| 摘要 |
PURPOSE:To avoid an error operation by using the zero level cut square wave, which is obtained at each terminal station, separately from the level cut square wave at positive polarity side of the power source end and at negative polarity side of the variable power source end. CONSTITUTION:A one-shot multivaibrator circuit 8A generates a pulse of 1/2 cycle width, simultaneously with a generation of output of a circuit 7A for providing a zero level cut square wave. A discrepancy detecting circuit 9A detects a discrepancy between outputs of the multivibrator 8A and the square wave conversion circuit 7A. A time limit circuit 10A makes a continuation of output of the discrepancy detecting circuit 9A. With an input current of the system frequency removed, the discepancy detecting circuit 9A generates an output, with this output made a continuation by the time limit circuit 10A, and an output of decision circuit 5A is locked by an AND circuit 11A, thus prventing a mistripping. |
