Device for detecting metal objects passing through an opening

A metal detection device comprising:

• a housing defining a central aperture;
• a detection coil mounted to said housing and surrounding said aperture for generating an output voltage when a metal object is passed near said coil;
• means for automatically calibrating said detection coil by comparing said output voltage to a reference voltage to establish a threshold voltage output which ignores transient environmental fluctuations in said coil output voltage;
• a plurality of pulse emitting members spaced along a first side portion of said housing aperture;
• a plurality of pulse reception members spaced along a second side portion of said housing aperture opposite said first side portion to receive and sense the output of said pulse emitting members upon activation thereof;
• means for simultaneously activating said pulse emitting members upon generation of a coil output voltage above said threshold voltage;
• and
• means for triggering a detection signal when at least one of said pulse reception members fails to register the output of one or more pulse emitting members upon simultaneous activation of said pulse emitting members.

A device for detecting metal objects as they are inserted into a receptacle having an open upper end, said device comprising:

• a housing sized and shaped to cover said receptacle open upper end, said housing defining a central aperture for access to said open upper end;
• inductive means disposed within said housing surrounding said aperture for generating an output voltage when a metal object passes proximate thereto;
• means for automatically calibrating said induction means by comparing said output voltage to a reference voltage to provide a threshold voltage which is unaffected by transient environmentally induced fluctuations in said output voltage;
• means disposed in said housing and spaced about said aperture for selectively sensing the presence of an object passing through said aperture, said sensing means generating an electric signal in response thereto upon activation of said sensing means;
• means for activating said sensing means upon generation of an inductive means output voltage above said threshold voltage;
• and
• means for triggering an alarm detection signal in response to generation of said sensing means electric signal.