Eddy current seam tracking device utillizing an e-shaped core with electromagnetically unequal pickup coils

Claim 1

APPARATUS RESPONSIVE TO A DISCONTINUITY IN A CONDUCTIVE MATERIAL, COMPRISING: (A) A SOURCE OF ALTERNATING CURRENT, (B) MEANS DISPOSED IN INDUCTIVE RELATION WITH SAID CONDUCTIVE MATERIAL, COMPRISING: A SUBSTANTIALLY E-SHAPED FERROMAGNETIC CORE HAVING AN INNER LEG AND FIRST AND SECOND OUTER LEGS, THE GEOMETRY OF SAID CORE BEING SUCH THAT, WHEN SAID CORE IS INDUCTIVELY COUPLED TO SAID MATERIAL, THE RELUCTANCE BETWEEN SAID INNER LEG AND SAID MATERIAL IS SUBSTANTIALLY GREATER THAN THE RELUCTANCE BETWEEN EITHER OF SAID OUTER LEGS AND SAID MATERIAL, FIRST COIL MEANS, CONNECTED TO SAID SOURCE AND COUPLED TO SAID INNER LEG, FOR INDUCING EDDY CURRENTS IN SAID MATERIAL, SECOND COIL MEANS COMPRISING FIRST AND SECOND ELECTROMAGNETICALLY UNEQUAL PICK-UP COILS WOUND ABOUT SAID FIRST AND SECOND OUTER LEGS, RESPECTIVELY, SAID PICK-UP COILS BEING CONNECTED TO EACH OTHER SO THAT VOLTAGES INDUCED THEREIN BY FLUX PRODUCED BY CURRENT IN SAID FIRST COIL MEANS ARE IN SERIES OPPOSITION, (C) MEANS, CONNECTED TO SAID SECOND COIL MEANS, FOR PRODUCING A D.C. SIGNAL DEPENDENT UPON THE DIFFERENCE BETWEEN THE PHASE OF THE VOLTAGE INDUCED IN SAID PICK UP COILS BY CURRENT IN SAID FIRST COIL MEANS AND THE PHASE OF THE VECTORIAL SUM OF ALL THE VOLTAGES INDUCED IN SAID PICK UP COILS.