Multiple coil eddy current probe and method of flaw detection

摘要

An improved eddy current probe system (1) and method for simultaneously detecting different types of flaws (4, 5, 6) at different depths within a metallic wall (2). The system (1) comprises a current generator (14) for generating alternating currents of substantially different frequencies, a probe head (8) including first (36), second (34) and third (32) concentrically arranged coils (32, 34, 36) in separate communication with the current generator (14), shielding material (23, 25, 27) disposed between the coils (32, 34, 36) and the pulsating magnetic field (9, 45, 46, 47) of the coils (32, 34, 36) adjacent to it, and a detector circuit (17) which may include an inductive bridge for providing an electrical output representative of the impedance changes in the respective coils (32, 34, 36). In operation, each of the coils (32, 34, 36) conducts current having substantially different frequencies.