초록 ▼

An apparatus is described for detecting the presence of metal objects which may be subterranean. The apparatus comprises an amplifier equipped with a feedback network for forcing the amplifier into oscillation. The amplifier is critically biased such that the minimum gain necessary to maintain oscil

An apparatus is described for detecting the presence of metal objects which may be subterranean. The apparatus comprises an amplifier equipped with a feedback network for forcing the amplifier into oscillation. The amplifier is critically biased such that the minimum gain necessary to maintain oscillation at the frequency of resonance is achieved. The presence of metal near the search coil which forms the tuned circuit of the amplifier loads the output circuit of the amplifier to a degree which suppresses oscillation. An indicator is provided to indicate when the oscillation has decreased in amplitude, whereby a metal object may be located.

대표청구항 ▼

A metal detecting device comprising: (a) a transistor amplifier including a tuned resonant circuit in the collector circuit of said transistor amplifier; said tuned resonant circuit being adapted to be located near a metal object; (b) a feedback circuit for providing a current from said resonant cir

A metal detecting device comprising: (a) a transistor amplifier including a tuned resonant circuit in the collector circuit of said transistor amplifier; said tuned resonant circuit being adapted to be located near a metal object; (b) a feedback circuit for providing a current from said resonant circuit to said transistor amplifier input for forcing said amplifier into an oscillating condition; (c) means for supplying a fixed biasing current to said transistor amplifier in response to a voltage occuring at said amplifier output upon momentary closure of a switch means connected to said amplifier output for maintaining the minimum gain necessary to cause said amplifier to oscillate at substantially the resonant frequency of said tuned resonant circuit in the absence of a metal object in proximity of said resonant circuit, said means providing a new fixed biasing current upon subsequent momentary actuation and release of said switch for reestablishing a minimum gain for producing oscillations in said amplifier compensating for a change in the effective Q of said resonant circuit due to the presence of said metal object; and (d) means for indicating when the amplitude of oscillations produced by said transistor amplifier decreases whereby the presence of said object is detected.