Excitation current waveform for eddy current testing on the thickness of ferromagnetic plates

摘要

Advantages of pulsed excitation current over conventional harmonic excitation for measuring the thickness of a ferromagnetic plate are studied. Compared with the sinusoidal voltage induced by harmonic excitation current, the time-domain voltage induced by pulsed current is highly more sensitive to the thickness. Quantitative proof of this conclusion is provided by solving the normalized derivatives with respect to the thickness. Furthermore, the effects of the time constant of pulsed current on the measuring sensitivity are examined, and an optimal range of the time constant is proposed. Finally, the theoretical model is verified by experimental results.