METAL PRESENCE DETECTION APPARATUS Russian patent published in 2007 - IPC G01V3/11 

FIELD: measuring instruments for detecting presence of metallic objects.

SUBSTANCE: apparatus includes self-excited oscillator with LC oscillation circuit whose inductor serves as sensing member; rectifier whose outlet is connected with threshold member; reference voltage generator made according to self-excited oscillator circuit with its own rectifier and LC compensating oscillating loop. Self-excited oscillator includes connected in series limiting amplifier and ramp amplifier. The last is connected with oscillation loop by forward feed circuit and limiting amplifier is connected with said loop by feedback circuit. Inductor of reference voltage generator is shifted relative to inductor of self-excited oscillator by value exceeding diameter of inductor of self-excited oscillator and it is screened against it and against environment. First inlet of threshold member is connected with outlet of self-excited oscillator; second inlet of threshold member is connected with outlet of reference voltage generator. Reference voltage generator may have metallic tuning shunt arranged in field of its inductance and made of metal of the same group as detected metal. Apparatus may have indicator connected n series with outlet amplifier.

EFFECT: enlarged temperature range, increased working gap at the same size of apparatus.

4 cl, 3 dwg