JP3393022B2 - Insulation resistance tester - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulation resistance tester, and more specifically, it is configured to selectively display both the resistance value of a resistor to be measured and the AC voltage value of an AC power supply on a measuring meter. Insulation resistance tester.

[0002]

2. Description of the Related Art As this type of insulation resistance meter capable of selectively displaying both the measured resistance value of a resistance to be measured and the AC voltage value of an AC power source, an insulation resistance meter 120 shown in FIG. Known from. The insulation resistance meter 120 shown in FIG.
A high-voltage generation circuit 121 that boosts the battery voltage of the battery 2 by switching to generate a high voltage, and a load current and a reference current that flow in the measured resistor 3 when the high voltage is applied to both ends of the measured resistor 3. The resistance value indicating current for logarithmically indicating the resistance value of the resistor 3 to be measured based on the following, and the battery 2 during the voltage monitoring operation of the battery 2
And a logarithmic amplifier circuit 122 for generating a battery voltage instruction current for instructing the meter M to indicate the battery voltage.

This insulation resistance tester 120 comprises a resistor 3 to be measured.
Is configured to be capable of measuring or monitoring the three items of resistance value measurement, AC voltage measurement, and battery voltage monitoring of the battery 2. The operation of the insulation resistance meter 120 during each measurement and the like will be described below.

First, the operation of measuring the resistance value will be described. At the time of this measurement, the measurement start switch S11
Is operated, the movable contact c of the measurement start switch S11
Is connected to the normally closed contact a, and the battery power of the battery 2 is supplied to the high voltage generation circuit 121 via the normally closed contact a and the movable contact c.
Entered in. The high voltage generation circuit 121 boosts the battery voltage and outputs it to the measurement terminal T1. When a high voltage is applied to the measuring terminal T1, the measured resistor 3 and the measuring terminal T
2, the load current I _L is input to one input portion of the logarithmic amplifier circuit 122 via the diode 123 and the resistor 124. On the other hand, the high voltage is divided by the resistors 125 and 126 and input to the non-inverting input section of the operational amplifier 127. In this case, the operational amplifier 127 outputs the reference current I _R1 having a value obtained by dividing the high voltage by the resistance value of the resistor 128 to the other input section of the logarithmic amplifier circuit 122.

The logarithmic amplifier circuit 122 outputs a meter indicating voltage V _{M represented} by the following formula to the meter M on the basis of the load current I _L and the reference current I _R1 so that the resistance of the measured resistor 3 is measured. Instruct the meter M to indicate the value. V _M = K × Log (I _L / I _R1 ) In this case, the value K means a predetermined coefficient.

Next, the operation of measuring the AC voltage will be described. First, in a state in which the measurement start switch S11 is not turned on (that is, the power is off), an AC power supply line to be measured is connected between the measurement terminals T1 and T2 instead of the measured resistor 3. In this state, when the AC voltage applied to the measuring terminal T1 is a positive voltage higher than the AC voltage applied to the measuring terminal T2, the AC current from the AC power supply line is applied to the measuring terminal T1. Is entered via
Resistor 131, diode 132 and capacitor 133
After passing through the parallel circuit of the series circuit of and the series circuit of the resistors 125 and 126, it is fed back to the measuring terminal T2 via the ground, the meter M and the diode 134. On the contrary, when the measuring terminal T2 has a positive voltage, the diode 13
The alternating current does not pass through the meter M because the current path is blocked by 4. As a result, the AC voltage is indicated to the meter M by the half-wave component of the AC power supply.

Next, a battery voltage monitoring operation will be described. During this monitoring operation, when the switch S12 is operated, the movable contact c is connected to the normally closed contact a and the battery 2
The battery current I _B of the transistor 141, the resistor 142,
Transistor 143, switch S12, and resistor 12
4 to the input part of the logarithmic amplifier circuit 122. In this state, the transistors 141 and 143 operate, and as a result, the high voltage generation circuit 121 passes through the transistor 141.
When the battery power is input to the high voltage generation circuit 1,
21 generates a high voltage. However, the transistor 14
3 operates, the signal S _S generated across the resistor 145 is input to the high-voltage generation circuit 121. Therefore, the high-voltage generation circuit 121 causes the internal bleeder resistor (not shown) as a pseudo load to generate a current. Flow and do not output to the outside.
On the other hand, the switch S13 also moves in conjunction with the switch S12, the movable contact c is connected to the normally closed contact a, and the reference voltage V
_{re f} is input to the non-inverting input of the operational amplifier 127. The operational amplifier 127 applies the reference voltage V _ref to the resistor 128.
Logarithmic amplification circuit 1 of the reference current I _R2 divided by the resistance value of
22 is output. The logarithmic amplifier circuit 122 has a battery current I _B.
Also, based on the reference current I _R2 , the meter indicating voltage V _M is output to the meter M in the same manner as when the resistance value is measured, thereby causing the meter M to indicate the voltage value of the battery 2 logarithmically.

As described above, in the insulation resistance tester 120,
Three items can be measured or monitored.

[0009]

However, the insulation resistance meter 120 has the following problems. That is, in the insulation resistance meter 120, the battery voltage of the battery 2 is boosted by switching. Therefore, the measured resistor 3
When measuring the resistance value of, the switching noise is superposed on the high voltage, so that the noise component causes an error in indicating the meter M.

In this case, originally, the high voltage generation circuit 1
It is ideal to eliminate switching noise within 21. However, the high voltage generation circuit 121 outputs a high voltage of, for example, about 2 KV. Therefore, if a capacitor for removing switching noise is provided in the high voltage generation circuit 121, the usable capacitor is of a very high withstand voltage and large capacity type, which is extremely large and expensive. As a result, the insulation resistance tester becomes large and expensive. On the other hand, in this type of insulation resistance tester, it is necessary to connect an AC line to the measuring terminals T1 and T2 and measure the AC voltage.
A capacitor for removing switching noise cannot be connected to T2 or the like. After all, in the conventional resistance value measurement, some errors of the insulation resistance meter 120 in the resistance value measurement are treated as unavoidable. As described above, the conventional insulation resistance meter 120 has a problem that it is difficult to perform highly accurate resistance value measurement due to switching noise.

The present invention has been made in view of the above problems, and provides an insulation resistance meter capable of highly accurately measuring the resistance value of a resistor to be measured without increasing the size and cost of the device. The purpose is to provide.

[0012]

In order to achieve the above object, an insulation resistance tester according to claim 1 has a high voltage generating circuit for boosting an input power source to generate a high voltage, and a high resistance for a resistor to be measured. 1 measuring terminal capable of outputting a voltage and another measuring terminal capable of inputting a load current flowing through the resistor to be measured 1
An instruction to generate an instruction current for instructing the measurement meter to indicate the resistance value of the resistor under test based on the load current input via the pair of measurement terminals and the other measurement terminals and the load current path. And a capacitor for removing an AC component that is connected to the load current path and removes an AC component superimposed on the high voltage, and the input of the power supply to the high voltage generation circuit is stopped. 1 instead of the measured resistor
While the AC power supply line is connected between the pair of measurement terminals, the AC current of the AC power supply line input from one measurement terminal is formed between the measurement meter and the other measurement terminal and is loaded. By being fed back to another measuring terminal through a current path different from the current path, the measuring meter can be instructed to indicate the AC voltage between the AC power supply lines.

In this insulation resistance tester, when measuring the resistance value of the resistance to be measured, the high voltage output from one measuring terminal is applied to the resistance to be measured, and the load current flowing through the resistance to be measured. Input to the instruction current generation circuit via the other measurement terminal and the load current path. At this time, the AC component such as switching noise contained in the load current is composed of at least an AC component removing capacitor connected to the load current path and a resistance to be measured which is generally a high resistance. Removed by a low pass filter. Therefore, it is possible to perform highly accurate resistance value measurement by reducing a measurement error that occurs due to addition of an AC component superimposed on a high voltage by a measuring meter and indicating the result. In this case, the high voltage is dropped by the resistor to be measured, and the dropped voltage is applied to the AC removing capacitor. Therefore, a low voltage type capacitor can be used as the AC removing capacitor. Further, since the resistance to be measured is generally high resistance, the cutoff frequency of the low-pass filter can be set to a low frequency by the resistance to be measured itself and the small-capacity AC removing capacitor. , It becomes possible to remove AC components in lower frequencies. When a resistance having a low resistance value may be included in the measurement target as the resistance to be measured, the resistance may be connected in series between the other measurement terminal and the DC removal capacitor.

On the other hand, during the AC voltage measurement, the AC current of the AC power supply line connected to the pair of measurement terminals is input from one measurement terminal, passes through the measurement meter, and is connected to the load current path. It returns to the other terminal for measurement through a path different from. Therefore, it becomes possible to eliminate the error in the AC voltage measurement due to the AC current flowing into the AC removing capacitor.

The insulation resistance meter according to a second aspect of the present invention is the insulation resistance meter according to the first aspect, wherein when the input to the high voltage generation circuit of the power supply is stopped, the charge accumulated in the AC component removing capacitor is removed. It is characterized in that a charge discharging circuit for discharging is provided.

When measuring the AC voltage, a measurement error due to the AC current of the object to be measured flowing into the AC component removing capacitor does not occur, but if an electric charge is accumulated in the AC component removing capacitor. However, the charge may interfere with accurate AC voltage measurement. In this insulation resistance tester, the charge discharge circuit discharges the charge accumulated in the AC component removal capacitor when the AC voltage measurement can be started, that is, when the input to the high voltage generation circuit of the power supply is stopped. Let As a result, accurate AC voltage measurement can be performed.

The insulation resistance tester according to claim 3 is the insulation resistance tester according to claim 2, wherein the charge discharge circuit is capable of discharging the charge accumulated in the AC component removing capacitor during operation, and a power supply. It is equipped with a charging capacitor that can be charged when the power is turned on, and when the input to the high-voltage generation circuit of the power supply is stopped, switching is performed by supplying the charge accumulated in the charging capacitor to the switching element. It is characterized in that the element is activated.

In this insulation resistance tester, the charging capacitor is charged when the power is turned on, and when the input of the power supply to the high voltage generation circuit is stopped, the accumulated charge is supplied to the switching element. To do. As a result, the switching element operates and the electric charge accumulated in the AC component removing capacitor is discharged. As described above, this charge discharging circuit has a simple structure, but can reliably discharge the charges accumulated in the AC component removing capacitor when the input of the power supply is stopped.

An insulation resistance tester according to a fourth aspect is the insulation resistance tester according to the third aspect, wherein the charge discharging circuit includes a first resistor connected between the switching element and the charging capacitor, and a switching element. A second resistor connected between the AC component removing capacitor and the second resistor, wherein the time constant based on the first resistor and the charging capacitor is greater than the time constant based on the second resistor and the AC component removing capacitor. It is characterized by being set large.

In this insulation resistance meter, the time constant based on the first resistance and the charging capacitor is larger than the time constant based on the second resistance and the AC component removing capacitor, so that the AC component is stored in the AC component removing capacitor. The electric charge being stored is surely discharged by the time the electric charge stored in the charging capacitor is completely discharged. This makes it possible to perform accurate AC voltage measurement.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an insulation resistance meter according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a circuit diagram of the insulation resistance meter 1. The insulation resistance meter 1 shown in FIG.
Similar to 0, it is configured to be able to measure or monitor the three items of the resistance value of the resistor to be measured, the AC voltage, and the battery voltage of the power source battery. The configuration will be described in detail below.

The insulation resistance tester 1 includes a high voltage generator 11 for boosting the battery voltage of the battery 2 to generate a high voltage.
The high voltage generator 11 includes a transformer 12 for boosting the battery power source by switching, a transistor 13 as a switching element, a PWM circuit 14 for controlling switching of the transistor 13, and a pulse width of a control pulse output from the PWM control circuit. And a rectifying circuit 16 for rectifying and smoothing the high-voltage alternating current output from the transformer 12.

In the high voltage generator 11, when the measurement start switch S1 is operated, a stabilization circuit (not shown)
The circuit power supplies + V and -V are generated and the generated circuit power is supplied to each circuit. Then, the PWM circuit 14
By starting oscillation and outputting a control pulse to the transistor 13, alternating current is generated in the output winding of the transformer 12. The rectifier circuit 16 half-wave rectifies this AC and smoothes it, and outputs a high voltage of a predetermined voltage to the measuring terminal T1 (corresponding to one measuring terminal in the present invention). On the other hand, the operational amplifier 17 provided on the output side of the rectifier circuit 16
However, the divided voltage obtained by dividing the high voltage by the resistors 18 and 19 is output to the selection circuit 15. The selection circuit 15 also inputs the voltage value input via the measurement terminal T2 (corresponding to another measurement terminal in the present invention) at the time of resistance measurement, and, for example, the resistance value of the measured resistor 3 is The PWM circuit 14 is set so that the high voltage output from the rectifier circuit 16 is maintained at a constant voltage when the resistance is 0.5 MΩ or more, and the constant current flows through the resistor 3 when the resistance is less than 0.5 MΩ. Control.

The insulation resistance tester 1 also includes a logarithmic amplification circuit 31 corresponding to the instruction current generation circuit of the present invention, and a linear amplification circuit 51.

The logarithmic amplifier circuit 31 includes two operational amplifiers 3.
2 and 33, two NPN type transistors 34 and 35 having the same characteristics, diodes 36 and 37, and resistors 38 to 42.
And capacitors 43 and 44. In the logarithmic amplifier circuit 31, the meter indicating voltage V for logarithmically indicating the resistance value of the resistor 3 to be measured by utilizing the non-linear voltage-current characteristic in the forward characteristic of the PN junction of the transistors 34 and 35. Generate _M. Specifically, the logarithmic amplifier circuit 31 includes the reference current I _R input to the operational amplifier 33 via the resistor 20, the measured resistor 3, and the measurement terminal T.
Based on the load current I _L which is input via the 2, according to the following equation, to generate a voltage V _M for meter instruction, and outputs the generated voltage V _M for meter indication to the meter M. V _M = K × Log (I _L / I _R ) In this case, the value K means a predetermined coefficient.

The linear amplifier circuit 51 is a circuit for generating an instruction current proportional to the battery voltage of the battery 2, and includes two operational amplifiers 52 and 53 and resistors 54 to 58. In this linear amplifier circuit 51, when the switch S2 is operated, the movable contact c is connected to the normally closed contact a in association with the switch S3. In this state, the battery voltage of the battery 2 is divided by the resistors 54 and 55. And the divided voltage is applied to the operational amplifier 52.
Is input to the non-inverting input section of. Operational amplifiers 52 and 53
Amplifies the divided voltage with a gain of 1 and a predetermined gain, respectively, and outputs an instruction current I _B having a negative polarity to the meter M via the resistor 58 and the switch S3. on the other hand,
The battery voltage indicating scale of the meter M is linearly and evenly allocated in proportion to the battery voltage, and the meter M causes the pointer to move to the position of the scale according to the current value of the input indicating current I _B. .

The insulation resistance tester 1 further includes a battery voltage detection circuit 61. The battery voltage detection circuit 61 has a function of stopping the generation of the high voltage by the high voltage generation unit 11 when the battery voltage of the battery 2 is detected and falls below a predetermined allowable voltage and when the battery voltage is monitored. And includes transistors 62 to 64 and resistors 65 to 72.

In the battery voltage detection circuit 61, in a normal state, the reference power supply V _ref generated by the stabilization circuit (not shown) is applied to the base of the transistor 64 via the resistor 69, and the circuit power supply + V is applied. Resistor 71,
The divided voltage divided by 72 is applied to the base of the transistor 63, and the transistor 63 is in the operating state. In this state, the base of the transistor 64 is
A base voltage V _B represented by the following formula is applied. V _B = R ₆₈ × V _ref / (R ₆₈ + R ₆₉ ), where R ₆₈ and R ₆₉ mean the resistance values of the resistors 68 and 69, respectively. Therefore, by setting the resistance value of the resistor 69 sufficiently larger than the resistance value of the resistor 68, the base voltage V _B of the transistor 64 is maintained in the vicinity of 0 V in a normal state.
4 has stopped operating. In this case, the transistor 64
Has a function of stopping the operation of the PWM circuit 14 at the time of operation, so in this state, the PWM circuit 1
4 operates normally.

On the other hand, the resistance values of the resistors 71 and 72 are the same as those of the battery 2
Is preselected to shut down the transistor 63 when the battery voltage drops below an acceptable voltage. Therefore, when the battery voltage of the battery 2 drops below the allowable voltage, the base voltage V _B represented by the following formula is applied to the base of the transistor 64. V _B = (R ₆₈ + R _P ) × V _ref / (R ₆₉ + R ₆₈ + R _P ), where R _P means the parallel resistance value of the series resistance value of the resistors 66 and 65 and the resistance value of the resistor 67. To do. Therefore,
Resistance values 65 to 67 are set so that the base voltage V _B in this state exceeds the on-voltage (about 0.7 V) of the transistor 64.
Is defined, the transistor 64 operates, and thus the operation of the PWM circuit 14 is stopped.
Therefore, since the control pulse is not input to the transistor 13, the generation of the high voltage by the high voltage generation unit 11 is stopped. As a result, the measurement of the resistance value is stopped, so that the incorrect measurement of the resistance value can be avoided.

When the battery voltage is monitored, when the switch S2 is operated to connect the movable contact c to the normally open contact a, a battery current flows through the resistor 65. In this case, the resistor 6
The resistance value of 5 is specified in advance so that power equivalent to the power consumed by the resistor 3 to be measured is measured during resistance measurement. To be able to do. Further, when the battery voltage is supplied, the transistor 62
As a result, the base voltage V _B of the transistor 63 drops, which causes the base of the transistor 64 to
A base voltage V _B represented by the following formula is applied. V _B = R ₆₇ × V _IN / (R ₆₆ + R ₆₇ ) + R ₆₇ × V _ref /
(R ₆₇ + R ₆₉ ), where R ₆₆ , R _67, and V _IN are the resistance 66
Means the resistance value of, the resistance value of the resistance 67 and the battery voltage,
In the above equation, the resistance value of the resistor 68 is 69, 67.
Since it is much smaller than the resistance value of, the effect of its existence is ignored. Since this base voltage V _B becomes higher than the ON voltage of the transistor 64, the transistor 64
As a result, the high voltage generation operation of the high voltage generation unit 11 is stopped.

Further, the insulation resistance tester 1 is provided with a P-channel type FET 81, a diode 82 and resistors 83 and 84 for forming a current path of an alternating current when measuring an alternating voltage. In this case, during the resistance measurement, the FET 81 is in the operation stopped state because the divided voltage obtained by dividing the circuit power supply + V by the resistors 83 and 84 is applied to the gate, and the power supply is cut off. In this state, the gate voltage becomes 0 V, so that the operating state is maintained. Therefore, in this insulation resistance tester 1, when the power supply is off, the measuring terminals T1 and T2 are used instead of the measured resistor 3.
If an AC line is connected between the two terminals, if the AC voltage applied to the measurement terminal T1 is a positive voltage than the AC voltage applied to the measurement terminal T2, the AC current input from the measurement terminal T1 Flows into the ground through a parallel circuit of a series circuit of the resistor 22, the diode 23, the normally closed contact b of the measurement starting switch S1, the movable contact c and the capacitor 21, and the series circuit of the resistors 18 and 19, and , Meter M, switch S3, FET 81 and diode 82
It returns to the measuring terminal T2 via. On the contrary, when the measuring terminal T2 has a positive voltage, the diode 82 cuts off the current path, so that the alternating current does not pass through the meter M. As a result, the AC voltage is indicated to the meter M by the half-wave component of the AC power supply.

In addition, the insulation resistance tester 1 includes an NPN type transistor 91 and an AC component removing device in the present invention for removing an AC component in the load current path between the measuring terminal T2 through which the load current I _L flows and the logarithmic amplifier circuit 31. A capacitor 92, which corresponds to a capacitor and is an electrolytic capacitor, and a resistor 93 are provided. When the load current I _L flowing through the resistor 3 to be measured is input to the logarithmic amplifier circuit 31 via the measuring terminal T2, the transistor 91 and the resistor 93, the capacitor 92
The switching noise of the transistor 13 superimposed on the load current I _L is removed. In this case, transistor 1
Although it is difficult to completely remove the switching noise of No. 3 in the rectifier circuit 16, if it is superposed on the load current I _L , it is added to the meter M and instructed, which causes a measurement error. Cause. Therefore, in the insulation resistance tester 1, switching noise is removed by a CR type low-pass filter formed by the resistor 3 to be measured, which is generally high resistance, and the capacitor 92. It is decreasing.

In this case, the high voltage output from the measuring terminal T1 is dropped by the resistor 3 to be measured, and the dropped voltage is applied to the capacitor 92.
For 2, a low voltage type can be used.
Further, since the resistance to be measured 3 is generally high resistance, the cutoff frequency of the CR type low-pass filter can be set to a low frequency with a small-sized and small-capacity capacitor. AC components such as noise can be removed. When a resistance having a low resistance value may be included in the measurement target as the resistance body 3 to be measured, between the collector of the transistor 91 and the resistance 93,
The cutoff frequency of the low pass filter may be set to a low frequency by connecting in series a resistor for forming a part of the CR type low pass filter.

Furthermore, the insulation resistance tester 1 includes a capacitor 92.
A charge discharge circuit 101 is provided for discharging the charge accumulated in the capacitor when the measurement of the AC voltage is started. The charge discharging circuit 101 includes a transistor 102 and an N-channel FET 10 corresponding to the switching element of the present invention.
3, diode 104, capacitor 105 corresponding to the charging capacitor in the present invention, and resistors 106 to 1
It is equipped with 09.

In the charge discharging circuit 101, when the AC voltage is measured, the path through which the AC current is fed back to the measuring terminal T2 is prevented from being cut off by the charges accumulated in the capacitor 92. Specifically, when measuring AC voltage,
The series circuit of the capacitor M and the transistor 91 is equivalently connected in parallel to the series circuit of the meter M, the FET 81, and the diode 82. Therefore, when the electric charge is accumulated in the capacitor 92 and the voltage between the terminals is equal to or higher than a predetermined value, a reverse bias is applied to the series circuit of the FET 81 and the diode 82, and as a result, the diode 82 is
May be cut off and the AC current path may be cut off. Therefore, it is necessary to discharge the electric charge accumulated in the capacitor 92 in the power-off state in which the AC voltage measurement is performed.

In this charge discharging circuit 91, the transistor 102 is maintained in the operating state while power is being supplied, and as a result, the collector potential of the transistor 102 is held at a negative potential. For this reason,
The FET 103 is in a cutoff state because a negative potential is applied to its gate via the resistor 108. Therefore, in this state, the electric charge accumulated in the capacitor 92 is not released, and the capacitor 92 does not receive the load current I.
Removes switching noise superimposed on _L. On the other hand, when the power is turned off, the transistor 102 is turned off. As a result, the charge accumulated in the capacitor 105 in the power-on state is passed through the resistors 107 and 108 to the FE.
It is supplied to the gate of T103. Therefore, FET10
As a result, the charge accumulated in the capacitor 92 is discharged to the ground through the resistor 109 and the FET 103, and as a result, the application of the reverse bias to the series circuit of the FET 81 and the diode 82 is blocked. In this case, the diode 104 blocks the discharge of the electric charge accumulated in the capacitor 105 to the power supply line side, and the diode 104 and the resistors 107 and 108 (both of which correspond to the first resistor in the present invention). Resistance value and capacitor 105
Is set to be larger than the time constant based on the capacitance value of the capacitor 92 and the resistance value of the resistor 109 (corresponding to the second resistor in the present invention). Therefore, the electric charge accumulated in the capacitor 92 is surely discharged before the electric charge accumulated in the capacitor 105 is completely discharged.

Next, the operation of the insulation resistance tester 1, particularly each operation during resistance value measurement, AC voltage measurement and battery voltage monitoring will be described.

First, the operation of measuring the resistance value will be described. In this measurement, when the measurement start switch S1 is operated, the movable contact c of the measurement start switch S1 is connected to the normally closed contact a, and the battery power of the battery 2 is changed to the normally closed contact a.
And is input to the transformer 12 via the movable contact c.
On the other hand, the PWM circuit 14 outputs a control pulse having a predetermined width to the transistor 13 under the control of the selection circuit 15. As a result, the rectifier circuit 16 outputs the high voltage boosted to a predetermined voltage to the measurement terminal T1. When a high voltage is applied to the measuring terminal T1, the measured resistor 3, the measuring terminal T2,
Through the transistor 91 and the resistor 93, the load current I
_L is input to the logarithmic amplifier circuit 31. At this time, the switching noise superimposed on the load current I _L is removed by the capacitor 92.

On the other hand, the high voltage is divided by the resistors 18 and 19 and is also input to the non-inverting input section of the operational amplifier 17. In this case, the operational amplifier 17 outputs the high voltage to the resistor 2
The reference current I _R having a value divided by the resistance value of 0 is output to the logarithmic amplifier circuit 31. The logarithmic amplifier circuit 31 uses the load current I _L and the reference current I _R to generate the voltage V for meter instruction described above.
Outputting _M to the meter M causes the meter M to logarithmically indicate the resistance value of the resistor 3 to be measured.

Next, the operation of measuring the AC voltage will be described. First, in the state in which the measurement start switch S1 is not turned on (that is, the power is off), an AC power supply line to be measured is connected between the measurement terminals T1 and T2 in place of the measured resistor 3. In this state, when the AC voltage applied to the measurement terminal T1 is a positive voltage than the AC voltage applied to the measurement terminal T2, the AC current from the AC power supply passes through the measurement terminal T1. Is input as a series circuit of resistor 22, diode 23 and capacitor 21 and resistor 1
After passing through the parallel circuit of the series circuit of 8 and 19, it is fed back to the measuring terminal T2 via the ground, the meter M, the switch S3, the FET 81 and the diode 82. On the contrary, when the measuring terminal T2 has a positive voltage, the diode 82
The alternating current does not pass through the meter M because the current path is blocked by. As a result, the voltage is indicated to the meter M by the half-wave component of the AC power supply.

Next, a battery voltage monitoring operation will be described. During this monitoring operation, when the switch S2 is operated, the movable contact c is connected to the normally closed contact a and the divided voltage obtained by dividing the battery voltage of the battery 2 by the resistors 54 and 55 is the non-inverting input of the operational amplifier 52. Input to the department. Operational amplifier 52
Outputs the divided voltage amplified by a gain of 1 to the operational amplifier 53. Then, the operational amplifier 53 is inverted and amplified by a predetermined gain, thereby, an instruction current I _B of a value obtained by dividing the resistance value of the resistor 58 and the output voltage is input to the meter M through a switch S3. In this case, since the battery voltage indicating scale of the meter M is linearly and evenly allocated in proportion to the battery voltage and the dynamic range of the battery voltage indicating scale is large, the measurer can easily determine the remaining capacity of the battery 2. As a result, the battery replacement timing can be surely determined.

As described above, according to the insulation resistance tester 1 of this embodiment, when measuring the resistance value of the resistance body 3 to be measured, the AC component such as the switching noise included in the load current I _L becomes the capacitor. 92 and the resistance 3 to be measured, which is generally high resistance, so that the AC component superposed on the high voltage is added to the meter M to give an instruction. The measurement error that occurs can be reduced, which allows highly accurate resistance value measurement. In this case, since a small and low-priced AC removing capacitor can be used, highly accurate resistance value measurement can be performed without inviting an increase in the size and cost of the device.

In the present embodiment, an example in which an electrolytic capacitor is used as the AC removing capacitor has been described, but the present invention is not limited to this, and various types of capacitors such as a ceramic type capacitor can be used. Of course.

Further, as a switching element in the charge discharging circuit, a transistor can be used instead of the FET, and an SCR (silicon controlled rectifying element) or the like can be used. Further, in the present invention, the circuit configuration itself of the charge discharging circuit can be appropriately changed.

[0046]

As described above, according to the insulation resistance tester of the present invention, the AC component such as the switching noise contained in the load current is connected to the load current path to remove the AC component. It is removed by the low-pass filter that is composed of at least the resistance to be measured, which is generally high resistance, so it is generated by adding the measurement meter for the AC component superimposed on the high voltage and instructing it. It is possible to reduce the measurement error that occurs, and thereby to perform the resistance value measurement with high accuracy without increasing the size and cost of the device. When measuring AC voltage, the AC current input from one measurement terminal is fed back to another measurement terminal via a path different from the load current path, so AC current may flow into the AC removal capacitor. The AC voltage can be accurately measured without causing an error in the AC voltage measurement due to

According to the insulation resistance tester of the present invention, the charge discharging circuit discharges the charge accumulated in the AC component removing capacitor when the input to the high voltage generating circuit of the power supply is stopped. As a result, accurate AC voltage measurement can be performed without being hindered by the charges accumulated in the AC component removing capacitor.

Further, according to the insulation resistance tester of claim 3, when the charging capacitor is charged when the power is on and the input of the power supply to the high voltage generating circuit is stopped,
The charge accumulated in the charging capacitor is supplied to the switching element, so that the charge accumulated in the AC component removing capacitor is released by the switching element. The charge accumulated in the capacitor can be surely discharged.

According to the insulation resistance tester of the present invention, the time constant based on the first resistance and the charging capacitor is larger than the time constant based on the second resistance and the AC component removing capacitor. The electric charge accumulated in the AC component removing capacitor is surely discharged by the time the electric charge accumulated in the charging capacitor is completely discharged, whereby accurate AC voltage measurement can be performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an insulation resistance tester according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional insulation resistance meter.

[Explanation of symbols]

1 Insulation resistance tester 2 batteries 3 Resistor to be measured 11 High voltage generator 31 logarithmic amplifier circuit 81 FET 82 diode 91 transistor 92 Capacitor 93 resistance 101 Charge emission circuit 103 FET 105 capacitor 107 resistance 108 resistance 109 resistance M meter T1 measurement terminal T2 measurement terminal

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-166416 (JP, A) JP-A-4-66877 (JP, A) JP-A-55-154472 (JP, A) Actual development Sho-62- 14385 (JP, U) Actual development 51-84570 (JP, U) Actual public 47-6395 (JP, Y1) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01R 27/02 G01R 19 / 00

Claims (4)

(57) [Claims] 1. A high-voltage generation circuit for boosting an input power supply to generate a high voltage, one measuring terminal capable of outputting the high voltage to a resistor to be measured, and a load flowing through the resistor to be measured. A resistance value of the measured resistor based on the pair of measuring terminals including another measuring terminal capable of inputting a current and the load current input via the other measuring terminal and the load current path. For generating an instruction current for instructing the measuring meter to indicate, and an AC component removing capacitor for removing an AC component that is connected to the load current path and is superimposed on the high voltage. In the state in which the input of the power supply to the high-voltage generation circuit is stopped and an AC power supply line is connected between the pair of measurement terminals instead of the measured resistor, the one measurement Input from the terminal for The alternating current of the alternating-current power supply line is formed between the measuring meter and the other measuring terminal and is fed back to the other measuring terminal via a current path different from the load current path. Therefore, the insulation resistance meter is configured to be able to indicate the AC voltage between the AC power supply lines to the measuring meter. 2. A charge discharging circuit for discharging the electric charge accumulated in the AC component removing capacitor when the input of the power source to the high voltage generating circuit is stopped. The insulation resistance meter according to claim 1. 3. The charge discharging circuit includes a switching element capable of discharging a charge accumulated in the AC component removing capacitor during operation, and a charging capacitor capable of charging when the power is turned on. The switching element is operated by supplying the electric charge accumulated in the charging capacitor to the switching element when the input of the power source to the high voltage generation circuit is stopped. Item 2. An insulation resistance tester. 4. The charge discharging circuit includes a first resistor connected between the switching element and the charging capacitor, and a first resistor connected between the switching element and the AC component removing capacitor. And a time constant based on the first resistor and the charging capacitor is set to be larger than a time constant based on the second resistor and the AC component removing capacitor. The insulation resistance meter according to claim 3.