1460 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1953 



equations for comparison. For such an open circuit decay curve, the flux 

 does not abruptly drop to zero because of induced core eddy currents. 

 The analysis of these data thus partly resolves into the determination of 

 some method for conveniently representing the eddy current effects. 



NEW APPROXIMATE FLUX DECAY EQUATION 



For a first approximation, use can be made of linear circuit theory. 

 Assuming the core behaves as a coupled single turn of conductance Ge 

 and inductance Li , and defining the core time constant as : 



te = L,Ge, (18) 



the flux decay equation is the well known solution : 





t ^ 0. 



(19) 



It is clear that the dynamic flux decay cannot be represented by the 

 above exponential equation, which has been drawn on Fig. 23 as the 

 upper straight line. 



1.0 



0.6 

 0.5 



0.3 



JL 0.2 



0.15 



0.10 

 0.08 



0.06 

 0.05 

 0.04 



0.2 0.4 0.6 o.e I.O 



.2 1.4 1.6 1.8 2.0 2.2 2.4 2.G 2.8 

 TIME t/te 



Fig. 23 — Comparison of measured open-circuit flux decay with one-term 

 exponential equations. 



