Magnetic metal detector utilizing a magnetic bridge formed with permanent magnets and a hall effect sensor

Claim 1

APPARATUS FOR DETECTING THE PRESENCE OF A BODY OF MAGNETIC MATERIAL COMPRISING: A MAGNETIC BRIDGE CIRCUIT INCLUDING A PLURALITY OF MAGNETICALLY PERMEABLE BAR MEMBERS ARRANGED IN A FIRST MAGNETIC LOOP AND A SECOND MAGNETIC LOOP, SAID SECOND LOOP INCLUDING AT LEAST TWO MAGNET MEMBERS, THE NORTH POLE OF ONE AND THE SOUTH POLE OF THE OTHER BEING BRIDGED BY AN AIR GAP, SAID AIR GAP OF SAID SECOND LOOP CREATING A GREATER MAGNETIC RELUCTANCE IN SAID SECOND MAGNETIC LOOP THAN THE MAGNETIC RELUCTANCE OF SAID FIRST MAGNETIC LOOP, SAID FIRST AND SECOND LOOPS INLCUDING AT LEAST ONE MAGNETICALLY PERMEABLE BAR MEMBER FORMING A COMMON FLUX PATH FOR SAID RESPECTIVE LOOPS; MEANS FOR INDUCING MAGNETIC FLUX FIELDS IN SAID RESPECTIVE LOOPS, SAID FLUX FIELD THROUGH SAID COMMON FLUX PATH DUE TO SAID FIRST MAGNETIC LOOP BEING EQUAL IN MAGNITUDE BUT OPPOSITE IN DIRECTION TO THE NORMAL FLUX FIELD THROUGH SAID COMMON PATH DUE TO SAID SECOND MAGNETIC LOOP SO THAT THE NORMAL EFFECTIVE FLUX FIELD IN SAID COMMON PATH IS ZERO; A HALL VOLTAGE GENERATOR POSITIONED IN SAID FLUX FIELD OF SAID COMMON PATH, SAID HALL GENERATOR INCLUDING MEANS FOR APPLYING A CONTROL CURRENT THERETO AND HALL VOLTAGE OUTPUT TERMINALS; A MAGNET MEMBER SUPPORTED IN SAID AIR GAP SEPARATING THE NORTH AND SOUTH POLES OF SAID MAGNET MEMBERS OF SAID SECOND LOOP, SAID MAGNET MEMBER IN SAID AIR GAP HAVING ITS NORTH AND SOUTH POLES CONTIGUOUS WITH THE RESPECTIVE NORTH AND SOUTH POLES OF SAID BAR MEMBERS OF SAID SECOND LOOP THEREBY CAUSING THE EFFECTIVE FLUX FIELD THROUGH SAID AIR GAP TO TAKE A MORE CIRCUITOUS PATH FROM ONE POLE TO THE OTHER OF SAID SECOND LOOP THAN WOULD BE THE CASE IN THE ABSENCE OF SAID MAGNET MEMBER; AND MEANS CONNECTING TO SAID HALL VOLTAGE TERMINALS FOR INDICATING A VOLTAGE OUTPUT FROM SAID HALL GENERATOR WHEN A BODY OF MAGNETIC MATERIAL IS DISPOSED IN THE VICINITY OF SAID AIR GAP IN SAID SECOND MAGNETIC LOOP THEREBY REDUCING THE RELUCTANCE OF SAID SECOND MAGNETIC LOOP AND PRODUCING A CORRESPONDING INCREASE IN THE FLUX FIELD MAGNITUDE THROUGH SAID COMMON PATH AND A HALL VOLTAGE OUTPUT CORRESPONDING TO THE RELATIVE POSITION OF SAID BODY OF MAGNETIC MATERIAL WITH RESPECT TO SAID AIR GAP IN SAID SECOND MAGNETIC LOOP.