GB575443A - Improvements in or relating to methods of detecting and/or locating by electrical means masses of electrically conducting or magnetic material - Google Patents

Abstract

575,443. Locating conductors ; temperature compensation. CINEMA-TELEVISION, Ltd., and WEST, S. S. March 29, 1943, Nos. 5059 and 5060. [Class 37] The proximity of masses of conducting or magnetic material is detected by a balanced bridge circuit with a search coil in one arm, temperature changes being compensated by the use of auxiliary non-inductive coils. The search coil may comprise the degaussing coil provided on a ship as a safeguard against magnetic mines. As shown, two arms 3, 4 of the bridge comprise the tapped secondary of a transformer fed from an electronic oscillator, alternator or the like. The other two arms of the bridge comprise a dust-core coil 2 of variable inductance, and the search coil 1. Associated physically with the search coil 1 is a non-inductive coil 5 which has the same resistance-temperature characteristic as the coil 1 and is connected in series with the coil 2. Another non-inductive coil 6 is associated with the coil 2 and connected in series with the coil 1 and with a variable resistance 7. The bridge is balanced by the adjustable elements 2, 7 ; and when the search coil approaches metal objects, the bridge is unbalanced and voltages appear across the output terminals 10, 11 which may be taken to an amplifier feeding an indicator. In a modification, Fig. 2 (not shown), the driving voltage is applied across a tapped resistance which replaces the input transformer. In this case the coil 2 need not be variable, but a variable resistance is included in one branch of the tapped resistance.