Patent GB-191389-A (GB)
Title: Improvements in and relating to electromagnetic underground prospecting
IPC: G01V3/06
Filed: 1923-01-04
Abstract: 191,389. Soc. Industrielle des Procedes W. A. Loth. Jan. 4, 1922, [Convention date]. Locating conductors; magnetic tests.-in prospecting electromagnetically to determine, for instance, the character of the subsoil or of submarine ground or to locate water pipes, electric lines, metallic or petroleum deposits or pools of water, a field of force, preferably an alternating field, is created and the inclination of the lines of force to the horizontal is determined at different points. The field may be created by means of an insulated cable 1, Fig. 1, supported above ground on posts 2, or buried in or lying on the ground or at the bottom of the sea, and connected at its ends, to earth plates 3, 4, a current being supplied to the cable directly or through a transformer 7 from an alternator 5 or other source and producing earth currents between the plates 3, 4. A metallic return wire beneath the cable 1 may also be used. The direction of the field of force is investigated and variations from the field to be inspected in homogeneous ground are determined by means of one or more receiving coils, the currents induced in the coils passing directly or through an amplifier and in some cases a rectifier to a current detector such as a galvanometer, a thermal or electrodynamic receiver, or a telephone with or without a resonator or loud speaker. A single, receiving coil may be supported on gimbals, or three fixed coils 10, 11, 12, Fig. 5, at right angles to one another may be connected singly or in pairs in series and in opposition to the detector, or may be connected to corresponding coils in a distant similar signaller system 13, 14, 15 having a movable coil 15<1> supported on gimbals and connected to the detector. The smaller system may be replaced by two systems of coils, one with three vertical coils two at right angles to each other and one movable, and the other system with fixed vertical and horizontal coils and a third coil movable about a horizontal axis. The system 13, 14, 15 may be supported on a pendulum or rested on the ground together with an indicator of the inclination of the ground to the horizontal. The receiving coils may be used above ground, underground in cavities or mining shafts, or under water, a repeater system being used to indicate the position of the distant coils so that allowance may be made for the inclination of the coils. A reception coil may be used in series with a line connected to earth at its ends, the coil receiving by induction and the line by conduction. Alternating current of musical frequency is preferably used, but ultra-audible or infra-audible frequencies with heterodyne or tikker reception systems, or interrupted direct current, or direct current with rotating receiving coils may also be used. A 3-phase alternator may be used in con nection with three cables 1 at 120‹ to each other. The apparatus for creating and investigating the magnetic field may be mounted on one carriage moved over the ground to be prospected, the cable 1 being unwound for use from a small drum.