RRi-ivs IX Till- nr.ij. .'^rsrr.M i.i 



■-usiu'iidi'd 1>\' a ri'i'd iiiidiT U'ii>i(in to prox idt' a rrsUiriiii; forci'. In 

 the DtluT, whicli was niori.' sfiisitixe Ijiit U-ss capable of carrying a 

 heavy sjiring loatl, the armature operated in a knife edge hinge and 

 the restoring ft)rce was graxily. 



Kach subscriber's line recinired a liie rela\- for ligliting a i.inii) w lien 

 the substation receiver was reimned troni the hook, a cutoff relay for 

 renio\ing the line rela>' from the circiiii w lu-n the operator responded, 

 and a suiier\isor>' rel<i\' for r<mtnillin!^ lamp signals to inform the 



Fi.L,'. 9— l.itu- ;iii(l lUtiilT n-lays 



operator whether the substation switch hook cc)iil,ict> were open or 

 closed. The circuit arrangement for the line and cutoff relays is 

 shown scheinatically in Fig. 8. 



The rapid extension of telephone ser\ice necessitated establishing 

 standards of e.xcellence, and definite requirements for apparatus 

 units were gradually formulated. At first, the available relays were 

 adapted as closch' as possible to existing conditions, l)ut as require- 

 ments became definiteh' established, relays were designed specificalh' 

 to meet them and careful consideration was given to manufacturing 

 costs, mounting space, maintenance expense and all other factors of 

 economic importance. By 1010 se\'eral million of the line and cutofT 

 rela\s shown in Fig. f) and the super\isi)r\' relay of Fig. 7 were in 

 service. 



The cutoff relay armature was of tin.- reed hinge t\pe, while both 

 the line and supervisory relays were assembled with the more sen- 

 sitive knife edge armature. The line relay was eventually wound 

 with 12,000 minimum turns to a resistance of 2000 ohms ± 5 per cent, 

 and after considerable service experience requirements were formulated 

 for a line relay which would lie a satisfactory substitute. These 

 requirements were as follows: ^ 



(1) Battery potential. '20 2S volts. 



