ESTIMATION AND CONTKOL OF Ol'KHATK TIMK OF KELAYS 



153 



problem can be finished. Slartiiiii; witli the power gi\'en and choosing an 

 arbitrary number of winding funis, the operate time is determined as 

 described above. If it falls into the load controlled class, then a different 

 numb(M" of turns is next assununl and a second time determined. This 

 procedure is repeated until a time cur\-e \'c>rsus number of turns similar 

 to Fig. 1 can be plotted, including a minimum. The best winding i this 

 minimum. A different curve and optimum number of turns will ai)i)ly to 

 each contact load assumed. Three comi)ut(Hl curves corres])<)nding to 

 the measur(xl 1-watt curves are shown on Fig. 4. These were deter- 

 mined using effective inductance values tlescribed earlier. 



Finite wire sizes permit only certain number of turns to be physically 

 realizable when the resistance has been specified, without sjilicing two 

 gauges of wire. The nearest gauge on the coarser wire size side is chosen, 

 resulting in slightly too many turns. Note that the curves rise less steeply 

 on the high turn side and the time penalty therefore is less than if too 

 few turns were supplied. 



80 

 75 

 70 

 65 

 60 

 55 



50 



Q 



Z 45 



O 



U 



111 



<£i 40 



_1 



_l 



5 35 



18 20 



25 

 X 10^ 



6 7 8 9 10 12 14 16 



NUMBER OF TURNS 



Fig. 4 — Typical computed maximum operate time curves for load controlled 

 relays. 



