270 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1956 



Total power consumption of the concentrator is between 5 and 8 watts 

 depending upon the number of connections being held. 



7. CONCENTRATOR OPERATION 



a. Line Scanning 



The sixty lines are divided into 12 groups of 5 lines each. These group- 

 ings are designated VG and VF respectively corresponding to the 

 vertical group and file designations used in the No. 5 crossbar system. 

 Each concentrator corresponds to a horizontal group in that system. 



To scan the lines two transistor ring counters, one of 12 stages and 

 one of 5 stages, are employed as shown in Fig. 17. These counters are 

 driven from pulses supplied from the central office control circuits and 

 only one stage in each is on at any one time. The steps and combinations 

 of these counters correspond to the group and file designation of a par- 

 ticular line. Each 0.002 second the five stage counter (VF) takes a 

 step and between the fifth and sixth pulse the r2-stage counter (VG) 

 is stepped. Thus the 5-stage counter receives 60 pulses or re-cycles 12 

 times in 120 milliseconds while the 12-stage counter cycles but once. 



Each line is provided with a scanner gate. The collector output of each 

 each stage of the VG counter biases this gate to enable pulses which 

 are generated by the collector circuit of the 5-stage counter to pass on 



-65V 



+ 30V 



+ SV 



-I6V 



115 V 

 AC 



MOTOR 

 GENERATOR 



TO 



COMMERCIAL 



AC 



REGULATORS 



Fig. 16 — Power supply transmission circuit. 



