28 BELL SYSTEM TECIIXIC.IL JOURNAL 



marginal relay adjusted to operate on any current greater than a par- 

 ticular \alue. The other two are polarized relays, one being adjusli-d 

 to respond to negati\e pulses only, while the other responds only 

 to positive pulses. 



Kach digit of any number traiismitleil over liie trunk to the manual 

 office consists of four pulses. The second and fourth of these jiulses are 

 alwa>'s negative, but either or both of them may be a light or hea\\' 

 negati\e. The first and thin! pulses may either be positive or 

 zero, a zero pulse repriseniini; a no current interval. This rom- 

 i)inalion ol |)ulses is shown in llie following table: 



.\s eacli puisi' inliTval nia\' consist of cillicr of two kinds of pulses, 

 tiiere are sixteen combinations wliicii (.m be tr.msniiiied bui >i\ ol 

 them are not used, as only ten are ri(|uin(l. 



The marginal relay is adjusted to oper.ile on heav\' pulses onl\- 

 and as all the positive pulses are light, it does not respond to an\ 

 l)ositive pulses or the light negative pul.ses. The negati\-e [wlarized 

 relay responds to both light and heavy negative pulses and the positi\c 

 polarized relay responds to all positive pulses. FOuring a zero pulse 

 period all of the relays remain unoperated. l-dr ilie secontl and fourth 

 pulse periods the negative polarized relav will i)e ojierated and the 

 marginal relay may or may not be operated. During the first and 

 third jjiilse periods the positive polarized relav' may be operated or 

 all the relav's mav- rem.iiii unoperated. From the operation of these 

 relays an arrangement of register relays is set up which lights before 

 the manual operator the lamps corresponding to the digits trans- 

 mitted. The marginal relav' used is a counting relay of the type shown 

 in Fig. 18, as this relav' has the qualities of sensitiveness, stabililv- 

 and permanence of adjustment that are essential for satisfactorv' 

 operation. The other two relavs are very sensitive polarized relays 

 with micrometer adjustment screws and are representative of the 

 best standards of design for relavs of iheir tv pe. This lvi)e of relav' is 

 shown in Fig. 20. 



Till-: .Si<(,)ii;n( !■. S\\ I K II 



Most of till' rel.iys prev iouslv' describe<i were designeil to nuet 

 specific re(|uirements of unusual severity which limited the design 

 to indiviilual structures having their armatures in close association 



