Security device for monitoring vertical plane - uses infrared beams criss crossing vertical plane with transmitter on vertical chassis and column of receivers

摘要

The security device is for protecting a vertical plane against intrusion and uses a simple arrangement of infrared beams criss-crossing the plane, which can typically be several hundred metres broad, and of more than a mans height. The system uses only two infrared sources. The device represents a simplification of similar equipment which uses many transmitters and receivers. It consists of a transmitter (3) mounted on a vertical chassis with a column of receivers (4) at one end of the plane and a similar arrangement (7, 8) at the other. Each transmitter excites all the receivers at the opposite end of the plane and these feed an AND gate (10, 13) in each case, which in turn excites the local transmitter. The system operates in a pulsed manner so that the interruption of any beam stops the local transmitter and triggers an alarm circuit.