Non-repeatability of Disaccommodation, An Investigation of High Permeability Ferrites

During routine evaluation of high permeability ferrite cores, the disaccommodation (DA) data were found to vary by more than +- 20 % in repeat measurements. Error analysis accounts for only +- 8% of this variation, the remainder could not be explained. An experimental investigation was undertaken to study this non-repeatability phenomenon in relation to the effects of core permeability, impedance, and various test parameters. Based on the results of our investigation, modifications have been proposed to core testing techniques, which will reduce the variation. Our data indicates that a +- 10% variation is the best that can be achieved with ac demagnetization at room temperature. It is recommended that the effects of B-H non-linearities, variations in the applied test signal due to constantly changing inductance values, and magnitude of the core permeability on DA repeatability be further investigated.