A system for measuring magnetic core noise as a function of the magnetization level

The problem of magnetic core noise is considered in terms of non-repeatability of the hysteresis loop trace for any repetition of the magnetization process. The examination condition is that the effect of eddy currents is reduced to as low a level as possible. Based on such premises, this paper presents a system which periodically extracts the fluctuation voltage, induced at an arbitrary but specified point of the impressed magnetic field, as an instantaneous value. The minimum extraction interval is mainly determined by the integration time of the digital voltmeter used to measure the voltage and by the time required for transferring the extracted data to a personal computer. Therefore, the upper limit of the repetition frequency for the magnetization is restricted to less than 1 Hz. The serially extracted time data is dealt with in a statistical manner and is arranged in order as a magnitude distribution. Two kinds of cores are tested, one is a Fe-Ni-based amorphous core and the other a supermalloy. The results reveal that each core has distinctive noise features