GB934963A - Improvements in or relating to intruder detection apparatus - Google Patents

Abstract

934,963. Locating conductive bodies. STANDARD TELEPHONES & CABLES Ltd. Sept. 12, 1961, No. 32716/61. Class 37. [Also in Group XXXVIII] An intruder detection system comprises a pair of single wire lines 10, 11 along the boundary to be protected, pulses being sent down the lines from a pulse generator 13, the arrangement being such that in the absence of an intruder any reflected signals will be equal and opposite and no reading will be obtained on the receiver 14, while in the presence of an intruder one of the reflected signals will be stronger, thereby producing an indication on the receiver of the position of the intruder. The generator 13 consists of a length of open wire transmission line 17 charged at one end from a D.C. source, the other end being left open, the pulses being produced by a chopper relay 20. Each of the lines 10, 11 is terminated in its characteristic impedance. The receiver 14 consists of a differential amplifier feeding a C.R.O. 22, the input to the receiver and to the lines 10, 11 from the transmitter being across the two diagonals respectively, of a resistance capacitance bridge 15. If the oscilloscope is polarity sensitive, it will also indicate which side of the boundary the intruder is in addition to this position. In another embodiment (Fig. 2), a resistance bridge 27 replaces the resistance capacitance bridge while in yet another embodiment (Fig. 3) a transformer 28 replaces the arms 25, 26. Each transmission line may consist of two or more conductors. Specification 933,495 is referred to.