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THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1952 



to connect the talking conductors associated with the particular column 

 to the talking conductors associated with the particular row. A cold- 

 cathode gas diode is also associated with each crosspoint relay, and this 

 diode in series with the winding of the relay is connected between the 

 control lead of the particular column and the control lead of the particu- 

 lar row. The third contact of the crosspoint relay is used to short-circuit 

 the associated gas diode. A typical crosspoint is shown schematically in 

 Fig. 9. The use of these crosspoint gas diodes in the control leads facili- 

 tates the identification and selection of idle paths through the switching 

 network and the short-circuiting of the diodes at operated crosspoints 

 facilitates the holding of an established connection through the net- 

 work at a lower power level than required for initial operation and the 

 maintenance of a busy indication along an established connection during 

 the path selection processes of subsequent calls. Dry-reed contact relays, 

 rather than a more conventional type, are used in the crosspoints to 

 provide the operating speed required for single control circuit operation. 

 Each secondary switch is a similar rectangular array except that the 

 horizontal rows are used as input terminals and the vertical columns as 

 switch outlets. Within a frame the horizontal outputs of the primary 

 switches are interconnected with the horizontal inputs of the secondary 



VERTICALS 



(control) 



-- >o 



(talking) 



Fig. 9 — Reed-diode switch — ^crosspoint connection. 



