Distributed security alarm network - detects several infringements separately and triggers appropriate timed alarm signal for each case

摘要

The distributed security alarm network is designed partic. for burglar alarm systems, in which a security infringement produces a timed alarm signal but leaves the rest of the network operational to detect any further infringements. The alarm network (1) contains a number of parallel circuits (2) each serving a number of local detection elements (9) arranged on pair of supply lines (8). These elements (9) essentially change impedance when a disturbance occurs, and this produces an imbalance voltage in a resistance bridge (11) in the evaluation circuit concerned. Each evaluation circuit also contains an amplifier (13) and logic array containing an inhibit flip flop (19) and all these circuits supply a logic unit (4), together these release an alarm (5, 6) when appropriate, and inhibit the relevant evaluation circuit by setting its flip flp (19), but leave the remaining circuits operational. An adjustable timer (7) allows the alarm signal duration to be set.