An accurate AC demagnetizing method using a linear inductance for high permeability cores

A new simple and accurate ac demagnetizing method for high permeability cores is presented. In this method, a linear inductance is connected in parallel with the winding of the core to stabilize the level of minor loops at zero flux level during the whole process of ac demagnetization. The ac demagnetization error is suppressed to less than 0.5% even in 50% Ni-Fe cores. The optimal ac demagnetizing time is longer than 0.5 sec., and the optimal ac demagnetizing waveform of current source is sinusoidal. Experimentally, high demagnetizing accuracy was obtained over a frequency range of 10 Hz-2 kHz. Two cores with the same dimensions and materials are simultaneously ac demagnetized by means of a linear inductance connected in parallel with the primary windings of two cores connected series-aiding, whose secondary windings are connected parallel-opposing and short circuited; thus, the remanent flux level after ac demagnetization is nondestructively detected by destructive readout in other core. This ac demagnetizing method is useful for measuring some magnetic properties such as initial permeability and BH curves and for resetting the small-signal transformer cores and second-harmonic analog memory elements.