| 摘要 |
PURPOSE:To measure insulation resistance, etc., regardless of temperature variation, secular change, etc., by providing the same characteristics to a circuit which generates a signal for detection, and the zero-phase device, amplifier, filter, etc., of a measuring circuit. CONSTITUTION:A low-frequency signal voltage for measurement with a frequency f1 different from the commercial frequency is applied to the cable run of a receiving transformer T with a load Z through a dual earth line LE by an oscillator OSC. Then, a component of frequency f1 in a leak current is detected by measuring circuit such as the zero-phase device ZCT, amplifier AMP, filter FIL1, etc., and supplied to a multiplying circuit MULT for synchronous detection. This circuit MULT is supplied with a detection signal from the circuit consisting of a zero-phase device ZCT1, amplifier AMP1, filter FIL1, phase shifter PS, etc., having the same characteristics with the phase device ZCT, etc., of the measuring circuit, so that temperature variation and secular change of each circuit element are canceled. Then, the insulation resistance, etc., of the cable run are measured from the leak current value without reference to temperature variation and a secular change.
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