Eddy current nondestructive testing techniques are used extensively in industry for detection of hidden cracks and corrosion in multi-layer conductive structures such as those found in aircraft. Most conventional eddy current techniques employ a probe coil excited with a continuous sine wave. The changes in the probe’s impedance are detected (usually with an electronic bridge circuit) and displayed in real time on an impedance plane CRT display. Interpretation of the impedance-plane trajectories that result from scanning the probe over a defect is difficult; it involves a considerable amount of operator skill and knowledge and the equipment is sometimes difficult to set up and operate. We have developed an eddy current inspection system using the pulsed eddy current technique, which greatly reduces the possibility of operator errors and subjectivity in the quantitative interpretation of test results.
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