| 摘要 |
<p>PURPOSE: To obtain measurement signals which has no remanence current and no fluctuation caused by a leakage by compensating for a voltage drop caused by a current which flows through a secondary winding of a second current transformer while compensating for an offset voltage of an amplifier. CONSTITUTION: A common node 7 of secondary wirings 5, 6 of current transformers 1, 2 is connected with a negative input terminal 13 of an amplifier 14, while an output terminal 15 of the amplifier 14 is connected with the negative input terminal 13 by way of a series circuit made of a condenser 16 and a resistance 17. A bias potential of an input terminal 18 of the amplifier 14 is obtained by filtering the output signal thereof by a low-pass filter 21 and then feeding the filtered output signal to the input terminal 18 by way of a resistance circuit 27, 28. This output signal is added to a signal from the amplifier 14 by way of a resistance 22. The value of the resistance 22 is calculated such that the resistance 22 compensates for a voltage drop of the wiring 6 especially. Furthermore, a feedback loop of the amplifier 14 which acts on the input terminal 18 is determined such that the output voltage does not reache a saturated threshold value. A bias potential of the input terminal 18 also compensates for offset voltages of the amplifiers 10, 14.</p> |
