Impact of crest factor on indication quality in the magnetic particle inspection process

Magnetic particle inspection is a well-established industrial process of quality control. The ISO standard for magnetic particle inspection requires control of the crest factor and recommends avoiding current waveforms with a crest factor larger than three without documented evidence of detection effectiveness. Modern test bench units often use thyristor regulation of the magnetization current, which enables broad control ranges to generate an adequate magnetic field. A possible method of evaluation of magnetic field for magnetic particle inspection is to quantify the force effect on a detection particle. The cumulative force effect can be expressed as an impulse of force on a detection particle. The method of evaluation by an impulse of force implies that crest factor does not have a major effect if the impulse is controlled. This work contains a theoretical analysis of force in magnetic field generated by thyristor controlled currents. In the experimental part a comparison of indications generated by magnetic fields of different crest factorsis performed. The results of the experiment are in line with the theoretical analysis and show that it is the impulse that plays the major role in the formation of an indication and not crest factor.