Patent US 4,112,463

A plural-camera television monitoring system in which scenes or objects to be monitored are scanned by a plurality of television cameras that are not synchronized with each other, in which time-division multiplexed image signals are derived from the video signals transmitted by the cameras for comparison with corresponding image signals that are stored at an earlier time to detect changes or motion in the scanned scenes, and in which a control signal is derived from time-division multiplexed synchronizing signals originating from the cameras and characterizes the end or beginning of either an odd or even field to initiate a sequence of operation involving the comparison of the time-division multiplexed image signals with their corresponding stored image signals.