JP2020085714A - Integration type current voltage conversion circuit, current measurement device and resistance measurement device - Google Patents

Abstract

To convert a current of a large current value into a voltage by an integration in a specified lapse time even if a capacitance value of an integration capacitor is subject to an upper limit.SOLUTION: An integration type current voltage conversion circuit has a computation amplifier 14 with a feedback circuit 15 connected between a reverse input terminal and output terminal, and converts a detection current I into a detection voltage Vo and outputs the detected voltage. The feedback circuit 15 has: capacitors 15ato 15a; and switches 15bto 15bthat are connected to between the output terminal and the reverse input terminal with the capacitor 15a corresponding to a selection range as an integration capacitor. The integration type current voltage conversion circuit comprises: a voltage variable power source 17 that outputs action voltages Vcc and Vee for the computation amplifier 14; a storage unit 18 in which a set of the capacitor 15a and voltage value of an action voltage, which correspond to each selection range, is stored; and a processing unit 20 that reads the set of the capacitor 15a and voltage value corresponding to the selection range from the storage unit 18, uses the capacitor 15 as the integration capacitor, and changes the action voltages Vcc and Vee from a power source 17 to the voltage value.SELECTED DRAWING: Figure 1

Description

The present invention relates to an integral type current-voltage conversion circuit, a current measuring device having this current-voltage converting circuit, and a resistance measuring device having this current-measuring device.

The basic circuit configuration of this type of integration-type current-voltage conversion circuit is disclosed in Patent Document 1 below as a configuration of an electrical measuring device as a conventional example. This electric measuring device is applied to a current measuring device, and as shown in FIG. 4, the current measuring device 51 has a predetermined measuring voltage V1 (current measuring device 51) to be applied to the resistor Rx to be measured. DC voltage source 52 for outputting a DC constant voltage with reference to the potential of the ground G as the reference potential in the above, and ON/OFF of application of the measured voltage V1 output from the DC voltage source 52 to the resistor Rx to be measured. A switch 53 for performing the measurement and a current-voltage conversion circuit 54 of an integration type that converts the current I flowing through the resistor Rx to be measured into a voltage (detection voltage) Vo and outputs the voltage I when the measurement voltage V1 is applied. In the current-voltage conversion circuit 54, an integrating capacitor 54b is connected between an inverting input terminal and an output terminal, and a non-inverting input terminal is connected to the ground G, and the operational amplifier is configured as an inverting amplification type integrator. 54a. The inverting input terminal of the operational amplifier 54a is connected to the measured resistor Rx via the switch 53. In addition, the current-voltage conversion circuit 54 includes a discharge circuit 54c that is formed of a series circuit of a resistor and a switch and that is connected in parallel with the integrating capacitor 54b.

In the current measuring device 51, when measuring the current I, first, the discharge circuit 54c is operated while the switch 53 is in the OFF state (the switch of the discharge circuit 54c is in the ON state). Be). Accordingly, the discharging circuit 54c short-circuits the integrating capacitor 54b (in this example, via the resistor in the discharging circuit 54c) to discharge the integrating capacitor 54b charged in the previous measurement, The charging voltage Vc of the integrating capacitor 54b is returned to zero volts. In this case, as shown in FIG. 5, the voltage Vo output from the current-voltage conversion circuit 54 is also returned to zero volts.

Next, as shown in FIG. 5, the operation of the discharge circuit 54c is stopped (the switch of the discharge circuit 54c is shifted to the off state), and subsequently, the switch 53 is shifted from the off state to the on state, After being kept in the on state for an integration period Ti (a period slightly longer than the elapsed time Ta from the first sampling time t1 to the second sampling time t2, which will be described later), which is a predetermined constant time, it is turned off. Will be returned. In the figure, after the operation of the discharge circuit 54c is stopped, the switch 53 is changed from the off state to the on state with a slight time lapse, and the discharge circuit 54c is operated at the same time when the switch 53 is changed to the off state. The switch 53 may be switched from the off state to the on state at the same time when the operation of the discharge circuit 54c is stopped, or the discharge circuit 54c may be operated after the switch 53 is switched from the off state.

Since the end of the measured resistor Rx on the side of the current-voltage conversion circuit 54 is virtually connected to the ground G via the pair of input terminals (the inverting input terminal and the non-inverting input terminal) of the operational amplifier 54a, During the integration period Ti, the measurement voltage V1 is continuously applied to the resistor Rx to be measured. As a result, in the integration period Ti, as shown in FIG. 4, the operational amplifier of the current-voltage conversion circuit 54 is passed from the DC voltage source 52 via the switch 53 in the ON state and the integration capacitor 54b of the current-voltage conversion circuit 54. The current I flows through the path to the output terminal of 54a (the path indicated by the chain line). The integrating capacitor 54b is continuously charged by this current I, and its charging voltage Vc increases in voltage value in proportion to time.

In this case, since the end (one end) of the integrating capacitor 54b connected to the inverting input terminal of the operational amplifier 54a is virtually connected to the ground G, the other end of the integrating capacitor 54b is connected. From the output terminal of the operational amplifier 54a, the negative voltage (negative voltage) having the same absolute value as the charging voltage Vc is output as the voltage Vo. Therefore, the voltage Vo decreases in proportion to time during the integration period Ti, as shown in FIG.

In this case, assuming that the capacitance value of the integrating capacitor 54b is represented by the symbol C and the current value of the current I is represented by the same symbol I as the current I, the variation Va(1 The differential voltage value between the voltage value of the voltage Vo at the second sampling time t1 and the voltage value of the voltage Vo at the second sampling time t2 is represented by the following formula.
Va=-(I*Ta/C)
Accordingly, the current value I of the current I is calculated by I=|Va|×C/Ta.

In addition, in the current measuring device 51, after the measurement of the change amount Va is completed, the switch 53 is turned off and the discharge circuit 54c is operated. As a result, the charged integrating capacitor 54b is discharged and the charging voltage Vc is returned to zero volt, so that the voltage Vo is returned to zero volt.

By the operation of integrating the current I in the current-voltage conversion circuit 54 and converting it into the voltage Vo, the influence of the noise component included in the current I on the voltage Vo can be reduced, and the degree of this reduction is the elapsed time Ta described above. The longer the time, the larger the time Ta, but the longer the elapsed time Ta, the longer the measurement time of the current I (the time required to complete the measurement). Therefore, the elapsed time Ta is defined in advance as a constant time determined by the balance between the degree of noise reduction and the measurement time. Along with this, the integration period Ti is also defined in advance as a fixed time slightly longer than the elapsed time Ta.

By the way, in the current-voltage conversion circuit 54 having such a configuration that the elapsed time Ta is constant and, as a result, the integration period Ti is also constant, one integration capacitor 54b is provided (one measurement range is provided). In this case, the maximum value of the charging voltage Vc in the integration period Ti increases as the current value I of the current I increases. Further, the voltage Vo as a negative voltage has a maximum absolute voltage value that increases as the current value I of the current I increases. In this case, the maximum absolute voltage value of the voltage Vo is limited by the voltage value of the operating voltage of the operational amplifier 54a.

Therefore, in order to measure the current I of a larger current value I, as shown in FIG. 6 as an example, the switch 54d ₁ is connected in series to the capacitor 54b ₁ as the integrating capacitor 54b, and this series circuit is connected. Capacitors 54b ₂ ,..., Capacitors 54b _n (n that are connected between the inverting input terminal and the output terminal of the operational amplifier 54a and have a larger capacitance value than the capacitor 54b _{1 and} that sequentially increase in capacitance value. Is an integer greater than or _{equal to 2.} Switches 54d ₂ ,..., 54d _n (including switch 54d ₁ (including switch 54d ₁ ) are also connected in series with capacitor 54b ₁ unless otherwise specified). 54d), and each of these series circuits is connected between the inverting input terminal and the output terminal of the operational amplifier 54a. Then, of the capacitors 54b ₁ , 54b ₂ ,..., 54b _n , the capacitor 54b corresponding to the current value I of the current I is selected, and the switch 54d connected in series to the selected capacitor 54d is turned on. By doing so, the selected capacitor 54d is connected as an integrating capacitor between the inverting input terminal and the output terminal of the operational amplifier 54a.

By adopting this configuration, the maximum voltage value of the charging voltage Vc (that is, the voltage Vo) during the integration period Ti can be suppressed to be less than the voltage value of the operating voltage of the operational amplifier 54a, and the current having a larger current value I can be obtained. It becomes possible to convert I into the voltage Vo.

As a specific example, in the current-voltage conversion circuit 54 shown in FIG. 4, the operational amplifier 54a receives an operating voltage of ±3.3 V (positive voltage Vcc=3.3 V, negative voltage Vee=−3.3 V). Is operated and the integration period Ti is regulated to, for example, 2.2 ms (time slightly longer than the elapsed time Ta=2 ms), the capacitor 54b having a capacitance value of 1.0 μF is connected as an integration capacitor. There is. In the current-voltage conversion circuit 54 having this configuration, the maximum absolute voltage value of the voltage Vo when the current value I is 1 mA is 2.2 V, which is within the range of the above-mentioned operating voltage, so that the elapsed time Ta It is possible to measure the current value I up to 1 mA based on the change amount Va of the voltage Vo (first range, see FIG. 7).

However, if the current value I to be measured is increased to 5 mA, the maximum absolute voltage value of the voltage Vo when the current value I is 5 mA becomes 11 V in the configuration in which the 1 μF capacitor 54b is used as the integrating capacitor. Exceeds the operating voltage range. Therefore, as in the configuration shown in FIG. 6, the switch 54d ₁ is connected in series by using the 1.0 μF capacitor 54b as the capacitor 54b ₁ and the series circuit is connected between the inverting input terminal and the output terminal of the operational amplifier 54a. In addition, a 4.7 μF capacitor, which is larger than the capacitor 54b ₁ , is used as the capacitor 54b ₂ and the switch 54d ₂ is connected in series to connect the series circuit between the inverting input terminal and the output terminal of the operational amplifier 54a. In the current-voltage conversion circuit 54 having this configuration, for the current I up to 1 mA, only the switch 54d ₁ is turned on to use the capacitor 54b ₁ as an integrating capacitor, and for the current I over 1 mA up to 5 mA, the switch 54 d ₁ is used. By turning on only 54d ₂ , the capacitor 54b ₂ is used as an integrating capacitor. In this case, when the current value I is 5 mA, the maximum absolute voltage value of the voltage Vo is 2.3 V, which is within the range of the above operating voltage, so that the current value I up to 5 mA can be measured. (Second range, see FIG. 7).

Furthermore, a 10 μF capacitor larger than the capacitor 54b ₂ is used as the capacitor 54b ₃ and the switch 54d ₃ is connected in series, and this series circuit is connected between the inverting input terminal and the output terminal of the operational amplifier 54a. In the current-voltage conversion circuit 54 having this configuration, for the current I up to 1 mA, only the switch 54d ₁ is turned on to use the capacitor 54b ₁ as an integrating capacitor, and for the current I over 1 mA up to 5 mA, By turning on only 54d ₂ , the capacitor 54b ₂ is used as an integrating capacitor, and for the current I exceeding 5 mA to 10 mA, turning on only the switch 54d ₃ causes the capacitor 54b ₃ to be used as an integrating capacitor. use. In this case, the maximum absolute voltage value of the voltage Vo when the current value I is 10 mA is 2.2 V, which is within the range of the above operating voltage, and therefore the current value I up to 10 mA can be measured. (3rd range, see FIG. 7).

Japanese Unexamined Patent Publication No. 2013-29466 (page 3-4, FIG. 3-4)

However, in the current-voltage conversion circuit 54, a capacitor satisfying a predetermined condition as the integrating capacitor (for example, the charging voltage Vc needs to be returned (reset) to zero volt, so that the condition that the dielectric absorption characteristic is excellent is required. Capacitors such as Teflon (registered trademark) type capacitors, polystyrene type capacitors, polypropylene type capacitors, etc. must be used, but there are few capacitors with large capacitance values. However, even if an attempt is made to convert the current I having a larger current value I into the voltage Vo, there is a problem to be solved that it cannot be converted because it is limited by the operating voltage of the operational amplifier 54a. For example, as shown in FIG. 7, even if the fourth range for measuring the current value I up to 50 mA is added to the measurement range, when the capacitance value of the capacitor satisfying the above conditions is about 22 μF at the maximum. , The maximum absolute voltage value of the voltage Vo when the current value I is 50 mA when using this capacitor is 5.0 V, which exceeds the range of the above operating voltage, the current value I of 50 mA is It cannot be converted to Vo.

In this case, it is possible to adopt a configuration in which a plurality of capacitors are connected in parallel to form an integrating capacitor. However, considering the increase in the mounting area on the board, the number of capacitors connected in parallel is limited, so the voltage Vo is converted. Although the possible current value I can be slightly increased, it is difficult to sufficiently solve the above problems.

The present invention has been made in view of the above problems, and converts a current having a large current value into a voltage by an integration operation in a predetermined elapsed time even in a situation where the capacitance value of the integrating capacitor has an upper limit. The main object of the present invention is to provide an integration-type current-voltage conversion circuit that can be used. Another main object is to provide a current measuring device having this current-voltage converting circuit and a resistance measuring device having this current measuring device.

In order to achieve the above object, in the current-voltage conversion circuit according to claim 1, the non-inverting input terminal is defined as a reference potential, and a feedback circuit including an integrating capacitor is connected between the inverting input terminal and the output terminal. A detection circuit configured to include an operational amplifier, the detection current supplied to the inverting input terminal appearing as a voltage with the reference potential as a reference in accordance with the charging voltage of the integrating capacitor charged with the detection current. An integration-type current-voltage conversion circuit that converts the voltage into a voltage and outputs the voltage from the output terminal, wherein the feedback circuit corresponds to any one measurement range selected from a plurality of capacitors and a plurality of measurement ranges. And a switch unit for connecting one or more capacitors among the plurality of capacitors as the integrating capacitors between the output terminal and the inverting input terminal, and an operating voltage for the operational amplifier. A variable voltage power supply capable of changing the voltage value and outputting the voltage, the one or more capacitors corresponding to the measurement range, and the combination of the voltage values corresponding to the measurement range are the plurality of measurement ranges. A storage unit stored in association with the control unit, and the control unit sets the selected measurement range to the selected measurement range when any one measurement range is selected from the plurality of measurement ranges. The corresponding one or more capacitors and the combination of the voltage values are read from the storage unit, and the read one or more capacitors are used as the integrating capacitors for the output terminal and the inverting input terminal. Range switching control to be connected between the voltage variable power supply and the switch section, and voltage switching control to change the operating voltage to the read voltage value and output the voltage value.

The current-voltage conversion circuit according to claim 2 is the integration-type current-voltage conversion circuit according to claim 1, wherein the voltage variable power supply has positive and negative voltages as operating voltages for the operational amplifier. It is configured to be able to output by changing the value.

The current measuring device according to claim 3 comprises the integral type current-voltage conversion circuit according to claim 1 or 2, and a processing part, wherein the processing part defines a voltage value of the detection voltage in advance for a predetermined time. Voltage measurement process for measuring twice by opening, a differential voltage value between two voltage values obtained by the two measurements, and one or more capacitors of the one or more capacitors corresponding to the selected measurement range. And a current measurement process for measuring the current value of the detected current based on the capacitance value and the elapsed time.

A resistance measuring device according to a fourth aspect includes the current measuring device according to the third aspect and a DC voltage source that outputs a measurement voltage based on the reference potential, and the processing unit includes the inverting input terminal. And a current flowing through the measurement target while applying the measurement voltage from the DC voltage source to the measurement target connected between the DC voltage source and the DC voltage source, the current measurement process is executed. The resistance value of the detected current is measured, and the resistance measurement process of measuring the resistance value of the measurement target is executed based on the measured current value and the voltage value of the measurement voltage.

According to the current-voltage conversion circuit of the first aspect, even when the capacitance value of the capacitor used as the integrating capacitor has an upper limit, the voltage value of the operating voltage of the operational amplifier is set to a larger current value. Since it can be changed to the voltage value corresponding to the measurement range for measurement, it is possible to accurately convert the detected current to the detected voltage by the integration operation for a predetermined elapsed time without being restricted by the operating voltage. You can

Further, according to the current-voltage conversion circuit of the second aspect, since the voltage variable power supply is configured to be able to output by changing each voltage value of the positive voltage and the negative voltage as the operating voltage for the operational amplifier, it is possible to perform the detection. Due to the configuration in which the current is supplied to the inverting input terminal of the operational amplifier, the configuration is not limited to the configuration in which the detection voltage is output as a negative voltage with the reference potential as a reference, but the configuration in which the detection current flows in the reverse direction Thus, even in the configuration in which the detection voltage is output as a positive voltage with the reference potential as the reference, the detection current can be accurately converted into the detection voltage by the integration operation in the elapsed time without being limited by the operation voltage. ..

Further, according to the current measuring device of claim 3, since the current-voltage converting circuit is provided, the accurate voltage value for two times measured by the accurate detection voltage output from the current-voltage converting circuit. The current value of the detected current up to the maximum measured current value in the selected range can be accurately measured based on the accurate differential voltage value calculated from

Further, according to the resistance measuring device of claim 4, since the current measuring device is provided, the object to be measured is based on the voltage value of the measurement voltage and the current value accurately measured by the current measuring device. The resistance value of can be measured accurately.

It is a block diagram which shows each structure of the current voltage conversion circuit 1, the current measuring device 2, and the resistance measuring device 3. It is explanatory drawing for demonstrating each measurement range from the 1st range to the 6th range in the current voltage conversion circuit 1 of FIG. 4 is an explanatory diagram for explaining each operation of the current-voltage conversion circuit 1, the current measuring device 2, and the resistance measuring device 3. FIG. It is a block diagram which shows each structure of the conventional current voltage conversion circuit 54 and the current measuring device 51. FIG. 6 is an explanatory diagram for explaining each operation of the current-voltage conversion circuit 54 and the current measuring device 51. It is a block diagram which shows each structure of the conventional current-voltage conversion circuit 54 and the current measurement apparatus 51 provided with the some measurement range. It is explanatory drawing for demonstrating each measurement range from the 1st range in the current voltage conversion circuit 54 of FIG. 6 to the 4th range.

Embodiments of an integral type current-voltage conversion circuit, a current measuring device, and a resistance measuring device will be described below with reference to the accompanying drawings.

First, regarding the configuration of the current-voltage conversion circuit 1 as the current-voltage conversion circuit, the configuration of the current measurement device 2 including the current-voltage conversion circuit 1, and the configuration of the resistance measurement device 3 including the current measurement device 2, FIG. Will be described.

The current-voltage conversion circuit 1 includes a signal input unit 11, a signal output unit 12, a switch 13, an operational amplifier 14, a feedback circuit 15, a discharge circuit 16, a voltage variable power supply 17, a storage unit 18, an operation unit 19 and a processing unit 20. Then, the detection current I input from the signal input unit 11 is integrated over a predetermined integration period Ti (the ON period of the switch 13) to obtain a reference potential (in this example, the current-voltage conversion circuit 1, The potential of the internal ground G, which is common to the current measuring device 2 and the resistance measuring device 3, which is zero volt, is converted into a detection voltage Vo based on which the signal is output from the signal output unit 12.

The switch 13 is connected between the signal input unit 11 and the inverting input terminal of the operational amplifier 14. Further, the switch 13 is controlled by the processing unit 20 that functions as a control unit, and is turned on during the integration period Ti and turned off during the period other than the integration period Ti. In this example, as an example, the elapsed time Ta described below is a combination of the degree of noise reduction and the measurement time (the time required to measure the current value I of the detection current I and the resistance value Rx of the measurement target Rx described later). In consideration of this, it is prescribed in advance for a fixed time (for example, 2 ms). Along with this, the integration period Ti is defined in advance as a constant time (2.2 ms) that is slightly longer than the elapsed time Ta. It should be noted that the elapsed time Ta and the integration period Ti are not limited to the above-mentioned time, and when the measurement time has a margin, the elapsed time Ta and the integration period Ti are specified to be longer than the above-mentioned time in order to further increase the degree of noise reduction. Alternatively, when there is not enough margin in the measurement time, the degree of noise reduction can be made lower within the allowable range, and the time can be specified to be shorter than the above time.

The operational amplifier 14 uses an operation voltage (to be described later as an example, a positive voltage Vcc and a negative voltage Vee (|Vee|=Vcc) based on a reference potential (potential of the internal ground G) output from the voltage variable power supply 17. )) works with. Further, in the operational amplifier 14, the inverting input terminal is connected to the signal input section 11 via the switch 13 as described above, the non-inverting input terminal is regulated to the reference potential (potential of the internal ground G), and the output terminal is the signal. A feedback circuit 15 including an integrating capacitor is connected between the output unit 12 and the inverting input terminal and the output terminal to form an inverting type integrating circuit.

The feedback circuit 15 is, for example, a measurement range (a detection range for selecting the current value I of the detection current I that can be detected by the current-voltage conversion circuit 1, and the current measurement device 2 selects the measurable current value I). Is a current measurement range for selecting the resistance value Rx that can be measured by the resistance measuring device 3) (n: n is an integer of 2 or more). capacitor _{15a 1, 15a 2, ···,} 15a n ( hereinafter, especially when no distinction is also referred to as the capacitor 15a) and, and a switch portion 15b. As an example in the present embodiment, the switch unit 15b, the capacitors _{15a 1,} 15a 2, · · ·, 15a as many selection and capacitor 15a connected in series to the _n switches _{15b 1,} 15b 2, · · ·, _15b n ( Hereinafter, unless otherwise specified, it is also referred to as a selection switch 15b). Further, the series circuit of the capacitor 15a ₁ and the selection switch 15b ₁ , the series circuit of the capacitor 15a ₂ and the selection switch 15b ₂ ,..., And the series circuit of the capacitor 15a _n and the selection switch 15b _n are respectively the inversion of the operational amplifier 14. It is connected in parallel between the input terminal and the output terminal. The ON/OFF of each selection switch 15b is controlled by the processing unit 20 that functions as a control unit.

Specifically, the current-voltage conversion circuit 1 is provided with six (n=6) measurement ranges (see FIG. 2) from the first range to the sixth range, and the feedback circuit 15 is Corresponding to, the series circuit of the capacitor 15a ₁ (1.0 μF) and the selection switch 15b ₁ corresponding to the first range (maximum measurement current value 1 mA), the capacitor 15a corresponding to the second range (maximum measurement current value 5 mA) ₂ (4.7 μF) and selection switch 15b ₂ in series circuit, capacitor 15a ₃ (10 μF) and selection switch 15b ₃ in series circuit corresponding to third range (maximum measurement current value 10 mA), 4th range (maximum measurement current) A series circuit of the capacitor 15a ₄ (22 μF) and the selection switch 15b ₄ corresponding to the value 50 mA), a series circuit of the capacitor 15a ₅ (22 μF) and the selection switch 15b ₅ corresponding to the fifth range (the maximum measured current value 100 mA), and A series circuit of a capacitor 15a ₆ (22 μF) and a selection switch 15b ₆ corresponding to the sixth range (maximum measured current value 500 mA) is provided. In the present example, since the series circuit of one capacitor 15a and the selection switch 15b corresponds to one measurement range, the selection switches 15b ₁ , 15b ₂ ,..., 15b ₆ forming the switch unit 15b are selected. Only one selection switch 15b corresponding to the measured range is controlled by the processing unit 20 to be in the ON state. Further, in the capacitor used as the capacitor 15a, the one having the maximum capacitance value is 22 μF, so this 22 μF capacitor is used as the capacitor 15a corresponding to the fourth range to the sixth range.

Although not shown, the switch unit 15b may be configured by one rotary switch having one circuit n-contact (in the specific example, one circuit 6-contact). Although not shown, a parallel circuit of two or more capacitors 15a of the capacitors 15a 1 _~ capacitor 15a _n, it is also possible to form a capacitor corresponding to one of the measurement range. In this configuration, the switches 15b corresponding to the two or more capacitors 15a forming the parallel circuit are simultaneously controlled to be in the ON state.

With this configuration, the operational amplifier 14 supplies the detection current I (current supplied to the inverting input terminal of the operational amplifier 14) input from the signal input unit 11 via the switch 13 in the ON state over the integration period Ti. detecting current integrating capacitor that is charged with I (the capacitors _{15a 1, 15a 2, ···,} any capacitor corresponding to one measurement range is a capacitor 15a (selected selected among 15a _n)) of In accordance with the charging voltage Vc, the output terminal converts the reference potential (potential of the internal ground G) into a detection voltage Vo that appears as a voltage (negative voltage in this example) based on the reference potential and outputs the detection voltage Vo to the signal output unit 12.

As an example, the discharge circuit 16 is configured by a series circuit of a discharge resistor 16a and a discharge switch 16b, and is connected between the inverting input terminal and the output terminal of the operational amplifier 14. Further, in the discharge circuit 16, the on/off state of the discharge switch 16b is controlled by the processing unit 20. With this configuration, when the discharge switch 16b is turned on by the processing unit 20, the discharging circuit 16 discharges the integrating capacitor via the discharging resistor 16a, and the charging voltage Vc charged in the integrating capacitor. To zero volts (reset charging voltage Vc). Although not shown, the discharge circuit 16 can be configured only by the discharge switch 16b.

The variable voltage power supply 17 is configured to be capable of outputting the operating voltages Vcc and Vee for the operational amplifier 14 by changing the voltage value thereof by being controlled by the processing unit 20 which functions as a control unit.

In this example, as an example, as described above, the capacitor 15a ₁ (capacitance value C: 1.0 μF) in the first range (maximum measurement current value 1 mA) and the second range (maximum measurement current value 5 mA) are used as integration capacitors. ), the capacitor 15a ₂ (capacitance value C: 4.7 μF), the third range (maximum measurement current value 10 mA), the capacitor 15a ₃ (capacity value C: 10 μF), the fourth range (maximum measurement current value 50 mA) capacitor 15a ₄ (capacitance value C: 22 .mu.F) is, the fifth range (maximum measured current value 100 mA) in the capacitor 15a ₅ (capacitance value C: 22 .mu.F) is, the sixth range (maximum measured current value 500mA) the capacitor _15a 6 ( A capacitance value C: 22 μF) is connected to the operational amplifier 14 and charged with the detection current I over the integration period Ti (2.2 ms).

Therefore, the maximum value of the charging voltage Vc of the capacitor 15a ₁ (1.0 μF) in the first range (maximum measured current value 1 mA) is +2.2 V (=1 mA×2.2 ms/1.0 μF), which is the second value. The maximum value of the charging voltage Vc of the capacitor 15a ₂ (4.7 μF) in the range (maximum measured current value 5 mA) is +2.3 V (=5 mA×2.2 ms/4.7 μF). Similarly, the maximum value of the charging voltage Vc of the capacitor 15a ₃ (10 μF) in the third range (maximum measurement current value 10 mA) is +2.2 V, and the capacitor 15a _{4 in} the fourth range (maximum measurement current value 50 mA) is The maximum value of the charging voltage Vc of (22 μF) is +5 V, the maximum value of the charging voltage Vc of the capacitor 15a ₅ (22 μF) in the fifth range (maximum measurement current value 100 mA) is +10 V, and the sixth range (maximum measurement current). The maximum value of the charging voltage Vc of the capacitor 15a ₆ (22 μF) at a value of 500 mA) is +50V.

Therefore, the detection voltage Vo as a negative voltage has a maximum absolute voltage value in the first range as shown in FIG. 2 (the detection voltage Vo is simply described as voltage Vo in the figure). The maximum absolute voltage value becomes 2.2V, the maximum absolute voltage value becomes 2.3V in the second range, the maximum absolute voltage value becomes 2.2V in the third range, and the maximum absolute voltage value becomes 5V in the fourth range. In the range, the maximum absolute voltage value is 10V, and in the sixth range, the maximum absolute voltage value is 50V.

When the capacitance value C of the capacitor 15a in the plurality of ranges is the same (in this example, the capacitance value C of the capacitor 15a in the fourth range to the sixth range is 22 μF, the same), the capacitor 15a and the selection switch 15b are the same. Instead of providing a series circuit for each of these ranges, it is also possible to adopt a configuration in which only one series circuit of the common capacitor 15a and the selection switch 15b is provided. With this configuration, it is possible to reduce the number of components of the feedback circuit 15, and thus the number of components of the current-voltage conversion circuit 1, and as a result, it is possible to reduce the product cost.

In this example, the operational amplifier 14 can output (detect) the maximum absolute voltage value of the detection voltage Vo in each measurement range without being restricted by the operating voltages Vcc and Vee in the above-mentioned first to sixth ranges. As shown in FIG. 2, the variable voltage power supply 17 sets the operating voltages Vcc and Vee to ±3.3 V for the first range to the third range, ±7.0 V for the fourth range, and the fifth range. Of ±12.0V and ±60.0V for the sixth range. The above-mentioned ±3.3V, ±7.0V, ±12.0V and ±60.0V are examples, and the maximum of the above-mentioned detection voltage Vo in the first to sixth ranges in which the operational amplifier 14 is described above. The operating voltages are Vcc and Vee that can output absolute voltage values, and are not limited to ±3.3V, ±7.0V, ±12.0V and ±60.0V.

The storage unit 18 is configured by a storage device such as a semiconductor memory or an HDD (hard disk device). In addition, as shown in FIG. 2, the storage unit 18 includes one or more capacitors corresponding to the respective measurement ranges of the first range to the sixth range (in this example, as described above, The condenser 15a ₁ corresponds, the condenser 15a ₂ corresponds to the second range, the condenser 15a ₃ corresponds to the third range, the condenser 15a ₄ corresponds to the fourth range, and the condenser 15a ₅ corresponds to the fifth range. , A single capacitor 15a for each range so that the capacitor 15a ₆ corresponds to the sixth range), and a combination of the voltage values of the operating voltages Vcc and Vee corresponding to each measurement range. (In this example, a combination including the capacitance value C of the capacitor corresponding to the measurement range) is stored as a data table DT in association with each measurement range.

The operation unit 19 is composed of, for example, a plurality of operation keys arranged on a keyboard or an operation panel (not shown), and processes start instructions and selection range information to function as a control unit according to the operation content of the operator. It is output to the unit 20.

The processing unit 20 includes, for example, a pre-stage amplifier, an A/D converter, and a CPU (not shown). The pre-stage amplifier is configured as, for example, an inverting-type amplifier capable of switching the gain in multiple stages, and corresponds to the maximum absolute voltage value (full scale value) of the detection voltage Vo in each measurement range of the first range to the sixth range. Then, the function is switched to a known gain to convert the voltage value of the detection voltage Vo output from the operational amplifier 14 into a positive voltage, and to adjust it to the input voltage range of the A/D converter arranged in the subsequent stage. Is equipped with. The A/D converter performs A/D conversion on the voltage output from the pre-stage amplifier to convert it into voltage data indicating the voltage value of this voltage, and outputs the voltage data to the CPU. The CPU (the processing unit 20 including this CPU) functions as a control unit to execute the range switching process and the voltage switching process, as well as the control process for the switch 13 and the discharge circuit 16 (specifically, the discharge switch 16b). To do.

In the range switching process, the processing unit 20 switches to one measurement range (hereinafter, also referred to as selection range) indicated by the selection range information output from the operation unit 19. Specifically, the processing unit 20 refers to the data table DT, and the capacitor 15a corresponding to the measurement range (one of the measurement ranges of the first range to the sixth range) that matches the selected range. And a combination of operating voltages Vcc and Vee is read out (specified). In addition, the processing unit 20 shifts only the selection switch 15b connected in series to the specified capacitor 15a (capacitor 15a corresponding to the selected range) to the ON state, and shifts the other selection switches 15b to the OFF state. Switching control is executed, and only the specified capacitor 15a is connected as an integrating capacitor between the inverting input terminal and the output terminal of the operational amplifier 14. Further, the processing unit 20 switches the gain of the pre-stage amplifier to a known gain corresponding to the maximum absolute voltage value (full scale value) of the detection voltage Vo in this selection range.

Further, in the voltage switching process, the processing unit 20 executes the voltage switching control for the variable voltage power supply 17 to set the operating voltages Vcc and Vee output from the variable voltage power supply 17 to the specified operating voltages Vcc and Vee (selection). The operating voltage is switched to the operating voltage Vcc, Vee) corresponding to the range. As a result, the operational amplifier 14 operates by receiving the supply of the specified operating voltages Vcc and Vee.

Further, in the control process for the switch 13 and the discharge circuit 16, when the processing unit 20 detects that the start instruction is output from the operation unit 19 (there is the output of the start instruction), as illustrated in FIG. Then, the switch 13 is temporarily turned off. Further, the processing unit 20 causes the discharge circuit 16 to perform the discharge operation by shifting the discharge switch 16b to the ON state for a certain period Tdc within the period in which the switch 13 is in the OFF state. Further, the processing unit 20 sets the switch 13 to an integration period Ti (a period starting from the time t0 when the switch 13 is changed from the OFF state to the ON state) after the fixed period Tdc in which the discharge circuit 16 is caused to perform the discharging operation is finished. To be turned on. Further, when the integration period Ti ends, the processing unit 20 shifts the switch 13 to the off state and causes the discharge circuit 16 to perform the discharge operation for a certain period Tdc.

With the above configuration, the current-voltage conversion circuit 1 operates with the operational voltages Vcc and Vee corresponding to the selection range (the measurement range corresponding to the current value I of the detection current I) in which the operational amplifier 14 is selected by the operator. , The detection current I is normally integrated (without being restricted by the operating voltages Vcc and Vee) over the integration period Ti by using the integration capacitor corresponding to the selected range and converted into the detection voltage Vo. It is possible to output the detection voltage Vo from the signal output unit 12.

The current measuring device 2 includes the current-voltage conversion circuit 1 and the output unit 21. Further, the processing unit 20 executes voltage measurement processing, current measurement processing, and output processing as processing in the current measuring device 2 in addition to the above-described processing in the current-voltage conversion circuit 1. In the range switching process when the processing unit 20 functions as a component of the current measuring device 2, the processing unit 20 matches the selected range (one of the first to sixth measurement ranges). When the combination of the capacitor 15a and the operating voltages Vcc and Vee corresponding to is read, the capacitance value C of this capacitor 15a is also read.

In the voltage measurement process, as shown in FIG. 3, the processing unit 20 measures the voltage value Vo of the detection voltage Vo twice during the integration period Ti, leaving a predetermined elapsed time Ta. In this example, as an example, the processing unit 20 measures the first voltage value Vo (also referred to as the voltage value Vo1 for easy understanding) at the sampling time t1 slightly delayed from the time t0 which is the start of the integration period Ti. Then, at the sampling time t2 slightly before the end of the integration period Ti, the second voltage value Vo (also referred to as the voltage value Vo2 for ease of understanding) is measured. In this case, in the processing unit 20, the CPU calculates the voltage value Vo based on the voltage data acquired from the A/D converter and the gain in the pre-stage amplifier at this time. The processing unit 20 also causes the storage unit 18 to store the voltage values Vo1 and Vo2. The timing of measuring the voltage values Vo1 and Vo2 is not limited to the above example, and may be any timing within the integration period Ti. However, in order to increase the degree of noise reduction described above, it is preferable to make the elapsed time Ta longer. Therefore, although not illustrated, the sampling time t1 which is the measurement timing of the voltage value Vo1 is set to the start of the integration period Ti. It is preferable that the sampling time t2, which is the measurement timing of the voltage value Vo2, coincides with or is as close as possible to the time t0 that is equal to, and the end of the integration period Ti.

In the current measurement process, the processing unit 20 calculates the differential voltage value Va (=Vo1-Vo2) between the voltage values Vo1 and Vo2 measured in the voltage measurement process. Further, the processing unit 20 sets the differential voltage value Va, the capacitance value C of the capacitor 15a corresponding to the measurement range that matches the selected range read in the range switching process, and the known elapsed time Ta into the following formula (1). By substituting, the current value I is calculated (measured) and stored in the storage unit 18.
I=|Va|×C/Ta (1)

Further, in the output process, the processing unit 20 causes the output unit 21 to output the current value I measured in the current measurement process. In this example, the output unit 21 is configured by a display device as an example. With this configuration, the output unit 21 displays (outputs) the current value I output from the processing unit 20 on the screen. Note that the output unit 21 can be configured by various interface circuits instead of the display device. When configured by an external interface circuit, this calculation is performed by an external device connected to the transmission path via the external interface circuit. The measured (measured) current value I is output, and when configured by the medium interface circuit, the calculated (measured) current value I is stored in the storage medium connected to the medium interface circuit.

With the above configuration, the current measuring device 2 including the current-voltage conversion circuit 1 detects the detection current in the selection range (the measurement range corresponding to the current value I of the detection current I) in which the current-voltage conversion circuit 1 is selected by the operator. I can be converted into a detection voltage Vo and output, and the processing unit 20 can measure the current value I of the detection current I based on the detection voltage Vo.

The resistance measuring device 3 includes the current measuring device 2 and the voltage applying unit 22 and the DC voltage source 23.

As shown in FIG. 1, the voltage application unit 22 is configured to be capable of connecting a measurement target (resistor to be measured) Rx to the signal input unit 11. The DC voltage source 23 is controlled by the processing unit 20 and supplies a measurement voltage V1 (for example, a predetermined DC constant voltage (a positive voltage whose voltage value is known)) based on a reference potential (potential of the internal ground G). Output to the voltage application unit 22.

In addition to the above-described processes in the current measuring device 2, the processing unit 20 executes a control process for the DC voltage source 23 and a resistance measuring process as processes in the resistance measuring device 3. Further, in the output process when the processing unit 20 functions as a component of the resistance measuring device 3, the resistance value Rx of the measurement target Rx calculated (measured) as described later in the resistance measuring process is output together with the current value I. The output unit 21 is caused to output. In this case, the output unit 21 displays (outputs) the current value I and the resistance value Rx on the screen when it is configured by a display device, and via the external interface circuit when configured by the external interface circuit. It outputs a current value I and a resistance value Rx to an external device connected by a transmission line, and when it is composed of a medium interface circuit, it outputs a current value I and a resistance value Rx to a storage medium connected to this medium interface circuit. Memorize

In the resistance measurement process, the processing unit 20 is connected between the signal input unit 11 and the DC voltage source 23 (specifically, is connected between the signal input unit 11 and the voltage application unit 22). The current flowing through the measurement target Rx while the measurement voltage V1 is being applied from the DC voltage source 23 to the target Rx is set as the detection current I, and the current measurement process is executed to measure the current value I of the detection current I, and the measurement is performed. The resistance value Rx of the measurement target Rx is measured based on the current value I and the voltage value V1 of the measurement voltage V1.

Next, the operation of the resistance measuring device 3 will be described with reference to the drawings including the operations of the current-voltage conversion circuit 1 and the current measuring device 2. It is assumed that a measurement target Rx is connected between the signal input unit 11 and the voltage applying unit 22 of the resistance measuring device 3 as shown in FIG.

In this state, when the operator operates the operation unit 19 and the selection range information indicating the measurement range (selection range) selected by the operator is output from the operation unit 19 to the processing unit 20, the processing unit 20 acquires this selected range information and executes range switching processing. As an example, the operator determines that the maximum value of the current value I of the detection current I flowing through the measurement target Rx is about 45 mA when the measurement voltage V1 is applied, and the detection current I of this current value I It is assumed that a suitable fourth range is selected as the measurement range. Further, as a result, the operation unit 19 outputs the selected range information indicating the fourth range, which is the selected range, to the processing unit 20.

In this range switching process, the processing unit 20 refers to the data table DT, the capacitor 15a ₄ corresponding to the measurement range that matches the acquired selected range (fourth range), its capacitance value C (=22 μF), and operation. The combination of the voltages Vcc and Vee (±7.0 V) is read (specified), only the selection switch 15b ₄ connected in series to the specified capacitor 15a ₄ is turned on, and the other selection switch 15b is turned off. Execute range switching control to shift to the state. Thus, only the capacitor 15a ₄ identified is connected between the inverting input terminal and the output terminal of the operational amplifier 14 as an integration capacitor. Further, in the processing unit 20, the gain of the pre-stage amplifier is switched to a known gain corresponding to the maximum absolute voltage value (full scale value) of the detection voltage Vo in this selection range (fourth range) by the CPU. The processing unit 20 also stores the read capacitance value C in the storage unit 18.

Further, the processing unit 20 executes a voltage switching process. In this voltage switching process, the processing unit 20 executes the voltage switching control for the variable voltage power supply 17 and sets the operating voltages Vcc and Vee output from the variable voltage power supply 17 to the specified operating voltages Vcc and Vee (±7). 0.0 V). As a result, the operational amplifier 14 operates by being supplied with the specified operating voltages Vcc and Vee (±7.0 V).

After that, when the operator operates the operation unit 19 and the start instruction is output from the operation unit 19 to the processing unit 20, the processing unit 20 detects the output of the start instruction, and first, the switch 13 And control processing for the discharge circuit 16 is executed. In this control processing, as shown in FIG. 3, the processing unit 20 causes the discharge circuit 16 to temporarily shift the switch 13 to the off state, and within the off state of the switch 13 for a certain period of time Tdc. Perform the discharge operation. Thus, capacitor connected 15a ₄ is discharged between the inverting input terminal of the operational amplifier 14 as an integration capacitor and an output terminal, the charging voltage Vc is reset to zero volts. The processing unit 20 stops the discharging operation of the discharging circuit 16 when Tdc ends for a certain period. In this state, the detection current I does not flow in the current-voltage conversion circuit 1 and the charging voltage Vc of the capacitor 15a ₄ is zero volt. Therefore, the detection voltage Vo output from the current-voltage conversion circuit 1 is as shown in FIG. It has been returned to zero volts as shown in.

Subsequently, the processing unit 20 executes the control process for the DC voltage source 23 to start the output of the measured voltage V1 to the voltage applying unit 22, and also executes the control process for the switch 13 to temporarily turn it off. As shown in FIG. 3, the switch 13 that has been shifted to the state is shifted to the on state at the time t0, and is kept in the on state for the integration period Ti. As a result, the measurement voltage V1 is applied to the measurement target Rx connected between the signal input unit 11 and the voltage application unit 22, so the voltage application unit 22, the measurement target Rx, and the signal input unit from the DC voltage source 23. 11, a path to the output terminal of the operational amplifier 14 via the switch 13 in the ON state and the feedback circuit 15 (specifically, the series circuit of the capacitor 15a ₄ and the selection switch 15b ₄ corresponding to the selected range) ( The detection current I flows in the path indicated by the alternate long and short dash line in FIG.

The current-voltage conversion circuit 1 converts the detection current I input from the signal input unit 11 into a detection voltage Vo and outputs it from the signal output unit 12. Since the charging voltage Vc of the capacitor 15a ₄ charged by the detection current I increases from time t0 in proportion to time, the detection voltage Vo is based on zero volt at time t0 as shown in FIG. It is output as a negative voltage whose absolute value increases in proportion to time.

In this case, in the current-voltage conversion circuit 1, since the capacitor 15a ₄ (capacitance value C: 22 μF) corresponding to the fourth range is connected to the operational amplifier 14 as the integrating capacitor, the maximum measured current in the fourth range The maximum absolute voltage value of the detection voltage Vo at the time when the integration period Ti (2.2 ms) has elapsed when the detection current I flows at a value of 50 mA is 5 V (the detection voltage Vo is a negative value of -5 V as shown in FIG. 2). However, since the operational amplifier 14 operates at the operating voltages Vcc and Vee (±7.0 V) corresponding to the fourth range, the operational amplifier 14 is not limited to the operating voltages Vcc and Vee, and the detection voltage Vo Is output correctly.

Next, the processing unit 20 executes a voltage measurement process as a component of the current measuring device 2. In this voltage measurement process, as shown in FIG. 3, the processing unit 20 measures the voltage value Vo of the accurately output detection voltage Vo twice during the integration period Ti with a predetermined elapsed time Ta. To do. Specifically, the processing unit 20 measures the voltage value Vo1 for the first time at the sampling time t1, measures the voltage value Vo2 for the second time at the sampling time t2 after the elapsed time Ta has elapsed, and stores it in the storage unit 18. Let

After the measurement of the voltage value Vo2 is completed, the processing unit 20 executes the control process for the DC voltage source 23 to stop the output of the measured voltage V1 to the voltage applying unit 22 and the control process for the switch 13. Switch to the off state. In addition, the processing unit 20 executes a control process on the discharge circuit 16 to cause the discharge circuit 16 to perform a discharge operation for a certain period Tdc. Thus, the capacitor 15a ₄ is discharged as the integrating capacitor, the charging voltage Vc is reset to zero volts, also the detection voltage Vo which is outputted from the current-voltage conversion circuit 1 is returned to zero volts.

Subsequently, the processing unit 20 executes a current measurement process as a component of the current measurement device 2. In this current measurement process, the processing unit 20 reads out the voltage values Vo1 and Vo2 from the storage unit 18 and calculates the difference voltage value Va (=Vo1-Vo2) between them. The processing unit 20 also determines the differential voltage value Va, the capacitance value C (=22 μF) of the capacitor 15 a ₄ corresponding to the selected range (fourth range) read out by the range switching process and stored in the storage unit 18, and the known value. The current value I is calculated (measured) by substituting the elapsed time Ta (=2 ms) into the above equation (1) and stored in the storage unit 18.

In this case, in the current measuring device 2, the current-voltage conversion circuit 1 outputs the operating voltages Vcc and Vee as described above in the fourth range (selection range selected by the operator) that is adapted to the current value I of the detected current I. To output the detection voltage Vo accurately without being limited, up to 50 mA based on the accurate detection voltage Vo (based on the accurate differential voltage value Va calculated from the accurate voltage values Vo1 and Vo2) The current value I of the detection current I is accurately measured.

Subsequently, the processing unit 20 executes resistance measurement processing as a component of the resistance measuring device 3. In the resistance measurement process, the processing unit 20 determines the resistance value Rx of the measurement target Rx based on the accurate current value I of the measured detection current I and the voltage value V1 of the measurement voltage V1 output from the DC voltage source 23. (=V1/I) is accurately calculated (measured) and stored in the storage unit 18.

In addition, the processing unit 20 executes an output process and outputs the measured current value I and resistance value Rx to the output unit 21. This completes the measurement of the current value I of the detected current I and the measurement of the resistance value Rx of the measurement target Rx.

Subsequently, the operator replaces the measurement target Rx measured using the fourth range as the selection range as described above with a new measurement target Rx (measurement target Rx having a smaller current value I of the detected current I). The operation for measuring is described. It is assumed that a new measurement target Rx is connected between the signal input unit 11 and the voltage application unit 22 of the resistance measuring device 3 instead of the measurement target Rx whose measurement has been completed. Further, description of the same operation as the above-described operation when the fourth range is the selected range is omitted.

Also in this case, the operator selects a suitable measurement range as the selection range based on the maximum value of the current value I of the detection current I flowing in the new measurement target Rx, and executes the operation on the operation unit 19, The selection range information indicating this selection range is output to the processing unit 20. For example, the operator determines that the maximum value of the current value I of the detection current I flowing through the new measurement target Rx is about 5 mA, and sets the second range suitable for the detection current I of this current value I as the measurement range. It is assumed that the selection range information indicating the second range, which is the selection range, is selected and output from the operation unit 19 to the processing unit 20.

The processing unit 20 acquires the selected range information and executes the range switching process. In this range switching process, the processing unit 20 operates in the same manner as when the fourth range is set as the selection range, refers to the data table DT, and selects a capacitor corresponding to the measurement range that matches the selection range (second range). 15a ₂ , its capacitance value C (=4.7 μF) and operating voltage Vcc, Vee (±3.3 V) are read (specified), and only the selection switch 15b ₂ connected in series to this specified capacitor 15a ₂ is read. the running range switching control to transition to the oN state, is connected between the inverting input terminal and the output terminal of the operational amplifier 14 to only the capacitor 15a ₂ identified as an integration capacitor. Further, in the processing unit 20, the gain of the pre-stage amplifier is switched by the CPU to a known gain corresponding to the maximum absolute voltage value (full scale value) of the detection voltage Vo in this selection range (second range). The processing unit 20 also stores the read capacitance value C in the storage unit 18.

Further, the processing unit 20 executes a voltage switching process to switch the operating voltages Vcc and Vee output from the variable voltage power supply 17 to the specified operating voltages Vcc and Vee (±3.3V). As a result, the operational amplifier 14 operates by receiving the supply of the specified operating voltages Vcc and Vee (±3.3V).

After that, when the start instruction is output from the operation unit 19 to the processing unit 20, the processing unit 20 detects the output of the start instruction, first executes the control process for the switch 13 and the discharge circuit 16, and the switch 13 is temporarily turned off, and the discharge operation of the discharge circuit 16 is performed for a certain period of time Tdc within the off-state period of the switch 13 to discharge the capacitor 15a ₂ and charge it. Reset the voltage Vc to zero volts. As a result, the detection voltage Vo output from the current-voltage conversion circuit 1 is returned to zero volts.

Subsequently, the processing unit 20 outputs the measurement voltage V1 from the DC voltage source 23 and shifts the switch 13 from the OFF state to the ON state, thereby supplying the detection current I from the DC voltage source 23 to the measurement target Rx. ..

The current-voltage conversion circuit 1 converts the detection current I input from the signal input unit 11 into a detection voltage Vo and outputs it from the signal output unit 12. In this case, in the current-voltage conversion circuit 1, since the capacitor 15a ₂ (capacitance value C: 4.7 μF) corresponding to the second range is connected to the operational amplifier 14 as an integrating capacitor, the maximum in the second range is obtained. As shown in FIG. 2, the maximum absolute voltage value of the detection voltage Vo at the time when the integration period Ti (2.2 ms) has elapsed when the detection current I flows at the measured current value 5 mA is 2.3 V (the detection voltage Vo is However, since the operational amplifier 14 operates at operating voltages Vcc and Vee (±3.3V) corresponding to the second range, it is limited to operating voltages Vcc and Vee. Output the detection voltage Vo accurately.

In the current-voltage conversion circuit 1, the operational amplifier 14 maintains the operating voltages Vcc and Vee (±5V) in the original fourth range without changing the operating voltages Vcc and Vee to ±3.3V. The detection voltage Vo can be accurately output without being limited to the operating voltages Vcc and Vee. However, in the processing unit 20, the signal output from the pre-stage amplifier that is switched to the gain corresponding to the selected range (specifically, the operating voltages Vcc and Vee) is used effectively in the input voltage range of the A/D converter. It is preferable to change it in order to reduce the error in the A/D converter. Therefore, in the current-voltage conversion circuit 1, the operating voltages Vcc and Vee of the operational amplifier 14 are changed to the operating voltages Vcc and Vee (±3.3 V) corresponding to the second range (in addition, the gain of the pre-stage amplifier is also set to this value). Change to a gain corresponding to the operating voltages Vcc and Vee).

Next, the processing unit 20 executes the voltage measurement process, measures the first voltage value Vo1 at the sampling time t1 during the integration period Ti, and measures the second voltage value Vo2 at the sampling time t2 after the elapsed time Ta has elapsed. Is measured and stored in the storage unit 18.

Subsequently, the processing unit 20 executes the current measuring process, the voltage value Vo1, Vo2 of the differential voltage value Va (= Vo1-Vo2), the capacitance value C of the capacitor 15a ₂ corresponding to the selected range (second range) By substituting (=4.7 μF) and the known elapsed time Ta (=2 ms) into the above equation (1), the current value I is calculated (measured) and stored in the storage unit 18.

In this case as well, in the current measuring device 2, the operating voltage Vcc, Vee as described above in the second range (selected range selected by the operator) in which the current-voltage conversion circuit 1 is adapted to the current value I of the detected current I. In order to output the detection voltage Vo accurately without being limited to 5 mA, based on the accurate detection voltage Vo (based on the accurate differential voltage value Va calculated from the accurate voltage values Vo1 and Vo2), 5 mA The current value I of the detection current I up to is accurately measured.

Subsequently, the processing unit 20 executes resistance measurement processing, and based on the measured current value I of the detected current I and the measured voltage value V1 of the voltage V1, the resistance value Rx (=V1/ of the measurement target Rx). I) is calculated (measured) and stored in the storage unit 18.

In addition, the processing unit 20 executes an output process and outputs the measured current value I and resistance value Rx to the output unit 21. This completes the measurement of the current value I of the detected current I and the measurement of the resistance value Rx of the measurement target Rx.

On the other hand, instead of the measurement target Rx measured by the operator using the fourth range as the selection range as described above, a new measurement target Rx (measurement target Rx in which the current value I of the detected current I becomes larger) The operation for measuring is described. It is assumed that a new measurement target Rx is connected between the signal input unit 11 and the voltage application unit 22 of the resistance measuring device 3 instead of the measurement target Rx whose measurement has been completed. Further, description of the same operation as the above-described operation when the fourth range is the selected range is omitted.

Also in this case, the operator selects a suitable measurement range as the selection range based on the maximum value of the current value I of the detection current I flowing in the new measurement target Rx, and executes the operation on the operation unit 19, The selection range information indicating this selection range is output to the processing unit 20. For example, the operator determines that the maximum value of the current value I of the detection current I flowing through the new measurement target Rx is about 100 mA, and sets the fifth range suitable for the detection current I of this current value I as the measurement range. It is assumed that the selected range information indicating the fifth range which is the selected range is output from the operation unit 19 to the processing unit 20.

The processing unit 20 acquires the selected range information and executes the range switching process. In this range switching process, the processing unit 20 operates in the same manner as when the fourth range is set as the selection range, refers to the data table DT, and selects a capacitor corresponding to the measurement range that matches the selection range (fifth range). 15a ₅ , its capacitance value C (=22 μF) and operating voltage Vcc, Vee (±12 V) are read (identified), and only the selection switch 15b ₅ connected in series to the identified capacitor 15a ₅ is turned on. run the migrated to range switching control, is connected between the inverting input terminal and the output terminal of the operational amplifier 14 to only the capacitor 15a ₅ identified as an integration capacitor. Further, in the processing unit 20, the gain of the pre-stage amplifier is switched by the CPU to a known gain corresponding to the maximum absolute voltage value (full scale value) of the detection voltage Vo in the selected range (fifth range). The processing unit 20 also stores the read capacitance value C in the storage unit 18.

In addition, the processing unit 20 executes a voltage switching process to switch the operating voltages Vcc and Vee output from the variable voltage power supply 17 to the specified operating voltages Vcc and Vee (±12V). As a result, the operational amplifier 14 operates by receiving the supply of the specified operating voltages Vcc and Vee (±12V).

After that, when the start instruction is output from the operation unit 19 to the processing unit 20, the processing unit 20 detects the output of the start instruction, first executes the control process for the switch 13 and the discharge circuit 16, and the switch 13 is temporarily turned off, and the discharge circuit 16 is caused to perform a discharge operation for a certain period Tdc within the off-state period of the switch 13 to discharge the capacitor 15a ₅ and charge it. Reset the voltage Vc to zero volts. As a result, the detection voltage Vo output from the current-voltage conversion circuit 1 is returned to zero volts.

Subsequently, the processing unit 20 outputs the measurement voltage V1 from the DC voltage source 23 and shifts the switch 13 from the OFF state to the ON state, thereby supplying the detection current I from the DC voltage source 23 to the measurement target Rx. ..

The current-voltage conversion circuit 1 converts the detection current I input from the signal input unit 11 into a detection voltage Vo and outputs it from the signal output unit 12. In this case, the current-voltage conversion circuit 1, the operational amplifier 14 as an integration capacitor (capacitor 15a corresponding to the 5 range) capacitor 15a ₅ of the same capacitance value C and the capacitor 15a ₄ (22 .mu.F) corresponding to the fourth range Since it is connected, the maximum absolute voltage value of the detection voltage Vo at the time when the integration period Ti (2.2 ms) has elapsed when the detection current I flows at the maximum measurement current value 100 mA in the fifth range is shown in FIG. As shown in, the voltage becomes 10 V (the detection voltage Vo is a negative voltage of −10 V), which is twice the maximum absolute voltage value of the detection voltage Vo in the fourth range. However, since the operational amplifier 14 operates at the operating voltages Vcc and Vee (±12V) corresponding to the fifth range, it is not limited to the operating voltages Vcc and Vee and outputs the detection voltage Vo accurately.

Next, the processing unit 20 executes the voltage measurement process, measures the first voltage value Vo1 at the sampling time t1 during the integration period Ti, and measures the second voltage value Vo2 at the sampling time t2 after the elapsed time Ta has elapsed. Is measured and stored in the storage unit 18.

Subsequently, the processing unit 20 executes the current measuring process, the voltage value Vo1, Vo2 of the differential voltage value Va (= Vo1-Vo2), the capacitance C of the capacitor 15a ₅ corresponding to the selected range (5th range) By substituting (=22 μF) and the known elapsed time Ta (=2 ms) into the above equation (1), the current value I is calculated (measured) and stored in the storage unit 18.

Also in this case, in the current measuring device 2, the operating voltage Vcc, Vee as described above in the fifth range (the selection range selected by the operator) in which the current-voltage conversion circuit 1 is adapted to the current value I of the detected current I. The detection voltage Vo is accurately output without being limited to 100 mA based on the accurate detection voltage Vo (accurate difference voltage value Va calculated from the accurate voltage values Vo1 and Vo2). The current value I of the detection current I up to is accurately measured.

Subsequently, the processing unit 20 executes the resistance measurement process, and based on the accurate current value I of the measured detection current I and the voltage value V1 of the measurement voltage V1, the resistance value Rx (= V1/I) is accurately calculated (measured) and stored in the storage unit 18.

In addition, the processing unit 20 executes an output process and outputs the measured current value I and resistance value Rx to the output unit 21. This completes the measurement of the current value I of the detected current I and the measurement of the resistance value Rx of the measurement target Rx.

Further, the operator replaces the measurement target Rx measured using the fifth range as the selection range as described above with a new measurement target Rx (the current value I of the detection current I is larger (to about 500 mA)). When measuring the measurement target Rx), the operation unit 19 is operated to select the sixth range suitable for the detected current I of the current value I as the measurement range, and the operation unit 19 selects the selected range. The selected range information indicating the certain sixth range is output to the processing unit 20.

In the range switching process, the processing unit 20 refers to the data table DT, the capacitor 15a ₆ corresponding to the measurement range that matches the selected range (sixth range), the capacitance value C (=22 μF), and the operating voltages Vcc and Vee. A combination of (±60 V) is read (identified), only the selection switch 15b ₆ connected in series to the identified capacitor 15a ₆ is turned on, and only the identified capacitor 15a ₆ is used as an integrating capacitor as an operational amplifier. Connected between the 14 inverting input terminal and the output terminal. Further, in the processing unit 20, the gain of the pre-stage amplifier is switched by the CPU to a known gain corresponding to the maximum absolute voltage value (full scale value) of the detection voltage Vo in this selection range (sixth range). The processing unit 20 also stores the read capacitance value C in the storage unit 18.

Further, the processing unit 20 executes the voltage switching process to switch the operating voltages Vcc and Vee output from the voltage variable power supply 17 to the specified operating voltages Vcc and Vee (±60V). As a result, the operational amplifier 14 operates by receiving the supply of the specified operating voltages Vcc and Vee (±60V).

After that, when the start instruction is output from the operation unit 19 to the processing unit 20, the processing unit 20 detects the output of the start instruction, first executes the control process for the switch 13 and the discharge circuit 16, and the switch 13 is temporarily turned off, and the discharge operation is performed by the discharge circuit 16 for a certain period Tdc in the off-state period of the switch 13, thereby discharging the capacitor 15a ₆ and charging it. Reset the voltage Vc to zero volts. As a result, the detection voltage Vo output from the current-voltage conversion circuit 1 is returned to zero volts.

Subsequently, the processing unit 20 outputs the measurement voltage V1 from the DC voltage source 23 and shifts the switch 13 from the OFF state to the ON state, thereby supplying the detection current I from the DC voltage source 23 to the measurement target Rx. ..

The current-voltage conversion circuit 1 converts the detection current I input from the signal input unit 11 into a detection voltage Vo and outputs it from the signal output unit 12. In this case, in the current-voltage conversion circuit 1, the capacitor 15a ₆ having the same capacitance value C (22 μF) as the capacitor 15a ₄ corresponding to the fourth range (the capacitor 15a corresponding to the sixth range) is used as the integrating capacitor in the operational amplifier 14. Since it is connected, the maximum absolute voltage value of the detection voltage Vo at the time when the integration period Ti (2.2 ms) has elapsed when the detection current I flows at the maximum measurement current value 500 mA in the sixth range is as shown in FIG. As shown in, the voltage becomes 50 V (the detection voltage Vo is a negative voltage of −50 V), which is 10 times the maximum absolute voltage value of the detection voltage Vo in the fourth range. However, since the operational amplifier 14 operates at the operating voltages Vcc and Vee (±60 V) corresponding to the sixth range, it is not limited to the operating voltages Vcc and Vee and accurately outputs the detection voltage Vo.

Therefore, the processing unit 20 executes the voltage measurement process to measure the respective voltage values Vo1 and Vo2, and also executes the current measurement process to accurately measure the current value I of the detected current I up to 500 mA, Also, the resistance measurement process is executed to accurately measure the resistance value Rx of the measurement target Rx.

As described above, in the current-voltage conversion circuit 1, the variable voltage power supply 17 that can output the operating voltages Vcc and Vee for the operational amplifier 14 that configures the circuit by changing the voltage value, and the first to sixth ranges. The combination of the capacitor 15a corresponding to each measurement range and the voltage values of the operating voltages Vcc and Vee is associated with each measurement range of the first range to the sixth range and stored in the storage unit 18 as a data table DT. The processing unit 20, which is provided and functions as a control unit, corresponds to the selected measurement range (selected range) when any one measurement range is selected from the measurement ranges of the first range to the sixth range. The capacitor 15a to be operated and the combination of the voltage values of the operating voltages Vcc and Vee are read from the data table DT of the storage unit 18, and the read capacitor 15a is connected as an integrating capacitor between the output terminal and the inverting input terminal of the operational amplifier 14. The voltage variable power supply performs the range switching control for the switch unit 15b and changes the operating voltages Vcc and Vee for the operational amplifier 14 to the read operating voltages Vcc and Vee and outputs the voltage. Execute for 17.

Therefore, according to the current-voltage conversion circuit 1, as described above, the operating voltage Vcc of the operational amplifier 14 is high even under the condition that the capacitance value of the capacitor used as the capacitor 15a has the upper limit (22 μF in this example). , Vee, the voltage value corresponding to the measurement range (the fifth range with the maximum measured current value of 100 mA, and the sixth range with the maximum measured current value of 500 mA) for measuring the current with the larger current value ( Since it can be changed to ±12 V in the fifth range and ±60 V in the sixth range), the detection current I can be changed by the integration operation at a predetermined elapsed time Ta without being restricted by the operating voltages Vcc and Vee. It can be accurately converted into the detection voltage Vo.

Further, in the current-voltage conversion circuit 1, the variable voltage power supply 17 is configured to be able to output by changing each voltage value of the positive voltage Vcc and the negative voltage Vee as the operating voltage for the operational amplifier 14. Therefore, according to the current-voltage conversion circuit 1, due to the configuration in which the detection current I flows into the signal input unit 11 (the configuration in which the DC voltage source 23 outputs the measured voltage V1 as a positive voltage with a known voltage value). The detection current Vo is not limited to be output as a negative voltage, and the detection current I flows in the opposite direction (that is, the detection current I flows out from the signal input unit 11 (the DC voltage source 23 changes the measured voltage V1 into a voltage value). Even if the detection voltage Vo is output as a positive voltage due to a known negative voltage)), the detection is performed by the integration operation at the elapsed time Ta without being restricted by the operating voltages Vcc and Vee. The current I can be accurately converted into the detection voltage Vo.

When the detection current I flows into the signal input unit 11 or the detection current I flows out from the signal input unit 11, the voltage variable power supply 17 operates in the positive voltage Vcc and It is also possible to employ a configuration in which only the voltage value corresponding to this one of the voltage values of the negative voltage Vee is changed and output. Further, in this case, the voltage variable power supply 17 is a so-called single power supply that outputs one of the positive voltage Vcc and the negative voltage Vee instead of the so-called plus/minus power supply (both positive and negative power supplies) that outputs the positive voltage Vcc and the negative voltage Vee. Can also be used. With this configuration, the current-voltage conversion circuit 1 can be realized with a simpler configuration.

In the current measuring device 2 including the current-voltage conversion circuit 1, the processing unit 20 measures the voltage value Vo of the detection voltage Vo twice with the elapsed time Ta (measures the voltage values Vo1 and Vo2). Based on the voltage measurement process, the difference voltage value Va between these two voltage values Vo1 and Vo2, the capacitance value (capacitance value C) of the capacitor 15a corresponding to the selected range, and the elapsed time Ta, the current value I of the detected current I The current measurement process of measuring (=|Va|×C/Ta) is executed.

Therefore, according to the current measuring device 2, the accurate differential voltage value Va calculated from the accurate voltage values Vo1 and Vo2 for two times measured by the accurate detection voltage Vo output from the current-voltage conversion circuit 1 is obtained. Based on this, the current value I of the detected current I up to the maximum measured current value in the selected range can be accurately measured.

Further, the resistance measuring device 3 including the current measuring device 2 includes the DC voltage source 23 that outputs the measurement voltage V1 with the potential (reference potential) of the internal ground G as a reference, and the processing unit 20 includes the measurement target Rx. The current value I is measured with the current flowing in the measurement target Rx as the detection current I when the measurement voltage V1 is applied from the DC voltage source 23 to the measured current value I and the voltage value of the measurement voltage V1. The resistance measurement process of measuring the resistance value Rx (=V1/I) of the measurement target Rx is executed based on

Therefore, the resistance measuring device 3 can accurately measure the resistance value Rx of the measurement target Rx based on the voltage value of the measurement voltage V1 and the current value I accurately measured by the current measuring device 2. You can

Each measurement range specified in the data table DT shown in FIG. 2, and the maximum measurement current value, the capacitance value of the capacitor, the maximum absolute voltage value of the detection voltage Vo, and the operating voltages Vcc, Vee corresponding to each measurement range are This is an example, and the present invention is not limited to this.

Further, in the above example, in the voltage measurement process, in order to avoid the fluctuation of the detection voltage Vo that may occur immediately after the time t0 and measure the differential voltage value Va more accurately, it is slightly delayed from the time t0. The voltage value Vo1 at the first time is measured at the sampling time t1, and the voltage value Vo2 at the second time is measured at a sampling time t2 slightly before the end of the integration period Ti, and the difference between the voltage values Vo1 and Vo2 is calculated as a difference. Although the configuration having the voltage value Va is adopted, the configuration is not limited to this configuration. For example, when the fluctuation of the detection voltage Vo that may occur immediately after the time t0 is negligible, although not shown, the detection voltage Vo is sampled once at a time after the elapsed time Ta from the time t0. (The voltage value Vo at this time will be referred to as a voltage value Vo1), and the configuration in which this voltage value Vo1 is used as the above-mentioned differential voltage value Va can also be adopted.

In the above example, the operator operates the operation unit 19 to output selection range information indicating one selected measurement range (selection range) to the processing unit 20 functioning as a control unit, and the processing unit 20. However, the configuration is adopted in which the selection range is switched based on the selection range information, but the present invention is not limited to this. For example, the processing unit 20 automatically determines the optimum measurement range for the measurement (detection) of the detection current I based on the voltage value of the detection voltage Vo output from the operational amplifier 14 and the information indicating the current selection range. It is also possible to adopt a configuration having a known autoranging function for selection.

1 Current-voltage conversion circuit
2 Current measuring device
3 resistance measuring device 11 a signal input unit 12 the signal output unit 14 operational amplifier 15 feedback circuit _{15a 1, 15a 2, ···,} 15a n capacitors _{15b 1, 15b 2, ···,} 15b n selection switch 17 voltage variable power supply 18 Storage unit 20 Processing unit
G Internal ground
I Detection current Vo Detection voltage

Claims (4)

A non-inverting input terminal is defined as a reference potential, and an operational amplifier having a feedback circuit including an integrating capacitor connected between the inverting input terminal and the output terminal is configured to be supplied to the inverting input terminal. Integrated current-voltage conversion for converting the detected current into a detected voltage that appears as a voltage with the reference potential as a reference according to the charging voltage of the integrating capacitor charged with the detected current and outputting the voltage from the output terminal. A circuit,
The feedback circuit uses a plurality of capacitors and one or more capacitors of the plurality of capacitors corresponding to any one measurement range selected from a plurality of measurement ranges as the integration capacitor. A switch unit connected between the output terminal and the inverting input terminal,
A variable voltage power supply capable of outputting the operating voltage for the operational amplifier by changing the voltage value,
A storage unit in which the one or more capacitors corresponding to the measurement range and the combination of the voltage values corresponding to the measurement range are stored in association with the plurality of measurement ranges.
And a control unit,
The control unit, when any one measurement range is selected from the plurality of measurement ranges, a combination of the one or more capacitors and the voltage value corresponding to the selected measurement range. Is read from the storage unit, and range switching control is performed on the switch unit to connect the read one or more capacitors as the integrating capacitor between the output terminal and the inverting input terminal. In addition, the integral-type current-voltage conversion circuit that executes voltage switching control for changing the operating voltage to the read voltage value and outputting the voltage value. 2. The integration-type current-voltage conversion circuit according to claim 1, wherein the variable voltage power supply is configured to be able to output by changing each voltage value of a positive voltage and a negative voltage as an operating voltage for the operational amplifier. An integration-type current-voltage conversion circuit according to claim 1 or 2, and a processing unit,
The processing unit is
A voltage measurement process of measuring the voltage value of the detected voltage twice twice with a predetermined elapsed time,
The detection based on a differential voltage value between two voltage values obtained by the two measurements, a capacitance value of the one or more capacitors corresponding to the selected measurement range, and the elapsed time. A current measuring device that performs a current measuring process of measuring a current value of a current. A current measuring device according to claim 3, and a DC voltage source for outputting a measured voltage based on the reference potential,
The processing unit, as the detection current, a current flowing through the measurement target while applying the measurement voltage from the DC voltage source to the measurement target connected between the inverting input terminal and the DC voltage source. A resistance measurement process of performing the current measurement process to measure the current value of the detected current and measuring the resistance value of the measurement target based on the measured current value and the voltage value of the measurement voltage. Resistance measuring device to perform.

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