AUTOMATIC MONITOR FOR DIGITAL TYPE PROTECTIVE RELAY

摘要

PURPOSE:To monitor a defective or nondefective analog input circuit by extremely simple circuit constitution by providing an adding circuit and a digital signal processing circuit and overlapping DC voltage to an input signal as a signal for monitor. CONSTITUTION:A DC voltage generating circuit 13 generating DC voltage as a signal for monitor, an adding circuit 14 overlapping DC voltage to an analog signal and inputting a value obtained by overlapping to an analog input circuit 100, and a digital signal processing circuit digitally processing a digital signal white comparing DC voltage with magnitude before overlapping and discriminating the defective or nondefective analog input circuit 100 on the basis of the result of the comparison are provided. That is, the abnormality of the analog input circuit 100 can be discriminated by the change of DC voltage superposed as the signal for monitor. Accordingly, simple low-cost constitution in which a complicate circuit such as the generating circuit of higher harmonics is not required can be formed.