20 BULL SVSrr.M rr.CILXIC.IL ./OCA'.V.//. 



A (iKNER.\L UtII-ITV RkI.AY 



The success of ihe punched-type line, cutoff, and super\isor\- 

 relays suggested ttir usv of this type for a general utility relay which 

 would carry a load ot eiilier one pair or se\-eral pairs of springs and 

 permit an almost unlimited numl)er of contact spring combinations 

 to be made. This was accomplished by increasing the cross section 

 of the core and armature of the line rela>' as the increase in iron cross 

 section provided maximum flux with large magnetizing forces. This 

 relay is shown in Fig. 13 and is now manufactured in large (luantities 

 with about 3,000 varieties of windings and spring arrangements. 

 About twenty million such rela\s are ahead\ in ser\ire and the 

 number is increasing constantK-. Mad it noi Ihtii for the (ie\elop- 

 ment of this punched-type rcla\', it would ha\e been necessary to 

 greatly increase the manufacturing facilities o\er those now |)ro\ided 

 because of tlu' magnitiidt' of tlu' manufacturing operalion on the 

 old basis. 



CiiKiAiN Ri;i..\\ C koii's 



Having outlined tiie (le\elopmeiU of tlie nio>i commonly known 

 relays and given the reasons responsible for major design changes, 

 it will be interesting to consider uses of simple rela\s in the full meclian- 

 ical system. In this system the removal of a substation switchiiook 

 causes a line relay in the central office to operate and associate a line 

 finder with the calling line, after which a cutoff relay remo\-es the 

 line rela>' from the circuit as i^> doni- in manual |)ra(iice. A sender 

 is associated with the calling liiU' and liie lirciiii i> conipleied through 

 the substation set dial and a rela\- in the sender, known as the pulse 

 relay, because it reproduces the dial pulses. 



A schematic for illustrating \hv principle of this circuit is shown 

 in Fig. 14. Referring to this figinc. it will be seen that the opera- 

 tion of the pulse rela\' pro\ides a ground for a slow release relay which 

 in turn extends the circuit of the stepping switch to the back contact 

 of the pulse relay. Supjjose thai the digit (> is dialed. Then the 

 resulting current interruptions consist, as shown in I'ig. II. ol tin 

 break pt-riod-- and \ru make periods, the final make period being 

 l)erman(iii .iiid the ninaining nine consisting of api)r()ximatel\- one- 

 third of the total time of a single pulse. The first break of the dial 

 opens the circuit through the pulse rela\-, which releases and open? 

 the circuit of the slow-release relay, but the latter remains ojierated 

 throiighoul the break period. The piiKv rel.i\- when rele ised, pro- 

 vitles a ground from its back contact, for the magnet of the stejiping 

 switch, through the make contact of the slow release relay. The 



