Calculating Permeance Coefficient
Permeance Coefficients (Pc) are important in material selection to ensure optimal design. The Permeance Coefficient of a magnet is also referred to as the "operating slope", load line or B/H of the magnet and usually, but not always, refers to the magnet in open circuit condition. It is calculated from the dimensions of the magnet and represents the Pc of the magnet in open circuit condition, that is, with no other permanent or soft magnetic material "nearby".
These calculations are based upon simplified equations of geometry (from Evershed) and approximations of the effective length of the material. The results are, therefore, only approximate. The calculated value represents the Pc at the neutral cross-section of the magnet. Our experience suggests the calculated results to be within about 10% of the measured values. A quite "readable" explanation of the calculation of Pc is available on pages 149-154 of Rollin J. Parker's book Advances in Permanent Magnetism. See our Reference Book list.
Starting in the 1960's and as a result of the development of ferrite magnets with a "square" intrinsic hysteresisgraph curve, R.I. Joseph, E. Schlomann and others advanced a calculation based on uniform magnetization throughout the magnet volume. More recently, additional calculations have been reported by Chen, Pardo, Sanchez, and others from the University of Madrid, Spain. Our lab measurements fall between these two methods of calculation and the user of these web-based calculations is reminded that they are approximate.
Please select which Permeance Coefficient calculation best suits your application by referring to the diagrams.
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