1028 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1952 



TENSION 



I 





CARD HOLDS 



CONTACTS 



APART 



TWIN 

 CONTACTS--- 



CARD PERMITS 

 CONTACTS 

 LOSE 



ICAKD PI 

 CONT> 

 TO CL 



UNOPERATED OPERATED 



(a) MAKE CONTACT 



STATIONARY 

 CONTACT :k. 



CARD DOES NOT 



TOUCH TWIN 



WIRES 



TENSION 



CARD FORCES 



CONTACTS 



APART 



UNOPERATED OPERATED 



(b) BREAK CONTACT 



-RESTORING 

 SPRING 



TWIN CONTACTS 

 (MAKE) 



COMMON 



STATIONARY 



CONTACT- 



TWIN CONTACTS 

 (BREAK) 



BACKSTOP- 



UNOPERATED 



(C) TRANSFER CONTACT 



Fig. 4 — Principle of contact operation. 



