| 摘要 |
PURPOSE:To suppress the voltage between terminals for fitting to a low level even when a resistance to be measured is detached by providing a reactance element with an opening/closing switch between current output terminals and opening the switch when the output of a synchronous detector is lower than a prescribed level. CONSTITUTION:When the resistance Rx to be measured is detached, the switch 9 is closed and an measurement current Is flows through the reactance element 8. At this time, the output level of a synchronous detector 11 is higher than the threshold voltage E of a comparator 14, so the switch 9 is still closed. At this time, the reactance voltage drop caused by the element 8 is developed between measurement terminals A and A'. Then when the resistance Rx is fitted, the current Is is shunt to the element 8 and resistance Rx and the output level of the detector 11 becomes lower than the voltage E, so that the switch 9 is opened. Then the current Is flows to the resistance Rx and the voltage between A and A' is in-phase with the voltage of an oscillator 1; and the output level of the detector 11 varies to 0 and the switch 9 is held open. At this time, the resistance voltage drop by the resistance Rx appears between the terminals A and A'.
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