Flaw detecting apparatus having null plane positioned sensors which are series connected

Claim 1

IN APPARATUS FOR THE DETECTION OF DISCONTINUITIES IN SAMPLE MATERIAL HAVING THICKNESS AS A MINOR DIMENSION, THE COMBINATION OF A PLURALITY OF "N" EXCITATION GENERATOR COILS DISPOSED ON A SIDE OF THE SAMPLE IN THE DIRECTION OF ITS THICKNESS WHERE "N" IS AN INTEGER GREATER THAN THREE, SAID COILS HAVING AXES WHICH ARE SUBSTANTIALLY PERPENDICULAR TO THE SAMPLE MATERIAL, A SOURCE OF POWER, TWO WIRE CONNECTIONS FROM SAID SOURCE TO EACH OF SAID EXCITATION GENERATOR COILS, THE COILS BEING WOUND IN SPACE AND CONNECTED TO SAID CONNECTIONS SUCH THAT A PORTION OF THE EXCITATION GENERATOR COILS HAVE, WITH RESPECT TO LOCATION OF SAMPLE MATERIAL, INSTANTANEOUS POLARITIES WHICH ARE OPPOSITE TO THE INSTANTANEOUS POLARITIES, WITH RESPECT TO LOCATION OF SAMPLE MATERAIL, OF THE REMAINDER OF SAID EXCITATION GENERATOR COILS, WHEREBY COILS OF UNLIKE POLARITY ESTABLISH NULL PLANES EXTENDING BETWEEN COILS AND EXTENDING THROUGH THE SAMPLE MATERIAL AND THEREBEYOND, A PLURALITY OF "X" EXCITATION RESPONSIVE SENSING DEVICES DISPOSED ON ONE SIDE OF THE SAMPLE IN THE DIRECTION OF ITS THICKNESS AND HAVING CENTERS OF RESPONSE SUBSTANTIALLY FALLING IN SAID NULL PLANES ESTABLISHED BETWEEN OPPOSITELY POLARIZED EXCITATION GENERATOR COILS, WHERE "X" IS A NUMBER WHICH IS A MULTIPLE OF TWO AND WHICH IS LESS THAN "N," CONNECTIONS CONNECTING 1/2X SENSING DEVICES IN SERIES WITH ONE ANOTHER, CONNECTIONS CONNECTING THE REMAINDER OF THE SENSING DEVICES IN SERIES WITH ONE ANOTHER, AND MEANS FOR DERIVING A USEFUL READOUT FROM COMPARISON OF SIGNALS FROM ALL OF SAID CONNECTIONS CONNECTING THE VARIOUS SENSING DEVICES.