Fecha de publicación: 15/10/1947 Fuente: WIPO "royal booby" 593,377. Locating conductors. CINEMATELEVISION, Ltd., and WEST, S. S. May 18, 1945, No. 12612. Addition to 574,808. [Class 37] An apparatus for detecting and locating metal objects whilst simultaneously ignoring the presence of a particular metallic substance, comprises two coils 20, 21, one only of which is tuned to resonance by a condenser 28 connected across the output of a valve amplifier and the other is connected across the input of the amplifier. When the coils approach a metal object, the amplifier circuit begins or ceases oscillation and a signal, heard in a pair of headphones, varies accordingly. This circuit is a modification of the circuit shown in Fig. 5 of the parent Specification in which both coils are tuned to resonance.