Burglar alarm system encompassing a number of subscribers - has three conductor link lines to different premises detecting impedance changes

摘要

Burglar alarm system consisting of a supply unit, a detector unit and a burglary recorder. The system is intended for more than one subscriber located in different premises. The premises are interlinked by a loop line which links up with a voltage variation detector and a burglary annunciator. The loop contains three conductors which link up to the plugs of each of the subscribers. A signal is produced when at least one of the conductors in the loop line is put in open circuit condition. The detector will react to a variation in one or more of the loop impedances. The detector of the supply and detector unit consists of an input circuit with two operational amplifiers. The output is fed through logic circuits to the annunciator coil. The sensitivity level of the detector can be set by a balancing resistor.