| 摘要 |
PROBLEM TO BE SOLVED: To detect the fault positively even a control circuit is defective and to prevent the transmission of unnecessary shielding output by judging the abnormality of digital data by the polarity of the instant values of the outputs of a pair of filters, and performing the operation only when the digital data are normal. SOLUTION: A polarity inverting circuit 14 for inverting the polarity of an output is added at the rear stage of a filter 2-2. In this circuit, in general, the inverting circuit using an operation amplifier is used. In an operating means 6, the digital data of the outputs of the filters 2-1 and 2-2 are read, and the fact that the polarities of these data are different is confirmed. It is judged that the data are normal when the polarities are different and that the data are abnormal when the polarities are equal. Only when the normal state is judged, the protecting relay operations of a main relay and an FD relay are performed. When the abnormality is judged, the specified alarming is performed, and the protecting relay operation is not performed. Therefore, even when the data for the main relay and the FD relay become abnormal at the same time, the unncessary shielding output is not transmitted. |
