PROXIMITY ALARM SYSTEM

摘要

The spatial separation of an object from a reference location is monitored utilizing a proximity alarm system which comprises a transceiver station mounted on the object and a repeater station at the reference location. Both stations function to generate and transmit an encoded rf signal in a half-duplex manner, with the transceiver station initiating the process. In one embodiment of the system, a phase delay is measured between a remote signal originating at the transceiver station and a corresponding decoded timing signal received from the repeater station. Correlation of the phase delay with a reference value ascertains the distance between the stations and an alarm at the transceiver station is actuated when the distance exceeds a predetermined value. A second embodiment of the system employs a clock driven counter that is stopped when a predetermined multiple of decoded timing signals is received at the transceiver station in response to iterative transmissions therefrom. The count value of the counter is read and correlated with a transit time reference value to ascertain the distance between stations. An alarm is actuated if the distance exceeds a predetermined maximum.