1G8 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



and eddy current effects in some convenient form. Approximations for 

 solutions have been developed which predict with good accuracy the 

 order of operate time attainable for a design, but not of sufficient ac- 

 curacy to exactly determine the best winding for a particular case. 

 Thus once a magnetic structure has been established, the operate time 

 data for a single relay necessarily have to be determined empirically by 

 measurements using controlled samples. 



Actually this procedure is quicker and easier, and besides it gives the 

 correct answer, including all the non-linear effects, such as eddy currents, 

 saturation and motion, no matter how complicated. Complete data for 

 the range of all relays and windings using the given structure can be 

 determined using one such relay with a full winding, through the use of 

 impedance transformation techniques and estimation of small A-ariation 

 effects, using the approximate solutions. By using the approximate 

 solutions only for corrections, the errors become of second or smaller 

 order. Thus single relay operate time data can be determined accurately 

 and presented in a form permitting either analysis or synthesis of per- 

 formance. 



The design of a best winding for load controlled operation, is accom- 

 plished by a variation of the method of successive approximations. 

 Appropriate battery voltage, winding temperature and resistance of 

 course are considered as part of the solution of the problem. A range of 

 windings is chosen and operate time data established for each winding. 

 If necessary, the range is extended in the appropriate direction until a 

 minimum operate time is included. This minimum determines the best 

 winding. 



For mass controlled operation, the contact spring load is immaterial, 

 and the data can be presented directly. As part of this type of study, 

 the relative importance of the several parameters affecting the operate 

 time has been determined. These show at a glance whether (1) a change 

 will have a significant effect or (2) what change or changes are neces- 

 sary to effect a necessary reduction in operate time. 



OPERATE TIME — SERIES RELAYS 



Series relays are two or more relays whose windings all are connected 

 in series, and energized by the same current, controlled bj^ a single con- 

 tact. The impedance of each one enters into the manner in which the 

 common current will increase, after contact closure. If the procedure 

 used for single relaj^s were followed, there would be a double infinity of 

 combinations to portray, or else experimentally study each combination 



