Effects of probe and inducer on saturation of crack signal in high-sensitivity AC field measurement technique

As in the eddy-current technique, a major problem in separating and sizing deep surface cracks in the AC field measurement (ACFM) technique is the saturation of the crack signal. It is essential that the operator ensures the crack signal does not reach saturation for the deepest possible crack. The paper explains how the parameters of the probe and inducer in the high-sensitivity ACFM technique with a rhombic inducer control the sensitivity and saturation level. Theoretical results are presented on the effects of the inducer size, probe position and probe length on the crack signal. It is shown that for an inspection task where there is an indication of the maximum crack depth, the saturation problem can be avoided by choosing the right size inducer, the right position for the probe and the correct probe length