| 摘要 |
PURPOSE:To enable positive measurement, by automatically generating a calibration assigning signal when a changeover switch circuit is switched to a current measuring circuit. CONSTITUTION:A changeover switch 5b of a changeover switching circuit 5a is set to the measurement of current with no signal generated, a voltage from a calibration assigning light source 7 is applied to an automatic zero calibration circuit 3 as calibration assigning signal 102 after passing through a timer 11 and the circuit 3 starts to compensate a drift voltage of the assigning signal 101 of a DC amplifier 2. Here, a timer 11 is cut off to be returned automatically to the original position when a sufficient time has elapsed for the circuit 3 to perform a calibrating operation. On the other hand, an output of an AND circuit 13 is at 0 level while the timer 11 is in operation and goes to 1 level upon the time-out of the timer 11. With such an arrangement, a current measuring display 14 comes on when the zero-point calibration is completed, indicating to a measuring person that a measurement is enabled. Then, the measuring person pinches a circuit to be measured with a current probe 1. This enables positive and accurate measurement of current.
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