New type of sample for incremental magnetic testing

For incremental tests, the normal practice of polarising the test core requires circuit modifications which increase the effective impedance of the a.c. excitation circuit. Also, the presence of even harmonics in the excitation current in such tests makes the flux wave unsymmetrical about the time axis, with unequal peak values. This paper presents a new and simple method of preparing samples for incremental tests, in which the d.c. polarising field can be introduced without any increase in the effective impedance of the a.c. exciting circuit. Also, in the proposed method, the flux wave is substantially free from asymmetry due to even harmonic distortion, and from unequal peaks for the two halfwaves. Selected oscillographic records have been included to illustrate the advantage of the proposed new sample over the conventional sample.