Strain measurement circuit and method for calculating strain resistance in said circuit

Abstract

To provide a strain measuring circuit capable of accurately measuring strain with high sensitivity while keeping a current value and a voltage value variable, and a strain measurement method based on the circuit.SOLUTION: A strain measuring circuit eliminates the need of Wheatstone bridge circuit by connecting in parallel connection terminals of a strain gauge 1 to a variable constant voltage power supply 3 via a variable constant current source 2 and a voltmeter 4, or via the variable constant current source 2 and a first voltmeter 41 to the variable constant voltage power supply 3 and the constant voltage power supply 3, and by connecting in parallel second voltmeters 42. A method is provided for measuring and calculating a resistance change value ΔR and strain ε of the strain gauge 1 by using a change value of a measured voltage of the voltmeter 4 after and before effect of external force or change in an added value of a measured value of the first voltmeter 41 and a measured value of the second voltmeter 42. A plurality of temperatures are set for the strain gauge 1 as a semiconductor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a circuit for measuring the change in strain gauge resistance value due to strain causes such as pressure and torque, and the strain generated as a result of the change in strain gauge resistance value, and to a method for specifically measuring and calculating the change in strain gauge resistance value and the strain in said circuit. [Background technology]

[0002] In strain gauges, when measuring strain resistance that has changed based on the cause of strain, conventional techniques employ a Wheatstone bridge circuit (hereinafter abbreviated as "bridge circuit") which uses the resistance of the strain gauge as a component.

[0003] However, in the case of a bridge circuit, it is impossible to accurately measure the strain gauge resistance change ΔR caused by an external force on the object being measured, or the strain gauge resistance change ΔR' caused by deformation of the object due to external forces and temperature changes.

[0004] The inventor of this patent application proposes the configuration of Patent Document 1 in order to overcome the aforementioned technical problems with respect to bridge circuits.

[0005] Patent Document 1, as described in claims 1 and 3, has the following strain measurement circuits (a) and (b) as its basic configuration. (a) A strain resistance measurement circuit characterized by the fact that a constant current power supply and a variable constant voltage power supply connected in series with a voltmeter are connected in parallel only to both connection terminals of a strain gauge intended for measuring strain resistance, the direction of conduction of the constant current power supply and the direction of application of the variable constant voltage power supply at each connection terminal are the same, and the measured value of the voltmeter can be set to zero by adjusting the voltage value of the variable constant voltage power supply, thereby eliminating the need for a Wheatstone bridge circuit. (b) A strain resistance measurement circuit characterized in that, with respect to only the two connection terminals of a strain gauge for the purpose of measuring strain resistance, a constant voltage power supply connected in series with a variable constant current power supply and a voltmeter is connected in parallel, the conduction direction of the variable constant current power supply at both of the connection terminals is the same as the application direction of the constant voltage power supply, and the measured value of the voltmeter can be set to zero by adjusting the current value of the variable constant current power supply, thereby eliminating the need for a Wheatstone bridge circuit.

[0006] In the basic configurations (a) and (b), sensitivity approximately four times that of a conventional bridge circuit can be achieved, and even when a temperature difference occurs, accurate measurement of the change value of strain resistance and strain can be realized.

[0007] However, the basic configuration (a) is premised on the use of a constant current power supply, and the basic configuration (b) is based on a constant voltage power supply, so it is impossible to further improve measurement sensitivity.

Prior Art Literature

Patent Literature

[0008]

Patent Literature 1

Summary of the Invention

Problem to be Solved by the Invention

[0009] An object of the present invention is to provide a strain measurement circuit that does not rely on a bridge circuit that has been used as an analog differential circuit, and that can accurately measure and calculate strain with high sensitivity after making a current value and a voltage value variable, and a strain measurement and calculation method based on the circuit.

Means for Solving the Problem

[0010] In order to solve the above problem, the present invention is based on the following basic configuration. ( 1)With respect to both connection terminals of a strain gauge intended for strain measurement, a variable constant-voltage power supply or a constant-voltage power supply connected in series with a variable constant-current power supply and a first voltmeter is connected in parallel, and a second voltmeter is connected to both connection terminals of the strain gauge; the conduction direction of the variable constant-current power supply at said both connection terminals is the same as the application direction of the variable constant-voltage power supply, and the resistance value of the strain gauge is measured by adding the measurement value of the first voltmeter and the measurement value of the second voltmeter, Furthermore, the resistance value R in a strain gauge when no external force is acting on it. 0 Regarding the measurement of the first voltmeter when an external force is acting, V 10 And the measurement value of the second voltmeter is V 20 Let's set the current value of the variable constant current power supply to I 0 In that case, R 0 =(V 10 +V 20 ) / 2I 0 It is based on the calculation that, and a Wheatstone bridge circuit is unnecessary, which is characterized by the above. A strain measurement circuit. ( 2 ) The ([( 1 ) strain measurement circuit, which is a method for measuring and calculating the strain gauge resistance change value and the generated strain through the following process. 1 Selection and setting of the variable constant current I0 in a state where no external force acts on the measurement object in contact with the strain gauge, and the voltage value V measured by the first voltmeter 10 measurement, and the voltage value V measured by the second voltmeter 20 measurement. 2 Setting of a state where an external force acts on the measurement object, and measurement of the voltage value V1 by the first voltmeter and measurement of the voltage value V2 by the second voltmeter. 3 ΔR=(V1+V2-V 10 -V 20 ) / 2I0 Calculation of the strain gauge resistance change value ΔR changed due to the external force applied to the measurement object. 4 After setting the gauge factor K with a predetermined numerical value, calculation of the strain ε generated by the aforementioned cause according to ε=(1 / K)(ΔR / R0). However, R0 is the resistance value of the strain gauge, and is calculated by R0=(V 10 +V 20 ) / 2I0 between after process 1 and before process 4. [Effects of the Invention]

[0011] Basic configuration ( 1 The basic structure is based on ( 2 The measurement method involves pre-setting the current value of the variable constant current power supply, but does not require adjustment of the variable constant voltage V0. A more accurate resistance change value ΔR can be measured and calculated by simple addition and subtraction, and the basis for this will be explained later in detail based on the specific calculations.

[0012] Furthermore, since the measurement is based on the values ​​of both the first and second voltmeters, it reduces the variation in measurement values ​​due to differences between voltmeters. As a result, it is possible to achieve measurement and calculation with less variation in the resistance value R0 and resistance change value ΔR of the strain gauge. [Brief explanation of the drawing]

[0013] [Figure 1] The basic configuration (1) and the circuit configuration of claim 1 are shown. In the basic configuration (1), both a variable constant voltage power supply and a constant voltage power supply can be selected, but Figure 1 shows the case of a variable constant voltage power supply. [Figure 2] A flowchart showing the sequential implementation of the basic configuration (2) and the process of claim 4 is provided. [Figure 3] The plan view photographs of each strain gauge show that the four types of strain foils and the base plates supporting them have different areas and can be selected from each other. [Figure 4] This graph shows the relationship between the measured voltage and the change in strain resistance when the load on the object being measured is sequentially changed, and shows the cases when a bridge circuit is used, when the circuit of basic configuration (1) is used and the variable constant current is set to 10mA, and when it is set to 30mA. [Figure 5]After selecting a semiconductor strain gauge, the graph shows the change state corresponding to each load Vf=I0ΔR in the measurement method of basic configuration (2) at room temperature and when cooled to below 0°C, where (a) shows the case at room temperature of 26°C (299K) and (b) shows the case at a cooled state of -196°C (77K). [Figure 6] A strain measurement circuit according to an example is shown. [Figure 7] The circuit configuration to be used as a reference is shown by employing one variable constant current power supply, one variable constant voltage power supply, and one voltmeter. [Modes for carrying out the invention]

[0014] The following describes each basic configuration.

[0015] Basic configuration ( 1 ) is, 1 As shown, a variable constant voltage power supply 3 or a constant voltage power supply 3 connected in series with a variable constant current power supply 2 and a first voltmeter 41 is connected in parallel to both connection terminals of a strain gauge 1 intended for strain measurement, and a second voltmeter 42 is connected to both connection terminals of the strain gauge 1, the direction of conduction of the variable constant current power supply 2 and the direction of application of the variable constant voltage power supply 3 at each connection terminal are the same, and the resistance value of the strain gauge 1 is measured by adding the measured values ​​of the first voltmeter 41 and the second voltmeter 42. Furthermore, the resistance value R when no external force is acting on strain gauge 1 0 Therefore, the measurement value of the first voltmeter 41 when an external force is acting is V 10 The measurement value of the second voltmeter 42 is V 20 Let's set the current value of the variable constant current power supply 2 to I 0 In that case, R 0 =(V 10 +V 20 ) / 2I 0 It is based on the calculation that, Furthermore, this distortion measurement circuit is characterized by not requiring a Wheatstone bridge circuit.

[0016] Basic configuration ( 1 ) employs a second voltmeter 42 that is connected to both terminals of strain gauge 1. However, the recruitmentAs a result, a method for calculating the resistance value R0 and resistance change value ΔR of strain gauge 1. Regarding, As will be explained later.

[0017] Basic configuration ( 1 In this configuration, the process of adding the measured value of the first voltmeter 41 and the measured value of the second voltmeter 42 is described later in the basic configuration ( 2 This corresponds to the operation that realizes process 1 in ).

[0018] Basic configuration ( 1 In this case, not only a variable constant voltage power supply 3 but also a constant voltage power supply 3 can be used as the voltage power supply, but the reason for this is the basic configuration described later ( 2) In process 1, the voltage value of the voltage power supply place This stems from the fact that it does not need to be adjusted to a fixed value.

[0019] Basic configuration ( 2 ) is the basic configuration ( 1 Based on the above, 2 As shown in the flowchart, the strain gauge resistance change value and the generated strain are measured and calculated through the following process. 1. Selection and setting of the variable constant current I0 when no external force is acting on the object being measured that is in contact with the strain gauge 1, and the voltage value V measured by the first voltmeter 41. 10 Measurement of the voltage V measured by the second voltmeter 42 20 Measurement. 2. Setting up conditions in which an external force acts on the object to be measured, and measuring the voltage value V1 using the first voltmeter 41 and the voltage value V2 using the second voltmeter 42. 3 ΔR=(V1+V2-V 10 -V 20 Calculation of the strain gauge resistance change value ΔR caused by external force applied to the object being measured using ) / 2I0. 4. After setting the gauge factor K according to a predetermined value, the strain ε generated by the above cause is calculated as ε = (1 / K)(ΔR / R0). However, R0 is the resistance value of the strain gauge, and between process 1 and process 4, R0 = (V 10+V 20 It is calculated by ) / 2I0.

[0020] To explain with specific calculations, if the current value of the variable constant current power supply 2 set in process 1 is I0, and the voltage value of the variable constant voltage power supply 3 or constant voltage power supply 3 is V0 (however, it is not necessary to select or set a specific value for V0), then the voltage value measured by the first voltmeter 41 is V 10 Regarding, V 10 =I0R0-V0 The condition is met, and the voltage value V measured by the second voltmeter 42 is obtained. 20 Regarding, V 20 =I0R0+V0 This is true. Therefore, I0R0=(V 10 +V 20 ) / 2 The following holds: R0 = (V 10 +V 20 It can be calculated by ) / 2I0.

[0021] In process 2, when the resistance value R0 changes to R0 + ΔR by setting a condition in which an external force acts on the object to be measured, the measured value V1 of the first voltmeter 41 is as follows: V1 = I0(R0 + ΔR) - V0 The following is true, and the measurement value V2 from the second voltmeter 42 is: V2 = I0(R0 + ΔR) + V0 This is true. Therefore, I0(R0+ΔR)=(V1+V2) / 2 This is true.

[0022] In process 3, (V1+V2-V 10 -V 20 ) / 2I0=R0+ΔR-R0=ΔR The resistance change value ΔR can be calculated using this method.

[0023] Basic configuration ( 2) in First Voltmeter 41 It is unnecessary to adjust the voltage value of the variable constant voltage power supply 3 to zero. As a result, the basic configuration ( 2 ) In this case, the constant voltage power supply 3 too choice do They can be hired.

[0024] Moreover, as is clear from the formula for calculating ΔR in Process 3, the resistance change value ΔR can be calculated by simple addition and subtraction. Furthermore, by employing two voltmeters, the first voltmeter 41 and the second voltmeter 42, it is possible to mitigate the variations in the voltmeters, thereby also mitigating the variations in the resistance value R0 and resistance change value ΔR of the strain gauge 1.

[0025] To explain in more detail, if the voltage value from the variable constant voltage power supply 3 is set to zero, then V 10 =V 20 If the equation V1=V2 holds true, and yet this equation does not hold true, then it is possible to detect that one of the voltmeters is malfunctioning by using another voltmeter other than the first and second voltmeters.

[0026] The following describes individual embodiments.

[0027] Various metals, such as alloys, that exhibit little change in resistivity with respect to temperature changes are used as strain resistance elements that form the strain resistance of strain gauges. However, in recent years, semiconductors have also been adopted as strain resistance elements. In the case of semiconductor strain gauges, the gauge factor K is approximately 2.0 for metal strain gauges, while it is 130 for silicon strain gauges currently sold in Japan, which is a much larger value of 65 times. Furthermore, each of the gauge factors K mentioned above is based on CGS units.

[0028] Therefore, when semiconductor strain gauges are used, the sensitivity V fSince / ε is proportional to K, when semiconductor strain gauges are used, even in the basic configurations (a) and (b), a sensitivity 4 × 65 = 260 times greater than that of a bridge circuit can be achieved.

[0029] In the basic configuration (1), distorted gauge 1 The area of ​​the strain foil constituting the electrical circuit and the area of ​​the base plate supporting the strain foil are both selectable. There is, Strain gauge 1 During the resistance measurement stage Current value I of variable constant current power supply 2 0 Or the current value V of the variable constant voltage power supply 3 0 Size Correspondingly, the area of ​​the distortion foil and base plate Size Select This mitigates the impact of heat generation. An embodiment characterized by this feature can be adopted.

[0030] Typically, strain gauges 1 In this configuration, the existing resistance value R0 is set to a constant value when no distortion occurs, and 120Ω and 350Ω are widely used as standard values. However, the amount of heat generated by the strain gauge foil in strain gauge 1 will naturally differ depending on the degree of the set variable constant current I0.

[0031] Moreover, the strain gauge foil is mounted on the strain gauge 1 If the device generates heat due to the application of current, a strain gauge resistance measurement value ΔR', i.e., an apparent strain gauge resistance change value ΔR', will occur due to the temperature change.

[0032] In such a case, in the above embodiment, Variable constant current power supply 2 current value When the area of ​​the strain foil and base plate is increased in response to a high I0 or set voltage V0, the effects of heat generation can be mitigated. Furthermore, in the above embodiment, the reason why not only the area of ​​the base plate but also the area of ​​the strain foil can be selected is that the larger the area of ​​the base plate, the larger the area of ​​the strain foil can be, thereby enabling uniform heat distribution.

[0033] figure 3 As shown, four types of strain gauges A, B, C, and D, each with different gauge foil and base plate areas, were attached to a copper plate. Then, 1mA, 10mA, and 30mA were selected as variable constant currents, and correspondingly, the variable constant voltages were set to 0.12V, 1.2V, and 3.6V, respectively. The measurement results regarding the degree of temperature rise in the strain gauges, i.e., the difference from the external temperature, are shown in the table below. However, the unit is °C. [table] TIFF0007914974000001.tif42108

[0034] According to the measurement results, the area of ​​the strain foil of strain gauge D is nine times that of strain gauge A, and the heat generated by the strain resistance element is nine times greater when a current of 30 mA is conducted through strain gauge D compared to when a current of 10 mA is conducted through strain gauge A.

[0035] Nevertheless, it was found that the degree of temperature rise was lower when strain gauge D was conducted at 30mA than when strain gauge A was conducted at 10mA.

[0036] To explain in more detail, when sensitivity is improved by appropriately selecting and setting the current value I0 in the variable constant current power supply 2, the heat generation energy in each strain foil naturally increases. However, the temperature rise measurement results in the table above support the usefulness of the embodiment in which the area of ​​the strain foil and the area of ​​the base plate can be freely selected.

[0037] The measurement results shown in the table above show the case where the current value I0 in the variable constant current power supply 2 is selected and set, but in the case of the above embodiment, even when the variable constant voltage V0 is appropriately selected and set, the strain gauge 1 The temperature rise in that region can be suppressed to a certain range.

[0038] In the circuit of basic configuration (1), if an embodiment is adopted in which a thermocouple is connected to the strain resistance element, and a control mechanism is interposed between the thermocouple and the variable constant current power supply 2 to keep the current value constant, or a control mechanism is present between the thermocouple and the variable constant voltage power supply 3 to keep the voltage value constant, then it becomes possible to keep the amount of heat generated in the strain resistance element constant when measuring in basic configuration (2).

[0039] As shown in Figure 7, in a strain measurement circuit employing one variable constant current power supply 2, one variable constant voltage power supply 3, and one voltmeter 4, ,figure 3 When strain gauge D is selected from the strain gauges shown, a variable constant voltage V0 of 1.2V is set, and currents of 10mA and 30mA are flowed, and when 10mA is supplied to the strain measurement circuit when the conventional strain gauge is configured as a bridge circuit, the load acting on the object to be measured (in units of N) is as follows: A copper plate with one end placed on the floor and the other end supported by strain gauge 1, and weighing 1 ton, is selected, and as the inclination angle θ of the copper plate changes, the load amount on strain gauge 1 in units of N (Newtons) changes. made In this case, the voltage measured by voltmeter 4 is V f The measured values ​​are shown in Figure 4 This is shown by the graph. Furthermore, the change in load due to the change in the inclination angle of the copper plate can be understood by considering the moment due to the action of the copper plate on the strain gauge, which is proportional to cosθ.

[0040] According to the graph above, in the case of a 10mA current, Indicates the degree of distortion Measured value V f This is four times the measurement value of the bridge circuit, but when 30mA is conducted, The aforementioned Measured value V f This is 12 times that of the bridge circuit, and 10mA is conducting. case It is three times greater, and it has been concretely confirmed that sensitivity is improved by selecting and setting the variable constant current I0.

[0041] figure 4 As shown in the graph, the measured value Vf Since the unit of =I0ΔR is mV, connect an oscilloscope to both ends of voltmeter 4, Measured value V f = I0ΔR can be measured using an oscilloscope. Furthermore, when measuring voltage values ​​using such an oscilloscope, the voltage value can be visually determined, and the changing voltage value can be observed in response to sequential changes in the load.

[0042] Basic configuration ( 2 The unit of the voltage value measured in process 3 of ) is mV, (V1+V2-V 10 -V 20 ) / 2 Since this calculation is performed, the measured value V f It is impossible to directly measure something like =I0ΔR using an oscilloscope.

[0043] However, in the embodiment characterized by connecting the outputs of the first voltmeter 41 and the second voltmeter 42 to a microcomputer, and further connecting the output of the microcomputer to an oscilloscope, and then measuring the voltage value I0·ΔR determined by process 3 with the oscilloscope, the (V1+V2-V) calculated by the microcomputer 10 -V 20 The value of ) / 2 can be measured using an oscilloscope, and a similar effect can be achieved.

[0044] figure 5 In (a) and (b), for comparison, the lowest position is set to a metal strain gauge 1. As shown in Figure 7 Each V measured by the circuit and bridge circuit f of table Furthermore, regarding the strain gauge 1 which is a semiconductor, As shown in Figure 7 V measured by the circuit f V measured by the bridge circuit as well f It also displays this.

[0045] figure 5 As shown in (a), the measured resistance R0 of the semiconductor strain gauge at 26°C is approximately 121Ω, as shown in Figure 5 As shown in (b), the measured resistance R0 of the semiconductor strain gauge at -196°C is approximately 352Ω.

[0046] In such cases, 5 By focusing on specific measurements in graph (a), K ≈ 0.40 / (10 × 0.05 × 121) ≈ 6.61 × 10 -3 You can obtain this. Similarly, Figure 5 By focusing on specific measurements in graph (b), K=0.5 / (1×352×0.3)≒4.72×10 -3 You can obtain this. Furthermore, the numerical values ​​of each gauge factor K mentioned above are based on MKS units.

[0047] Basic configuration ( 2 In the above embodiment of ) teeth , below It is possible to realize the characteristic features. a. By performing cooling using liquid nitrogen, such as at -196°C, the resistance value of semiconductor strain gauges increases significantly compared to room temperature, while the gauge factor K decreases. b. General formula V in process 4 f As shown in / ε=KI0R0, by increasing the resistance R0 of the strain gauge through cooling based on the use of liquid nitrogen for the semiconductor strain gauge, while setting the variable constant current I0 during the cooling stage to a smaller value than in the case of room temperature, the measurement range of strain ε can be set to a range of an order of magnitude larger than in the case of room temperature. c. Despite the changes in the measurement range as described in b above, the measurement value of the voltmeter 4 can be set to the unit of mV in both the case of room temperature and when cooled, and measurement with an oscilloscope is also possible.

[0048] The following describes some examples. [Examples]

[0049] Examples are shown in Figure 6 As shown, the constant voltage power supply 3 is connected to both ends of the variable resistor element 5, and on the output side of the variable resistor element 5, one of the two connecting terminals of the strain gauge 1 is connected to one end of the variable resistor element 5, and the other terminal is connected to the other end of the variable resistor element 5 via the first voltmeter 41 in a slidable state, and furthermore, the one terminal and the other terminal of the variable resistor element 5 and the second voltmeter 42 are connected in parallel, thus forming the basic configuration ( 1 It is characterized by comprising a variable constant voltage power supply 3.

[0050] In the embodiment, the V1 measured by the first voltmeter 41 is as follows: V 10 =I0·R0-xE This is true.

[0051] Considering the voltage measured by the second voltmeter 42, the internal resistance of the second voltmeter 42 is on the order of GΩ, which is orders of magnitude larger than the resistance R0 of the strain gauge 1.

[0052] In such cases, 6 As shown, the variable resistor element r is divided into a region x and a region 1-x, and the variable constant voltage V2' applied to the x region and the parallel circuit of the second voltmeter 42 and strain gauge 1 is such that the resistance value R0 of the strain gauge 1 is overwhelmingly larger than the maximum value r of the variable resistor 5. That is, the above r is the resistance value R 0 It is overwhelmingly smaller than If we take that into consideration, V2´={xrR0E / (xr+R0)} / {(1-x)r+xrR0 / (xr+R0)} ≈ xrE / {(1-x)r+xr} =xE This is true.

[0053] Considering that the voltages I0R0 from the variable constant current power supply 2 are applied in the same direction, the voltage value V at the second voltmeter 42 is 20 Regarding, V 20 =I0R0+V2'=I0R0+xE This is achieved, and a variable constant voltage power supply 3 with a simple configuration can be secured. [Industrial applicability]

[0054] Thus, in the present invention, which is based on the basic configurations (1) and (2), by employing a combination of a variable constant current power supply and a variable constant voltage power supply without employing a bridge circuit, it is possible to accurately measure and calculate changes in strain in a strain gauge with high sensitivity. At the same time, it is possible to measure strain resistance over a wide measurement range in embodiments in which multiple temperatures in the strain gauge are set. Furthermore, even if the amount of heat generated in the strain resistance element changes due to changes in the current value I0 of the variable constant current and the variable constant voltage V0, it is possible to employ embodiments that can mitigate such changes. This has groundbreaking significance in the field of strain measurement, and as a result, a wide range of applications can be expected. [Explanation of Symbols]

[0055] 1. Strain gauge 2. Variable constant current power supply 3. Variable constant voltage power supply or constant voltage power supply 4. Voltmeter 41 First Voltmeter 42. Second Voltmeter 5. Variable resistors and variable resistor elements

Claims

1. A strain measurement circuit characterized in that, for both connection terminals of a strain gauge intended for strain measurement, a variable constant current power supply and a variable constant voltage power supply or constant voltage power supply connected in series with a first voltmeter are connected in parallel, and a second voltmeter is connected to both connection terminals of the strain gauge, the direction of conduction of the variable constant current power supply and the direction of application of the variable constant voltage power supply at each connection terminal are the same, the resistance value of the strain gauge is measured by adding the measured values ​​of the first voltmeter and the second voltmeter, and the resistance value R0 when no external force is acting on the strain gauge is calculated as R0 = (V10 + V20) / 2I0 when an external force is acting, and a Wheatstone bridge circuit is not required.

2. The strain measurement circuit according to claim 1, characterized in that the area of ​​the strain foil constituting the electrical circuit of the strain gauge and the area of ​​the base plate supporting the strain foil are both selectable, and the effect of heat generation is mitigated by selecting the size of the area of ​​the strain foil and the base plate in accordance with the magnitude of the current value I0 of the variable constant current power supply or the current value V0 of the variable constant voltage power supply during the resistance measurement stage of the strain gauge.

3. The strain measurement circuit according to claim 1, characterized in that a constant voltage power supply is connected to both ends of a variable resistor element having a resistance value overwhelmingly smaller than the resistance value R0, and on the output side of the variable resistor element, one of the two connection terminals of the strain gauge is connected to one end of the variable resistor element, and the other terminal is connected to the other end of the variable resistor element via a first voltmeter in a slidable manner, and furthermore, the one terminal and the other terminal of the variable resistor element, the second voltmeter and the variable constant current power supply are connected in parallel, thereby constituting a variable constant voltage power supply and a variable constant current power supply.

4. A method for measuring and calculating the strain gauge resistance change value and the generated strain in the strain measurement circuit according to claim 1, by the following process.

1. Variable constant current I when no external force is acting on the object being measured that is in contact with the strain gauge. ０ The selection and setting of, and the voltage value V measured by the first voltmeter. 10 Measurement of the voltage V measured by the second voltmeter. 20 Measurement.

2. Setting the conditions under which an external force acts on the object to be measured, and the voltage value V measured by the first voltmeter. 1 Measurement of the voltage and the voltage value V measured by the second voltmeter ２ Measurement. 3 ΔR = (V １ + V ２ - V 10 - V 20 ) / 2I ０ Calculation of strain gauge resistance change value ΔR changed due to external force on the measurement object.

4. After setting the gauge factor K according to a predetermined value, ε = (1 / K)(ΔR / R ０ ) Calculation of strain ε generated by the aforementioned cause. However, R ０ R is the resistance value possessed by the strain gauge, and between the end of process 1 and the end of process 4, ０ = (V 10 +V 20 ) / 2I ０ It is calculated by [the method described].

5. The outputs of the first voltmeter and the second voltmeter are connected to a microcomputer, and the output of the microcomputer is further connected to an oscilloscope. The voltage values ​​I, determined by process 3, are measured sequentially in response to the changes in load measured by the first voltmeter and the second voltmeter, and then the voltage values ​​I are determined by process 3. ０ A method for measuring and calculating the changed strain gauge resistance value and the generated strain according to claim 4, characterized in that ΔR is visually measured using an oscilloscope.

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