Alternating current leakage flux flaw detection device null for plane surface flaw detection

摘要

PURPOSE:To achieve a higher flaw detection processing capacity by turning and scanning a leakage magnetic flux detector within a plane of a excitation magnetic field formed between AC excitation magnetic poles. CONSTITUTION:A detection coil 4 has two coils connected differentially adjacent to each other in a vertical way or horizontally along the rotary circumference and as to a direction thereof, the coils are made perpendicular to the surface of a steel plate 8 as material to be inspected and orthogonal to a parallel leakage flux in a plane space. A probe scans over the steel plate 8 and when a cracking flaw on a plane between excitation magnetic poles 2 and 2 and a leakage flux phi generated from the cracking flaw interlinks with the detection coil 4 so that an induction voltage is produced to detect a flaw. A liftoff signal due to a vibration or the like of the steel plate 8 is turned to an induction voltage by a parallel magnetic field on the surface of the steel plate and differs significantly in phase from an induction voltage by a leakage flux phi generated from the cracking flaw. Thus, the induction voltage can be removed easily by a phase analysis with a processing circuit thereby obtaining a better S/N ratio.