Electronic energy door surveillance for intruder alarm system - uses latch plate and contacts to provide alarm signal in response to abnormal contact operating sequence

摘要

The electronic surveillance uses contacts (FK,RK) associated with the door latch plate and the door latch to provide an alarm signal when the door is opened, before the latch contact (RK) is operated during normal unlocking, or if both contacts (FK,RK) are operated simultaneously. The alarm signal is only inhibited if a normal delay interval between operation of the latch contact (RK) and the latch plate contact (FK) is obtained. Pref. the two contacts (FK,RK) are coupled to an OR-gate (OG) controlling a monostable flip-flop (MFF), in turn controlling a bistable flip-flop (BFF), providing the alarm signal (A) in response to an abnormal operating sequence.