Strain gauge measuring device and measuring method

Abstract

A strain gauge measurement device capable of performing temperature correction of the measured value of a strain gauge with a relatively simple configuration is provided. [Solution] A strain gauge measurement device 100 of the present invention includes a resistor bridge circuit 70 that generates an output voltage of the strain gauge between output nodes N1 and N2, an instrumentation amplifier 120 that amplifies the output voltage of the strain gauge input from the output nodes N1 and N2 of the resistor bridge circuit 70, a thermocouple 30 that detects the temperature of an object to be measured to which the strain gauge is attached, a signal processing unit 140 that receives the measurement value VS of the strain gauge output from the instrumentation amplifier 120, and a control unit 160. The control unit 160 calculates an initial output voltage e0 of the strain gauge corresponding to an initial resistance value R0 of the strain gauge at an initial temperature T0, then calculates a change ΔR in the initial resistance value R0 of the strain gauge based on the temperature T detected by the thermocouple 30, calculates the output voltage e of the strain gauge based on the change ΔR, and corrects the measurement value VS of the strain gauge based on the difference between the output voltage e and the initial output voltage e.

Description

[Technical Field]

[0001] The present invention relates to a strain gauge measurement device and a temperature compensation method thereof, and more particularly to temperature compensation of the output of a strain gauge. [Background technology]

[0002] A wireless communication sensor system has been put into practical use, in which multiple slave units are installed in remote locations and transmit the measured values ​​sensed by the multiple slave units to a master unit (for example, Patent Document 1). The slave units are installed, for example, in structures, facilities, bridge piers, etc. located in mountainous areas, lakes and marshes, or on the sea, and sense changes in the state of such measurement objects, and the master unit determines the presence or absence of abnormalities, deterioration, fatigue, damage, etc. in the measurement objects based on the sensing results transmitted from the slave units.

[0003] Strain gauges are known for measuring the state of an object to be measured. A strain gauge changes the resistance value of a resistor in proportion to the expansion and contraction of the object to be measured. The strain gauge is adhered or attached to the object to be measured, and the strain of the object to be measured is calculated by measuring the change in resistance of the strain gauge. Because the change in resistance of a strain gauge is minute, it is usually measured by converting the resistance change into a voltage using a Wheatstone bridge circuit. For example, Patent Document 2 discloses a strain measurement device that can measure the strain of an object to be measured in an environment where the ambient temperature changes over a wide range from low to high temperatures. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6251363 [Patent Document 2] Japanese Patent Application Publication No. 4-351901 Summary of the Invention [Problem to be solved by the invention]

[0005] Strain gauges using resistance bridge circuits are sensitive to temperature changes, and the sensing value of the strain gauge needs to be corrected. Temperature correction of strain gauges is generally performed using the following procedure. (1) Attach a strain gauge and a temperature sensor to the same object (object to be measured) (2) Measure the output of the strain gauge (3) At the same time, the temperature sensor measures the temperature of the object. (4) Correlate the strain gauge output with the temperature of the temperature sensor and analyze the relationship. (5) Understand how the strain gauge output changes when the temperature changes, and calculate the correction value to compensate for that change. (6) Apply compensation according to temperature changes to correct the strain gauge output

[0006] One strain gauge manufacturer provides strain gauges and data loggers, and performs temperature compensation of the strain gauge output using the temperature information of the object being measured that is monitored and recorded by the data logger. However, the specific method of temperature compensation is not disclosed, and data loggers are relatively expensive, making it difficult to adopt from a cost perspective.

[0007] SUMMARY OF THE INVENTION An object of the present invention is to provide a strain gauge measuring device and a measuring method that can solve the above-mentioned conventional problems and perform temperature correction of the output of a strain gauge with a relatively simple configuration. [Means for solving the problem]

[0008] The strain gauge measurement device according to the present invention includes a resistor bridge circuit that generates an output voltage of the strain gauge between a first output node and a second output node; an amplifier that includes input terminals connected to each of the first and second output nodes, amplifies the output voltage of the strain gauge input from the resistor bridge circuit, and outputs the amplified voltage as a measurement value VS of the strain gauge; detection means that detects the temperature of an object to be measured to which the strain gauge is attached; and signal processing means electrically connected to the amplifier and the detection means, wherein the signal processing means includes first calculation means that calculates an initial output voltage e0 of the strain gauge corresponding to an initial resistance value R0 of the strain gauge at an initial temperature T0; second calculation means that calculates a change ΔR in the initial resistance value R0 of the strain gauge based on the temperature T of the object to be measured detected by the detection means and a displacement temperature ΔT of the initial temperature T0, and calculates a corrected output voltage e of the strain gauge based on the change ΔR; and correction means that corrects the measurement value VS of the strain gauge based on the difference between the initial output voltage e0 and the output voltage e.

[0009] In one embodiment, a voltage is supplied to one node of the resistor bridge circuit, the other node is connected to a reference potential, a strain gauge and a resistor are connected in series between the one node and the other node, and the signal processing means includes an analog-to-digital converter (ADC), which receives a voltage V1 between the one node and the other node and a voltage V2 between the first or second output node and the other node and converts the voltages V1 and V2 into digital values. The ADC also receives the output voltage of the amplifier and converts the output voltage into a digital value. In one embodiment, the first calculation means calculates an initial resistance R0 based on the digitally converted voltages V1 and V2. In one embodiment, the initial resistance R0 is expressed as R0 = (V2 × R2) / (V1 - V2), where R2 is the resistor connected in series with the strain gauge. In another embodiment, the change ΔR is expressed as ΔR = R0 × GF × α × ΔT, where GF is the gauge factor and α is the thermal expansion coefficient of the strain gauge material. In one aspect, the correction means calculates a correction value VC by (output voltage e - initial output voltage e0) x (amplifier GAIN), and calculates a corrected strain gauge measurement value VSC by (strain gauge measurement value VS - correction value VC). In one aspect, the signal processing means further includes a peak hold circuit between the amplifier and the ADC, and the peak hold circuit outputs the maximum voltage value of the strain gauge measurement value. In one aspect, the detection means includes a thermocouple or a temperature sensor.

[0010] A strain gauge measurement method according to the present invention is for a strain gauge measurement device including a resistor bridge circuit that generates an output voltage of a strain gauge between a first output node and a second output node, and includes the steps of: calculating an initial output voltage e0 of the strain gauge corresponding to an initial resistance value R0 of the strain gauge at an initial temperature T0; detecting the temperature T of the object to be measured to which the strain gauge is attached, and calculating a change ΔR in the initial resistance value R0 of the strain gauge based on the initial temperature T0 and a displacement temperature ΔT between the detected temperature T; calculating an output voltage e of the strain gauge based on the change ΔR; and correcting the measured value of the strain gauge based on the difference between the output voltage e and the initial output voltage e0.

[0011] In one embodiment, a voltage is supplied to one node of the resistor bridge circuit, the other node is connected to a reference potential, a strain gauge and a resistor are connected in series between the one node and the other node, and an ADC (analog-to-digital converter) converts a voltage V1 between the one node and the other node and a voltage V2 between the first or second output node and the other node into digital values, and an initial resistance R0 is calculated based on the converted digital values. In one embodiment, the measurement method further includes a step of amplifying the output voltage of the strain gauge, converting the amplified output voltage of the strain gauge into a digital value using the ADC as a measured value of the strain gauge, and calculating the output voltage e and the initial output voltage e0 using the converted digital value. In one embodiment, the step of calculating the initial resistance R0 calculates the initial resistance R0 by (V2 × R2) / (V1 - V2) (R2 is a resistor connected in series with the strain gauge). [Effects of the Invention]

[0012] According to the present invention, temperature compensation of strain gauge measurements can be performed with a relatively simple configuration, thereby reducing the cost of strain gauge measurement devices. Furthermore, instead of using a relatively expensive data logger, temperature compensation of strain gauge measurements can be performed by using a general-purpose, inexpensive ADC. [Brief explanation of the drawings]

[0013] [Figure 1] 1A and 1B show an example of a mounting bracket for mounting a strain gauge, with FIG. 1A being a side view of the mounting bracket and FIG. 1B being a front view of the mounting bracket. [Figure 2] 10 is a schematic cross-sectional view showing an example of attaching a mounting bracket to a flange of a tower. FIG. [Figure 3] FIG. 3(A) is a diagram showing an example of the configuration of a strain gauge measurement device according to an embodiment of the present invention, and FIG. 3(B) is a diagram showing an example of the internal configuration of a signal processing unit of FIG. 3(A). [Figure 4] FIG. 4A is a diagram showing an example of bias of an output signal when the differential input voltage is positive, and FIG. 4B is a diagram showing an example of bias of an output signal when the differential input voltage is negative. DETAILED DESCRIPTION OF THE INVENTION

[0014] The strain gauge measurement device of the present invention measures a voltage corresponding to a change in the resistance of a strain gauge, and is used, for example, as a strain sensor, a pressure sensor, etc. The strain gauge measurement device of the present invention has a function of correcting the measurement voltage of the strain gauge according to a change in the temperature of the object to be measured to which the strain gauge is attached. [Example]

[0015] Next, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 shows an example of a mounting bracket equipped with a strain gauge, where Fig. 1(A) is a side view of the mounting bracket and Fig. 1(B) is a front view of the mounting bracket. Fig. 2(A) is a schematic cross-sectional view showing an example of mounting the mounting bracket to a flange, and Fig. 2(B) is a diagram showing an example of connecting a strain gauge to a resistance bridge circuit.

[0016] The shape, size, material, type, etc. of the object to be measured to which the strain gauge is attached are arbitrary, but here, as shown in Figure 1(A), a strain gauge 20 is attached to a U-shaped mounting bracket 10. Mounting bracket 10 has a top surface 12 with a generally flat main surface, a bottom surface 14 with a generally flat main surface, and a side surface 16 connecting one end of top surface 12 to one end of bottom surface 140, and each of top surface 12 and bottom surface 16 is formed with a through hole 18 for inserting a bolt. Mounting bracket 10 is made of, for example, stainless steel and can be formed by bending a flat steel plate.

[0017] The strain gauge 20 is attached approximately in the center of the side surface 16 of the mounting bracket 10. The attachment position and attachment method of the strain gauge 20 are arbitrary, but for example, the strain gauge 20 is fixed to the surface of the side surface 16 using an adhesive. A thermocouple 30 for detecting the temperature of the mounting bracket 10 is attached near the strain gauge 20. The attachment position and attachment method of the thermocouple 30 are not particularly limited, but for example, the thermocouple 30 is attached to the surface of the side surface 16 together with the strain gauge 20 using an adhesive. In another embodiment, the thermocouple 30 is attached to the side surface 16, top surface 12, or bottom surface 14 at a position different from that of the strain gauge 20 using an adhesive or other jig.

[0018] 2, the mounting bracket 10 is fixed to flanges 40, 42 of, for example, a wind power tower. Here, an example is shown in which the upper cylindrical flange 40 and the lower cylindrical flange 42 are fastened together with one bolt 50 and nut 52, but in reality, the flanges 40, 42 are fastened together with a greater number of bolts 50 and nuts 52.

[0019] The mounting bracket 10 is attached from the outside of the abutting upper and lower flanges 40, 42, the upper and lower through holes 18 of the mounting bracket 10 are aligned with the bolt fastening holes in the flanges 40, 42, bolts 50 are passed through those holes, and the bolts 50 are fastened with nuts 52. Reinforcing brackets or washers 60, 62 may be interposed between the top surface 12 of the mounting bracket 10 and the bolt 50, and between the bottom surface 14 of the mounting bracket 10 and the nut 52.

[0020] The bolts 50 are tightened to a specified load, and as the bolts 50 are tightened, the top surface 12 deforms somewhat elastically, with the vicinity of the fixed portion of the side surface 16 as a fulcrum, and the bottom surface 14 similarly deforms somewhat elastically, with the vicinity of the fixed portion to the side surface 16 as a fulcrum. The strain gauges 20 detect strain occurring in the side surface 16, making it possible to detect, for example, loosening of the bolts or loosening between flanges caused by bolt deterioration.

[0021] 2(B), the strain gauge 20 is electrically connected in series with a resistor R2 of a resistor bridge circuit 70, and as will be described later, the resistor bridge circuit 70 generates an output voltage corresponding to the strain of the strain gauge 20. In addition, the temperature of the mounting bracket 10 detected by the thermocouple 30 is provided to a strain gauge measurement device, for example, via a signal line.

[0022] 3 is a diagram showing the configuration of a strain gauge measurement device according to an embodiment of the present invention. The strain gauge measurement device 100 of this embodiment includes a thermocouple 30 attached to a mounting bracket 10, which is the object to be measured, a resistor bridge circuit 70, and a measurement circuit 110 that measures the strain gauge based on signals from the thermocouple 30 and the resistor bridge circuit 70. The measurement circuit 110 is configured to include an instrumentation amplifier 120, a peak hold circuit 130, a signal processing unit 140, an input interface (I / F) 150, and a control unit 160. The strain gauge measurement device 110 of this embodiment has a function of correcting the measurement value of the strain gauge based on the temperature of the object to be measured detected by the thermocouple 30.

[0023] Resistor bridge circuit 70 forms a Wheatstone bridge circuit and includes strain gauges R0 / R1 (corresponding to strain gauge 20 shown in FIG. 2) and a resistor R2 connected in series therewith, and resistor R3 and a resistor R4 connected in series therewith. Node P1 connecting resistors R2 and R4 is connected to voltage supply unit 72, and voltage V1 is supplied to node P1. Node P2 connecting strain gauges R0 / R1 and resistor R3 is connected to GND as a reference potential.

[0024] An output voltage corresponding to the strain of strain gauges R0 / R1 is generated between output node N1, which connects strain gauges R0 / R1 and resistor R2, and output node N2, which connects resistors R3 and R4. When resistors R2 = R3 = R4, and the strain of the strain gauges is zero, ideally the output voltage of the strain gauges between output nodes N1 and N2 will be zero. On the other hand, when strain occurs in the strain gauges, resistor R1 changes, and an output voltage of the strain gauge corresponding to the changed resistance R1 is generated between output nodes N1 and N2.

[0025] The output node N1 is connected to the non-inverting input terminal (+) of the instrumentation amplifier 120, and the output node N2 is connected to the inverting input terminal (-). The output voltage of the strain gauge generated by the resistor bridge circuit 70 is input to the instrumentation amplifier 120 as a differential input voltage between the non-inverting input terminal (+) and the inverting input terminal (-). The instrumentation amplifier 120 amplifies the differential input voltage within the range of +VDD to -VDD according to the gain (GAIN). The output voltage Vout amplified by the instrumentation amplifier 120 is output to the peak hold circuit 130. The output voltage Vout of the instrumentation amplifier 120 is a measurement value of the strain gauge and is a function representing the strain of the strain gauge 20.

[0026] In one embodiment, the output voltage Vout of the instrumentation amplifier 120 can be biased to the reference voltage Vref by a bias voltage BV set by the control unit 160. In this case, the output voltage Vout of the instrumentation amplifier 120 is expressed as follows: Output voltage Vout = GAIN × differential input voltage + BV BV: bias voltage of the instrumentation amplifier GAIN: Gain of the instrumentation amplifier Differential input voltage: (+ terminal) - (- terminal)

[0027] 4 shows examples of bias of the output voltage Vout when it is assumed that +VDD=+5V, −VDD=−5V, and BV=2.048V of the instrumentation amplifier 120. FIG. 4(A) shows an example of bias when the differential input voltage Vin>0, and FIG. 4(B) shows an example of bias when the differential input voltage Vin<0.

[0028] In Figure 4(A), the input signal swings between ±5V around 0V, but because the differential input voltage Vin>0, the input signal is on the + side. On the output side, a bias of +2.048V is applied, so the output signal swings between 0V and BV around +2.048V. Because the differential input voltage Vin>0, the output signal appears on the + side, which is G times the differential input voltage Vin.

[0029] In Figure 4(B), the differential input voltage Vin<0, so the input signal is on the negative side. On the output side, a bias of +2.048V is applied, so the output signal swings between 0V and BV, centered around +2.048V. Because the differential input voltage Vin<0, the output signal appears on the negative side, the input signal multiplied by G.

[0030] The peak hold circuit 130 receives the output voltage Vout of the instrumentation amplifier 120, holds the maximum voltage value within a certain period, and outputs this. The configuration of the peak hold circuit 130 is not particularly limited, but for example, in the case of a circuit that holds a voltage in a capacitor, the held voltage may be reset (discharged) by a reset signal from the control unit 160.

[0031] The signal processing unit 140 is connected to the peak hold circuit 130 and the control unit 160. As shown in FIG. 3B, the signal processing unit 140 preferably includes an ADC (analog-to-digital converter), which receives the voltage Vs held by the peak hold circuit 130, i.e., the measurement value of the strain gauge, and converts it into a digital value. The ADC further receives the voltage V1 between nodes P1 and P2 applied to the strain gauges R0 / R1 and resistor R2 of the resistor bridge circuit 70, and the voltage V2 between the output node N1 and node P2 applied to the strain gauges R0 / R1, and converts the voltages V1 and V2 into digital values.

[0032] The conversion from analog to digital values ​​is performed according to the following formula:

number

[0033] Vref / (2^15-1) represents the minimum step size (1LSB) of the ADC resolution. Vref is the reference voltage and the maximum input voltage when digitizing the input signal. The digital value converted by the ADC is, for example, I 2 The signal is provided to the control unit 160 via synchronous serial communication such as an Inter-Integrated Circuit (C).

[0034] The input I / F 150 receives the detection signal of the thermocouple 30, A / D converts the detection signal, and provides the digitally converted detection signal to the control unit 160. The input I / F 150 provides the detection signal to the control unit 160 by serial communication synchronized with a clock using, for example, an SPI (Serial Peripheral Interface).

[0035] The control unit 160 is configured using hardware and / or software resources, such as a microprocessor or microcontroller including memory such as ROM / RAM. In one embodiment, the control unit 160 executes a program or software application stored in the memory to enable calculation of strain gauge measurements and correction of the strain gauge measurements based on the temperature of the object being measured detected by the thermocouple 30.

[0036] In one embodiment, control unit 160 stores data necessary for calculating strain gauge measurement values ​​or temperature compensation in memory. For example, the memory stores the power supply voltages +VDD and −VDD applied to instrumentation amplifier 120, the gain G of instrumentation amplifier 120, the bias voltage BV of the output voltage of instrumentation amplifier 120, the gauge factor GF, the thermal expansion coefficient α of the material of the strain gauge, and the like, and control unit 160 calculates strain gauge measurement values ​​or performs temperature compensation using the data read from the memory.

[0037] Next, a specific operation of the strain gauge measurement device of this embodiment will be described. The strain gauge measurement device 100 of this embodiment uses the thermocouple 30 to collect the initial temperature T0 of the surface of the mounting bracket 10 and the temperature T at the time of sensing (measurement), calculates the difference from the initial value, and corrects the strain gauge value measured at that time.

[0038] First strain gauge measurement (1) Strain gauge measurement ⇒VS (Temperature compensation is not performed) The signal processing unit 140 receives the voltage VS held by the peak hold circuit 130 , that is, the measured value of the strain gauge, converts it into a digital value, and provides it to the control unit 160 .

[0039] (2) Measure V1 and V2 with an ADC ⇒V1 ⇒V2 A voltage V1 between nodes P1 and P2 applied to strain gauges R0 / R1 and resistor R2 of resistor bridge circuit 70, and a voltage V2 between output node N1 and node P2 applied to strain gauges R0 / R1 are supplied to signal processing unit (ADC) 140. Signal processing unit 140 converts voltages V1 and V2 into digital values ​​and provides them to control unit 160. Control unit 160 stores the digital values ​​of voltages V1 and V2 in memory.

[0040] (3) Calculation of the initial resistance value R0 of the strain gauge at the initial temperature T0

number

[0041] (4) Calculate the initial output voltage e0 of the strain gauge

number

[0042] (5) Measure the surface temperature T0 of the mounting bracket 10 using a thermocouple. ⇒T0 Input I / F 150 receives the detection signal from thermocouple 30, converts it into a digital signal, and provides control unit 160 with the digital signal representing the initial temperature T0 of mounting bracket 10. Control unit 160 stores the initial temperature T0 in memory.

[0043] Strain gauge measurements from the second time onwards (1) Strain gauge measurement ⇒VS (temperature compensation performed) The signal processing unit 140 receives the voltage Vs held by the peak hold circuit 130, i.e., the measured value of the strain gauge, converts it into a digital value, and provides it to the control unit 160. The control unit 160 performs temperature compensation of the measured value Vs of the strain gauge, as will be described later.

[0044] (2) Measure the surface temperature T of the mounting bracket using a thermocouple. ⇒T The input I / F 150 receives the detection signal from the thermocouple 30 , converts it into a digital signal, and provides the digital signal representing the temperature T of the fitting 10 to the control unit 160 .

[0045] (3) Calculate the displacement temperature value △T △T=T-T0 The control unit 160 calculates the temperature change value ΔT according to the above formula.

[0046] (4) Calculate the displacement resistance value △R △R=R0×GF×α×△T×V1; Displacement from R0 due to temperature change GF: Strain gauge sensitivity (gauge factor) α: strain expansion coefficient of the material The control unit 160 reads out the initial resistance values ​​R0, GF, α, and voltage V1 stored in the memory, and calculates the displacement resistance value ΔR, where GF is a constant of the strain gauge.

[0047] (5) Calculate the strain gauge output voltage e with temperature change

number

[0048] (6) Calculate the strain gauge correction value VC VC=(e-e0)×GAIN (instrumentation amplifier gain) The control unit 160 calculates the correction value VC according to the above formula.

[0049] (7) Correct the measured strain gauge value VS VSC=VS-VC The control unit 160 calculates the corrected final strain gauge measurement value VSC according to the above formula.

[0050] Next, the temperature compensation method using the strain gauge measurement device of this embodiment will be verified. conditions V1=1V BV (bias voltage) = 2.048V +VDD=+5V -VDD=-5V GAIN=601 R2=R3=R4=120Ω / 0.1% or less GF=2.1 α=1.1μ

[0051] First strain gauge measurement (1) Strain gauge measurement ⇒ VS (no temperature correction required) (2) Measure V1 and V2 with an ADC ⇒V1=1V (measurement) ⇒V2=501.5mV (measured) (3) Calculate the initial resistance R0 of the strain gauge at the initial temperature T0.

number

number

[0052] Example 1: Measurement of strain gauge from the second time onwards (T = 30°C) (1) Strain gauge measurement ⇒VS (2) Measure the surface temperature T of the mounting bracket using a thermocouple. ⇒T=30℃ (3) Calculate the displacement temperature value △T △T=T-T0=30-20=10 (4) Calculate the displacement resistance value △R △R=R0×GF×α×△T =120.7×2.1×11×10 -6 ×10=27.882mΩ (5) Calculate the strain gauge output voltage e with temperature change

number

[0053] Example 2: Measurement of strain gauge from the second time onwards (T = 10°C) (1) Strain gauge measurement ⇒VS (2) Measure the surface temperature T of the mounting bracket using a thermocouple. ⇒T=10℃ (3) Calculate the displacement temperature value △T △T=T-T0=10-20=-10 (4) Calculate the displacement resistance value △R △R=R0×GF×α×△T =120.7×2.1×11×10 -6 ×(-10)=-27.882mΩ (5) Calculate the strain gauge output voltage e with temperature change

number

[0054] Example 3: Measurement of strain gauge from the second time onwards (T=-10 degrees) (1) Measure the strain gauge ⇒VS (2) Measure the surface temperature T of the mounting bracket with a thermocouple ⇒ Set T = -10 °C (3) Calculate the displacement temperature value ΔT ΔT = T - T0 = -10 - 20 = -30 (4) Calculate the displacement resistance value ΔR ΔR = R0 × GF × α × ΔT = 120.7 × 2.1 × 11 × 10 -6 × (-30) = -83.645 mΩ (5) Calculate the output voltage e of the strain gauge with temperature change

Equation

[0055] [Results of validity proof] When T > T0, VSC = VS - VC, and the correction value is subtracted from the measured value. When T < T0, VSC = VS - (-VC), and the correction value is added to the measured value. Therefore, it is proved that the temperature correction method of this embodiment is effective. [[ID=4,8]]

[0056] [[ID=,51]]Thus, according to this embodiment, without using a relatively expensive data logger, with a simple configuration using a general-purpose and inexpensive ADC, the temperature correction of the measured value of the strain gauge can be performed.

[0057] In the above embodiment, a peak hold circuit is provided between the instrumentation amplifier 120 and the signal processing unit (ADC) 140, but this is just one example, and it is also possible to use, for example, a sample hold circuit that samples the measurement value of the strain gauge output from the instrumentation amplifier 120 at a constant period, and the sample hold circuit may be built into the ADC or connected between the instrumentation amplifier 120 and the ADC. Also, in the above embodiment, a thermocouple is used to detect the temperature of the object to be measured, but this is just one example, and it is also possible to use other temperature sensors.

[0058] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0059] 10: Mounting bracket 20: Strain gauge 30: Thermocouple 70: Resistor bridge circuit 100: Measuring equipment 110: Measurement circuit 120:Instrumentation amplifier 130: Beakhold circuit 140: Signal processing unit 150: Input interface (I / F) 160: Control unit

Claims

1. A strain gauge measurement device, a resistor bridge circuit for generating an output voltage of the strain gauge between a first output node and a second output node; an amplifier including input terminals connected to the first and second output nodes, respectively, for amplifying the output voltage of the strain gauge input from the resistor bridge circuit and outputting the amplified voltage as a measurement value VS of the strain gauge; a detecting means for detecting the temperature of the object to be measured to which the strain gauge is attached; signal processing means electrically connected to the amplifier and the detection means; The signal processing means includes a first calculation means for calculating an initial output voltage e0 of the strain gauge corresponding to an initial resistance value R0 of the strain gauge at an initial temperature T0; a second calculation means for calculating a change ΔR in the initial resistance value R of the strain gauge based on the temperature T of the object to be measured detected by the detection means and a displacement temperature ΔT of the initial temperature T, and for calculating a corrected output voltage e of the strain gauge based on the change ΔR; and a correction means for correcting the measured value VS of the strain gauge based on the difference between the initial output voltage e0 and the output voltage e.

2. a voltage is supplied to one node of the resistor bridge circuit, the other node is connected to a reference potential, and a strain gauge and a resistor are connected in series between the one node and the other node; 2. The strain gauge measurement device according to claim 1, wherein the signal processing means includes an ADC (analog-to-digital converter), which receives a voltage V1 between the one node and the other node and a voltage V2 between the first or second output node and the other node, and converts the voltages V1 and V2 into digital values, and further receives an output voltage of the amplifier, and converts the output voltage into a digital value.

3. 3. The strain gauge measurement device according to claim 2, wherein the first calculation means calculates the initial resistance value R0 based on the digitally converted voltages V1 and V2.

4. 4. The measuring device according to claim 3, wherein the initial resistance value R0 is expressed as R0=(V2×R2) / (V1−V2) (R2 is a resistor connected in series to the strain gauge).

5. 3. The strain gauge measurement device according to claim 2, wherein the amount of change .DELTA.R is expressed as .DELTA.R=R0.times.GF.times..alpha..times..DELTA.T (GF is a gauge factor, and .alpha. is a thermal expansion coefficient of the material of the strain gauge).

6. 2. The strain gauge measurement device according to claim 1, wherein the correction means calculates a correction value VC by (output voltage e - initial output voltage e0) x (amplifier GAIN), and calculates a corrected strain gauge measurement value VSC by (strain gauge measurement value VS - correction value VC).

7. 3. The strain gauge measurement device according to claim 2, wherein said signal processing means further includes a peak hold circuit between said amplifier and said ADC, said peak hold circuit outputting a maximum voltage value of said amplifier.

8. 2. The strain gauge measurement device according to claim 1, wherein the detecting means includes a thermocouple or a temperature sensor.

9. A measurement method for a strain gauge measurement device including a resistor bridge circuit that generates an output voltage of a strain gauge between a first output node and a second output node, comprising: Calculating an initial output voltage e0 of the strain gauge corresponding to an initial resistance value R0 of the strain gauge at an initial temperature T0; a step of detecting a temperature T of the object to which the strain gauge is attached, and calculating a change ΔR in the initial resistance value R of the strain gauge based on the initial temperature T and a displacement temperature ΔT of the detected temperature T; calculating an output voltage e of the strain gauge based on the change ΔR; correcting the measurement value of the strain gauge based on the difference between the output voltage e and the initial output voltage e0; Measurement methods including:

10. a voltage is supplied to one node of the resistor bridge circuit, the other node is connected to a reference potential, and a strain gauge and a resistor are connected in series between the one node and the other node; 10. The measurement method according to claim 9, further comprising converting the voltage V1 between the one node and the other node and the voltage V2 between the first or second output node and the other node into digital values ​​using an ADC (analog-to-digital converter), and calculating the initial resistance R0 based on the converted digital values.

11. The measurement method further includes the step of amplifying an output voltage of the strain gauge; 11. The measurement method according to claim 10, wherein the amplified output voltage of the strain gauge is converted into a digital value by an ADC as a measurement value of the strain gauge, and the output voltage e and the initial output voltage e0 are calculated using the converted digital value.

12. 11. The measurement method according to claim 10, wherein the step of calculating the initial resistance value R0 calculates the initial resistance value R0 by (V2×R2) / (V1−V2), where R2 is a resistance connected in series to the strain gauge.

Images