JP2013029466A - Electric measurement device including integration type current/voltage conversion circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exclude a measurement error caused by a dielectric absorption phenomenon inherent in a capacitor for integration in an electric measurement device including an integration type current/voltage conversion circuit.SOLUTION: The electric measurement device includes an integration type current/voltage conversion circuit 20 including a capacitor 22 for integration in a feedback circuit connected between one input terminal 21a and an output terminal 21c of an operational amplifier 21, and a DC voltage source 10. The electric measurement device is configured so that a resistor Rx to be measured is connected between the DC voltage source 10 and the one input terminal 21a of the operational amplifier 21, and a predetermined element characteristic included in the resistor Rx to be measured is measured based on an output voltage Vo appearing on the output terminal 21c of the operational amplifier 21 in accordance with electric charge to be charged to the capacitor 22. The electric measurement device further includes a DC current source 40 for reverse charge which after measuring the element characteristic of the resistor Rx to be measured by applying a predetermined voltage to the resistor Rx to be measured by the DC voltage source 10, charges the capacitor 22 for integration in a direction reverse to a charging direction for the element characteristic measurement.

Description

The present invention relates to an electrical measurement apparatus having an integration type current-voltage conversion circuit, and more particularly to a technique for eliminating measurement errors due to a dielectric absorption phenomenon of an integration capacitor connected to a feedback circuit.
The electrical measuring device of the present invention is particularly mounted in an automatic inspection machine, and is suitable for repeatedly measuring, for example, a minute current such as a leakage current of a ceramic capacitor and an insulation resistance.

  An integration type current-voltage conversion circuit is described in, for example, Patent Documents 1 and 2, etc., but a general conventional example in which an electric measurement device having an integration type current-voltage conversion circuit in FIG. First, this will be described.

  As shown in FIG. 3, the current measuring device includes a DC voltage source 10 that applies a predetermined DC voltage to the resistor Rx to be measured, a current-voltage conversion circuit 20 that converts the current flowing through the resistor Rx to be measured, and a voltage. Is provided.

  The current-voltage conversion circuit 20 is of an integration type, and an integration capacitor 22 is connected to a feedback circuit between one input terminal 21a and an output terminal 21c of an operational amplifier (high input impedance amplifier) 21.

  In this example, one input terminal 21a is on the negative side, the resistor under test Rx is connected to this terminal 21a via the switch SW1, and the other input terminal 21b on the positive side is grounded. 21 operates as an inverting amplifier.

  A discharge circuit 30 in which a resistance element 31 and a switch SW2 are connected in series is connected to the integrating capacitor 22 in parallel. The switches SW1 and SW2 operate so that when one is on (off), the other is off (on).

  Referring also to the timing chart of FIG. 4, before measuring the current of the resistor Rx to be measured, the switch SW1 is turned off and the switch SW2 is turned on, and the output Vo of the output terminal 21c is 0V.

  At the time of measuring the current of the resistor Rx to be measured, the switch SW1 is turned on at the same time as the switch SW2 is turned off, and the integration capacitor 22 is charged by the current i flowing from the DC voltage source 10 through the resistor Rx to be measured.

  When the capacitance of the integrating capacitor 22 is C and the charging time (measurement time) is t, a voltage Vo = i × t / C appears at the output terminal. Thereby, the current i flowing through the measured resistor Rx is obtained by i = C × Vo / t.

  After the current of the resistor Rx to be measured is measured, the switch SW1 is turned off and the switch SW2 is turned on at the same time, so that the charge charged in the integrating capacitor 22 is discharged and returned to the initial reset state.

JP-A-7-72180 JP 2001-174492 A

  By the way, when the current measurement device Rx repeatedly measures the current of the resistor Rx to be measured, the value of the output voltage Vo appearing at the output terminal 21c gradually increases depending on the number of measurements due to the dielectric absorption phenomenon of the integrating capacitor 22. This becomes an error factor.

  In particular, when the current measuring device described above is used in an automatic inspection machine or the like, since the repetition time (measurement interval) is short and it is used for a long time, the output voltage Vo appearing at the output terminal 21c. The change of becomes large.

  Considering this point, if a capacitor having a small dielectric absorption phenomenon is used as the integrating capacitor 22, the change in the output voltage Vo when measuring the same number of times is smaller than when using a capacitor having a large dielectric absorption phenomenon. However, if the measurement is repeated for a longer time and the number of times of measurement is increased, the same problem will occur, so this is not a fundamental solution.

  Further, the voltage applied to the resistor Rx to be measured is V1, the current flowing through the resistor Rx to be measured is i, and the insulation resistance value R of the resistor Rx to be measured is expressed as V1 / i. Accordingly, since the current i flowing through the resistor Rx to be measured is obtained by i = C × Vo / t, the insulation resistance value R of the resistor Rx to be measured is V1 × t / Although it can be measured as (C × Vo), in this insulation resistance measurement as well, a problem caused by the dielectric absorption phenomenon of the integrating capacitor 22 occurs.

  Accordingly, an object of the present invention is to eliminate a measurement error due to a dielectric absorption phenomenon inherent in an integrating capacitor in an electrical measuring apparatus that has an integrating current-voltage conversion circuit and performs current measurement and insulation resistance measurement.

  In order to solve the above problems, the present invention includes an integration type current-voltage conversion circuit having an integration capacitor in a feedback circuit between one input terminal and an output terminal of an operational amplifier, and a DC voltage source, A resistor to be measured is connected between the DC voltage source and one input terminal of the operational amplifier, and the output voltage appears at the output terminal of the operational amplifier according to the charge charged in the integrating capacitor. In the electrical measuring apparatus for measuring a predetermined element characteristic of the resistor to be measured, after measuring a device characteristic of the resistor to be measured by applying a predetermined voltage to the resistor to be measured from the DC voltage source, A DC current source for reverse charging that charges the integrating capacitor in a direction opposite to that at the time of measuring the element characteristics is provided.

  In the present invention, a variable DC current source having a variable output current is used as the DC current source for reverse charging.

  According to a preferred aspect of the present invention, a first switch for selectively connecting the resistor to be measured is provided on one input terminal side of the operational amplifier, and a resistive element and a second switch are connected to the integrating capacitor. Are connected in parallel, and the DC current source for reverse charging is connected to one input terminal side of the operational amplifier of the integrating capacitor via a third switch. Connected between the pole and ground.

  The present invention further includes a control unit that controls at least the first, second, and third switches, and the control unit switches from the state in which the first switch is off and the second switch is on. As one step, the first switch is turned on, the second switch is turned off, a predetermined voltage is applied to the measured resistor from the DC voltage source, and element characteristics of the measured device are measured. As a second step, the first switch is turned off, the second switch is turned on, and the charge charged in the integrating capacitor is discharged by the discharge circuit. Then, as the third step, the second switch Is turned off, the third switch is turned on, and the integrating capacitor is charged in the opposite direction to the measurement of the element characteristics by the DC current source for reverse charging, and then the fourth step. As has turned the second switch, a reverse charge stored in the integration capacitor in the third step to clear the third switch, wherein the discharging by the discharge circuit.

  The charge amount to the integration capacitor during reverse charging in the third step is the same as the charge amount to the integration capacitor during current measurement in the first step, but the third step It is preferable that the current value and the charging time at the time of reverse charging at are the same as the current value and the measuring time at the time of element characteristic measurement in the first step.

  The element characteristic of the measured resistor measured by the electrical measuring device is a current value or an insulation resistance value.

  According to the present invention, when measuring element characteristics (current measurement or insulation resistance measurement), the integrating capacitor is charged by the current flowing through the resistor to be measured, but after the current measurement, the integrating capacitor is reverse charged. As a result, the dielectric absorption phenomenon also occurs in the opposite direction and cancels out. Therefore, measurement errors due to the dielectric absorption phenomenon inherent to the capacitor can be eliminated even if the measurement of the resistor under measurement is repeated.

The typical block diagram which shows embodiment which performs the electric current measurement of a to-be-measured resistor with the electrical measuring apparatus by this invention. The timing chart for operation | movement description in the said embodiment. The typical block diagram which shows the conventional electric current measuring apparatus which has an integration type current-voltage conversion circuit. The timing chart for operation | movement description in the said prior art example.

  Next, an embodiment of the present invention will be described with reference to FIGS. 1 and 2, but the present invention is not limited to this. In the description of this embodiment, the same reference numerals are used for components that do not require any change from the conventional example described in FIG.

  As shown in FIG. 1, the current measuring device according to the present invention is used as a current measuring device, and the current measuring device according to this embodiment is also used in the current measuring device according to this embodiment. Similarly, the basic configuration includes a DC voltage source 10 that applies a predetermined DC voltage to the resistor Rx to be measured, and a current-voltage conversion circuit 20 that converts a current flowing through the resistor Rx to be measured into a voltage.

  Note that the current measured in this embodiment is assumed to be a minute leakage current such as a ceramic capacitor, but the resistor Rx to be measured is not limited to this.

  The current-voltage conversion circuit 20 is of an integration type, and an integration capacitor 22 is connected to a feedback circuit between one input terminal 21a and an output terminal 21c of an operational amplifier (high input impedance amplifier) 21.

  Also in this embodiment, the measured resistor Rx is connected to one negative input terminal 21a via a switch SW1 (first switch in claim 3), and the other positive input terminal 21b is grounded. Since it is connected, the operational amplifier 21 operates as an inverting amplifier. On the other hand, the positive input terminal 21b may be used as a current input terminal, and the negative input terminal 21a may be connected to the ground to form a non-inverting amplifier.

  Further, a discharge circuit 30 in which a resistance element 31 and a switch SW2 (second switch in claim 3) are connected in series is connected to the integrating capacitor 22 in parallel. The switches SW1 and SW2 operate so that when one is on (off), the other is off (on).

  In addition to the above-described configuration, the present invention includes a DC current source 40 for reverse charging that charges the integrating capacitor 22 in the direction opposite to that during current measurement. As this DC current source 40, a variable DC current source whose output current is variable is used.

  The DC current source 40 for reverse charging is connected between the pole on the one input terminal 21a side of the operational amplifier 21 in the integrating capacitor 22 and the ground via a switch SW3 (third switch in claim 3). The current flow direction is the ground side.

  In addition, the current measuring device according to this embodiment includes a control unit 50 that performs on / off control of each of the switches SW1, SW2, and SW3. The control unit 50 is preferably a CPU (Central Processing Unit) or a microcomputer.

  In addition to the on / off control function of the switches SW1 to SW3, the control unit 50 has a current value i flowing through the measured resistor Rx from the output voltage Vo (= i × t / C) appearing at the output terminal 21c of the operational amplifier 21. A calculation function for obtaining (= C × Vo / t) may be provided.

  Next, the operation of this current measuring apparatus will be described with reference to the timing chart of FIG.

  Prior to the current measurement of the resistor Rx to be measured, the switches SW1 and SW3 are turned off and the switch SW2 is turned on, and the output Vo of the output terminal 21c is 0V.

  First, in the first step from time t1 to time t2, current measurement of the resistor Rx to be measured is performed. At this time, the switch SW1 is turned on and at the same time the switch SW2 is turned off (the switch SW3 is kept off), and the integrating capacitor 22 is charged by the current i flowing from the DC voltage source 10 through the resistor Rx to be measured.

  When the capacitance of the integrating capacitor 22 is C and the charging time (measurement time) is t, a voltage Vo = i × t / C appears at the output terminal. Thereby, the current i flowing through the measured resistor Rx is obtained by i = C × Vo / t.

  Next, as a second step, from time t2 to time t3 after measuring the current of the resistor Rx to be measured, the switch SW1 is turned off and the switch SW2 is turned on at the same time (the switch SW3 is kept off). The charged charge is discharged and returned to the initial reset state.

  As a third step thereafter, reverse charging is performed on the integrating capacitor 22 from t3 to t4. At this time, the switch SW3 is turned on at the same time as the switch SW2 is turned off (the switch SW1 is kept off), and the reverse charging direct current source 40 causes the current in the direction opposite to that during current measurement to the integrating capacitor 22. Ir is flushed.

  As a fourth step, at time t4 when the reverse charging is finished, the switch SW3 is turned off and at the same time the switch SW2 is turned on (the switch SW1 remains off), and the initial reset state is restored.

  In the third step, the current value of the reverse current ir that flows through the integrating capacitor 22 is the same as the current value of the current i that flows through the integrating capacitor 22 during the current measurement in the first step. The charging time (t3 to t4) is also preferably the same as the charging time t (t1 to t2) at the time of current measurement.

  As another embodiment, the insulation resistance of the resistor Rx to be measured can be measured with the same circuit configuration as the current measuring device of FIG.

  That is, the voltage applied to the measured resistor Rx is V1, and the current flowing through the measured resistor Rx is i, and the insulation resistance value R of the measured resistor Rx is expressed as V1 / i. According to the current measuring device according to the above embodiment, since the current i flowing through the measured resistor Rx is obtained by i = C × Vo / t, the measured resistor has the same circuit configuration as the current measuring device. The insulation resistance value R of Rx can be measured as V1 × t / (C × Vo).

  Note that the voltage V1 applied to the resistor Rx to be measured may be a voltage generated by the DC voltage source 10, or a voltage across the terminals of the resistor Rx to be measured measured by a voltage measuring unit (not shown). Also good.

  Also in this insulation resistance measurement, the controller 50 reverse-charges the integrating capacitor 22 in the same way as during current measurement by performing on / off control of the switches SW1 to SW3 in a predetermined order according to the timing chart of FIG. be able to.

  According to each of the above embodiments, after the current measurement or the insulation resistance measurement, after discharging the charge accumulated in the integration capacitor 22, the integration capacitor 22 is subjected to the current measurement or the insulation resistance measurement. By charging in the reverse direction for the same time at the same current value, the dielectric absorption phenomenon in the integrating capacitor 22 also occurs in the reverse direction and cancels out.

  Therefore, even if it is mounted on an automatic inspection machine or the like and current measurement or insulation resistance measurement is repeated, measurement errors due to the dielectric absorption phenomenon inherent to the integrating capacitor can be eliminated. In addition, when selecting an integration capacitor, it is not necessary to use much attention to the magnitude of the dielectric absorption, and the degree of freedom in selecting the integration capacitor is increased.

  In each of the above embodiments, the integration capacitor is charged in the reverse direction for the same time and with the same current value as during current measurement or insulation resistance measurement. Since it is only necessary to charge the same amount of charge as that charged during current measurement or insulation resistance measurement, as an example, the reverse charge current ir is twice the current i during measurement and the reverse charge time is measured. You may make it 1/2.

DESCRIPTION OF SYMBOLS 10 DC voltage source 20 Integral current voltage conversion circuit 21 Operational amplifiers 21a, 21b Input terminal 21c Output terminal 22 Integration capacitor 30 Discharge circuit 31 Resistive element 40 DC current source for reverse charging 50 Control unit Rx Resistor to be measured SW1 SW3 switch

Claims (8)

An integration type current-voltage conversion circuit having an integrating capacitor in a feedback circuit between one input terminal and an output terminal of the operational amplifier and a DC voltage source, and one input of the DC voltage source and the operational amplifier A resistor to be measured is connected to the terminal, and a predetermined element characteristic of the resistor to be measured is provided on the basis of an output voltage appearing at the output terminal of the operational amplifier according to the charge charged in the integrating capacitor. In the electrical measuring device to measure,
After applying a predetermined voltage from the DC voltage source to the resistor to be measured to measure the element characteristics of the resistor to be measured, the capacitor for integration is charged in the opposite direction to the measurement of the element characteristics. An electrical measuring apparatus comprising a direct current source for charging.   2. The electrical measuring apparatus according to claim 1, wherein the DC current source for reverse charging is a variable DC current source having a variable output current.   A discharge circuit in which a first switch for selectively connecting the resistor under test is provided on one input terminal side of the operational amplifier, and a resistance element and a second switch are connected in series to the integrating capacitor Are connected in parallel, and the reverse charging DC current source is connected between the pole on the one input terminal side of the operational amplifier of the integrating capacitor and the ground via a third switch. The electrical measuring device according to claim 1, wherein the electrical measuring device is provided. A control unit that controls at least the first, second, and third switches; the control unit from a state in which the first switch is off and the second switch is on;
As a first step, the first switch is turned on, the second switch is turned off, a predetermined voltage is applied to the measured resistor from the DC voltage source, and element characteristics of the measured device are measured.
Thereafter, as a second step, the first switch is turned off, the second switch is turned on, and the electric charge charged in the integrating capacitor is discharged by the discharge circuit,
Thereafter, as a third step, the second switch is turned off and the third switch is turned on, and the integration capacitor is charged in the opposite direction to the measurement of the element characteristics by the DC current source for reverse charging. ,
Thereafter, as a fourth step, the second switch is turned on and the third switch is turned off, and the charge reversely charged in the integrating capacitor in the third step is discharged by the discharge circuit. Item 4. The electrical measuring device according to Item 3.   The charge amount to the integration capacitor at the time of reverse charging in the third step is the same as the charge amount to the integration capacitor at the time of measuring element characteristics in the first step. The electrical measurement device according to claim 4.   6. The current value and charging time during reverse charging in the third step are the same as the current value and measuring time during device characteristic measurement in the first step. Current measuring device.   7. The electrical measuring apparatus according to claim 1, wherein an element characteristic of the measured resistor measured by the electrical measuring apparatus is a current value.   7. The electrical measuring apparatus according to claim 1, wherein an element characteristic of the measured resistor measured by the electrical measuring apparatus is an insulation resistance value. 8.

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