SLOW hi:lkask rklay design 211 



The most important of these is the uncertainty as to the sleeve tem- 

 perntiiro that applies to any measurem(Mit made in central office main- 

 tenance, unless the relay to be tested is cut out of scrNicc tor an hour or 

 more before measurement. The conduct i\il\- of cojjixm- \aries approxi- 

 mately as its absolute temperature, or, for engineei-ing estimates, as 

 o5)0 + Tv , where 7V is the temperature in degrees Fahrenheit. Coil 

 temperatures of 225°F are permitted in normal relay operation. As the 

 time varies as the sleeve conductance, a relay with its sleeve at this 

 temperature would have a release time in the ratio 470/615 or 76/100 to 

 the rated release time for 80°F. Allowance for \'ai'iation in this I'aiige is 

 made in circuit design, but a corresponding uncertainty as to the condi- 

 tion applying in adjustment would effectively double this variation. 

 Cun-ent flow adjustment is free of this difficulty, and the variations in 

 the correlation of release time with release ampere turns are less than 

 tliose resulting from the temperature uncertainty in any convenient pro- 

 cedure for timing measurements. Current flow adjustment has the further 

 advantage of using eciuipment that is employed for other relays in central 

 office maintenance. It is the more commonly used criterion of adjust- 

 ment for Bell System relays. 



Operate Considerations 



A slow release relay must not only provide the desired release per- 

 formance: it must also operate its load. The operate pull characteristics 

 are similar to those of other relaj^s of the same general type, as the domed 

 pole face, in particular, gives nearly the same pull at an open gap as a 

 plane pole face of the same total area. Thus the pull characteristics of 

 the AG relay are similar to those of the AJ relay for the same travel. 

 The sleeve retards the flux development, and makes operation slower 

 than that for the same coil input without the sleeve. In most applications 

 of slow release relays, this has little or no effect on circuit operation. 

 Faster operation can be obtained by increasing the steady state power 

 applied, but this is limited by heating considerations. The large part of 

 the winding space used for the sleeve limits the operate sensitivity of slow 

 release relays, and increases the power required for a given load. The 

 load for a given relay design determines a minimum ampere turn value 

 for operation, and this is related to the steady state power by the iden- 

 tity: {Xry- = T-R N-/R. As the coil constant N'-/R, or Gc , is determined 

 by the available winding space aN^ailable foi- the coil, the power require- 

 ments of slow release relays are higher than those of similar i-ehiys having 

 the full winding space available for the coil. 



