TESTING MAGNETIC CORES

摘要

Several varieties of high frequency soft magnetic cores are used. Applications include power, filtering, EMI suppression, and measurement. Useful testing of magnetic cores depends on the type of core and the intended application. Ferrite cores are tested for permeability, loss factor, Q, core losses, saturation, resistivity, DC Bias performance, and the temperature effects of each of these. The ferrite properties are interrelated, and an understanding of how temperature, drive level, bias, and frequency interact is necessary in order to construct useful tests. In addition, fixturing has an impact on the measurements obtained, and it is important to understand the effects of bobbin fill, leakage flux, and the specification of air gaps. Powder cores such as MPP, High Flux, and Kool Mμ~(~R) toroids are used in many applications similar to those of ferrite, yet the behavior of powder cores is different in significant ways. An understanding of the performance of powder cores at various conditions is necessary for proper testing. Tape wound toroid cores, laminated rings, and tape wound cut cores are built with alloys such as Orthonol~(~R), permalloy, silicon steel, and supermalloy. These materials exhibit behaviors distinct from ferrites and powder cores, and understanding the differences is a vital tool for the engineer who needs to take proper account of the performance of cores when designing tests. This paper addresses the considerations a test engineer should apply in the testing of high frequency magnetic cores.