EDDY CURRENT DEFECT DETECTING METHOD BY RECTANGULAR PULSE EXCITATION

摘要

PURPOSE:To make it possible to check the existence of a defect and to detect depth and shape defects, by making a decision on variation of transient response characteristics due to rectangular pulse vibrations. CONSTITUTION:When a coil forming an insertion-type, penetration-type and differential-type self-comparison type bridge of a steel pipe or rod is excited by rectangular pulses from rectangular-pulse oscillator 1, a steep pulse voltage is developed at the rise and fall of the pulse and then applied to differential amplifier 4 via balancing circuit 3. The penetration depth of an eddy current varying in penetration depth due to a defect of the pipe or rod decreases as a frequency increases. Therefore, decidion unit 5 of an oscilloscope, etc., makes a decision on the voltage waveform corresponding to transient characteristics of the output of amplifier 4, so that the existence of a defect will be detected as well as the depth and shape of the defect.