Measurement circuit

Abstract

The present invention provides a measurement circuit capable of improving noise resistance performance and measurement accuracy. This measurement circuit (1) comprises: a resistance element array (2) which has m first lines (21), n second lines (22), and a plurality of measurement resistance elements (20) connected between the m first lines (21) and the n second lines (22), and in which m×n≥2; a voltage control circuit (3) which, by using an operational amplifier (30) between an input terminal (3a) connected to a first connection line (L1) to which a constant current is supplied from a constant current source (9) and an output terminal (3b), controls the voltage of the output terminal (3b) so as to reduce the difference between the voltage of the input terminal (3a) and the voltage of the output terminal (3b); and a selection circuit (4) which connects one of the m first lines (21) to the first connection line (L1), connects one of the n second lines (22) to a second connection line (L2) connected to a ground, connects the rest of the m first lines (21) and the n second lines (22) to the output terminal (3b), and is capable of selecting the measurement resistance element (20) to which the constant current is supplied from among the plurality of measurement resistance elements (20).

Description

measurement circuit

[0001] The present disclosure relates to measurement circuits.

[0002] Patent Document 1 discloses a resistive element array circuit. The resistive element array circuit includes a plurality of word lines, a plurality of bit lines, a plurality of resistive elements, a selection unit, a differential amplifier, and a ground terminal. The word lines are connected to a power supply. The resistive elements are respectively arranged at a plurality of intersections between the word lines and the bit lines. The selection unit selects an arbitrary one of the word lines and an arbitrary one of the bit lines. The differential amplifier includes a positive input terminal connected to a selected bit line selected by the selection unit from among the plurality of bit lines, a negative input terminal connected to both an unselected bit line from among the plurality of bit lines not selected by the selection unit and an unselected word line from among the plurality of word lines not selected by the selection unit, and an output terminal connected to the negative input terminal. The ground terminal is connected to the positive input terminal.

[0003] Japanese Patent Application Laid-Open No. 2020-34514

[0004] The resistor element array circuit (measurement circuit) disclosed in Patent Document 1 has a problem with noise resistance because the power supply is a constant voltage source. When the power supply is a constant voltage source, the current flowing through the resistor element itself changes due to a change in the resistance value of the resistor element, which changes the amount of self-heating and may affect measurement accuracy.

[0005] The present disclosure provides a measurement circuit that enables improved noise immunity and measurement accuracy.

[0006] A measurement circuit according to one aspect of the present disclosure comprises a resistor array having m first lines, n second lines, and a plurality of measurement resistor elements connected between the m first lines and the n second lines, where m×n≧2; an input terminal connected to a first connection line to which a constant current is supplied from a constant current source; an output terminal; and an operational amplifier and / or transistor located between the input terminal and the output terminal, a voltage control circuit that controls the voltage of the output terminal using the operational amplifier and / or transistor so that a difference between the voltage of the input terminal and the voltage of the output terminal becomes small; and a selection circuit that connects one of the m first lines to the first connection line, connects one of the n second lines to a second connection line connected to ground, and connects the remaining m first lines and the n second lines to the output terminal, and is capable of selecting the measurement resistor element to which the constant current is supplied from the plurality of measurement resistor elements.

[0007] Aspects of the present disclosure enable improved noise immunity and measurement accuracy.

[0008] Graph showing an error in the difference between the voltage of the first connection line and the voltage of the second connection line relative to the measured temperature in the measurement circuit according to the second embodiment. Graph showing an error in the resistance value of the measurement resistor relative to the measured temperature in the measurement circuit according to the second embodiment. Schematic circuit diagram of a measurement circuit according to a third embodiment. Schematic circuit diagram of a measurement circuit according to a fourth embodiment. Graph showing an example of a current flowing in the measurement circuit according to the fourth embodiment. Graph showing an example of a current flowing in the measurement circuit according to the fourth embodiment. Schematic circuit diagram of a first example of a voltage control circuit of a measurement circuit according to a modified example.

[0009] [1. Embodiments] Hereinafter, embodiments of the present disclosure will be described, with reference to the drawings where appropriate. However, the following embodiments are merely examples for explaining the present disclosure, and are not intended to limit the present disclosure to the following content (e.g., the shape, dimensions, and arrangement of each component). Positional relationships, such as up, down, left, and right, are based on the positional relationships shown in the drawings unless otherwise specified. Each figure described in the following embodiments is a schematic diagram, and the ratios of the size and thickness of each component in each figure do not necessarily reflect the actual dimensional ratios. Furthermore, the dimensional ratios of each element are not limited to the ratios shown in the drawings.

[0010] In the following description, when it is necessary to distinguish between multiple components, prefixes such as "first" and "second" are added to the names of the components. However, when the components can be distinguished from each other by the symbols attached to them, the prefixes such as "first" and "second" may be omitted in consideration of readability of the text.

[0011] In the following description, when it is necessary to distinguish between multiple components, suffixes such as "-1" and "-2" are added to the symbols of the components. However, when it is not necessary to distinguish between multiple components, the suffixes "-1" and "-2" may be omitted to improve readability.

[0012] [1.1 First Embodiment] [1.1.1 Configuration] Fig. 1 is a schematic circuit diagram of a measurement circuit 1 according to a first embodiment. The measurement circuit 1 is used to measure a physical quantity. In this embodiment, the physical quantity measured by the measurement circuit 1 is temperature. The temperature is not particularly limited, but may be the temperature of the human body, particularly a predetermined part of the human body. The predetermined part is the esophagus. The measurement circuit 1 is used to measure the temperature of the human esophagus.

[0013] The measurement circuit 1 includes a resistance element array 2 , a voltage control circuit 3 , a selection circuit 4 , a reference resistance element 5 , a current measuring device 6 , a processing circuit 8 , and a constant current source 9 .

[0014] Furthermore, the measurement circuit 1 has a first connection line L1 and a second connection line L2. The first connection line L1 is connected to a constant current source 9. A constant current is supplied to the first connection line L1 from the constant current source 9. The second connection line L2 is connected to ground. In this embodiment, in order to enable the resistor element array 2 to be placed in the human esophagus, the first connection line L1 and the second connection line L2 are configured so that the distance between the resistor element array 2 and the constant current source 9 and the processing circuit 8 can be set to approximately 5 m.

[0015] The constant current source 9 is configured to output a constant current of a set value. The constant current source 9 may be a conventionally known constant current source, and therefore a detailed description thereof will be omitted.

[0016] The resistor element array 2 is used to measure a physical quantity. The resistor element array 2 has m first lines 21-1 to 21-3, n second lines 22-1 to 22-3, and a plurality of measuring resistor elements 20-1 to 20-9. Here, m and n are both integers. m×n≧2. In this embodiment, m=3, n=3, and m×n=9.

[0017] The m first lines 21-1 to 21-3 are independent of each other and are not connected to each other.

[0018] The n second lines 22-1 to 22-3 are independent of each other and are not connected to each other.

[0019] The plurality of measurement resistor elements 20-1 to 20-9 are arranged in a 3x3 array. Although the size of the area in which a single measurement resistor element 20 can measure a physical quantity is limited, by arranging the plurality of measurement resistor elements 20 in an array, it becomes possible to measure the physical quantity over a larger area. In this embodiment, the plurality of measurement resistor elements 20 have the same reference resistance value. The reference resistance value is the resistance value at a predetermined temperature. The predetermined temperature is, for example, 25°C.

[0020] The plurality of measurement resistor elements 20-1 to 20-9 are connected between m first wires 21-1 to 21-3 and n second wires 22-1 to 22-3. In this embodiment, each of the plurality of measurement resistor elements 20-1 to 20-9 is connected between one of the m first wires 21-1 to 21-3 and one of the n second wires 22-1 to 22-3 so that the plurality of measurement resistor elements 20-1 to 20-9 correspond to a plurality of different combinations of the m first wires 21-1 to 21-3 and the n second wires 22-1 to 22-3, respectively.

[0021] Specifically, first ends of the measurement resistors 20-1 to 20-3 are commonly connected to the first wire 21-1, and second ends of the measurement resistors 20-1 to 20-3 are individually connected to the second wires 22-1 to 22-3. First ends of the measurement resistors 20-4 to 20-6 are commonly connected to the first wire 21-2, and second ends of the measurement resistors 20-4 to 20-6 are individually connected to the second wires 22-1 to 22-3. First ends of the measurement resistors 20-7 to 20-9 are commonly connected to the first wire 21-3, and second ends of the measurement resistors 20-7 to 20-9 are individually connected to the second wires 22-1 to 22-3.

[0022] Each measurement resistor element 20 is a resistor element whose resistance value changes depending on the physical quantity of the object to be measured. In this embodiment, the physical quantity of the object to be measured is temperature, and the measurement resistor element 20 is a thermistor. Examples of thermistors include, but are not limited to, NTC (negative temperature coefficient) thermistors, PTC (positive temperature coefficient) thermistors, and CTR (critical temperature resistor) thermistors.

[0023] The voltage control circuit 3 has an input terminal 3a, an output terminal 3b, and an operational amplifier 30 located between the input terminal 3a and the output terminal 3b. The voltage control circuit 3 controls the voltage of the output terminal 3b using the operational amplifier 30 so that the difference between the voltage of the input terminal 3a and the voltage of the output terminal 3b becomes small. The input terminal 3a is connected to the first connection line L1. The voltage of the input terminal 3a corresponds to the voltage of the first connection line L1, i.e., the output voltage of the constant current source 9. The output terminal 3b is connected to the processing circuit 8.

[0024] In this embodiment, the voltage control circuit 3 is a voltage follower. In the voltage control circuit 3, an operational amplifier 30 has a non-inverting input terminal, an inverting input terminal, and an output terminal, and the inverting input terminal and the output terminal are connected to each other. The non-inverting input terminal of the operational amplifier 30 is connected to an input terminal 3a of the voltage control circuit 3, and the output terminal of the operational amplifier 30 is connected to an output terminal 3b of the voltage control circuit 3.

[0025] The selection circuit 4 connects one of the m first lines 21-1 to 21-3 to a first connection line L1, connects one of the n second lines 22-1 to 22-3 to a second connection line L2 that is connected to ground, and connects the remaining m first lines 21-1 to 21-3 and n second lines 22-1 to 22-3 to the output terminal 3b, thereby being able to select a measurement resistance element 20 to which a constant current is supplied from the multiple measurement resistance elements 20-1 to 20-9.

[0026] In this embodiment, the selection circuit 4 has a first selection unit 4a and a second selection unit 4b.

[0027] The first selection unit 4a connects one of the m first lines 21-1 to 21-3 to the first connection line L1 and connects the remaining m first lines 21-1 to 21-3 to the output terminal 3b. The first selection unit 4a has a plurality of controllable changeover switches 41-1 to 41-3. Each of the changeover switches 41-1 to 41-3 has a common terminal, a first terminal, and a second terminal, and is switchable between a first state in which the common terminal is connected to the first terminal and a second state in which the common terminal is connected to the second terminal. The common terminals of the changeover switches 41-1 to 41-3 are connected to the first lines 21-1 to 21-3, respectively. The first terminals of the changeover switches 41-1 to 41-3 are connected to the first connection line L1. The second terminals of the changeover switches 41-1 to 41-3 are connected to the output terminal 3b.

[0028] The second selection unit 4b connects one of the n second lines 22-1 to 22-3 to the second connection line L2 and connects the remaining n second lines 22-1 to 22-3 to the output terminal 3b. The second selection unit 4b has a plurality of controllable changeover switches 42-1 to 42-3. Each of the changeover switches 42-1 to 42-3 has a common terminal, a first terminal, and a second terminal, and is switchable between a first state in which the common terminal is connected to the first terminal and a second state in which the common terminal is connected to the second terminal. The common terminals of the changeover switches 42-1 to 42-3 are connected to the second lines 22-1 to 22-3, respectively. The first terminals of the changeover switches 42-1 to 42-3 are connected to the second connection line L2. The second terminals of the changeover switches 42-1 to 42-3 are connected to the output terminal 3b.

[0029] The reference resistor element 5 is used to correct the output of the resistor element array 2. The reference resistor element 5 is connected between the second connection line L2 and ground. The reference resistor element 5 is a fixed resistor element. If the resistance value of the reference resistor element 5 is too large compared to the reference resistance value of the measurement resistor elements 20, it becomes difficult to obtain a sufficient voltage fluctuation amount in response to changes in the resistance value of the measurement resistor elements 20. Therefore, in this embodiment, the resistance value of the reference resistor element 5 is smaller than the reference resistance values ​​of the multiple measurement resistor elements 20. It is desirable that the resistance value of the reference resistor element 5 be sufficiently lower than the reference resistance values ​​of the measurement resistor elements 20. The resistance value of the reference resistor element 5 depends on the performance of the analog-to-digital converter circuit 8c (described below) or the required correction accuracy, but it is believed that a sufficient voltage fluctuation amount can be obtained if it is 1 / 10 or less of the reference resistance value of the measurement resistor elements 20. Therefore, it is preferable that the resistance value of the reference resistor element 5 be 1 / 10 or less of the reference resistance value of the multiple measurement resistor elements 20.

[0030] The current measuring device 6 measures the current value of the current supplied from the output terminal 3b of the voltage control circuit 3. The current measuring device 6 includes a current measuring resistor element connected to the output terminal 3b of the voltage control circuit 3. In the current measuring device 6, the voltage across the current measuring resistor element indicates the current value of the current supplied from the output terminal 3b of the voltage control circuit 3.

[0031] The processing circuit 8 is a computer system having a processor and memory as hardware, such as a SiP (System in Package). Examples of the processor include a semiconductor integrated circuit (IC), a large scale integrated circuit (LSI), a field programmable gate array (FPGA) that is programmed after the LSI is manufactured, and an ASIC (Application Specific Integrated Circuit).

[0032] The processing circuit 8 is connected to the first selection unit 4a and the second selection unit 4b of the selection circuit 4 so as to be able to control them.

[0033] The processing circuit 8 is connected to the output terminal 3b of the voltage control circuit 3 via an analog-digital converter circuit 8a, and acquires the voltage (voltage value) V1 of the output terminal 3b of the voltage control circuit 3.

[0034] The processing circuit 8 is connected to the current measuring device 6 so as to acquire the voltage across the current measuring resistor element of the current measuring device 6. In this embodiment, the processing circuit 8 is connected to the low-voltage terminal of the current measuring resistor element via an analog-to-digital converter circuit 8b, and acquires the voltage (voltage value) V2 at the low-voltage terminal. As can be seen from FIG. 1 , voltage V2, rather than voltage V1, is input to the inverting input terminal of the operational amplifier 30 of the voltage control circuit 3. Therefore, voltage V2 corresponds to the voltage of the first connection line L1.

[0035] The processing circuit 8 is connected to the second connection line L2 via an analog-to-digital converter circuit 8c, and acquires the voltage (voltage value) V3 of the second connection line L2.

[0036] The processing circuit 8 executes a measurement process to determine values ​​indicating the resistance values ​​of the plurality of measurement resistor elements 20-1 to 20-9 in the resistor element array 2. In the measurement process, the resistance values ​​of the plurality of measurement resistor elements 20-1 to 20-9 in the resistor element array 2 are determined in order. To this end, the processing circuit 8 controls the selection circuit 4 to cause a constant current to flow from the constant current source 9 to one of the plurality of measurement resistor elements 20-1 to 20-9.

[0037] 1, the changeover switch 41-1 of the first selection unit 4a is in the first state, the changeover switches 41-2 and 41-3 are in the second state, and the changeover switch 42-3 of the second selection unit 4b is in the first state, and the changeover switches 42-1 and 42-2 are in the second state. In this case, among the plurality of measurement resistor elements 20-1 to 20-9 of the resistor element array 2, a constant current flows only through the measurement resistor element 20-3 connected between the first line 21-1 and the second line 22-3.

[0038] If the set value of the constant current of the constant current source 9 is I and the resistance value of the measurement resistor 20 is Rv, then V2-V3 can be expressed as V2-V3=I×Rv. Although the constant current source 9 is configured to output a constant current of set value I, the actual current value of the constant current output from the constant current source 9 may not match the set value I due to various factors such as the surrounding environment. Therefore, in order to accurately measure the resistance value Rv of the measurement resistor 20, it is desirable to make a correction taking into account fluctuations in the constant current of the constant current source 9, that is, the deviation of the actual current value of the constant current from the set value I. If the actual current value of the constant current of the constant current source 9 is I1 and the correction value of the constant current is Cal, then Cal can be expressed as Cal=I / I1.

[0039] In this embodiment, the processing circuit 8 calculates a value indicating the resistance value Rv of the measurement resistor element 20 to which the constant current is supplied from the difference between the voltage V2 of the first connection line L1 and the voltage V3 of the second connection line L2 and the constant current correction value Cal. The processing circuit 8 calculates Cal×(V2−V3) as the value indicating the resistance value Rv of the measurement resistor element 20 to which the constant current is supplied. Cal×(V2−V3) corresponds to the voltage across the measurement resistor element 20 when a constant current of the set value I flows through the measurement resistor element 20.

[0040] The processing circuit 8 calculates the correction value Cal of the constant current from the set value I of the constant current, the current value of the current flowing through the reference resistance element 5, which is determined by the voltage between both ends of the reference resistance element 5 (voltage V3 of the second connection line L2) and the resistance value of the reference resistance element 5, and the current value measured by the current measuring instrument 6.

[0041] Next, a method for determining the correction value Cal will be described with reference to FIG. 2. FIG. 2 is an explanatory diagram of an example of the current flowing through the measurement circuit 1. In FIG. 2, as in FIG. 1, a constant current flows only through the measurement resistor element 20-3, which is connected between the first line 21-1 and the second line 22-3, among the multiple measurement resistor elements 20-1 to 20-9 in the resistor element array 2. In FIG. 2, to make it easier to see the current flowing through the measurement circuit 1, the reference numerals of the components of the measurement circuit 1 have been omitted as appropriate, and for reference numerals not shown in FIG. 2, refer to FIG. 1.

[0042] I1 indicates the actual current value of the constant current output from the constant current source 9. I2 indicates the current value of the current output from the output terminal 3b of the voltage control circuit 3. The current output from the output terminal 3b of the voltage control circuit 3 splits into a path via the changeover switch 41-2 and the first line 21-2 and a path via the changeover switch 41-3 and the first line 21-3, then merges together and flows through the second line 22-3 and the changeover switch 42-3 to the reference resistance element 5. Therefore, if the current value of the current flowing through the reference resistance element 5 is I5, I1 is expressed by the following equation (1):

[0043]

[0044] The current value I5 can be calculated from the resistance value of the reference resistor element 5 and the voltage V3 of the second connection line L2. When the resistance value of the reference resistor element 5 is R5, I5 is expressed by the following equation (2).

[0045]

[0046] The current value I2 can be obtained using a current measuring device 6. The difference in voltage between both ends of the current measuring resistor element of the current measuring device 6 is expressed as V1-V2. If the resistance value of the current measuring resistor element is R6, I2 is expressed by the following equation (3).

[0047]

[0048] From equations (1) to (3), the following equation (4) is obtained.

[0049]

[0050] Equation (4) can be transformed into the following equation (5).

[0051]

[0052] Since the resistance value R5 of the reference resistor element 5 and the resistance value R6 of the current measurement resistor element are known, I1 can be expressed from equation (5) as shown in the following equation (6): In equation (6), α=-1 / R6 and β=1 / R5.

[0053]

[0054] Therefore, the correction value Cal=I / I1 of the constant current is expressed by the following equation (7).

[0055]

[0056] The processing circuit 8 uses the correction value Cal to determine a value (= Cal x (V2 - V3)) indicating the resistance value Rv of each measurement resistor element 20 in the resistor element array 2, and determines the temperature at each measurement resistor element 20 from the value indicating the resistance value Rv of each measurement resistor element 20.

[0057] In this embodiment, the measurement resistor element 20 is a thermistor, a device whose resistance value changes with temperature. By supplying a constant current or applying a constant voltage to the thermistor, changes in the temperature of the thermistor can be detected as changes in the voltage across the thermistor or the current flowing through the thermistor. Figure 3 is a graph showing an example of the resistance-temperature characteristics of the measurement resistor element 20. As can be seen from Figure 3, the resistance value Rv of the measurement resistor element 20 decreases as the temperature increases.

[0058] Therefore, if a voltage-temperature conversion equation is determined in advance from the resistance-temperature characteristics of the thermistor and the change in voltage across the thermistor when the constant current source 9 is set to a constant current setting of I, it becomes possible to determine the temperature of the thermistor from the voltage across the thermistor. For example, if the voltage across the thermistor when the constant current source 9 is set to a constant current setting of I is Vth and the temperature of the thermistor is T [°C], T can be expressed by the following equation (8). In equation (8), A and B are parameters. Specifically, the processing circuit 8 can determine the temperature T of the measuring resistor element 20 by substituting Cal×(V2−V3) for Vth in equation (8).

[0059]

[0060] The measurement circuit 1 described above uses a constant current from the constant current source 9 to obtain a value indicating the resistance value Rv of each measurement resistor element 20 in the resistor element array 2. In other words, the voltage across each measurement resistor element 20 is used to evaluate the resistance value Rv of each measurement resistor element 20. This improves noise resistance and measurement accuracy compared to using a constant voltage source to obtain a value indicating the resistance value Rv of each measurement resistor element 20 in the resistor element array 2. Furthermore, when a thermistor is used with a constant voltage source, changes in the thermistor's resistance change the current flowing through the thermistor, which changes the thermistor's self-heating and affects accuracy. In this embodiment, the constant current source 9 allows the current value to be controlled at a constant value, thereby controlling the thermistor's self-heating, thereby improving measurement accuracy and preventing thermal runaway.

[0061] In an actual usage environment, due to problems such as external noise, changes in environmental temperature, and aging, in order to design a constant current source 9 that always flows a constant current with high precision, it may be necessary to take measures such as tightening the circuit size or the control accuracy range of each component. However, in this embodiment, the processing circuit 8 uses the correction value Cal to determine a value indicating the resistance value Rv of each measurement resistive element 20 in the resistive element array 2. Therefore, even if the constant current from the constant current source 9 fluctuates, highly accurate measurements can be performed.

[0062] [1.1.2 Evaluation] Next, to confirm that the measurement accuracy of the measurement circuit 1 has been improved, a simulation was performed to evaluate the measurement accuracy. In the simulation, the error in the constant current of the constant current source 9 was varied to determine the measurement temperature error relative to the measurement temperature. The error of the constant current source 9 is the error relative to the set value of the constant current of the constant current source 9. As described above, if the actual current value of the constant current of the constant current source 9 is I1 and the set value is I, the error of the constant current source 9 is expressed as (I1 - I) / I x 100 [%]. Note that the simulation was performed to confirm that high-precision measurements can be performed even when the constant current from the constant current source 9 fluctuates, and therefore the error of the measurement resistor element 20 was not taken into account.

[0063] FIG. 4 is a graph showing the results of evaluation of the measurement circuit 1 according to the first embodiment. In FIG. 4, the horizontal axis represents the measured temperature (the temperature of the measurement resistor element 20), and the vertical axis represents the temperature measurement error. F1 represents the case where the error of the constant current source 9 is set to +0.5%, F2 represents the case where the error of the constant current source 9 is set to +0.1%, F3 represents the case where the error of the constant current source 9 is set to -0.5%, and F4 represents the case where the error of the constant current source 9 is set to -0.1%. F5 represents the case where the error of the constant current source 9 is set to +0.5%, +0.1%, -0.5%, or -0.1%, and correction is performed using the correction value Cal. It is clear from FIG. 4 that temperature measurement error is reduced by correcting using the correction value Cal.

[0064] [1.1.3 Effects, etc.] The measurement circuit 1 described above has m first lines 21, n second lines 22, and a plurality of measurement resistor elements 20 connected between the m first lines 21 and the n second lines 22, where m×n≧2; an input terminal 3a connected to a first connection line L1 to which a constant current is supplied from a constant current source 9; an output terminal 3b; and an operational amplifier 30 located between the input terminal 3a and the output terminal 3b. The operational amplifier 30 detects the voltage at the input terminal 3a and the voltage at the output terminal 3b. and a selection circuit 4 that connects one of the m first wires 21 to a first connection line L1, connects one of the n second wires 22 to a second connection line L2 that is connected to ground, and connects the remaining m first wires 21 and n second wires 22 to the output terminal 3b, and is capable of selecting, from the plurality of measurement resistor elements 20, a measurement resistor element 20 to which a constant current is supplied. This configuration enables improvements in noise resistance and measurement accuracy.

[0065] The measurement circuit 1 further includes a reference resistor element 5 connected between the second connection line L2 and ground, and a current measuring device 6 that measures the current value I2 of the current supplied from the output terminal 3b. This configuration enables improved measurement accuracy.

[0066] In the measurement circuit 1, the resistance value R5 of the reference resistance element 5 is smaller than the reference resistance values ​​of the plurality of measurement resistance elements 20. This configuration makes it possible to improve measurement accuracy.

[0067] In the measurement circuit 1, the resistance value R5 of the reference resistance element 5 is equal to or less than 1 / 10 of the reference resistance value of the plurality of measurement resistance elements 20. This configuration makes it possible to improve measurement accuracy.

[0068] In the measuring circuit 1, the current measuring device 6 has a current measuring resistor element connected to the output terminal 3b. This configuration makes it possible to simplify the circuit configuration of the measuring circuit 1 and reduce manufacturing costs.

[0069] The measurement circuit 1 further includes a processing circuit 8 that calculates a value indicating the resistance value Rv of the measurement resistor element 20 to which the constant current is supplied, from the difference between the voltage V2 on the first connection line L1 and the voltage V3 on the second connection line L2, and a constant current correction value Cal. The constant current correction value Cal is calculated from the constant current setting value I, the current value I5 of the current flowing through the reference resistor element 5, which is determined by the voltage across the reference resistor element 5 (the voltage V3 on the second connection line L2) and the resistance value R5 of the reference resistor element 5, and the current value I2 measured by the current measuring instrument 6. This configuration enables improved measurement accuracy.

[0070] The measuring circuit 1 further comprises a constant current source 9. This configuration allows for improved measurement accuracy.

[0071] 5 is a schematic circuit diagram of a measurement circuit 1A according to embodiment 2. The measurement circuit 1A includes a resistor array 2, a voltage control circuit 3, a selection circuit 4, a reference resistor 5, a current measuring device 6, a linearization resistor 7, a processing circuit 8A, and a constant current source 9.

[0072] The linearization resistor element 7 is used to set the change width of the voltage of the first connection line L1 in response to changes in the resistance value of the measurement resistor element 20 of the resistor element array 2 within a desired range. The linearization resistor element 7 is connected in parallel with the resistor element array 2 through the first connection line L1. In this embodiment, the linearization resistor element 7 is directly connected to ground. This makes it possible to shorten the path between the linearization resistor element 7 and ground, thereby improving measurement accuracy. The linearization resistor element 7 is a fixed resistor element. The resistance value of the linearization resistor element 7 is set appropriately with respect to the reference resistance value of the measurement resistor element 20.

[0073] The processing circuit 8A executes the measurement process in the same manner as the processing circuit 8, but unlike the processing circuit 8, does not use the correction value Cal.

[0074] The processing circuit 8A determines the resistance value Rv of each measurement resistor 20 in the resistor array 2, and determines the temperature at each measurement resistor 20 from the resistance value Rv of each measurement resistor 20.

[0075] Next, referring to FIG. 6, a method for determining the resistance value Rv of the measurement resistor element 20 to which a constant current is supplied will be described. FIG. 6 is an explanatory diagram of an example of the current flowing through the measurement circuit 1A. In FIG. 6, as in FIG. 5, among the multiple measurement resistor elements 20-1 to 20-9 of the resistor element array 2, a constant current flows only through the measurement resistor element 20-3 connected between the first line 21-1 and the second line 22-3. In FIG. 6, to make it easier to see the current flowing through the measurement circuit 1A, the reference numerals of the components of the measurement circuit 1A have been omitted as appropriate, and for reference numerals not shown in FIG. 6, refer to FIG. 5.

[0076] I1 indicates the actual current value of the constant current output from the constant current source 9. I2 indicates the current value of the current output from the output terminal 3b of the voltage control circuit 3.

[0077] The constant current output from the constant current source 9 is divided into a current flowing through the measurement resistor 20 (20-3) and the reference resistor 5, and a current flowing through the linearization resistor 7. I11 indicates the current value of the current flowing through the measurement resistor 20 (20-3). I12 indicates the current value of the current flowing through the linearization resistor 7. Here, I1 is expressed by the following equation (9):

[0078]

[0079] The current output from the output terminal 3b of the voltage control circuit 3 branches into a path via the changeover switch 41-2 and the first line 21-2 and a path via the changeover switch 41-3 and the first line 21-3, and then these two paths merge and reach the second line 22-3. The second line 22-3 is connected to ground via the changeover switch 42-3, the second connection line L2, and the reference resistor element 5. Therefore, the current output from the output terminal 3b of the voltage control circuit 3 flows from the second line 22-3 to the reference resistor element 5.

[0080] The resistance value Rv of the measuring resistor element 20 is expressed by the following equation (10).

[0081]

[0082] In the reference resistance element 5, the current output from the output terminal 3b of the voltage control circuit 3 flows in the same direction as the constant current output from the constant current source 9. If the current value of the current flowing through the reference resistance element 5 is I5, I5 is expressed by the following equation (11).

[0083]

[0084] From equations (2) and (11), the following equation (12) is obtained.

[0085]

[0086] From equations (3) and (12), I11 is expressed by the following equation (13).

[0087]

[0088] From equations (10) and (13), Rv is expressed by the following equation (14).

[0089]

[0090] Since the resistance value R5 of the reference resistor element 5 and the resistance value R6 of the current measurement resistor element are known, Rv can be obtained from V1, V2, and V3 acquired by the processing circuit 8.

[0091] If a resistance-temperature conversion equation is determined in advance from the resistance-temperature characteristics of the measurement resistor 20, the temperature of the measurement resistor 20 can be determined from the resistance value Rv of the measurement resistor 20. For example, if the temperature of the measurement resistor 20 is T [°C], the relationship between T and Rv is expressed by the following equation (15). In equation (15), A, B, and C are parameters.

[0092]

[0093] Equation (14) does not include the actual current value I1 of the constant current of the constant current source 9. This indicates that Rv is not affected by the constant current source 9. In other words, calculating Rv removes the effect of fluctuations in the constant current of the constant current source 9. Unlike the processing circuit 8, the processing circuit 8A does not use a correction value to correct fluctuations in the constant current of the constant current source 9 in order to calculate Rv.

[0094] [1.2.2 Evaluation] Next, to confirm that the measurement accuracy of the measurement circuit 1A has been improved, a simulation was performed to evaluate the measurement accuracy. In the simulation, the error in the constant current of the constant current source 9 was varied to determine the error in the difference between the voltage V2 of the first connection line L1 and the voltage V3 of the second connection line L2 relative to the measurement temperature, and the error in the resistance value Rv of the measurement resistor element 20 relative to the measurement temperature. The error in the constant current source 9 is the error relative to the set value of the constant current of the constant current source 9. As described above, if the actual current value of the constant current of the constant current source 9 is I1 and the set value is I, the error in the constant current source 9 is expressed as (I1 - I) / I x 100 [%]. Note that the simulation was performed to confirm that high-precision measurements can be performed even when the constant current from the constant current source 9 fluctuates, and therefore the error in the measurement resistor element 20 was not taken into account.

[0095] 7 is a graph showing the error of the difference between the voltage V2 of the first connection line L1 and the voltage V3 of the second connection line L2 versus the measured temperature. The horizontal axis represents the measured temperature (the temperature of the measurement resistor element 20), and the vertical axis represents the error of the difference between the voltage V2 of the first connection line L1 and the voltage V3 of the second connection line L2. F11 represents the median (when the error of the constant current source 9 is 0.0%), F12 represents the case when the error of the constant current source 9 is +0.5%, and F13 represents the case when the error of the constant current source 9 is -0.5%. From FIG. 7, it is clear that the error of the constant current source 9 is reflected in the difference between the voltage V2 of the first connection line L1 and the voltage V3 of the second connection line L2.

[0096] FIG. 8 is a graph showing the error in the resistance value Rv of the measurement resistor 20 versus the measurement temperature. The horizontal axis represents the measurement temperature (the temperature of the measurement resistor 20), and the vertical axis represents the error in the resistance value Rv. F21 represents the median (when the error of the constant current source 9 is 0.0%), F22 represents the case when the error of the constant current source 9 is +0.5%, and F23 represents the case when the error of the constant current source 9 is −0.5%. In FIG. 8, F21, F22, and F23 are all consistent. Therefore, it is clear from FIG. 8 that the error of the constant current source 9 is reduced in the process of calculating the resistance value Rv.

[0097] [1.2.3 Effects, etc.] The measurement circuit 1A described above further includes a linearization resistance element 7 connected in parallel with the resistance element array 2 to the first connection line L1. This configuration makes it possible to set the variation range of the voltage V2 of the first connection line L1 in response to a change in the resistance value Rv of the measurement resistance element 20 within a desired range.

[0098] In the measurement circuit 1A, the linearization resistance element 7 is directly connected to ground. This configuration shortens the path between the linearization resistance element 7 and ground, enabling improvement in measurement accuracy.

[0099] The measurement circuit 1A further includes a reference resistor 5 connected between the second connection line L2 and ground, a current meter 6 that measures the current value I2 of the current supplied from the output terminal 3b, and a processing circuit 8A. The processing circuit 8A calculates the resistance value Rv of the measurement resistor 20 to which the constant current is supplied from the difference between the voltage V2 of the first connection line L1 and the voltage V3 of the second connection line L2, the current value I2 measured by the current meter 6, and the current value I5 of the current flowing through the reference resistor 5, which is determined by the voltage across the reference resistor 5 (the voltage V3 of the second connection line L2) and the resistance value R5 of the reference resistor 5. This configuration enables improved measurement accuracy.

[0100] 9 is a schematic circuit diagram of a measurement circuit 1B according to embodiment 2. The measurement circuit 1B includes a resistor array 2, a voltage control circuit 3, a selection circuit 4, a reference resistor 5, a current measuring device 6, a linearization resistor 7, a processing circuit 8B, and a constant current source 9.

[0101] In the measurement circuit 1B, the linearization resistance element 7 is connected to the second connection line L2 and is connected to the ground via the reference resistance element 5.

[0102] The processing circuit 8B, like the processing circuit 8, executes the measurement process using the correction value Cal.

[0103] Next, with reference to FIG. 10 , a method for calculating the correction value Cal by the processing circuit 8B will be described. FIG. 10 is an explanatory diagram of an example of the current flowing through the measurement circuit 1B. In FIG. 10 , of the multiple measurement resistor elements 20-1 to 20-9 in the resistor element array 2, a constant current flows only through the measurement resistor element 20-3 connected between the first line 21-1 and the second line 22-3. In FIG. 10 , to make it easier to see the current flowing through the measurement circuit 1B, the reference numerals of the components of the measurement circuit 1B have been omitted as appropriate, and for reference numerals not shown in FIG. 10 , refer to FIG. 9.

[0104] As is clear from Figure 10, the constant current output from the constant current source 9 is divided into a current flowing through the measurement resistance element 20 (20-3) and a current flowing through the linearization resistance element 7, but the current flowing through the measurement resistance element 20 (20-3) and the current flowing through the linearization resistance element 7 join at the second connection line L2 and flow to the reference resistance element 5.

[0105] Therefore, the current value I5 of the current flowing through the reference resistance element 5 satisfies I5=I1+I2, and therefore I1=I5-I2. Therefore, in this embodiment, as in the first embodiment, I1 can be expressed by the above formula (6), and the constant current correction value Cal=I / I1 can also be expressed by the above formula (7).

[0106] In the measurement circuit 1B, the linearizing resistor element 7 can set the variation width of the voltage V2 of the first connection line L1 in response to a change in the resistance value Rv of the measurement resistor element 20 within a desired range, but since the linearizing resistor element 7 is connected to the second connection line L2, it is not necessary to take the resistance value R7 of the linearizing resistor element 7 into consideration when calculating the correction value Cal, which makes it possible to simplify the calculation of the correction value Cal.

[0107] [1.3.2 Evaluation] Next, to confirm that measurement accuracy can be improved by measurement circuit 1B, measurement accuracy was evaluated by simulation, and results were obtained that were similar to those of measurement circuit 1. It was confirmed that temperature measurement errors were also reduced in measurement circuit 1B by performing correction using the correction value Cal.

[0108] [1.3.3 Effects, etc.] The measurement circuit 1B described above further includes a linearization resistor element 7 connected to the first connection line L1 in parallel with the resistor element array 2. This configuration makes it possible to set the variation range of the voltage V2 of the first connection line L1 in response to a change in the resistance value Rp of the measurement resistor element 20 within a desired range.

[0109] In the measurement circuit 1B, the linearization resistance element 7 is connected to the second connection line L2. This configuration makes it possible to easily calculate the correction value Cal.

[0110] The measurement circuit 1B further includes a reference resistor 5 connected between the second connection line L2 and ground, a current meter 6 for measuring the current value I2 of the current supplied from the output terminal 3b, and a processing circuit 8B. The processing circuit 8B calculates a value indicating the resistance value Rv of the measurement resistor 20 to which the constant current is supplied from the difference between the voltage V2 of the first connection line L1 and the voltage V3 of the second connection line L2 and a constant current correction value Cal. The constant current correction value Cal is calculated from the constant current setting value I, the current value I5 of the current flowing through the reference resistor 5, which is determined by the voltage across the reference resistor 5 (the voltage V3 of the second connection line L2) and the resistance value R5 of the reference resistor 5, and the current value I2 measured by the current meter 6. This configuration improves measurement accuracy.

[0111] 11 is a schematic circuit diagram of a measurement circuit 1C according to embodiment 4. The measurement circuit 1C includes a resistor array 2, a voltage control circuit 3, a selection circuit 4, a processing circuit 8C, a constant current source 9, and a correction resistor 10. Unlike the measurement circuits 1, 1A, and 1B, the measurement circuit 1C does not include a reference resistor 5, and the second connection line L2 is directly connected to ground.

[0112] The correction resistor element 10 is a linearization resistor element connected in parallel to the resistor element array 2 via the first connection line L1. This allows the change in voltage of the first connection line L1 in response to changes in the resistance value of the measurement resistor element 20 of the resistor element array 2 to be set within a desired range. In this embodiment, the correction resistor element 10 is directly connected to ground. This shortens the path between the correction resistor element 10 and ground, enabling improved measurement accuracy. The correction resistor element 10 is a fixed resistor element. The resistance value of the correction resistor element 10 is set appropriately with respect to the reference resistance value of the measurement resistor element 20.

[0113] The processing circuit 8C is connected to the output terminal 3b of the voltage control circuit 3 via the analog-digital converter circuit 8a, and acquires the voltage (voltage value) V1 of the output terminal 3b of the voltage control circuit 3. As can be seen from Fig. 11, the voltage V1 is input to the inverting input terminal of the operational amplifier 30 of the voltage control circuit 3. Therefore, the voltage V1 of the output terminal 3b corresponds to the voltage of the first connection line L1.

[0114] The measurement circuit 1C determines a value indicating the resistance value Rv of the measurement resistive element 20 to which the constant current is supplied from the voltage V1 of the first connection line L1 (the voltage at the output terminal 3b) and the correction value Cal of the constant current. In this embodiment, the measurement process includes a first process for determining the correction value Cal and a second process for determining the voltage V1 of the first connection line L1 corresponding to the measurement resistive element 20 to which the constant current is supplied.

[0115] In the first process, the processing circuit 8C calculates the correction value of the constant current from the current value of the current flowing through the correction resistor element 10, which is determined by the voltage between both ends of the correction resistor element 10 obtained when none of the m first lines 21 are connected to the first connection line L1 and the resistance value of the correction resistor element 10, and the set value I of the constant current.

[0116] 12 and 13, a method for calculating the correction value Cal in the first process by the processing circuit 8C will be described. FIG. 12 is an explanatory diagram of an example of the current flowing through the measurement circuit 1C in the first process. In FIG. 12, all of the changeover switches 41-1 to 41-3 of the first selection unit 4a are in the second state, and all of the changeover switches 42-1 to 42-3 of the second selection unit 4b are in the second state. In this case, no constant current flows through any of the multiple measurement resistive elements 20-1 to 20-9 of the resistive element array 2. In FIG. 12, to clearly show the current flowing through the measurement circuit 1C, the reference numerals of the components of the measurement circuit 1C have been omitted as appropriate. For reference numerals not shown in FIG. 12, refer to FIG. 11.

[0117] 12, the constant current output from the constant current source 9 flows only through the correction resistor element 10. Therefore, when the resistance value of the correction resistor element 10 is R10, the current value I1 of the constant current output from the constant current source 9 is expressed by the following equation (16):

[0118]

[0119] Since the resistance value R10 of the corrective resistor 10 is known, I1 can be expressed as the following equation (17) from equation (17): In equation (17), α=1 / R10.

[0120]

[0121] Therefore, the correction value Cal=I / I1 of the constant current is expressed by the following equation (18).

[0122]

[0123] In the second process, the processing circuit 8C controls the selection circuit 4 to pass a constant current from the constant current source 9 to one of the multiple measurement resistance elements 20-1 to 20-9, and acquires the voltage V1 at the output terminal 3b of the voltage control circuit 3.

[0124] 13 is an explanatory diagram of an example of the current flowing through the measurement circuit 1C in the second process. In FIG. 13, the selector switch 41-1 of the first selection unit 4a is in the first state, the selector switches 41-2 and 41-3 are in the second state, the selector switch 42-3 of the second selection unit 4b is in the first state, and the selector switches 42-1 and 42-2 are in the second state. Of the multiple measurement resistor elements 20-1 to 20-9 in the resistor array 2, a constant current flows only through the measurement resistor element 20-3 connected between the first line 21-1 and the second line 22-3. In FIG. 13, to clearly show the current flowing through the measurement circuit 1C, the reference numerals of the components of the measurement circuit 1C have been omitted as appropriate. For reference numerals not shown in FIG. 13, refer to FIG. 11.

[0125] 13, the constant current output from the constant current source 9 is divided into a current flowing through the measurement resistor element 20 (20-3) and a current flowing through the correction resistor element 10. As a result, the processing circuit 8C acquires the voltage V1 at the output terminal 3b of the voltage control circuit 3 for the measurement resistor element 20 through which the constant current from the constant current source 9 flows.

[0126] In this embodiment, the first connection line L1 is connected in parallel to the measurement resistor 20 and the correction resistor 10. The voltage V1 at the output terminal 3b is expressed by the following equation (34) using the combined resistance value of the resistance value Rv of the measurement resistor 20 and the resistance value R10 of the correction resistor 10, and the current value I1 of the constant current from the constant current source 9.

[0127]

[0128] If a voltage-temperature conversion equation is determined in advance from the resistance-temperature characteristics of the measuring resistor 20 and the change in voltage V1 at the output terminal 3b when the constant current of the constant current source 9 is set to a value I, it becomes possible to determine the temperature of the measuring resistor 20 from the voltage V1 at the output terminal 3b. For example, if T is the temperature of the measuring resistor 20, T can be expressed by the following equation (20): In the following equation (35), A, B, C, D, E, and F are parameters.

[0129]

[0130] The measurement circuit 1C calculates a value indicating the resistance value Rv of the measurement resistive element 20 to which the constant current is supplied from the correction value Cal of the constant current calculated in the first process and the voltage V1 of the first connection line L1 calculated in the second process. The measurement circuit 1C uses Cal×V1 as a value indicating the resistance value Rv of the measurement resistive element 20 to which the constant current is supplied.

[0131] The measurement circuit 1C may alternately execute the first process and the second process while changing the measurement resistive element 20 to which the constant current is supplied. However, if it is considered that the fluctuation of the constant current is small, the first process may be executed each time the second process is executed multiple times while changing the measurement resistive element 20 to which the constant current is supplied, or the first process may be executed before or after executing the second process for all the measurement resistive elements 20. By reducing the number of times the first process is executed, the time required for the entire measurement process can be shortened.

[0132] [1.4.2 Evaluation] Next, in order to confirm that the measurement accuracy can be improved by the measurement circuit 1 C, the measurement accuracy was evaluated by simulation. The simulation was performed in the same manner as in the first embodiment.

[0133] FIG. 14 is a graph showing the evaluation results of the measurement circuit 1C according to the fourth embodiment. In FIG. 14, the horizontal axis represents the measured temperature (the temperature of the measurement resistor element 20), and the vertical axis represents the temperature measurement error. F31 represents the case where the error of the constant current source 9 is set to +0.5%, F32 represents the case where the error of the constant current source 9 is set to +0.1%, F33 represents the case where the error of the constant current source 9 is set to -0.5%, and F34 represents the case where the error of the constant current source 9 is set to -0.1%. F35 represents the case where the error of the constant current source 9 is set to +0.5%, +0.1%, -0.5%, or -0.1%, and correction is performed using the correction value Cal. It is clear from FIG. 14 that correction using the correction value Cal reduces the temperature measurement error.

[0134] [1.4.3 Effects, etc.] The measurement circuit 1C described above further includes a correction resistor 10 connected in parallel with the resistor array 2 via the first connection line L1, and a processing circuit 8C that calculates a value indicating the resistance value Rv of the measurement resistor 20 to which a constant current is supplied from the voltage V1 of the first connection line L1 and the constant current correction value Cal. The processing circuit 8C calculates the constant current correction value Cal from the voltage across the correction resistor 10 (the voltage V1 of the first connection line L1) obtained when none of the m first wires 21 are connected to the first connection line L1, the current value of the current flowing through the correction resistor 10 determined by the resistance value R10 of the correction resistor 10, and the constant current setting value I. This configuration improves measurement accuracy.

[0135] In the measurement circuit 1C, the correction resistor element 10 is a linearization resistor element connected in parallel with the resistor element array 2. This configuration allows the change in voltage of the first connection line L1 in response to a change in the resistance value of the measurement resistor element 20 to be set within a desired range.

[0136] In the measuring circuit 1C, the second connection line L2 is directly connected to ground. This configuration simplifies the circuit configuration of the measuring circuit 1C and reduces manufacturing costs.

[0137] [2. Modifications] The embodiments of the present disclosure are not limited to the above-described embodiments. The above-described embodiments can be modified in various ways depending on the design, etc., as long as the object of the present disclosure can be achieved. Modifications of the above-described embodiments are listed below. The modifications described below can be applied in appropriate combinations.

[0138] In the following, reference will be made to the symbols used in embodiment 1, even though they are applicable to any of the above embodiments 1 to 4. However, this is merely to simplify the description and is not intended to exclude application to embodiments 2 to 4.

[0139] In one modified example, the configuration of the resistor element array 2 is not particularly limited. The number and arrangement of the measurement resistor elements 20 may be appropriately set depending on the measurement target. The measurement resistor elements 20 are not limited to thermistors, and may be resistor elements whose resistance value changes depending on the target physical quantity, for example, resistor elements whose resistance value changes depending on mechanical deformation such as vibration or distortion. Furthermore, the number of first wires 21 may be one or more, and the number of second wires 22 may be one or more, but it is preferable that the number of first wires 21 and the number of second wires 22 do not simultaneously equal one.

[0140] In one modification, the configuration of the voltage control circuit 3 is not particularly limited. The voltage control circuit 3 may be configured to control the voltage at the output terminal 3b using an operational amplifier and / or transistor located between the input terminal 3a and the output terminal 3b so as to reduce the difference between the voltage at the input terminal 3a and the voltage at the output terminal 3b. Figures 15 and 16 show voltage control circuits 3D and 3E of measurement circuits according to modifications.

[0141] As shown in FIG. 15, the voltage control circuit 3D is a buffer circuit using transistors. The buffer circuit of FIG. 15 is also called a diamond buffer circuit. The voltage control circuit 3D has an input terminal 3a, an output terminal 3b, and transistors Q1 to Q4 located between the input terminal 3a and the output terminal 3b. The voltage control circuit 3D controls the voltage at the output terminal 3b using the transistors Q1 to Q4 so that the difference between the voltage at the input terminal 3a and the voltage at the output terminal 3b is small. More specifically, the voltage control circuit 3D includes four transistors Q1 to Q4 and resistors R31 and R32. The transistors Q1 and Q4 are PNP-type bipolar transistors, and the transistors Q2 and Q3 are NPN-type bipolar transistors. The emitter of the transistor Q1 is connected to the internal power supply Vcc via the resistor R31, the collector is connected to ground, and the base is connected to the input terminal 3a. The collector of transistor Q2 is connected to the internal power supply Vcc, the emitter is connected to ground via resistor R32, and the base is connected to input terminal 3a. The collector of transistor Q3 is connected to the internal power supply Vcc, the emitter is connected to output terminal 3b, and the base is connected between the emitter of transistor Q1 and resistor R31. The emitter of transistor Q4 is connected to output terminal 3b, the collector is connected to ground, and the base is connected between the emitter of transistor Q2 and resistor R32.

[0142] As shown in FIG. 16 , the voltage control circuit 3E is an amplifier circuit with an amplification factor of 1. The voltage control circuit 3E has an input terminal 3a, an output terminal 3b, and operational amplifiers 31 and 32 located between the input terminal 3a and the output terminal 3b. The voltage control circuit 3E controls the voltage at the output terminal 3b using the operational amplifiers 31 and 32 so as to reduce the difference between the voltage at the input terminal 3a and the voltage at the output terminal 3b. More specifically, the voltage control circuit 3E includes the operational amplifiers 31 and 32 and resistors R33 to R36. The operational amplifier 31 has a non-inverting input terminal connected to ground, an inverting input terminal connected to the input terminal 3a via resistor R33, and an output terminal connected to the inverting input terminal via resistor R34. The operational amplifier 32 has a non-inverting input terminal connected to ground, an inverting input terminal connected to the output terminal of the operational amplifier 31 via resistor R35, and an output terminal used as the output terminal 3b of the voltage control circuit 3E and connected to the inverting input terminal via resistor R36.

[0143] In one modified example, there is no particular limitation on the configuration of the selection circuit 4. The selection circuit 4 may have a configuration that can selectively pass a constant current through any number of the measurement resistive elements 20 among the plurality of measurement resistive elements 20 in the resistive element array 2.

[0144] In one modification, the reference resistance element 5 may be a single resistance element or a circuit configured of a plurality of resistance elements. The reference resistance element 5 is not essential and may be omitted.

[0145] In one modified example, the current measuring device 6 is not limited to a configuration including a current measuring resistor element, but may be a conventionally known configuration such as a current transformer.

[0146] In one modification, the linearization resistance element 7 may be a single resistance element or a circuit configured of a plurality of resistance elements. The linearization resistance element 7 is not essential and may be omitted.

[0147] In one modification, the linearization resistance element 7 may be a single resistance element or a circuit configured of a plurality of resistance elements. The linearization resistance element 7 is not essential and may be omitted.

[0148] In one modified example, the correction resistor element 10 does not need to be constantly connected to the first connection line L1, but may be configured to be connectable to the first connection line L1 when the resistor element array 2 is separated from the first connection line L1. "Connectable" means that the correction resistor element 10 may be capable of being disconnected from the first connection line L1 by a switch or the like. For example, the correction resistor element 10 may be connected to the first connection line L1 via a switch, and the switch may be turned on in the first process and turned off in the second process.

[0149] [3. Aspects] As is clear from the above-described embodiment and modifications, the present disclosure includes the following aspects.

[0150] [Aspect 1] A measurement circuit comprising: a resistor array having m first lines, n second lines, and a plurality of measurement resistor elements connected between the m first lines and the n second lines, where m×n≧2; a voltage control circuit having an input terminal connected to a first connection line to which a constant current is supplied from a constant current source, an output terminal, and an operational amplifier and / or a transistor between the input terminal and the output terminal, the voltage control circuit controlling the voltage of the output terminal by the operational amplifier and / or the transistor so that a difference between the voltage of the input terminal and the voltage of the output terminal becomes small; and a selection circuit connecting one of the m first lines to the first connection line, connecting one of the n second lines to a second connection line connected to ground, and connecting the remaining m first lines and the n second lines to the output terminal, so that the measurement resistor element to which the constant current is supplied can be selected from the plurality of measurement resistor elements.

[0151] [Aspect 2] The measurement circuit of Aspect 1, further comprising: a reference resistor element connected between the second connection line and the ground; and a current measuring device that measures the current value of the current supplied from the output terminal.

[0152] [Aspect 3] The measurement circuit of Aspect 2, wherein the resistance value of the reference resistance element is smaller than the reference resistance values ​​of the plurality of measurement resistance elements.

[0153] [Aspect 4] The measurement circuit of Aspect 3, wherein the resistance value of the reference resistance element is 1 / 10 or less of the reference resistance value of the plurality of measurement resistance elements.

[0154] [Aspect 5] The measurement circuit according to any one of Aspects 2 to 4, wherein the current measuring device has a current measuring resistive element connected to the output terminal.

[0155] [Aspect 6] The measurement circuit of any one of Aspects 2 to 5, further comprising a processing circuit that determines a value indicating a resistance value of a measurement resistor element to which the constant current is supplied, from a difference between a voltage of the first connection line and a voltage of the second connection line and a correction value of the constant current, wherein the correction value of the constant current is determined from a set value of the constant current, a current value of a current flowing through the reference resistor element, which is determined by the voltage across the reference resistor element and the resistance value of the reference resistor element, and a current value measured by the current measuring device.

[0156] Aspect 7 The measurement circuit of Aspect 1, further comprising a linearization resistor connected in parallel with the resistor array to the first connection line.

[0157] [Aspect 8] The measurement circuit of aspect 7, wherein the linearization resistance element is directly connected to ground.

[0158] [Aspect 9] The measurement circuit of Aspect 8 further comprises: a reference resistor connected between the second connection line and the ground; a current measuring device that measures the current value of the current supplied from the output terminal; and a processing circuit that determines the resistance value of the measurement resistor to which the constant current is supplied, from the difference between the voltage of the first connection line and the voltage of the second connection line, the current value measured by the current measuring device, and the current value of the current flowing through the reference resistor, which is determined by the voltage across the reference resistor and the resistance value of the reference resistor.

[0159] [Aspect 10] The measurement circuit of Aspect 7, wherein the linearization resistance element is connected to the second connection line.

[0160] [Aspect 11] The measurement circuit of Aspect 10 further comprises: a reference resistor element connected between the second connection line and the ground; a current measuring device that measures the current value of the current supplied from the output terminal; and a processing circuit that determines a value indicating the resistance value of the measurement resistor element to which the constant current is supplied, from the difference between the voltage of the first connection line and the voltage of the second connection line and a correction value of the constant current, wherein the correction value of the constant current is determined from the set value of the constant current, the current value of the current flowing through the reference resistor element, which is determined by the voltage across the reference resistor element and the resistance value of the reference resistor element, and the current value measured by the current measuring device.

[0161] [Aspect 12] The measurement circuit of Aspect 1 further comprises: a correction resistor element connectable in parallel with the resistor element array to the first connection line; and a processing circuit that determines a value indicating a resistance value of a measurement resistor element to which the constant current is supplied, from the voltage of the first connection line and a correction value of the constant current, wherein the processing circuit determines the correction value of the constant current from a set value of the constant current and a current value of a current flowing through the correction resistor element, which is determined by the voltage value of the voltage between both ends of the correction resistor element obtained when none of the m first lines are connected to the first connection line and the resistance value of the correction resistor element.

[0162] [Aspect 13] The measurement circuit of Aspect 12, wherein the correction resistor element is a linearization resistor element connected in parallel with the resistor element array.

[0163] [Aspect 14] The measurement circuit according to claim 12 or 13, wherein the second connection line is directly connected to the ground.

[0164] [Aspect 15] The measurement circuit according to any one of Aspects 1 to 14, further comprising the constant current source.

[0165] Aspects 2 to 15 are optional elements and are not essential.

[0166] The present disclosure is applicable to a measurement circuit, particularly to a measurement circuit including a resistive element array.

[0167] 1, 1A, 1B, 1C Measuring circuit 2 Resistor element array 20 Measuring resistor element 21 First line 22 Second line 3, 3D, 3E Voltage control circuit 3a Input terminal 3b Output terminal 4 Selection circuit 5 Reference resistor element 6 Current measuring device 7 Linearization resistor element 8, 8A, 8B, 8C Processing circuit 9 Constant current source 10 Correction resistor element

Claims

1. A measurement circuit comprising: a resistor array having m first lines, n second lines, and a plurality of measurement resistor elements connected between the m first lines and the n second lines, where m×n≧2; a voltage control circuit having an input terminal connected to a first connection line to which a constant current is supplied from a constant current source, an output terminal, and an operational amplifier and / or a transistor between the input terminal and the output terminal, the voltage control circuit controlling the voltage of the output terminal by the operational amplifier and / or the transistor so that a difference between the voltage of the input terminal and the voltage of the output terminal becomes small; and a selection circuit connecting one of the m first lines to the first connection line, connecting one of the n second lines to a second connection line connected to ground, and connecting the remaining m first lines and the n second lines to the output terminal, thereby enabling selection of the measurement resistor element to which the constant current is supplied from the plurality of measurement resistor elements.

2. The measurement circuit of claim 1, further comprising: a reference resistive element connected between said second connection line and said ground; and a current measuring device that measures the current value of the current supplied from said output terminal.

3. The measurement circuit according to claim 2, wherein the resistance value of the reference resistance element is smaller than the reference resistance values ​​of the plurality of measurement resistance elements.

4. The measurement circuit according to claim 3, wherein the resistance value of the reference resistance element is 1 / 10 or less of the reference resistance value of the plurality of measurement resistance elements.

5. The measurement circuit according to any one of claims 2 to 4, wherein the current measuring device has a current measuring resistor element connected to the output terminal.

6. The measurement circuit of any one of claims 2 to 5, further comprising a processing circuit which determines a value indicating a resistance value of a measurement resistive element to which the constant current is supplied, from a difference between the voltage of the first connection line and the voltage of the second connection line and a correction value of the constant current, wherein the correction value of the constant current is determined from a set value of the constant current, a current value of a current flowing through the reference resistive element determined by the voltage between both ends of the reference resistive element and the resistance value of the reference resistive element, and a current value measured by the current measuring device.

7. The measurement circuit according to claim 1, further comprising a linearization resistor element connected in parallel with said resistor array to said first connection line.

8. The measurement circuit according to claim 7, wherein the linearization resistance element is directly connected to ground.

9. The measurement circuit of claim 8, further comprising: a reference resistor element connected between the second connection line and the ground; a current meter that measures a current value of a current supplied from the output terminal; and a processing circuit that determines a resistance value of the measurement resistor element to which the constant current is supplied, from a difference between a voltage of the first connection line and a voltage of the second connection line, the current value measured by the current meter, and a current value of a current flowing through the reference resistor element, the current value being determined by the voltage across the reference resistor element and the resistance value of the reference resistor element.

10. The measurement circuit according to claim 7, wherein the linearization resistance element is connected to the second connection line.

11. The measurement circuit of claim 10, further comprising: a reference resistor element connected between the second connection line and the ground; a current meter that measures the current value of the current supplied from the output terminal; and a processing circuit that determines a value indicating the resistance value of the measurement resistor element to which the constant current is supplied, from the difference between the voltage of the first connection line and the voltage of the second connection line and a correction value of the constant current, wherein the correction value of the constant current is determined from the set value of the constant current, the current value of the current flowing through the reference resistor element, which is determined by the voltage between both ends of the reference resistor element and the resistance value of the reference resistor element, and the current value measured by the current meter.

12. The measurement circuit of claim 1, further comprising: a correction resistor element connectable in parallel with the resistor element array for the first connecting line; and a processing circuit that determines a value indicating a resistance value of a measurement resistor element to which the constant current is supplied, from the voltage of the first connecting line and the correction value of the constant current, wherein the processing circuit determines the correction value of the constant current from a set value of the constant current and a current value of a current flowing through the correction resistor element, which is determined by the resistance value of the correction resistor element and the voltage value of the voltage between both ends of the correction resistor element obtained in a state in which none of the m first lines are connected to the first connecting line.

13. The measurement circuit according to claim 12, wherein the compensation resistor element is a linearization resistor element connected in parallel with the resistor array.

14. The measurement circuit according to claim 12 or 13, wherein the second connection line is directly connected to the ground.

15. The measurement circuit according to any one of claims 1 to 14, further comprising the constant current source.

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