210 THE BELL SYSTEM TECHNICAL JOURXAL, JANUARY 1954 



Values of Ge thus determined agree with those estimated from (22) 

 within the level of uncertaint}^ as to the applicable value of ( in this 

 equation. 



G DESIGN OF SLOW" RELEASE RELAYS 



The following discussion is confined to the bearing on design decisions 

 of the performance relations developed in the preceding sections, and 

 does not cover the manufacturing considerations involved. The develop- 

 ment of a specific design depends on the initial choice between certain 

 alternative features which require description. 



Design Alternatives 



The features considered here are: (1) the adjustment means, (2) the 

 form of sleeve, (3) the criterion of adjustment. 



The two methods of adjustment that have been used are (a) residual 

 screw adjustment, (b) spring load adjustment. The former affects the 

 release time by changing the reluctance and the residual flux, the latter 

 by changing the flux or ampere turn value at which release occurs. The 

 differences in the two methods relate more to the stability of the adjust- 

 ment than to its ease or initial accurac}^ Spring adjustment permits the 

 use of the domed pole face, which is inherently stable except as the finish 

 thickness may be affected by wear. 



The two forms of sleeve are the interior sleeve, which uses the full 

 length of the winding space, but only part of the depth, and the slug, 

 which uses the full depth, but only part of the length. As shown in Sec- 

 tion 5, the values of Gs and Gc , or coil constant N^R, attainable with a 

 given winding space are independent of which arrangement is used. The 

 slug provides some flexibility as to operate time, on which its retarding 

 effect is a maximum when it is near the gap, and a minimum when it is 

 away from it. It is subject to smaller temperature changes, with conse- 

 quent changes in conductance, than the sleeve. The other differences 

 between the two arrangements relate to manufacture, and to the costs 

 of both coil and sleeve. The interior sleeve is used with the flat type 

 relays of the Bell System. 



The two different criteria of adjustment used are the release current, 

 and the release time. The former is an indirect control, using a measure- 

 ment of release ampere turns to determine the time that will result for 

 the sleeve conductance used: the other is a direct measurement of the 

 quantity to be controlled. In principle, the latter method would appear 

 preferable, but its use is attended with several disadvantages. 



