GB845504A - A new or improved method of and apparatus for detection and location of discontinuities in electric cables - Google Patents

Abstract

845,504. Finding faults in cables. MILNER, F. E. Nov. 5, 1956 [Aug. 4, 1955], No. 21087/55. Class 37. Discontinuity in the core of a cable is located by providing an inductive or capacitive pick-up movable relative to the cable and including the coupling provided thereby in the feed-back circuit of an oscillator and detecting the change in the oscillator state (e.g. commencement or cessation of oscillation, or change in amplitude or frequency) as the pick-up moves past the Discontinuity. As shown the two, stage amplifier V 1 V 2 has its output coupled via condenser C9 to one of the conductors T 1 T 3 of a three cored cable by a switching mechanism S 1 . The cable is then run through a channeled coupling member CM connected to the input of the amplifier, the coupling between the member and the core being sufficient to cause the amplifier to oscillate when the discontinuity is reached the coupling is broken and oscillation ceases. The presence of the oscillations is detected by rectifiers W 2 , W 3 which operate. relay K 1 to light a lamp A 2 . If the cable is already laid an extended screened lead for a coupling member may be connected to terminal T 4 and extended leads for lamp may be connected to T 5 and T 6 . Alternatively earphones (connected between T 7 and earth) or measuring instruments may be used to detect variations in the state of oscillation. In a modification the oscillations may be caused to start only when the coupling is broken. In this case the feed-back circuit contains a bridge circuit balanced when normal coupling is effected between the coupling member and the core but unbalanced when a discontinuity is encountered.