134 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



Fig. 7 



MAGNETOMOTIVE FORCE, 7 — *- 



Field energy relations in release. 



netization and a variable magnetic field pattern. In an approximation 

 neglecting the latter effect, no advantage is derived from an accurate 

 formulation of the former, and a linear approximation to the demagneti- 

 zation curve may be employed. 



NORMAL UNPROTECTED RELEASE 



As indicated above, a rough approximation to the decay of the gap 

 flux, and hence of the pull, may be obtained by assuming that this flux 

 decays in conformity with equation (2), with G = Ge , where the eddy 

 current conductance Ge has the same value as in operate. As a linear 

 approximation to the demagnetization curve, the reluctance (R can be 

 taken as the closed gap reluctance (R(0). Allowance may be made for 

 residual magnetism by postulating a steady state magnetomotive force 

 57o = (R(0)<po • Then integration of (2) gives the following expression for 

 the time t at which the flux has decayed to the value (p from its initial 

 value (fi : 



i = tE hi 



<Pi 



<Po 



(25) 



