274 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 



of the mark pulses is stopped and a reset pulse is sent to the concentra- 

 tor to return the mark bi-stable circuit, counters and all operated selec- 

 tor relays to normal. The concentrator remains in this condition until 

 it is resynchronized with the regular line scanning cycle. 



A complete functional schematic of the concentrator integrating the 

 circuits described above is shown in Fig. 21. Fig. 22(a) and (b) show an 

 experimental concentrator built for field tests. 



8. CENTRAL OFFICE CIRCUITS 



The central office circuits for controling one or more concentrators 

 are composed of wire spring relays as well as transistors, diode and reed 



VG 



RS 



VF 



M 



-20V 



-20 V 

 o- 



VF-5 STAGE 

 COUNTER 





r 



-65V 



n 



04 



03 



02 



00 



6 RELAY I W-, wo w<- ,^, -o p 



PACKAGE J '-|„p_„p_^_p-_-p-^Ui 



TO CONTACTS OF 4 

 INTERMEDIATE RELAYS 



6 RELAY 

 PACKAGE 



TO CONTACTS OF 4 . 

 INTERMEDIATE RELAYS 



n 



L 



59 



n 



58 



i^ 



34 33 32 31 30 , 



29 28 27 26 25 I 5^ 



57 56 55 



TO 4 



INTERMEDIATE 



RELAYS 



' 



-/ *■ 



I 



I I 2 



b^'" 



/ 7_ 

 8_ 

 9 



10 





cr 



LU 



h- 



z 



o 

 o 



< 



I- 



OJ 



I 



(J 

 > 



I 



TO 4 

 INTERMEDIATE il 

 RELAYS 



P^ig. 19 — Line selection and marking. 



I 



