System for time stamping events using a remote master clock

Abstract

Events at spaced locations, such as contact activity in the protective relays of an electric power distribution network, are time stamped using a single remote clock by a system which includes one or more slave stations monitoring the events. Each slave station initiates a count of locally generated clocking pulses of fixed duration upon detection of the first event monitored by it. Identification of the first event is stored in a first slot in memory. Additional memory slots each store the identification of a subsequent event and the count at the occurrence of that subsequent event. Upon command from a remote master station, the current count is stored in the first slot and the contents of the first slot and of the additional slots are transmitted over a communications network to the master station. The master station calculates the absolute time of each event using its master clock, the transmitted counts, the fixed duration of the clocking pulses, and the transmission time required to transmit the data from the particular slave station to the master station. The master station then sends a clear command to reset the count and clear the memory slots. If the number of events detected by a slave station before a clear command is received exceeds the number of memory slots available, the information on the first event stored in the first slot is retained, and the additional slots retain data on as many of the most recent events as there are additional slots.