Metal detector having one emitter and two receiver coils in head - producing complementary signals to differential amplifier in presence of metallic object such that constant output is maintained

摘要

The detector head articulated on a metal or plastic cone and connected by means of an electrical cable to a box containing the electronic and regulating equipment. The detector head consists of a sealed or non-sealed box containing three distinct coils. One coil serves as the emitter and is connected to an oscillator. The other two coils are receivers arranged such that a signal appears on each receiver when an oscillator signal is emitted by the emitter coil. Two receiver arrangements are possible. Either, in the presence of a large metallic mass, the signals issuing from the receivers diminish or augment simultaneously and are associated with a differential system so that the output voltage remains constant. Or, in the presence of a large metallic mass, the signal issuing from one of the receivers augments while the other diminishes and are associated with a summing system so that the output voltage remains constant. Each receiver has an amplification chain of identical gain, low noise, and high temp. stability.