MAGNETIC MEASUREMENTS AT LOW FLUX DENSITIES 61 



A Cross-sectional area of magnetic core; cm.^ 



a Permeability-magnetizing force coefficient; = AtoMmX. 



B Instantaneous flux density in core; gauss. 



Bm Maximum flux density in core subject to alternating magnetizing 



force. 

 c Residual resistance coefficient. 

 C Distributed capacitance of coil winding; farad. 

 d Effective magnetic diameter of annular core; cm. 

 e Eddy current resistance coefficient of core. 

 Cc Eddy current resistance coefficient of coil winding. 

 / Frequency of alternating current. 



G Distributed leakance of coil winding; mho. 

 h = {aBm + c). 



H Instantaneous magnetizing force in core; oersted. 

 Hm Maximum magnetizing force in core subject to alternating 



magnetizing force. 

 im Maximum of alternating current wave in coil; ampere. 

 / Effective or r.m.s. current in coil. 



L Inductance, due to core and residual air space only; henry. 

 Ld Inductance due to residual air space. 

 La Inductance due to coil with air core. 



Lm Inductance with current of maximum value im due to core only. 

 Lfm Inductance due to core only, with current of maximum value im, 



at frequency/ (i.e., subject to magnetic shielding). 

 Lo,8. Total inductance observed at frequency high enough to give 



increases due to distributed capacitance and leakance of 



the coil winding. 



Permeability-flux density coefficient; = 



Mm "~ Mo 



juo Initial permeability of core. 



)u»n Permeability corresponding to Lm. 



Hfm Permeability corresponding to L/m. 



p Ratio of eddy current to hysteresis resistance at maximum 



frequency. 



P Total power dissipated in core ; watt. 



Pe Eddy current power dissipated in core. 



Pk Hysteresis power dissipated in core. 



q Fraction of core loss tolerated as error due to capacitance, 



leakance, and copper eddy current loss in winding. 



Q Insulation quality factor = uC/G. 



R Resistance due to core and winding only; ohm. 



Re Direct current resistance of copper winding. 



