Magnetic testing apparatus for measuring internal diameter and surface variations in wall casing

Claim 1

CALIPERING MEANS FOR DETERMINING INTERNAL SURFACE DIMENSIONS OF A FERROMAGNETIC WELL TUBING WALL COMPRISING: AN ALTERNATING CURRENT ELECTROMAGNET ADAPTED FOR LONGITUDINAL MOVEMENT IN SAID TUBING AND INCLUDING A SPOOL SHAPED CORE WHOSE AXIALLY SPACED APART CYLINDRICAL POLES ARE DISK SHAPED AND WHOSE PERIPHERAL FACES ARE DIMENSIONED FOR PRESENTATION IN RADIAL GAP RELATIONSHIP TO THE TUBING WALL AND HAVING AN ALTERNATING CURRENT SOLENOID POSITIONED BETWEEN SAID DISKS, ONE OF SAID POLE DISKS HAVING A LONGITUDINAL PERIPHERAL SURFACE AREA GREATER THAN THE LONGITUDINAL PERIPHERAL FACE AREA OF THE OTHER POLE DISK, A PLURALITY OF CIRCULARY SPACED APART FLUX SENSING ELEMENTS ARRANGED IN CIRCUMFERENTIAL ALIGNMENT WITH ONE ANOTHER AND FIXEDLY POSITIONED IN THE FLUX PATH SURROUNDING THE PERIMETER OF SAID OTHER POLE DISK FOR PRODUCING AN OUTPUT VOLTAGE PROPORTIONAL TO THE RELUCTANCE OF SAID GAP, INDICATOR MEANS ELECTRICALLY CONNECTED WITH EACH SENSING ELEMENT AND RESPONSIVE TO VARIATIONS IN MAGNITUDE OF OUTPUR VOLTAGE AT ANY INSTANT DURING RELATIVE LONGITUDINAL MOVEMENT OF THE ELECTROMAGNET AND THE TUBING, SAID INDICATOR MEANS INCLUDING SEPARATE CIRCUITS EACH CONNECTED WITH ALL OF THE SENSING ELEMENTS, MAXIMUM VOLTAGE READING CIRCUIT AND DEMODULATOR MEANS IN ONE OF THE CIRCUITS CONNECTING WITH ALL SENSING ELEMENTS, VOLTAGE AVERGING CIRCUIT AND DEMODULATING MEANS IN ANOTHER OF THE CIRCUITS CONNECTING WITH ALL OF THE SENSING ELEMENTS, AND A RECORDER CONNECTED WITH AND ACTUATED IN RESPONSE TO DEMODULATED SIGNALS RECEIVED FROM THE LAST TWO MENTIONED CIRCUITS.