1048 THE BELL SYSTEM TECHNICAL JOURN'AL, NOVEMBER 1952 



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 POWER INPUT IN WATTS 



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Fig. 18 — Typical operate times of speed relaj-s with optimum coil designs for 

 high speed operation. 



Speed of Operation and Release 



Typical operate and release times of the AF relay are shown in Figs. 

 18 and 19. Fig. 18 shows the operate times for "speed relays" in which 

 the speed is limited primarily bj' the time needed to accelerate the mass 

 of the moving system, and is not affected appreciably by the spring 

 loads. These are relays with coil windings of about 1000 ohms resistance, 

 or less, corresponding to power inputs of 2.3 watts, or greater, when 

 connected to a 48-volt supply. For each value of resistance, the operate 

 time shown is obtained A\ith "s\'indings having the optimum number of 

 turns for shortest operate time. Tliis time is plotted as a function of 

 power input for various armature travels. Short travel relays have typi- 

 cal operate times varjdng from about 2.5 to 7 milhseconds as the power 

 is reduced from 23 to 2.3 watts, or as the resistance is increased from 100 

 to 1000 ohms, using the appropriate number of turns in each case. Inter- 

 mediate and long travel relays have longer times. For comparison, a 

 short travel U relay is also shown. This relaj' requires about twice the 

 time to operate as the corresponding AF relay. The improvement with 

 the AF relay is due primarily to the lighter mass of the mo\ang system 

 and slightly shorter travel due to better control of tolerances. Better 

 control is inherent with the single card system for contact actuation and 

 is accompUshed \A'ithout individual adjustment of contact or backstop 

 position, both of which are hand adjusted on U relays. 



