Patent GB-577080-A (GB)
Title: Method and device for the location of faults, depth determination and tracing of electrical conductors
IPC: G01V3/06
Filed: 1944-02-09
Abstract: 577,080. Locating conductors ; detecting, indicating and locating faults. PLANER, V., and PLANER, F. E. Feb. 9, 1944, No. 2378. [Class 37] A device for the location of faults, depth determination and tracing of electrical conductors, comprises detector coils wherein at least two separate windings are provided for arrangement at different positions relative to each other and to a current carrying conductor, and wherein the detectors comprise sub-divided or laminated cores of ferro-magnetic material, and the windings are so connected as to allow individual displacement of either detector and/or superposition of the induced voltages in direct and opposite senses. Fig. 2 shows a detector coil having a core E composed of thin insulated strips of high permeability alloy. The turns D are arranged on the core E so as to occupy almost the complete surface. The whole is enclosed in a moulded cover consisting of two parts, F, G, of distinctive marking or colour. The cover may be provided with locating devices determining the position of the detector in the carrying case. Two such detectors are carried in a larger case from which they may be withdrawn. The case also houses an amplifier with its batteries and headphones and is provided with a shoulder strap or handles for transport. For locating a fault f, Fig. 3, the two detector coils D<3>, D' are connected so that the voltages induced in them by an alternating current in the cable C are additive and are applied to the input of an amplifier A supplying headphones T. The apparatus is moved along the cable until a reduction in the sound denotes approximately the position of the fault. The detectors D<3>, D<4> are then connected in opposition either by reversing one of the detectors or by operating a selector switch and reversing the connections of the windings. Normally a minimum sound is observed, a sudden rise in volume occurring at the position of the fault. For determining the depth of a cable two identical detectors connected in opposition to the input terminals of an amplifier are located at the same distance from the cable, as determined by the absence of sound in the headphones. The sensitivity of one of the detectors is then altered, e.g., by a change in the number of turns in the winding, a change in the core, or the addition of an auxiliary coil. Balance is then restored by raising the detector of greater sensitivity to a greater height until minimum sound is produced. The distance through which this detector has been moved is proportional to the depth of the conductor. Alternatively balance may be obtained by rotating one of the detectors, the depth being read from a calibrated scale. In a modification balance between two detectors D<1>, D<2> Fig. 1, located at different distances from the conductor may be established electrically. The voltage induced in the detector D<1> is balanced by means of a potentiometer P against a fraction of the voltage derived from the detector D<2>, the potentiometer being graduated to read the depth of the conductor. The resistances R, P may be equal so that the two voltages are approximately in phase, provided the input impedance of the amplifier Z is high compared with the resistances R, P. The apparatus is applicable also to depth measurement of pipes &c. A selector switch is provided for making the necessary connections for depth and fault determinations. A source of alternating current of audible frequency is connected between one end of the conductor and ground. The source may consist of an oscillator, an alternator, or an interrupter.