Strain measuring circuit and strain resistance calculation method for the same

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] The present invention relates to a circuit for measuring a change in strain gauge resistance caused by strain due to pressure, torque, etc., using a strain gauge, and a strain occurring in association with the change in strain gauge resistance, and a method for specifically measuring and calculating the change in strain gauge resistance and the strain in the circuit. [Background technology]

[0002] When measuring the strain resistance of a strain gauge that changes due to the cause of strain, the conventional technique uses a Wheatstone bridge circuit (hereinafter referred to as "bridge circuit") that 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 value ΔR that has changed due to an external force on the object to be measured, or the strain gauge resistance change value ΔR' that has changed due to the deformation of the object to be measured caused by the external force on the object to be measured and temperature changes.

[0004] The inventor of the present patent application has proposed the configuration of Patent Document 1 in order to overcome the above-mentioned technical problems with respect to bridge circuits.

[0005] In Patent Document 1, as set forth in claims 1 and 3, the distortion measuring circuits of the following (a) and (b) are basically configured. (a) A strain resistance measurement circuit characterized in that a variable constant voltage power supply, which is connected in series with a constant current power supply and a voltmeter, is connected in parallel only to both connection terminals of a strain gauge intended for measuring strain resistance, and the conduction direction of the constant current power supply and the application direction of the variable constant voltage power supply at each of the connection terminals are the same, and the measurement 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 a constant voltage power supply, which is connected in series with a variable constant current power supply and a voltmeter, is connected in parallel only to both connection terminals of a strain gauge intended for measuring strain resistance, and the conduction direction of the variable constant current power supply and the application direction of the constant voltage power supply at each of the connection terminals are the same, and the measurement 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] The basic configurations (a) and (b) can achieve sensitivity approximately four times that of conventional bridge circuits, and can also accurately measure the change in strain resistance and strain even when a temperature difference occurs.

[0007] However, in the case of basic configuration (a), it is assumed that a constant current power supply is used, and in the case of basic configuration (b), it is based on a constant voltage power supply, so it is impossible to further improve the measurement sensitivity. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Patent No. 7254388 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide a distortion measurement circuit that does not rely on a bridge circuit that has been used as an analog differential circuit, but which allows current and voltage values ​​to be varied and enables accurate measurement and calculation of distortion with high sensitivity, and a distortion measurement and calculation method based on said circuit. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention is based on the following basic configuration. (1) A strain measurement circuit characterized in that a variable constant voltage power supply, which is connected in series with a variable constant current power supply and a voltmeter, is connected in parallel to both connection terminals of a strain gauge intended for strain measurement, the conduction direction of the variable constant current power supply at each of the connection terminals being the same as the application direction of the variable constant voltage power supply, and the resistance value of the strain gauge is measured by selecting and setting either the voltage value of the variable constant voltage power supply or the current value of the variable constant current power supply, and the other is adjusted so that the measurement value of the voltmeter is zero, thereby measuring the resistance value of the strain gauge and eliminating the need for a Wheatstone bridge circuit. (2) A method for measuring and calculating the strain gauge resistance change value and the generated strain in the strain measurement circuit of (1) above by 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, and adjustment of the variable constant voltage V0 so that the voltmeter reading is zero. 2. Setting the condition in which an external force acts on the object to be measured, and the voltage value V measured by the voltmeter in that condition f Measurement of. 3 ΔR=V f Calculation of the strain gauge resistance change ΔR caused by an external force on the object being measured by / I0. 4. After setting the gauge factor K by a predetermined value, calculate the strain ε caused by the above-mentioned factor, ε = (1 / K)(ΔR / R0). Note that R0 is the existing resistance value of the strain gauge, and is calculated from process 1 to process 4 by R0=V0 / I0. (3) A method for measuring and calculating the strain gauge resistance change value and the generated strain in the strain measurement circuit of (1) above by the following process. 1. Selection and setting of the variable constant voltage V0 when no external force is acting on the object being measured that is in contact with the strain gauge, and adjustment of the variable constant current I0 so that the voltmeter reading is zero. 2. Setting the condition in which an external force acts on the object to be measured, and the voltage value V measured by the voltmeter in that condition f Measurement of. 3 ΔR=V fCalculation of the strain gauge resistance change ΔR caused by an external force on the object being measured by / I0. 4. After setting the gauge factor K by a predetermined value, calculate the strain ε caused by the above-mentioned factor, ε = (1 / K)(ΔR / R0). Note that R0 is the existing resistance value of the strain gauge, and is calculated from process 1 to process 4 by R0=V0 / I0. (4) A strain measurement circuit characterized in that 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 are connected in parallel to both connection terminals of a strain gauge for the purpose of strain measurement, and a second voltmeter is connected to both connection terminals of the strain gauge, the conduction direction of the variable constant current power supply and the application direction of the variable constant voltage power supply at each of the connection terminals are the same, 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, and a Wheatstone bridge circuit is not required. (5) A method for measuring and calculating the strain gauge resistance change value and the generated strain in the strain measurement circuit of (4) above by the following process. 1. Select and set the variable constant current I0 when no external force is acting on the object being measured that is in contact with the strain gauge, and measure the voltage V by the first voltmeter. 10 and the voltage value V measured by the second voltmeter. 20 Measurement of. 2. Setting a state in which an external force acts on the object to be measured, and measuring the voltage value V1 using the first voltmeter and the voltage value V2 using the second voltmeter. 3 ΔR=(V1+V2-V 10 -V 20 ) / 2I0 to calculate the strain gauge resistance change ΔR caused by an external force on the object being measured. 4. After setting the gauge factor K by a predetermined value, calculate the strain ε caused by the above-mentioned factor, 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) / 2I0. [Effects of the Invention]

[0011] The distortion measurement circuit of basic configuration (1) employs a variable constant current power supply instead of the constant current power supply on which basic configuration (a) is based, and employs a variable constant voltage power supply instead of the constant voltage power supply on which basic configuration (b) is based.

[0012] The distortion measurement circuit of basic configuration (4) differs from basic configuration (a) in that it uses a variable constant current power supply instead of the constant current power supply on which basic configuration (a) is based, while basic configuration (b) is also different in that it can use a variable constant voltage power supply instead of the constant voltage power supply on which basic configuration (b) is based, but it is partially similar to basic configuration (b) in that it can also use a constant voltage power supply.

[0013] In these basic configurations (1) and (4), like basic configurations (a) and (b), a bridge circuit is not required. However, in the case of basic configuration (1), the measurement methods of basic configurations (2) and (3) achieve measurements that are clearly more sensitive than those using a bridge circuit, and in the case of basic configuration (4), the measurement method of basic configuration (5) achieves measurements that are clearly more sensitive than those using a bridge circuit.

[0014] Moreover, the measurement methods using basic configurations (2) and (3), which are based on basic configuration (1), can measure strain with higher sensitivity than the measurement methods using the circuits of basic configurations (a) and (b). The specific basis for this is the measured voltage value V corresponding to the strain gauge resistance change value ΔR. f and the strain value ε, as will be described later.

[0015] The measurement method of basic configuration (5), which is based on basic configuration (4), is similar to basic configuration (2) in that the current value of the variable constant current power supply is set in advance. However, compared to the measurement method of basic configuration (2), it does not require adjustment of the variable constant voltage V0 in process 1 of basic configuration (2), and can measure and calculate a more accurate resistance change value ΔR by simple addition and subtraction. The reason for this will be described later in conjunction with specific calculations.

[0016] Moreover, since it is based on the measurements of both the first and second voltmeters, the variation in the measurements due to differences in the voltmeters is reduced, and as a result, it is possible to achieve measurements and calculations with less variation in the measurements of the resistance value R0 and resistance change value ΔR of the strain gauge compared to basic configuration (2). [Brief explanation of the drawings]

[0017] [Figure 1] The basic configuration (1) and the circuit configuration of claim 1 are shown. [Figure 2] 1 shows a flowchart for sequentially realizing the process of the basic configuration (2) and claim 7. [Figure 3] 10 shows a flowchart for sequentially realizing the process of the basic configuration (3) and claim 10. [Figure 4] The circuit configuration of the basic configuration (4) and claim 2 is shown. In the basic configuration (4), not only a variable constant voltage power supply but also a constant voltage power supply can be selected, but Fig. 4 shows the case of a variable constant voltage power supply. [Figure 5] 13 shows a flowchart for sequentially realizing the process of the basic configuration (5) and claim 13. [Figure 6] 1 shows planar photographs of four types of strain gauges, each showing a state in which the base plates supporting the strain foils have different areas and are freely selectable. [Figure 7]This is a graph showing the relationship between the measured voltage and the change in strain resistance value when the load on the object to be measured is changed sequentially, in the cases where a bridge circuit is used, and where the circuit of basic configuration (1) is used and the variable constant current is set to 10 mA, and further, where it is set to 30 mA. [Figure 8] Graphs showing the change in Vf=I0ΔR corresponding to each load in the measurement method of basic configuration (2) when a semiconductor strain gauge is selected and when cooled to 0°C or below, where (a) shows the change at room temperature of 26°C (299K), and (b) shows the change at cooled state of -196°C (77K). [Figure 9] 1 shows distortion measuring circuits according to embodiments, where (a) shows the case of embodiment 1 and (b) shows the case of embodiment 2. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] Each basic configuration will be explained below.

[0019] As shown in FIG. 1, the basic configuration (1) is a strain measurement circuit characterized in that a variable constant voltage power supply 3, which is connected in series with a variable constant current power supply 2 and a voltmeter 4, is connected in parallel to both connection terminals of a strain gauge 1 for the purpose of strain measurement, and the conduction direction of the variable constant current power supply 2 at each connection terminal and the application direction of the variable constant voltage power supply 3 are the same, and the resistance value of the strain gauge 1 is measured by selecting and setting either the voltage value of the variable constant voltage power supply 3 or the current value of the variable constant current power supply 2, and the other is adjusted so that the measurement value of the voltmeter 4 is zero, thereby measuring the resistance value of the strain gauge 1 and eliminating the need for a Wheatstone bridge circuit.

[0020] The requirement that the conduction direction of the variable constant current power supply 2 and the application direction of the variable constant voltage power supply 3 are the same at both connection terminals of the strain gauge 1 means that the polarities of the variable constant current power supply 2 and the variable constant voltage power supply 3 are the same at both connection terminals.

[0021] In Figure 1, the conduction direction of variable constant current power supply 2 and the application direction of variable constant voltage power supply 3 are the same, which means that there is a voltage source with a direction opposite to the application direction of variable constant voltage power supply 3 at both connection terminals of strain gauge 1 for voltmeter 4.

[0022] In such a case, the measurement value of the voltmeter 4 can be set to zero by adjusting the voltage value of the variable constant voltage power supply 3, and further, the measurement value of the voltmeter 4 can be set to zero by adjusting the current value of the variable constant current power supply 2.

[0023] In the basic configuration (1), the process of selecting and setting either the voltage value of the variable constant voltage power supply 3 or the current value of the variable constant current power supply 2, and adjusting the other so that the measurement value of the voltmeter 4 becomes zero, corresponds to the operation of process 1 in the basic configurations (2) and (3).

[0024] The basic configuration (2) is based on the basic configuration (1), and measures and calculates the strain gauge resistance change value and the generated strain through the following process, as shown in the flowchart of FIG. 1. Selecting and setting 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 adjusting the variable constant voltage V0 so that the measurement value of the voltmeter 4 is zero. 2. Setting the state in which an external force acts on the object to be measured, and the voltage value V measured by the voltmeter 4 in that state f Measurement of. 3 ΔR=V f Calculation of the strain gauge resistance change ΔR caused by an external force on the object being measured by / I0. 4. After setting the gauge factor K by a predetermined value, calculate the strain ε caused by the above-mentioned factor, ε = (1 / K)(ΔR / R0). Here, R0 is the resistance value of the strain gauge.

[0025] To explain this in terms of specific calculations, when the constant current I0 set in process 1 is conducted through both connection terminals of the strain gauge 1 having a resistance value R0, and then the variable constant voltage V0 is adjusted so that the measured voltage at both connection terminals becomes zero, the following occurs between the existing resistance value R0 of the strain gauge 1: I0R0-V0=0 holds, and the resistance value R0 can be calculated by R0=V0 / I0. However, the calculation of R0 only needs to be performed after process 1 and before process 4, and does not necessarily need to be performed between process 1 and process 2. This also applies to basic configuration (3) and basic configuration (5), as well as to the embodiments of each of these basic configurations. Furthermore, the "zero" in Process 1 does not mean "zero" in the mathematically strict sense, but rather means "approximately zero" based on the measured value. Specifically, the error in the measured value is 10 -2 The error can be ignored in the following cases: The above idea also applies to the case of "zero" in each basic configuration for other methods.

[0026] If the change in strain gauge resistance caused by an external force on the object being measured in process 2 is ΔR, the measurement value V measured by voltmeter 4 corresponding to that ΔR is f Regarding V f =(R0+ΔR)I0-V0 =ΔRI0 (1) holds, and in process 3, for ΔR, ΔR=V f / I0 In process 4, the strain ε is calculated as ε=(1 / K)(ΔR / R0) (2) The amount is calculated as follows. Note that K is the gauge factor, which is a correction coefficient required to provide an accurate numerical value for the strain ε in the strain gauge 1. In the case of a strain gauge that uses metal foil, a value of approximately 2 is usually adopted.

[0027] The sensitivity of the ΔR in the distortion measurement is the ratio of the calculated distortion ε to the measurement voltage corresponding to the occurrence of distortion, that is, V in the case of the basic configuration (2) f When / ε is set, from the above formulas (1) and (2), V f / ε=KI0R0 (3) holds true.

[0028] In the case of the basic configuration (a), the current value I0 in the above equation (3) is a constant current, whereas in the case of the basic configuration (2) based on the basic configuration (1), I0 is a variable constant current. Therefore, by selecting and setting a current value higher than I0 in the basic configuration (a), the sensitivity according to the above equation (3) can be improved.

[0029] The basic configuration (3) is based on the basic configuration (1), and measures and calculates the strain gauge resistance change value and the generated strain through the following process, as shown in the flowchart of FIG. 1. Select and set the variable constant voltage V0 when no external force is acting on the object being measured that is in contact with the strain gauge 1, and adjust the variable constant current I0 so that the measurement value of the voltmeter 4 is zero. 2. Setting the state in which an external force acts on the object to be measured, and the voltage value V measured by the voltmeter 4 in that state f Measurement of. 3 ΔR=V f Calculation of the strain gauge resistance change ΔR caused by an external force on the object being measured by / I0. 4. After setting the gauge factor K by a predetermined value, calculate the strain ε caused by the above-mentioned factor, ε = (1 / K)(ΔR / R0). Here, R0 is the resistance value of the strain gauge.

[0030] To explain this in terms of specific calculations, when the constant voltage V0 set in process 1 is applied to both connection terminals of the strain gauge 1 having a resistance value R0, and the variable constant current I0 is adjusted so that the measurement value of the voltmeter 4 at both connection terminals becomes zero, the following occurs between the existing resistance value R0 of the strain gauge 1: R0I0-V0=0 is established.

[0031] In process 2, if the change in strain gauge resistance caused by an external force on the measurement object is ΔR, the measurement value V measured by the voltmeter 4 corresponding to that ΔR is f Regarding V f =(R0+ΔR)I0-V0 =ΔRI0 holds, and in process 3, for ΔR, ΔR=V f / I0 In process 4, the strain ε is calculated as ε=(1 / K)(ΔR / R0) The amount is calculated as follows.

[0032] In the case of basic structure (3), which is based on basic structure (1), if sensitivity is set using the same scale as in the case of basic structure (2), V f / ε=KI0R0 =KV0 (3) holds true.

[0033] In the case of the basic configuration (b), the voltage value V0 in the above equation (3) is a constant voltage, whereas in the case of the basic configuration (3), the sensitivity according to the above equation (3) can be improved by selecting and setting a constant voltage V0 higher than the constant voltage V0 in the basic configuration (b).

[0034] As shown in FIG. 4, the basic configuration (4) is a strain measurement circuit characterized in that a variable constant voltage power supply 3, which is connected in series with a variable constant current power supply 2 and a first voltmeter 41, or a constant voltage power supply 3 is connected in parallel to both connection terminals of a strain gauge 1 for the purpose of strain measurement, and a second voltmeter 42 is connected to both connection terminals of the strain gauge 1, the conduction direction of the variable constant current power supply 2 and the application direction of the variable constant voltage power supply 3 at both connection terminals are the same, the resistance value of the strain gauge 1 is measured by adding the measurement value of the first voltmeter 41 and the measurement value of the second voltmeter 42, and a Wheatstone bridge circuit is not required.

[0035] The basic configuration (4) differs from the basic configuration (1) in that it employs a second voltmeter 42 connected to both terminals of the strain gauge 1. As a result, the method of calculating the resistance value R0 and the resistance change value ΔR of the strain gauge 1 is also different, as will be described later.

[0036] In the basic configuration (4), the process of adding the measurement value of the first voltmeter 41 and the measurement value of the second voltmeter 42 corresponds to the operation that realizes the process 1 in the basic configuration (5) described later.

[0037] In the basic configuration (4), not only the variable constant voltage power supply 3 but also the constant voltage power supply 3 can be used as the voltage power supply. The reason for this is that in process 1 of the basic configuration (5) described below, it is not necessary to adjust the voltage value of the voltage power supply to a constant value.

[0038] The basic configuration (5) is based on the basic configuration (4), and measures and calculates the strain gauge resistance change value and the generated strain through the following process, as shown in the flowchart of FIG. 1. Selection and setting of a variable constant current I0 when no external force is acting on the object to be measured that is in contact with the strain gauge 1, and measurement of a voltage value V by the first voltmeter 41. 10 and the voltage value V 20 Measurement of. 2. Setting a state in which an external force acts on the object to be measured, and measuring a voltage value V1 using the first voltmeter 41 and a voltage value V2 using the second voltmeter 42. 3 ΔR=(V1+V2-V 10 -V 20 ) / 2I0 to calculate the strain gauge resistance change ΔR caused by an external force on the object being measured. 4. After setting the gauge factor K by a predetermined value, calculate the strain ε caused by the above-mentioned factor, 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 ) / 2I0.

[0039] To explain this in terms of 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 the constant voltage power supply 3 is V0 (however, it is not necessary to select and set a specific value for V0), the voltage value V measured by the first voltmeter 41 is 10 Regarding V 10 =I0R0-V0 holds, and the voltage value V measured by the second voltmeter 42 20 Regarding V 20 =I0R0+V0 holds true. Therefore, I0R0=(V 10 +V 20 ) / 2 holds, and for R0, R0=(V 10 +V 20 ) / 2I0.

[0040] In process 2, as in the basic configurations (2) and (3), when a state in which an external force acts on the measurement object is set and the resistance value R0 changes to R0+ΔR, the measured value V1 of the first voltmeter 41 is: V1=I0(R0+ΔR)-V0 holds, and the measured value V2 by the second voltmeter 42 is V2=I0(R0+ΔR)+V0 holds true. Therefore, I0(R0+ΔR)=(V1+V2) / 2 holds true.

[0041] In process 3, (V1+V2-V 10 -V 20 ) / 2I0=R0+ΔR-R0=ΔR The resistance change value ΔR can be calculated by

[0042] The technical purpose of Process 4 is the same as that of Process 4 in Basic Configurations (2) and (3). As already explained, process 1 of basic configuration (2) and process 1 of basic configuration (5) have in common the point of selecting and setting the current I0 of the variable constant current power supply 2, but in basic configuration (5), it is not necessary to adjust the voltage value of the variable constant voltage power supply 3 so as to set the voltage value of the voltmeter 4 to zero as in basic configuration (2). As a result, the constant voltage power supply 3 can be selectively employed in the basic configuration (5).

[0043] 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, the variability of the voltmeters can be alleviated, thereby also alleviating the variability of the resistance value R0 and the resistance change value ΔR of the strain gauge 1.

[0044] Specifically, when the voltage value of the variable constant voltage power supply 3 is set to zero, V 10 =V 20 is true and V1=V2 should be true, but if this equation is not true, it is possible to search for a voltmeter other than the first and second voltmeters to determine whether one of the voltmeters has an error.

[0045] Individual embodiments will be described below.

[0046] As the strain resistance element forming the strain resistance of the strain gauge, various metals such as alloys whose resistivity changes little with temperature changes are used. However, in recent years, semiconductors have also been adopted as strain resistance elements, and in the case of semiconductor strain gauges, the gauge factor K is approximately 2.0 for metal strain resistors, while it is 130 for silicon-based strain gauges currently on the market in Japan, a value 65 times larger. Each gauge factor K is based on the CGS unit.

[0047] Therefore, when semiconductor strain gauges are used, the sensitivity V f Since / ε is proportional to K, when semiconductor strain gauges are used, even in the basic configurations (a) and (b), it is possible to achieve 4 x 65 = 260 times the sensitivity of a bridge circuit.

[0048] In the basic configuration (1), an embodiment can be adopted in which a strain gauge 1 having a constant existing resistance value R0 when no strain is generated is placed, and the area of ​​the strain foil that constitutes the electrical circuit of the gauge and the area of ​​the base plate that supports the strain foil are both freely selectable, and an embodiment can be adopted in which the areas of the strain foil and base plate are selected according to the amount of heat generated by the strain gauge during the resistance measurement stage of the strain gauge.

[0049] In general, the existing resistance value R0 of a strain gauge when no strain occurs is set to a constant value, and standard values ​​of 120 Ω and 350 Ω are widely used. However, the amount of heat generated by the strain gauge foil in the strain gauge 1 naturally differs depending on the degree of the variable constant current I0 selected and set in the basic configuration (2) or the variable constant voltage V0 selected and set in the basic configuration (3).

[0050] Furthermore, when the strain gauge on which the strain gauge foil is placed generates heat due to the passage of electricity, a measured resistance value ΔR' of the strain gauge, that is, an apparent resistance change value ΔR' of the strain gauge occurs due to the temperature change.

[0051] In such a case, in the above embodiment, if the areas of the distorted foil and base plate are set large in response to a state in which the set current I0 or the set voltage V0 is large, the effect of the heat generation can be mitigated. In addition, in the above embodiment, the area of ​​not only the base plate but also the distorted foil can be freely selected because the larger the area of ​​the base plate, the larger the area of ​​the distorted foil, which allows for more uniform heat distribution.

[0052] As shown in Figure 6, 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, and the variable constant current was set to 1 mA, 10 mA, and 30 mA. Corresponding to these selections, the variable constant voltage was set to 0.12 V, 1.2 V, and 3.6 V, respectively. The measurement results for 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] TIFF2025178118000002.tif42108

[0053] 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 energy of the strain resistance element when a current of 10 mA is passed through strain gauge A is nine times that when a current of 30 mA is passed through strain gauge D.

[0054] Nevertheless, it is clear that the degree of temperature rise when 30 mA is conducted to strain gauge D is less than when 10 mA is conducted to strain gauge A.

[0055] To be more specific, in the case of the basic configuration (2), when the 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 distorted foil also naturally increases, but the measurement results of the temperature rise in the table above confirm the usefulness of the embodiment described above, which allows the area of ​​the distorted foil and the area of ​​the base plate to be freely selected.

[0056] The measurement results shown in the table above are for the case where the current value I0 in the variable constant current power supply 2 is selected and set as shown in basic configuration (2). However, in the case of the above embodiment, even when the variable constant voltage V0 is appropriately selected and set as shown in basic configuration (3), the temperature rise in the strain gauge can be suppressed within a certain range.

[0057] In the circuit of basic configuration (1), if an embodiment is adopted in which a thermocouple is connected to the strain-sensitive resistor element and a control mechanism that keeps the current value constant is interposed between the thermocouple and variable constant current power supply 2, or a control mechanism that keeps the voltage value constant is present between the thermocouple and variable constant voltage power supply 3, it is possible to keep the amount of heat generated in the strain-sensitive resistor element constant when measuring basic configurations (2) and (3).

[0058] In the circuit of basic configuration (1), strain gauge D is selected from the strain gauges shown in Figure 6, and a variable constant voltage V0 of 1.2 V is set and 10 mA and 30 mA are applied. Also, when 10 mA is applied to a strain measurement circuit in which the strain gauges of the prior art are configured as a bridge circuit, the load (unit: N) acting as the measurement object is a copper plate with one end placed on the floor and the other end supported by strain gauge 1, weighing 1 ton. By changing the inclination angle θ of the copper plate, the load amount in units of N (Newton) is changed on strain gauge 1. When measured by the measurement method of basic configuration (2), the V measured by voltmeter 4 is f The measured values ​​are shown in the graph of FIG. Furthermore, the change in the load amount 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, in that the load amount of the copper plate on the strain gauge is proportional to cosθ.

[0059] According to the graph, in the case of 10 mA conduction, the measured value V in process 3 of basic configuration (2) f is four times the measured value of the bridge circuit, but when 30 mA is conducted to the circuit of basic configuration (1), the measured value V of basic configuration (1) f is 12 times that of the bridge circuit and 3 times that of the basic configuration (1) in which 10 mA is conducted, and it is specifically proven that the sensitivity is improved by selecting and setting the variable constant current I0. Although the graph in FIG. 7 is based on measurements using the basic configuration (2), measurements using the basic configuration (3) also support a similar improvement in sensitivity.

[0060] As shown in the graph of FIG. 7, the measured values ​​V f Since the unit of =I0ΔR is mV, in basic configuration (2), an embodiment can be adopted in which an oscilloscope is connected to both ends of voltmeter 4 and I0ΔR determined in process 3 is measured using the oscilloscope, and this is also true for basic configuration (3). In the case of measuring the voltage value using such an oscilloscope, the voltage value can be visually determined, and in addition, the voltage value that changes as the load changes can be observed.

[0061] The unit of the voltage value measured in process 3 of basic configuration (5) is mV, (V1+V2-V 10 -V 20 ) / 2 Therefore, the measured values ​​of the basic configurations (2) and (3) are V f It is not possible to measure it directly using an oscilloscope, such as =I0ΔR.

[0062] However, in the case of an embodiment characterized in that the outputs of the first voltmeter 41 and the second voltmeter 42 are connected to a microcomputer, and the output of the microcomputer is further connected to an oscilloscope, and the voltage value I0·ΔR determined by process 3 is measured by the oscilloscope, the voltage value (V1+V2-V 10 -V 20 The value of ) / 2 can be measured using an oscilloscope, and the same effect can be achieved.

[0063] In the basic configuration (2), an embodiment can be adopted in which a semiconductor strain gauge is selected, multiple temperatures are set for the strain gauge 1, and then the strain gauge resistance change value and the generated strain are measured and calculated for each of the multiple temperatures by the following process. 1. Selecting and setting 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 adjusting the variable constant voltage V0 so that the measurement value of the voltmeter 4 is zero. 2. Setting the state in which an external force acts on the object to be measured, and the voltage value V measured by the voltmeter 4 in that state f Measurement of. 3 ΔR=V f Calculation of the strain gauge resistance change ΔR caused by an external force on the object being measured by / I0. 4. After setting the gauge factor K by a predetermined value, calculate the strain ε caused by the above-mentioned factor, ε = (1 / K)(ΔR / R0). Here, R0 is the resistance value that the strain gauge has at each of a plurality of temperatures, and is calculated from process 1 to process 4 by R0=V0 / I0.

[0064] To explain based on specific data, the V measured in the above embodiment when the temperature of the P-type silicon semiconductor strain gauge was set to 299 K, i.e., 26 ° C, and when it was set to 77 K, i.e., -196 ° C, f The change in =I0ΔR is shown in Figures 8(a) and 8(b). The setting of -196°C is based on cooling with liquid nitrogen.

[0065] In Figures 8(a) and (b), for comparison, the metal strain gauge 1 is placed at the bottom, and the V measured by the circuit of basic configuration (1) and the bridge circuit are shown. f Furthermore, for the semiconductor strain gauge 1, the V measured by the circuit of basic configuration (1) is presented. f Not only V measured by the bridge circuit f Also displays:

[0066] As shown in Figure 8(a), the measured resistance R0 of the semiconductor strain gauge at 26°C is approximately 121Ω, and as shown in Figure 8(b), the measured resistance R0 of the semiconductor strain gauge at -196°C is approximately 352Ω.

[0067] In such cases, by focusing on specific measurements in the graph in Figure 8(a), K ≒ 0.40 / (10 × 0.05 × 121) ≒ 6.61 × 10 -3 can be obtained. Similarly, by focusing on a particular measurement in the graph of Figure 8(b), K=0.5 / (1×352×0.3)≒4.72×10 -3 can be obtained. The values ​​of the gauge factors K are based on MKS units.

[0068] In the embodiment of the basic configuration (2), the following features can be confirmed. a) By cooling the semiconductor strain gauge to a temperature such as -196°C based on liquid nitrogen, the resistance value clearly increases and the gauge factor K decreases compared to that at room temperature. b General formula V in process 4 fAs shown by / ε=KI0R0, the resistance value R0 of the strain gauge is increased by cooling the semiconductor strain gauge using liquid nitrogen, while the measurement range of strain ε can be set to a range one order of magnitude larger than that at room temperature by setting the variable constant current I0 during the cooling stage to a value smaller than that at room temperature. c. Despite the change in the measurement range as described in b. above, the measurement value of the voltmeter 4 can be set to mV units both at room temperature and when cooled, and measurement using an oscilloscope is also possible.

[0069] In the basic configuration (3), an embodiment can also be adopted in which a semiconductor strain gauge is selected, multiple temperatures are set for the strain gauge 1, and then the strain gauge resistance change value and the generated strain are measured and calculated by the following process. 1. Select and set the variable constant voltage V0 when no external force is acting on the object being measured that is in contact with the strain gauge 1, and adjust the variable constant current I0 so that the measurement value of the voltmeter 4 is zero. 2. Setting the state in which an external force acts on the object to be measured, and the voltage value V measured by the voltmeter 4 in that state f Measurement of. 3 ΔR=V f Calculation of the strain gauge resistance change ΔR caused by an external force on the object being measured by / I0. 4. After setting the gauge factor K by a predetermined value, calculate the strain ε caused by the above-mentioned factor, ε = (1 / K)(ΔR / R0). Note that R0 is the existing resistance value of the strain gauge, and is calculated from process 1 to process 4 by R0=V0 / I0.

[0070] The above embodiment differs in that, instead of selecting and setting a variable current I0 as in the embodiment of basic configuration (2), a variable constant voltage V0 is selected and set as in basic configuration (3), and, instead of adjusting the variable constant voltage V0 as in the embodiment of basic configuration (2), a variable constant current I0 is adjusted as in basic configuration (3).

[0071] Despite these differences, in both embodiments, the voltage value V measured by the voltmeter 4 f The common point is that the measurement is performed, and then ΔR and strain ε are calculated. Therefore, the features a, b, and c can be realized in the embodiment of the basic configuration (3).

[0072] In the basic configuration (5), an embodiment can also be adopted in which a semiconductor strain gauge is selected, multiple temperatures are set for the strain gauge 1, and the strain gauge resistance change value and the generated strain are measured and calculated for each of the multiple temperatures by the following process. 1. Selection and setting of a variable constant current I0 when no external force is acting on the object to be measured that is in contact with the strain gauge 1, and measurement of a voltage value V by the first voltmeter 41. 10 and the voltage value V 20 Measurement of. 2. Setting a state in which an external force acts on the object to be measured, and measuring a voltage value V1 using the first voltmeter 41 and a voltage value V2 using the second voltmeter 42. 3 ΔR=(V1+V2-V 10 -V 20 ) / 2I0 to calculate the strain gauge resistance change ΔR caused by an external force on the object being measured. 4. After setting the gauge factor K by a predetermined value, calculate the strain ε caused by the above-mentioned factor, ε = (1 / K)(ΔR / R0). Here, R0 is the resistance value that the strain gauge has at each of the multiple temperatures, and R0 = (V 10 +V 20 ) / 2I0.

[0073] For the same reasons as in the embodiments of the basic configurations (2) and (3), the features a, b, and c can also be realized in the embodiment of the basic configuration (5).

[0074] Examples will be described below. [Example]

[0075] As shown in FIG. 9(a), Example 1 is characterized in that a constant-voltage power supply 3 is connected to both ends of a variable resistance element 5, and at the output side of the variable resistance element 5, one of the two connection terminals of a strain gauge 1 is connected to one end of the variable resistance element 5, and the other terminal is connected to the other end of the variable resistance element 5 via a voltmeter 4 in a freely slidable state, thereby constituting a variable constant-voltage power supply 3 of basic configuration (1).

[0076] As shown in Figure 9(a), when the variable resistance element r is divided into the region x and the region 1-x, the voltage value V measured by the voltmeter 4 interposed between the other end of the variable resistance element r and the strain gauge 1 is calculated by taking into consideration that a voltage of I0·R0 is applied in the opposite direction by the variable constant current power supply 2. V=I0·R0-xE holds true. In this way, by adjusting the division ratio x, it is possible to realize a variable constant voltage power supply 3 with a simple configuration. [Example]

[0077] As shown in FIG. 9(b), Example 2 is characterized in that a constant-voltage power supply 3 is connected to both ends of a variable resistance element 5, and at the output side of the variable resistance element 5, one of the two connection terminals of a strain gauge 1 is connected to one end of the variable resistance element 5, and the other terminal is connected to the other end of the variable resistance element 5 via a first voltmeter 41 in a state where it can slide freely, and further, one terminal and the other terminal of the variable resistance element 5 are connected in parallel to a second voltmeter 42, thereby constituting a variable constant-voltage power supply 3 of basic configuration (4).

[0078] In the second embodiment, the voltage V1 measured by the first voltmeter 41 is the same as the voltage measured by the voltmeter 4 in the first embodiment, V 10 =I0·R0-xE holds true.

[0079] 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.

[0080] In such a case, as shown in FIG. 9(b), the variable resistance element r is divided into an area of ​​x and an area of ​​1-x, and the variable constant voltage V2' applied to the area of ​​x and the parallel circuit of the second voltmeter 42 and the strain gauge 1 is determined as follows, taking into consideration that the resistance value R0 of the strain gauge 1 is overwhelmingly larger than the maximum value r of the variable resistor 5: V2´={xrR0E / (xr+R0)} / {(1-x)r+xrR0 / (xr+R0)} ≒xrE / {(1-x)r+xr} =xE holds true.

[0081] Considering that the voltage I0R0 from the variable constant current power supply 2 is applied in the same direction, the voltage value V 20 Regarding V 20 =I0R0+V2´=I0R0+xE holds, and similarly to the first embodiment, a variable constant voltage power supply 3 with a simple configuration can be ensured. [Industrial Applicability]

[0082] As described above, the present invention, which is based on the basic configurations (1), (2), (3), (4), and (5), does not employ a bridge circuit, but rather employs a combination of a variable constant current power supply and a variable constant voltage power supply, thereby enabling accurate measurement and calculation of 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 by setting multiple temperatures in the strain gauge. 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 an embodiment that can mitigate such changes. This is a groundbreaking invention in the field of strain measurement, and as a result, it is expected to be used in a wide range of applications. [Explanation of symbols]

[0083] 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 resistance elements

Claims

1. A strain measurement circuit characterized in that a variable constant voltage power supply, which is connected in series with a variable constant current power supply and a voltmeter, is connected in parallel to both connection terminals of a strain gauge used to measure strain, the direction of conduction of the variable constant current power supply at each of the connection terminals being the same as the direction of application of the variable constant voltage power supply, and the resistance value of the strain gauge is measured by selecting and setting either the voltage value of the variable constant voltage power supply or the current value of the variable constant current power supply, and the other is adjusted so that the measurement value of the voltmeter is zero, thereby measuring the resistance value of the strain gauge and eliminating the need for a Wheatstone bridge circuit.

2. A strain measurement circuit characterized in that 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 are connected in parallel to both connection terminals of a strain gauge for the purpose of strain measurement, and a second voltmeter is connected to both connection terminals of the strain gauge, the conduction direction of the variable constant current power supply and the application direction of the variable constant voltage power supply at each of the connection terminals are the same, 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, and a Wheatstone bridge circuit is not required.

3. The existing resistance value R when no strain is generated in each strain gauge ０ 3. A strain measuring circuit as claimed in claim 1, wherein a strain gauge having a constant strain is mounted, and the area of ​​the strain foil constituting the electrical circuit of the gauge and the area of ​​the base plate supporting the strain foil are both selectable.

4. 4. The strain measuring circuit according to claim 3, wherein the areas of the strain foil and the base plate are selected in accordance with the amount of heat generated by the strain gauge during the resistance measurement step.

5. 2. The distortion measuring circuit according to claim 1, wherein a constant voltage power supply is connected to both ends of the variable resistance element, and at the output side of the variable resistance element, one of the two connection terminals of the strain gauge is connected to one end of the variable resistance element, and the other terminal is connected to the other end of the variable resistance element via a voltmeter in a freely slidable state, thereby forming a variable constant voltage power supply.

6. 3. The distortion measuring circuit according to claim 2, wherein a constant voltage power supply is connected to both ends of the variable resistance element, and at the output side of the variable resistance element, one of the two connection terminals of the strain gauge is connected to one end of the variable resistance element, and the other terminal is connected via a first voltmeter in a state where it can slide freely relative to the other end of the variable resistance element, and further wherein one terminal and the other terminal of the variable resistance element are connected in parallel to a second voltmeter to form a variable constant voltage power supply.

7. 2. The strain measurement circuit of claim 1, wherein the strain gauge resistance change and the generated strain are measured and calculated by the following process:

1. Variable constant current I when no external force is acting on the measurement object in contact with the strain gauge ０ and the variable constant voltage V so that the voltmeter reading is zero. ０ Adjustment.

2. Setting the state in which an external force acts on the object to be measured, and the voltage value V measured by the voltmeter in that state ｆ Measurement of. 3 ΔR = V ｆ / I ０ Calculation of the strain gauge resistance change value ΔR caused by an external force on the measurement object.

4. After setting the gauge factor K to a predetermined value, ε = (1 / K)(ΔR / R ０ ) Calculation of the strain ε caused by the above-mentioned cause. However, R ０ is the resistance value of the strain gauge, and R ０ =V ０ / I ０ It is calculated as follows.

8. Connect an oscilloscope to both ends of the voltmeter and measure V ｆ 8. The method for measuring and calculating the strain gauge resistance change and the generated strain according to claim 7, wherein the change in the resistance of the strain gauge and the generated strain are measured by an oscilloscope.

9. 8. The method for measuring and calculating strain according to claim 7, wherein a semiconductor strain gauge is selected, and a plurality of temperatures are set for the strain gauge, and the strain gauge resistance change value and the generated strain are measured and calculated for each of the plurality of temperatures by the following process.

1. Variable constant current I when no external force is acting on the measurement object in contact with the strain gauge ０ and the variable constant voltage V so that the voltmeter reading is zero. ０ Adjustment.

2. Setting the state in which an external force acts on the object to be measured, and the voltage value V measured by the voltmeter in that state ｆ Measurement of. 3 ΔR = V ｆ / I ０ Calculation of the strain gauge resistance change value ΔR caused by an external force on the measurement object.

4. After setting the gauge factor K to a predetermined value, ε = (1 / K)(ΔR / R ０ ) Calculation of the strain ε caused by the above-mentioned cause. However, R ０ is the resistance value of the strain gauge at each of a plurality of temperatures, and R ０ =V ０ / I ０ It is calculated as follows.

10. 2. The strain measurement circuit of claim 1, wherein the strain gauge resistance change and the generated strain are measured and calculated by the following process:

1. Variable constant voltage V when no external force is acting on the measurement object in contact with the strain gauge ０ and the variable constant current I so as to zero the voltmeter reading. ０ Adjustment.

2. Setting the state in which an external force acts on the object to be measured, and the voltage value V measured by the voltmeter in that state ｆ Measurement of. 3 ΔR = V ｆ / I ０ Calculation of the strain gauge resistance change value ΔR caused by an external force on the measurement object.

4. After setting the gauge factor K to a predetermined value, ε = (1 / K)(ΔR / R ０ ) Calculation of the strain ε caused by the above-mentioned cause. Furthermore, R ０ is the resistance value of the strain gauge, and R ０ =V ０ / I ０ It is calculated as follows.

11. After connecting an oscilloscope to both ends of the voltmeter, the voltage value I ０ The method for measuring and calculating the strain gauge resistance change and the generated strain according to claim 10, characterized in that ΔR is measured by an oscilloscope.

12. 11. The method for measuring and calculating strain according to claim 10, wherein a semiconductor strain gauge is selected, and a plurality of temperatures are set for the strain gauge, and then the strain gauge resistance change value and the generated strain are measured and calculated for each of the plurality of temperatures by the following process.

1. Variable constant voltage V when no external force is acting on the measurement object in contact with the strain gauge ０ and the variable constant current I so as to zero the voltmeter reading. ０ Adjustment.

2. Setting the state in which an external force acts on the object to be measured, and the voltage value V measured by the voltmeter in that state ｆ Measurement of. 3 ΔR = V ｆ / I ０ Calculation of the strain gauge resistance change value ΔR caused by an external force on the measurement object.

4. After setting the gauge factor K to a predetermined value, ε = (1 / K)(ΔR / R ０ ) Calculation of the strain ε caused by the above-mentioned cause. Furthermore, R ０ is the resistance value of the strain gauge at each of a plurality of temperatures, and R ０ =V ０ / I ０ It is calculated as follows.

13. 3. The strain measuring circuit of claim 2, wherein the strain gauge resistance change and the generated strain are measured and calculated by the following process:

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

2. Setting a state in which an external force acts on the measurement object, and measuring the voltage value V 1 and the voltage value V ２ Measurement of. 3 ΔR = (V １ +V ２ -V 10 -V 20 ) / 2I ０ Calculation of the strain gauge resistance change value ΔR caused by an external force on the measurement object.

4. After setting the gauge factor K to a predetermined value, ε = (1 / K)(ΔR / R ０ ) Calculation of the strain ε caused by the above-mentioned cause. However, R ０ is the resistance value of the strain gauge, and R ０ = (V 10 +V 20 ) / 2I ０ It is calculated as follows.

14. The outputs of the first and second voltmeters are connected to a microcomputer, and the output of the microcomputer is connected to an oscilloscope. Then, the voltage value I, which is determined by process 3, is measured. ０ The method for measuring and calculating the changed resistance change of the strain gauge and the generated strain according to claim 13, characterized in that ΔR is measured by an oscilloscope.

15. 14. The method for measuring and calculating the strain resistance change value and the generated strain according to claim 13, wherein a semiconductor strain gauge is selected, and a plurality of temperatures are set for the strain gauge, and the strain gauge resistance change value and the generated strain are measured and calculated for each of the plurality of temperatures by the following process:

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

2. Setting a state in which an external force acts on the measurement object, and measuring the voltage value V 1 and the voltage value V ２ Measurement of. 3 ΔR = (V １ +V ２ -V 10 -V 20 ) / 2I ０ Calculation of the strain gauge resistance change value ΔR caused by an external force on the measurement object.

4. After setting the gauge factor K to a predetermined value, ε = (1 / K)(ΔR / R ０ ) Calculation of the strain ε caused by the above-mentioned cause. However, R ０ is the resistance value of the strain gauge at each of a plurality of temperatures, and R ０ = (V 10 +V 20 ) / 2I ０ It is calculated as follows.

Images