The extraction of characteristic quantity of shallow defects in pulsed magnetic flux leakage signal

In order to enhance the testing ability of pulsed magnetic flux leakage(PMFL) for shallow defects, the method of second difference for dealing with testing signals is put forward, which separates the damp components, namely second differential signals, caused by eddy current effect from the signals in pulsed magnetic flux leakage. From second differential signals, a new characteristic quantity of the depth of shallow defects-peak time Pt is extracted and the feasibility of the method of second difference is verified. The experimental results show that compared with the value of signal amplitude, the resolution of the depth of defects is higher while testing shallow defects if Pt is taken as the characteristic quantity of shallow defects and at the same time, the problem of the seriously decreasing resolution of the characteristic quantity of defects caused by the lift-off of the testing probe can be solved.