Surveillance alarm detection system - uses monitored coil inductance change caused by object removal from airgap between ferrite core halves to activate alarm

摘要

The surveillance alarm system, employs a detector coil (2) the inductance of which is monitored and the alarm operated by a variation in the coil inductance. - The surveillance object (6) is coupled directly to the two halves of a ferrite core (3), between which the coil winding (2) is positioned, so that the size of an air-gap (4) is dependent on the force applied to the core halves by the object (6). The removal of the latter causes a variation in the air gap, changing the value of the coil inductance which activates an alarm via a difference circuit.