| 摘要 |
PURPOSE:To obtain correct results, by automatically adjusting variations in phase characteristics of an insulation resistance measuring circuit to always keep phase relationship between an input signal of a synchronous detector and a reference signal constant. CONSTITUTION:A series circuit of a capacitor and a switch is inserted in parallel with a ground wire LE, the switch is opened or closed at a cycle T and a part of an output of a filter FIL is provided to a synchronous detector MULT2 as input while a reference signal for a synchronous detector MULT1 is inputted into the other input terminal thereof through a 90 deg. phase shifter PSS. A component of frequency 1/T is extracted with a band pass filter BP from a second synchronous detection output to be inputted into a detector DET and an automatic phase adjustor PC which is inserted between an output terminal of a low frequency oscillator OSC and input terminals of the detector MULT1 and the phase shifter PSS is controlled by a DC voltage to be obtained at the output of the detector to maximize the DC voltage of the detector DET thereby enabling the obtaining of correct results of measurement.
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