by reference numerals Cx and Cy, respectively. There will be capacity. In this case, the bridge circuit 10 is equivalently represented by a bridge circuit 10 'shown in FIG. That is, in the bridge circuit 10, the first side 10a ′ is configured by a parallel circuit of the resistor 13 and the capacitance component 14 corresponding to the stray capacitance Cx, and the second side 10b ′ is configured by the resistor 15 and the stray capacitance Cy. The third side 10c ′ and the fourth side 10d ′ are substantially equivalent to the bridge circuit 10 ′ configured by the resistors 8 and 9, respectively. Here, the first to fourth sides 10a ′ to 10d ′ of the bridge circuit 10 ′ (hereinafter referred to as equivalent bridge circuit 10 ′) are sides corresponding to the first to fourth sides 10a to 10d of the bridge circuit 10, respectively. is there. The resistor 13 on the first side 10a ′ of the equivalent bridge circuit 10 ′ is a resistor having a combined resistance value of the strain gauge 1 and the first lead wire 4a, and the resistor 15 on the second side 10b ′. Is a resistor having a combined resistance value of the resistor 6 and the second lead wire 4b.

  Note that stray capacitance also exists between the first lead wire 4a and the second lead wire 4b in FIG. 3, but the corresponding capacitance component is the power supply input section I1 in the equivalent bridge circuit 10 ′ of FIG. , I2 is interposed. Therefore, it may be considered that the capacitance component does not affect the output eout of the equivalent bridge circuit 10 ′ (which is substantially equal to the output of the bridge circuit 10). Therefore, the capacitance component is omitted in FIG.

  Strictly speaking, there is a capacitive component in parallel with the resistor 8 on the third side 10c 'and a capacitive component in parallel with the resistor 9 on the fourth side 10d'. However, the values of these capacitance components are sufficiently smaller than the capacitance components 14 and 16 of the first side 10a ′ and the second side 10b ′, and the third side 10c ′ and the fourth side 10d ′ It can be considered that the values are almost the same. Therefore, the capacitance components of the third side 10c ′ and the fourth side 10d ′ have little influence on the potential of the output part O2 of the bridge circuit 10 ′ that is the intersection of these sides, and consequently the output eout of the bridge circuit 10 ′. You can think of it not. For this reason, these capacitive components are also omitted in FIG. Supplementally, the potential of the output unit O2 is maintained at ½ of the power supply voltage ein.

  In the equivalent bridge circuit 10 ′, the component eoutR in phase with the AC power supply voltage ein, which becomes a basic signal for distortion measurement, of the output eout when the AC power supply voltage ein is applied to the power supply input portions I1 and I2. The real part component of eout (hereinafter referred to as the real output component eoutR) is given by the following equation when the resistance values of the resistors 13 and 15 and the capacitance values of the capacitance components 14 and 16 are R1, R2, C1, and C2, respectively. Given by (1).

ここで、この式（１）の大括弧［ ］内の第１項に関し、ひずみゲージ１のひずみが生じていない初期状態ではＲ１＝Ｒ２であるので、上記第１項は、容量成分１４，１６の容量値Ｃ１，Ｃ２によらずに、上記初期状態では０になる。すなわち、第１項は、等価ブリッジ回路１０’のゼロ点（あるいは初期不平衡）には影響を及ぼさない。該第１項は、主に、ひずみゲージ１の抵抗値変化（Ｒ１の変化）に対する実出力成分ｅoutRの変化の度合い、すなわち感度に影響する項である。但し、容量成分１４，１６の容量値Ｃ１，Ｃ２の総和が例えば１０００ｐＦ〜１００００ｐＦの範囲で変化しても、上記第１項による等価ブリッジ回路１０’の実出力成分ｅoutRの変化は微小である。実際、交流電源電圧ｅinの周波数を例えば１０ｋＨｚ、ひずみゲージ１の抵抗値（公称抵抗値）を１２０Ωとしたとき、容量値Ｃ１，Ｃ２の総和が例えば１０００ｐＦ〜１００００ｐＦの範囲で変化しても、第１項による実出力成分ｅoutRの変化は、０．５％以下であり、実用上、無視しても支障が無い程度である。従って、第１項に関しては、容量値Ｃ１，Ｃ２の変化は、ブリッジ回路１０を用いたひずみ測定値の精度にほとんど影響を及ぼさないと考えてよい。

Here, regarding the first term in the square brackets [] in the formula (1), R1 = R2 in the initial state where the strain of the strain gauge 1 is not generated. Regardless of the capacitance values C1 and C2, the initial value is zero. That is, the first term does not affect the zero point (or initial unbalance) of the equivalent bridge circuit 10 ′. The first term is a term that mainly affects the degree of change in the actual output component eoutR with respect to the change in the resistance value of the strain gauge 1 (change in R1), that is, the sensitivity. However, even if the sum of the capacitance values C1 and C2 of the capacitance components 14 and 16 changes within a range of, for example, 1000 pF to 10000 pF, the change in the actual output component eoutR of the equivalent bridge circuit 10 ′ according to the first term is very small. Actually, when the frequency of the AC power supply voltage ein is 10 kHz, for example, and the resistance value (nominal resistance value) of the strain gauge 1 is 120 Ω, the sum of the capacitance values C1 and C2 may be changed in the range of 1000 pF to 10,000 pF, for example. The change in the actual output component eoutR due to the first term is 0.5% or less, which is practically negligible. Therefore, regarding the first term, it can be considered that changes in the capacitance values C1 and C2 have little influence on the accuracy of the strain measurement value using the bridge circuit 10.

  On the other hand, the second term in square brackets [] in equation (1) becomes 0 if the capacitance values C1 and C2 of the capacitance components 14 and 16 are equal, but does not become 0 if they are not equal. That is, the second term mainly affects the zero point (or initial unbalance) of the equivalent bridge circuit 10 '. Further, when the sum of the capacitance values C1 and C2 changes, the degree of change in the actual output component eoutR due to the second term tends to be larger than that in the first term.

  Therefore, in order to minimize the influence on the actual output component eoutR of the equivalent bridge circuit 10 ′ due to the capacitance values C1 and C2 or the change thereof, and consequently the influence on the distortion measurement due to the output eout of the bridge circuit 10, the expression (1) It is desirable that the second term in square brackets [] be as small as possible. For this purpose, it is desirable that the capacitance value C1 of the capacitance component 14 of the first side 10a 'and the capacitance value C2 of the capacitance component 16 of the second side 10b' be as equal as possible.

  In this case, in the strain measurement system of the present embodiment, as described above, the first to third lead wires 4a to 4c that generate the stray capacitance that is the source of the capacitance components 14 and 16 are wired along each other, In addition, their lengths are substantially the same, and their materials and diameters are also the same. For this reason, the capacitance values C1 and C2 of the capacitance components 14 and 16 are substantially equal. Further, since the changes in the capacitance values C1 and C2 due to changes in the environmental temperature and the like occur in the same way, even if the environmental temperature changes, the capacitance values C1 and C2 are maintained substantially equal.

  Therefore, the second term in the square brackets [] in the formula (1) is always maintained at almost zero. As a result, the capacitance values C1 and C2 of the capacitance components 14 and 16 and their changes resulting from the stray capacitance between the first to third lead wires 4a to 4c are the actual output component eoutR of the equivalent bridge circuit 10 ', and Of the output eout of the bridge circuit 10, the real component used for actual strain measurement is hardly affected. As a result, according to the strain measurement system of the present embodiment, the strain measurement can be accurately performed without being affected by the stray capacitance between the first to third lead wires 4a to 4c.

  5 to 8 are graphs illustrating the measurement data according to the example of the present embodiment and the measurement data according to the comparative example as solid lines and broken lines, respectively. In the examples of FIGS. 5 to 8, in the strain measurement system (system of FIG. 1) of the present embodiment, the ambient temperature (atmosphere temperature of the cable 4) in a state where the strain of the strain gauge 1 is not generated. 3 shows the data of strain measurement values when strain measurement is carried out while maintaining three temperatures at 0 ° C., 25 ° C., and 50 ° C. Further, in all of the comparative examples of FIGS. 5 to 8, the connection configuration of the strain gauge and the bridge box (configuration of incorporating the strain gauge into the bridge circuit) is the same as the conventional configuration shown in FIG. In the strain measurement system in which the configuration other than that is the same as that of the present embodiment, data of strain measurement values when strain measurement is performed under the same temperature conditions as in the above example are shown. 5 to 8, the horizontal axis is the environmental temperature, and the vertical axis is the relative value of the strain measurement value (strain at 25 ° C.) based on the strain measurement value when the environment temperature is 25 ° C. Change from measured value).

  In this case, in the embodiment of FIG. 5, the frequency of the AC power supply voltage ein is 5 kHz, and the diameters of the first to third lead wires 4a to 4c (the diameter of the conducting wire portion) are 0.18 mm. The same applies to the comparative example of FIG. Further, in the embodiment of FIG. 6, the frequency of the AC power supply voltage ein is 5 kHz, and the diameters of the first to third lead wires 4a to 4c (the diameter of the conducting wire portion) are 0.5 mm. The same applies to the comparative example of FIG. Further, in the embodiment of FIG. 7, the frequency of the AC power supply voltage ein is 20 kHz, and the diameters of the first to third lead wires 4a to 4c (the diameter of the conducting wire portion) are 0.18 mm. The same applies to the comparative example of FIG. Further, in the embodiment of FIG. 8, the frequency of the AC power supply voltage ein is 20 kHz, and the diameters of the first to third lead wires 4a to 4c (the diameter of the conducting wire portion) are 0.5 mm. The same applies to the comparative example of FIG.

  In any of the embodiments, the length of the first to third lead wires 4a to 4c (the length of the cable 4) is 20 m, and this is the same for the comparative example.

As apparent from FIGS. 5 to 8, in the examples according to the present embodiment, the measured strain values when the environmental temperature is 0 ° C. and 50 ° C. are almost the same as the measured strain values at 25 ° C. Therefore, it is hardly affected by the environmental temperature. From this, it can be seen that even if the stray capacitance between the first to third lead wires 4a to 4c changes due to the change of the environmental temperature, it hardly affects the strain measurement. In addition, this effect is caused by the frequency of the AC power supply voltage ein,
It does not depend on the diameters of the first to third lead wires 4a to 4c.

  On the other hand, in the comparative example according to the prior art, when the environmental temperature is different, the strain measurement value is greatly changed as compared with the example. In particular, this tendency becomes prominent when the frequency of the AC power supply voltage ein is high (in the case of 20 kHz), and becomes prominent when the lead wire diameter is small (in the case of 0.18 mm).

  From this, it can be seen that the present embodiment can suitably eliminate the influence of stray capacitance between the first to third lead wires 4a to 4c.

1 is a block diagram showing the overall configuration of an embodiment of a carrier-type three-wire strain measurement system of the present invention. The figure which shows the bridge circuit comprised with the system of FIG. FIG. 2 is an explanatory diagram of stray capacitance existing between lead wires in the system of FIG. 1. The circuit diagram which shows the equivalent circuit of the bridge circuit of FIG. The graph which shows the comparative example of the example of the strain measurement value in embodiment of FIG. 1, and the strain measurement value by the strain measurement system of a conventional structure. The graph which shows the comparative example of the example of the strain measurement value in embodiment of FIG. 1, and the strain measurement value by the strain measurement system of a conventional structure. The graph which shows the comparative example of the example of the strain measurement value in embodiment of FIG. 1, and the strain measurement value by the strain measurement system of a conventional structure. The graph which shows the comparative example of the example of the strain measurement value in embodiment of FIG. 1, and the strain measurement value by the strain measurement system of a conventional structure. The figure which shows the bridge circuit in the conventional three-wire-type distortion measurement system.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Strain gauge, 4a ... 1st lead wire, 4b ... 2nd lead wire, 4c ... 3rd lead wire, 6 ... 2nd side resistor, 7 ... Resistance circuit, 8 ... 3rd side resistor, 9 ... 4th side resistor, 10 ... bridge circuit, 10a to 10d ... side of bridge circuit, I1, I2 ... power input part, O1, O2 ... output part.

Claims (1)

By connecting the first lead wire connected to one end of the resistance strain gauge and the second lead wire connected to the other end to a resistor circuit composed of a plurality of resistors having fixed resistance values, the first side is The strain gauge and the first lead wire are configured, and the second side connected to the first side via the other end of the strain gauge is configured of the second lead wire and a resistor having a fixed resistance value. In addition, a bridge circuit is formed in which the third side and the fourth side, which are opposite sides of the first side and the second side, are composed of resistors having fixed resistance values, and the first side and the second side of the bridge circuit are formed. As an intersection between the first side and the second side, an AC power supply voltage is applied to the power input unit by using the intersection of the four sides and the intersection of the second side and the third side as a pair of power input units. A pair of the other end of the strain gauge and the intersection of the third side and the fourth side. A signal voltage generated at the output unit as an output unit is measured using a third lead wire connected to the other end of the strain gauge separately from the second lead wire, and is generated from the measured signal voltage at the strain gauge. In the carrier type 3-wire strain measurement system that measures the strain,
Of the resistor and the second lead wire constituting the second side of the bridge circuit, the resistor is arranged in the vicinity of the strain gauge, and the resistor and the second lead wire are arranged in this order on the strain gauge. A carrier-type three-wire strain measurement system characterized in that it is connected in series from the other end, and the end of the second lead wire opposite to the resistor is connected to a resistor constituting the third side.

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