GB1424351A - Intrusion detector system - Google Patents

Abstract

1424351 Intruder alarms EMI Ltd 17 Jan 1973 [27 Jan 1972] 3797/72 Addition to 1289513 Headings G4N and G4H An intruder alarm comprises a plurality of fence sections S 1 , S 2 ... S n connected in series around a protected area, each section acting as a waveguide for electromagnetic energy injected by a transmitter T x and received by a receiver R x , repeaters R 12 , R 23 ..., between each pair of sections including an arrangement for sensing an intrusion in the leading section and for impressing upon the energy transmitted into the trailing section a code indicative of the leading section in the event of intrusion and a further arrangement including a detector DU and a console CC of lamps selectively lit in response to the code to indicate in which section an intrusion occurs. In each repeater shown in Fig. 2 the signal received by R x is applied via a pulse shaper PS for setting a bi-stable BS which in turn triggers a monostable MS for producing a pulse of predetermined duration which enables an AND gate A and keeps BS latched on via an inverter I and an OR gate X. When an echo pulse resulting from intrusion is received, it is sensed by gate A for modulating the regenerated signal transmitted by T x . A code detector DPC detects and enhances codes already present in the incoming signal.