176 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



5 6 7 8 9 10 



E^ 



TOTAL POWER = 



R, + R2 



Fig. 12 — Optimum turns ratio for speed on relay No. 1, No. 2 known. 



THE OMISSION OF EDDY CURRENT CORRECTIONS 



The foregoing discussion of series connected relays developed trans- 

 formation relationships ignoring eddy current effects. The following 

 discussion will qualitatively show that ignoring the eddy current effects 

 introduces second or smaller order errors. 



For very large coil constants and different magnetic structures, the 

 core constants can be ignored. With large coils, the current and flux rise 

 are influenced very little by the core constant. As the coil constant is 

 reduced, the core effect becomes more important, but not significantly 

 so until the speed class is reached. Unfortunately, we are generally only 

 interested in the speed case. In the following, the most affected high 

 speed applications are considered. It is found that the virtual constant 

 potential point is only slightly affected by the eddy currents, and that 

 equivalent single relays for each of the series relays determined using 

 only the winding resistance and turns, with the relay reluctance cor- 

 rection as described above, are sufficiently accurate. The operate time 

 for each relay itself, is affected by the core. This effect of course is in- 

 cluded in the measured timing data which are used after equivalents 

 are determined. The present discussion is directed toward the effect 

 of the core eddy currents on the voltage division. 



