Magnetics offers various tape wound core materials such as 80% nickel-iron alloys (Permalloy), 50% nickel-iron alloys (Orthonol, Alloy 48), 3% grain-oriented silicon-iron alloy (Magnesil), and a highly refined 50% cobalt-iron alloy (Supermendur). The alloy is manufactured, wound into tape cores, and annealed, all with the aim of meeting various characteristics such as good squareness, low coercive force, good saturation flux density, and low core losses. Especially because the material is magnetically square, it is difficult or impossible to make repeatable inductance measurements.
Magnetics has in the past attempted to respond to customer requirements for inductance minimums with testing and process control. These efforts were largely unsuccessful, because the material is not suited to control of inductance. Therefore, Magnetics does not guarantee permeability for these materials – which is to say Magnetics does not guarantee inductance for these materials.
While it is not uncommon for customers to propose an inductance test for a tape wound core, measurement of inductance is not a practical inspection test. We understand the desire to do so. The measurement is straight-forward, and it would seem to bear on exciting current performance. Nevertheless, a measurement or guarantee of inductance for these materials is misleading and not rooted in scientific theory.
***Magnetics does offer a specially refined 80% nickel-iron alloy (Supermalloy) with an initial permeability guarantee at a low drive level of 20 Gauss.