. The Bell System technical journal . 10 10^ 10-^ COIL RESISTANCE, R, IN OHMS Figs. 10 and 11 — K^ and NI values versus resistance for various wire gaugesfor a typical relay. COST WHEN OPTIMUM RESISTANCE CONDITION IS NOT SATISFIED There will, of course, be cases in practice where the optimum re-sistance is not used, for such reasons as standardizing of certain coilsizes, need for speed, or insufficient winding space. The penalty in costfrom departing from the ideal winding size may be found by comparingthe cost for any value of resistance, (cfiuation 21), with the cost if re-sistance were opti
. The Bell System technical journal . 10 10^ 10-^ COIL RESISTANCE, R, IN OHMS Figs. 10 and 11 — K^ and NI values versus resistance for various wire gaugesfor a typical relay. COST WHEN OPTIMUM RESISTANCE CONDITION IS NOT SATISFIED There will, of course, be cases in practice where the optimum re-sistance is not used, for such reasons as standardizing of certain coilsizes, need for speed, or insufficient winding space. The penalty in costfrom departing from the ideal winding size may be found by comparingthe cost for any value of resistance, (cfiuation 21), with the cost if re-sistance were optimum, (equation 23): C _ Kx/R + K2R Co 2 \R ^ 7?„ (24) 244 THE BELL SYSTEM TECHNICAL JOI^RNAL, JANUARY 1954. 2 3 RATIO OF RESISTANCE TO OPTIMUM RESISTANCE, R/Rq Fig. 12— Cost when resistance is not optimum. Thus, the fractional change in cost caused by any departure from thebest resistance is readily estimated, expressed in ratio form as R/Rq .This relation is shown in Fig. 12. SUMMARY In summary of Part II, methods have been given for deciding on themagnet coil design which will provide the cheapest net cost in the switch-ing system. When the conditions of use are known, a series of chartsmay be prepared such as the one shown, from which the applicationsengineer may decide the proper coil design, and how much it may beworth to the system. As experience will show, the cost of departing froman optimum design may run well over $ per individual relay, withthe result that aggregate savings in the whole central office may run tothousands of dollars compared to the cost when this problem is ignored. New relay development may be guided by the use
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