GB574955A - Unitary balanced-inductor system - Google Patents

Abstract

574,955. Locating conductors ; magnetic tests. HAZELTINE CORPORATION. Dec. 24, 1943, No. 21683. Convention date, Dec. 31, 1942. [Class 37] [Also in Group XXXV] A unitary balanced inductor system, particularly for detecting buried metal objects or bodies of ore comprises a pair of relatively fixed inductors of the same shape but different sizes so proportioned that alternating currents of predetermined relative magnitudes and phases therein produce a magnetic. field which has zero intensity over a predetermined surface in space. A third inductor is positioned in fixed relation to the pair of inductors and lying in this surface, so that it has zero inductive coupling to the pair of inductors when carrying the predetermined currents and in the absence of external concentrated bodies of magnetic or conductive materials but has substantial inductive coupling in the presence of such materials. The complete indicating system shown in Fig. 1, includes an oscillation generator 10 and a receiver 11 having an indicating device 12 in its output circuit. The balanced inductor system 14 comprises a pair of inductors 15, 16 which are connected in series opposition to the oscillator 10. A third coil 18 is connected to the receiver 11. Normally the magnetic fields due to the coils 15, 16 neutralise one another at the position where the coil 18 is located, and no signal is developed in the receiver 11. The presence of a metal object in the vicinity upsets this balance and a signal is obtained. A construction of the inductor system is shown in Fig. 2. Each of the coils 15, 16, 18 is wound of thin insulated copper or aluminium ribbon cemented so as to be self-supporting. Each coil is mounted by spaced rubber beads 21 in concentric circular grooves 22, 23 cut in two flat pieces of wood. These are cemented together with crossed grain. The coils 15, 16 may alternatively be in parallel planes and the coil 18 may be in the same plane as one of these coils or may be otherwise arranged provided that the combined inductive effect on it of the coils 15, 16 is normally zero but is considerable in the presence of a conducting object. The coils 15, 16, 18 may alternatively be of square shape. The inductor system may have a carrying handle and may be counterweighted so as to maintain its relation to the surface of the ground while being carried. Specification 231,820, [Class 37], is referred to.