ECONOMICS OF TKLKl'llOXE RELAY APPLICATION.S 



24i) 



applicable to other speed problems, once the value of speed is known, 



and onec the infhuMico of the design chanji-o and its cost arc known. 



Part \' -C'noicE ov \\'ixdixg fou Maximum Combined IiIconomy 

 OF Speed and Power 



In the selection of magnet designs for use in circuits where speed is 

 important, much can be gained by modifying the mass, the stroke, the 

 force against the stop, etc., but when all these devices have been ex- 

 hausted there remains the possibility of supplying more power to the 

 magnet coil. If this is done in enough cases, an over-all penalty in central 

 office cost is incurred through the added over-all power plant capacity 

 that may be needed. As already seen in Section 1.3, this cost penalty is 

 proportional to the base value of one watt-hour-per-year, the voltage 

 sciuared, and the hours per year energized, but is inversely proportional 

 to the resistance. In telephone usage, the voltage is usually fixed at 50 

 \'olts, and etiuation (18) may be rewritten as 



kph 



IT' 



where 



Cp = 



(28) 



l\ 



CpE' 



Z 0.70 



< 0.30 



0.010 0.020 0.030 0.040 0.050 



STROKE IN INCHES 



Fig. 14 — Optimizing a speed relay design. 



