Probe lift-off compensation method for pulsed eddy current thickness measurement

The pulsed eddy current nondestructive testing signal for ferromagnetic plate thickness testing is sensitive to the plate´s thickness and probe lift-off effect simultaneously. This feature leads to the difficulty of eigen-value extraction in thickness quantification. To remove the probe lift-off effect, a method based on calculating the time-varied relative magnetic flux changing rate is presented. Experiment result shows the relative magnetic flux changing rate is approximately lift-off independent and only determined by the plate thickness.