Question

Difference between phase lag and phase lead

Answer 1

Phase lag is a parameter of the eddy current signal that makes it possible to obtain information about the depth of a defect within a material. Phase lag is the shift in time between the eddy current response from a disruption on the surface and a disruption at some distance below the surface.
A phase shift of 90 degrees is a shift of 1/4 of the period of the wave, etc. Phaseshift may be considered positive or negative, i.e., one waveform may be delayed relative to another one, or one waveform may be advanced relative to another one. These conditions are called phase lag and phase lead respectively.