SIGNAL TRANSMITTER

PURPOSE:To securely grasp an abnormal accident by storing history data of a current signal sent to a load side as a trend in specific form at specific intervals of time, and accessing the history data at need and referring to the past history data. CONSTITUTION:A microprocessor CPU stores data corresponding to the current signal I0 sent to the load side in an electrically rewritable EEPROM 2 at constant intervals of time, e.g. one hour or one day as a fixed-time process based upon a processing program stored in a read-only memory ROM. Consequently, the history data of the current signal I0 are stored in the memory EEPROM 2 in sequence. When the history data are accessed, a request command for the history data is sent as burst waveform serial data from a communication device HHT to terminals '+' and '-' of a conversion part 11 through transmission lines L1 and L2.