Flaw finding apparatus having capacitive sensors spaced apart along line of movementof a metallic sample while included in a bridge circuit feeding a difference amplifier

Claim 1

IN ELECTRICAL BRIDGE CIRCUIT APPARATUS FOR THE DISCOVERY OF FLAWS IN A RELATIVELY MOVING SAMPLE OF COMPLETELY CONDUCTIVE METALLIC MATERIAL, FOUR BRIDGE ARMS IN SUCCESSIVE ADJACENCY, FOUR NODES OF JUNCTURE ESTABLISHED BY THE SUCCESSIVE ADJACENCY OF SAID ARMS, SAID NODES COMPRISING FIRST AND SECOND NODES WHICH ARE GENERALLY OPPOSITE ONE ANOTHER AND THIRD AND FOURTH NODES WHICH ARE GENERALLY OPPOSITE ONE ANOTHER AND WHICH INTERVENE BETWEEN THE FIRST AND SECOND NODES, THE FIRST NODE BEING FORMED BY A TOTALLY GROUNDED CONDUCTIVE METALLIC MATERIAL SAMPLE WHICH IS MOVING AND IN WHICH IS IT DESIRED TO FIND A FLAW, A FIRST ONE OF THE ARMS COMPRISING A CAPACITOR FORMED BY A CONDUCTIVE METALLIC SENSING ELEMENT AND THE TOTALLY GROUNDED METALLIC SAMPLE, SAID SENSING ELEMENT SURROUNDING SAID METALLIC WITHOUT SAID DIELECTRIC INTERVENTING BETWEEN SENSING ELEMENT AND SAID SAMPLE A SECOND OF SAID ARMS COMPRISING A CAPACITOR FORMED BY ANOTHER METALLIC SENSING ELEMENT AND THE GROUNDED METALLIC SAMPLE WITHOUT SOLID DIELECTRIC INTERVENTING THEREBETWEEN, SAID OTHER SENSING ELEMENT SURROUNDING SAID SAMPLE AND THE TWO SENSING ELEMENTS BEING SPACED FROM ONE ANOTHER ALONG THE DIRECTION OF SAMPLE MOVEMENT AND THUS SPACED AS REGARDS THEIR TIME OF ASSOCIATION WITH ANY PARTICULAR FLAW, A THIRD CAM COMPRISING AN IMPEDANCE, A FOURTH ARM COMPRISING AN IMPEDANCE WHICH IS OF THE SAME NATURE (CAPACITIVE RESISTIVE OR INDUCTIVE) AND OF THE SAME VALUE AS THE IMPEDANCE IN THE THIRD ARM, MEANS INCLUDING AN A.C. EXCITATION SOURCE AND CONNECTIONS FOR APPLYING SAID SOURCE ACROSS THE OPPOSITE FIRST AND SECOND NODES, MEANS INCLUDING CONNECTIONS THERETO FROM THE THIRD AND FOURTH NODES AND FROM THE GROUNDED FIRST NODE FOR AMPLIFYING AND NORMALLY CANCELLING SIGNALS ASSOCIATED WITH ONE OF THE SENSING ELEMENTS BY SIGNALS ASSOCIATED WITH THE OTHER.