JP5320929B2 - Current measuring device - Google Patents

Description

  The present invention relates to a current measuring device that measures current as voltage.

  Patent Documents 1 and 2 below disclose current-voltage conversion circuits. Such a current-voltage conversion circuit is composed of an operational amplifier and a feedback resistor connected between the negative phase input terminal and the output terminal of the operational amplifier, and is input from the outside toward the negative phase input terminal. The converted current is converted into the voltage at the output terminal of the operational amplifier.

Such a current-voltage conversion circuit is used for measuring the insulation resistance of a capacitor to be measured, for example, in combination with a voltage source. That is, the insulation resistance measuring device using the current-voltage conversion circuit connects the positive electrode end of the voltage source to one end of the measurement target capacitor and the other end of the measurement target capacitor to the reverse phase input end of the operational amplifier. In addition, by grounding the negative terminal of the voltage source and the positive phase input terminal of the operational amplifier, the measurement current flowing from the measurement target capacitor to the feedback resistor is converted to the voltage at the output terminal of the operational amplifier based on the insulation resistance value of the measurement target capacitor. Is detected.
The following Patent Documents 3 and 4 disclose a two-terminal circuit element measuring apparatus using the current-voltage conversion circuit.
JP 2003-309438 A JP 2002-043858 A JP 2004-020246 A Japanese Patent Laid-Open No. 2004-245584

  By the way, in the above conventional insulation resistance measuring device, the measurement target capacitor is brought into a connected state by contact-connecting the pair of measurement terminals and each end of the measurement target capacitor, but when both are not in normal contact, It is measured as a resistance value that is impossible to measure or an insulation resistance value of the capacitor to be measured is extremely high. Therefore, the conventional insulation resistance measuring apparatus has a problem that it cannot be determined whether the high resistance value is measured in a normal contact state or whether the high resistance value is measured due to the connection abnormality.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to realize a highly reliable measurement by detecting a connection abnormality between an external device such as a capacitor to be measured and a measurement terminal.

In order to achieve the above object, according to the present invention, as a first solution, in a current measuring device that detects a current input from an external device by converting it into a voltage, a predetermined ramp signal is transmitted to the measuring terminal. By comparing the predetermined ramp signal with a signal obtained by superimposing a signal obtained by converting a current input to the measurement terminal into a voltage applied to the predetermined ramp signal with the predetermined ramp signal, A means is provided that includes a connection abnormality detection means for detecting a connection abnormality with an external device .

  As a second solution means, in the first solution means, the connection abnormality detection means is connected between the operational amplifier having the negative phase input terminal connected to the measurement terminal, the negative phase input terminal and the output terminal of the operational amplifier. A current-voltage conversion circuit comprising a feedback resistor, a ramp signal generating means for generating a ramp signal having a positive slope and a reverse slope and outputting the ramp signal to the positive phase input terminal of the operational amplifier, and output from the ramp signal generating means A differential means for outputting a difference between the ramp signal and the voltage at the output terminal of the operational amplifier, and determining whether the measurement terminal and the external device are abnormally connected based on whether the output of the differential means exceeds a predetermined threshold value And a means for detecting the current input to the measurement terminal as a voltage at the output terminal of the operational amplifier.

  As a third solving means, in the second solving means, the ramp signal generating means includes a negative phase integrating circuit using a second operational amplifier, and an input terminal of the negative phase integrating circuit is set to a positive voltage or a negative voltage. A means is adopted which comprises an input switching circuit for switching and a switch for short-circuiting the negative phase input terminal and the output terminal of the second operational amplifier.

  As a fourth solution, based on the current flowing in the capacitor to be measured which is further provided with a voltage source in the second or third solution and is connected between one output terminal of the voltage source and the measurement terminal. Then, means for detecting the insulation resistance value of the capacitor to be measured as the voltage at the output terminal of the operational amplifier is adopted.

  According to the present invention, since the connection abnormality detecting means for detecting the connection abnormality between the measurement terminal and the external device by comparing the current input to the measurement terminal with a predetermined lamp signal is provided, the measurement terminal and the external device are provided. It is possible to separate the measurement of abnormal minute current due to abnormal connection with the measurement of normal minute current when the connection between the measurement terminal and the external device is normal, thus realizing more reliable current measurement than before can do.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing a configuration of an insulation resistance measuring apparatus A (current measuring apparatus) according to the present embodiment. In this figure, T1 and T2 are a pair of measurement terminals, 1 is a current-voltage conversion circuit, 2 is a voltmeter, 3 is a lamp signal generation circuit, 4 is a contact failure detection circuit, 5 is a voltage source, and 6 is an operation control unit. Cx is a capacitor to be measured.

  The current-voltage conversion circuit 1 includes an operational amplifier U1 and a feedback resistor R1, and the ramp signal generation circuit 3 includes an operational amplifier U2, an integrating capacitor C1, an integrating resistor R2, and three switches S1 to S3 ( The contact failure detection circuit 4 includes a differential amplifier 7 and a comparator 8. Among these components, a pair of measurement terminals T1, T2, excluding the measurement target capacitor Cx, current-voltage conversion circuit 1, voltmeter 2, ramp signal generation circuit 3, contact failure detection circuit 4, voltage source 5 and operation control unit 6 constitutes the insulation resistance measuring apparatus A as a unit. Note that the voltage source 5 may not be provided integrally in the insulation resistance measuring apparatus A but may be provided as a separate body in consideration of user convenience.

  Among the measurement terminals T1 and T2, the current-voltage conversion circuit 1, the voltmeter 2, the ramp signal generation circuit 3, the contact failure detection circuit 4, the voltage source 5 and the operation control unit 6 constituting the insulation resistance measuring apparatus A The measurement terminals T1 and T2, excluding the voltmeter 2, the current-voltage conversion circuit 1, the ramp signal generation circuit 3, the contact failure detection circuit 4, the voltage source 5 and the operation control unit 6 are connected abnormality detection means in this embodiment. It is composed.

  Of the pair of measurement terminals T1 and T2, one measurement terminal T1 is connected to the reverse phase input terminal of the operational amplifier U1 and one end of the measurement target capacitor Cx. The other measurement terminal T2 is connected to the voltage source 4 at the positive electrode end and to the other end of the measurement target capacitor Cx.

  The current-voltage conversion circuit 1 is a current-voltage conversion circuit including an operational amplifier U1 and a feedback resistor R1 provided between the negative phase input terminal and the output terminal of the operational amplifier U1. Such a current-voltage conversion circuit 1 generates a voltage V2 based on the current I1 input through the one measurement terminal T1 and the voltage V1 input from the ramp signal generation circuit 3, A voltage is output to the outside and an evaluation signal is output to one input terminal (for example, a positive phase input terminal) of the differential amplifier 7.

  The voltmeter 2 is an integral voltmeter that measures the measurement voltage output from the current-voltage conversion circuit 1. The ramp signal generating circuit 3 has an operational amplifier U2, an integration capacitor C1 provided between the negative phase input terminal and the output terminal of the operational amplifier U2, and one end connected to the negative phase input terminal of the operational amplifier U2. And an integrating resistor R2, and a switch S1 provided between the other end of the integrating resistor R2 and the positive reference voltage + Vref, the other end of the integrating resistor R2 and the negative reference voltage − A switch S2 provided between Vref and a switch S3 connected in parallel to the integrating capacitor C1.

  Such a ramp signal generating circuit 3 generates a voltage V1 composed of a ramp signal having a positive slope, a ramp signal having a reverse slope, or a constant voltage signal in accordance with the open / closed state of the three switches S1 to S3. It outputs to the phase input terminal and the other input terminal (for example, reverse phase input terminal) of the differential amplifier 7. This ramp signal generating circuit 3 is a ramp signal generating means in this embodiment. Of the three switches S1 to S3, two switches S1 and S2 are input switching circuits in the present embodiment.

Contact failure detection circuit 4 includes a differential amplifier 7 which outputs a voltage V3 by amplifying a difference between the voltages V1 and V2, the voltage V3 predetermined teeth at the timing of determination pulse input from the operation control section 6 Comparing with a threshold value comparator 8, the output of the comparator 7 is output to the outside as a contact failure detection signal. Such a contact failure detection signal is a signal indicating whether the connection state of the capacitor Cx to be measured at the pair of measurement terminals T1 and T2 is normal connection due to normal contact or abnormal connection due to contact failure. The differential amplifier 7 is a difference means in this embodiment, and the comparator 8 is a determination means in this embodiment.

The voltage source 5 is a constant voltage source that outputs a constant voltage Vd. The operation control unit 6 receives the user's operation instruction and operates the switches S1 to S3 and the comparator 6 based on the operation instruction and a control program stored in advance, so that the entire insulation resistance measuring apparatus A is entirely operated. It controls the operation.
The capacitor Cx to be measured is a capacitor well-known as an electronic element, and there is no particular feature in its type. That is, the measurement target capacitor Cx may be any type of electrolytic capacitor, various film capacitor, and the like. This measurement target capacitor Cx is an external device in the present embodiment.

  Next, the characteristic operation of the insulation resistance measuring apparatus A configured as described above will be described in detail with reference to FIG.

  The insulation resistance measurement using this insulation resistance measuring apparatus A is completed through three steps as shown in FIG. The first process is a connection check process, the second process is a discharge process, and the third process is an insulation resistance measurement process.

When the user connects the capacitor Cx to be measured to the measurement terminals T1 and T2, charging is started by the voltage source 5 (not shown). When the operation control device 6 is instructed to start measurement after full charge, the operation control device 6 turns off the switch S1 and sets the switch S2 to the period Ta (integration time) from time t1 to t2 in the first connection check process. ) Only in the ON state, and the switch S3 is set in the OFF state from time t1 in synchronization with the switch S2. In such a set state of the switches S1 to S3, the negative reference voltage -Vref is supplied to the negative phase integrating circuit of the ramp signal generating circuit 3 over the period Ta, so that the output voltage V1 is shown in FIG. As shown in FIG. 4, the ramp signal has a positive slope whose value increases with a constant slope sequentially with time.

  Such a voltage V1 is represented by the following equation (1) including a negative reference voltage -Vref, an integrating resistor R2, an integrating capacitor C1, and a time variable t. Such a ramp signal having a positive slope is input to the positive phase input terminal of the operational amplifier U1.

  Since the negative phase input terminal of the operational amplifier U1 is controlled to be the same as the positive phase input terminal by negative feedback control, the same signal as the voltage V1 is generated. As a result, the current I1 corresponding to the measurement target capacitor Cx (capacitance) is input to the measurement terminal T1 as shown in the following equation (2). That is, the current I1 is obtained by assuming that the value of the voltage V1 at time t2 is Vp, and that the insulation resistance value of the measurement target capacitor Cx is sufficiently large, the measurement target capacitor Cx (capacitance), the voltage Vp, It is represented by the following formula (2) consisting of

  When such a current I1 and the ramp signal having the positive slope are input to the current-voltage conversion circuit 1, the voltage V2 at the output terminal of the current-voltage conversion circuit 1 (operational amplifier U1) is as shown in FIG. The voltage ΔVc generated by the current I1 and the feedback resistor R1 is superimposed on the positive ramp signal. If the input impedance of the operational amplifier U1 is sufficiently large, the voltage ΔVc depends on the current I1 and the feedback resistor R1, and thus has a value reflecting the capacitance of the measurement target capacitor Cx.

Here, the voltage ΔVc is a value indicating the capacitance of the measurement target capacitor Cx when the measurement target capacitor Cx is normally contact-connected to the measurement terminals T1 and T2. When the measurement terminals T1 and T2 are not normally contact-connected, the capacitance between the measurement terminals T1 and T2 is much smaller than the measurement target capacitor Cx. The value does not indicate capacity.

  Such a voltage V2 and the positive slope ramp signal are differentially amplified by the differential amplifier 7, and the voltage V3 which is the output of the differential amplifier 7 is defined by the magnitude of the current I1 as shown in FIG. The above signal. Then, the comparator 8 outputs a contact failure detection signal by comparing the voltage V3 indicating the voltage ΔVc with a predetermined threshold at the timing of the determination pulse input from the operation control unit 6.

  This threshold is determined by taking into account the difference in capacitance between the measurement terminals T1, T2 depending on whether the measurement target capacitor Cx is normally connected or abnormally connected (connection failure). The connection failure detection signal is set as a value that can identify whether the connection state between the measurement terminals T1 and T2 is normal or abnormal, and the contact failure detection signal indicates whether the connection state between the measurement target capacitor Cx and each measurement terminal T1 or T2 is normal / normal. It becomes a signal having a different logic level depending on the abnormality, that is, a signal indicating whether the connection state is normal or abnormal by a difference in logic level.

  As described above, in the connection check process immediately after the start of measurement, the voltage ΔVc is large (that is, the capacitance between the measurement terminals T1 and T2) with the switch S1 in the ON state and the switches S2 and S3 in the OFF state. Is detected to detect normality / abnormality of the connection state between the measurement target capacitor Cx and each of the measurement terminals T1, T2, and a contact failure detection signal indicating the detection result is output to the outside.

  Subsequently, the discharge process is performed after the connection check process. As shown in FIG. 2, the switch S1 is turned on for the period Tb (integration time) from time t3 to t4, and the switches S2 and S3 are turned on. By setting the switch to the OFF state, the voltage V2 is changed to a ramp signal having a negative slope. The voltage V2 at this time is expressed by the following expression (3) because the positive phase reference voltage + Vref is supplied to the negative phase integrating circuit of the ramp signal generating circuit 3.

  In such a discharge process, the voltage V2 is used as a ramp signal having a negative slope, so that the charge accumulated in the measurement target capacitor Cx in the previous connection check process is completely discharged. As a result, in the subsequent insulation resistance measurement step, an excessive discharge current flows through the measurement target capacitor Cx to damage the measurement target capacitor Cx, and the operational instability of the operational amplifier U1 is avoided.

  In the final insulation resistance measurement step, as shown in FIG. 2, by setting the switches S1 and S2 to the OFF state and the switch S3 to the ON state, the voltage V2 is set to the ground potential (the positive phase input terminal of the operational amplifier U2). Potential). Therefore, the potential of the positive phase input terminal of the operational amplifier U1 in the current-voltage conversion circuit 1 is also the ground potential.

  In this insulation resistance measurement step, as shown in the figure, the measurement target capacitor Cx is in a fully charged state, so the current I1 becomes a voltage ΔVi indicating the insulation resistance value of the measurement target capacitor Cx. Such a voltage V2 (= ΔVi) is measured by the voltmeter 2 and substituted into the following equation (4) consisting of the voltage V2, the feedback resistor R1 and the output voltage Vd of the voltage source 5 to obtain the insulation resistance value Rx. It is done.

According to the present embodiment, in the connection check process performed as a pre-process of the insulation resistance measurement process, the measurement target capacitor Cx and the measurement terminals T1, T2 are evaluated by evaluating the capacitance between the measurement terminals T1, T2. Therefore, it is possible to realize highly reliable insulation resistance measurement for the measurement target capacitor Cx.
Further, since the discharging process is performed, it is possible to prevent an excessive discharge current caused by a short circuit or the like from flowing in the measurement target capacitor Cx in a subsequent process and damaging the measurement target capacitor Cx.

In addition, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) In the above embodiment, the present invention is applied to the measurement of the insulation resistance of the capacitor Cx to be measured. However, the present invention is not limited to such measurement of the insulation resistance, and various electronic components can be used. It can be applied to measurement of insulation resistance and various current measurements.

(2) In the above embodiment, the discharge process is performed after the connection check process. However, the discharge process may be deleted as necessary. Moreover, in the said embodiment, although the connection check process was made into the front process of the insulation resistance measurement process, it is good also as a post process of an insulation resistance measurement process.

(3) In the above embodiment, the ramp signal generating means of the present invention is configured as the ramp signal generating circuit 3, but the configuration of the ramp signal generating means is not limited to the ramp signal generating circuit 3. For example, the ramp signal generation means may be configured to generate a signal equivalent to the output signal of the ramp signal generation circuit 3 by a waveform generation program.

(4) In the above embodiment, the difference means of the present invention is configured as the differential amplifier 7 and the determination means of the present invention is configured as a comparator, but the present invention is not limited to this. For example, the functions of the differential amplifier 7 and the comparator 8 may be realized by digital signal processing based on software.

It is a circuit diagram which shows the structure of the insulation resistance measuring apparatus A concerning one Embodiment of this invention. It is a wave form diagram which shows operation | movement of the insulation resistance measuring apparatus A concerning one Embodiment of this invention.

Explanation of symbols

  A ... insulation resistance measuring device, T1, T2 ... measurement terminal, 1 ... current-voltage conversion circuit, 2 ... voltmeter, 3 ... lamp signal generation circuit, 4 ... contact failure detection circuit, 5 ... voltage source, 6 ... operation control unit , Cx: capacitor to be measured, U1, U2: operational amplifier, R1: feedback resistor, C1: integration capacitor, R2: integration resistor, S1 to S3: switch, 7: differential amplifier, 8: comparator

Claims (4)

In the current measurement device that detects by converting the current input from the external device to the measurement terminal into a voltage,
A signal obtained by converting a current input to the measurement terminal into a voltage in a state where the predetermined ramp signal is applied to the measurement terminal is superimposed on the predetermined ramp signal is compared with the predetermined ramp signal. Thus , a current measurement device comprising a connection abnormality detection means for detecting a connection abnormality between the measurement terminal and the external device. Connection abnormality detection means
A current-voltage conversion circuit comprising an operational amplifier having a negative phase input terminal connected to the measurement terminal, and a feedback resistor connected between the negative phase input terminal and the output terminal of the operational amplifier;
A ramp signal generating means for generating a ramp signal having a forward slope and a reverse slope and outputting the ramp signal to the positive phase input terminal of the operational amplifier;
Differential means for outputting a difference between the ramp signal output from the ramp signal generating means and the voltage at the output terminal of the operational amplifier;
A determination means for determining a connection abnormality between the measurement terminal and the external device based on whether the output of the difference means exceeds a predetermined threshold;
The current measuring apparatus according to claim 1, wherein the current input to the measuring terminal is detected as a voltage at an output terminal of the operational amplifier. The ramp signal generating means includes:
A negative phase integrating circuit using a second operational amplifier;
An input switching circuit for switching the input terminal of the negative-phase integrating circuit to a positive voltage or a negative voltage;
The current measuring device according to claim 2, further comprising: a switch that short-circuits the negative-phase input terminal and the output terminal of the second operational amplifier.   A voltage source; and an insulation resistance value of the measurement target capacitor based on a current flowing in the measurement target capacitor connected between one output terminal of the voltage source and the measurement terminal. The current measuring device according to claim 2, wherein the current measuring device is detected as a voltage.

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