Metal detector system producing small changes in DC signals - has search coil connected to oscillator coil generating HF alternating field

摘要

The metal detector uses a search coil coupled to the oscillator coil. The search coil voltage is dependent on the coupling factor and it is rectified to form the d.c.-voltage signal. A scanning and holding circuit has a measuring voltage input for the d.c.-voltage signal and a timing input connected to a mining generator. A reference voltage output receives the d.c.-voltage signal valve stored by the holding circuit and readjusted via the scanning circuit. A comparator has one input for the instantaneous value of the d.c.-voltage signal and another input for the reference voltage. Scanning and holding circuit (13).