

1158 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956 



thej'' can be connected to ground and to battery through lamps for cir- 

 cuit closure indications. The switching functions of the relay can then 

 be checked by operating the test key and observing that signal lamp (1) 

 extinguishes and that (2) lights. 



While such an arrangement can adequately test most switching cir- 

 cuits of any complexity by further extension of the basic scheme, when 

 supplemented by internal circuit connections where necessary, the 



SIGNAL 

 LAMPS 



(2) (C 



(I) 



S: 



^ 



X 





> 



MANUALLY OPERATED 

 TEST KEY 



X 



PIN 

 JACKS 



PIN 

 PLUGS 



CONTACT 

 FIXTURE 



/ 



^ 



— ^ 



^ 



TEST CABLE-" 



/Cl 



CIRCUIT 

 TERMINALS 



PORTION OF 

 RELAY CKT 

 UNDER TEST 



Fig. 2 — Simplified circuit sketch for manual test operation. 



WATCHING 

 1 RELAYS 



SIGNAL 

 RELAYS 



CONTACT 

 CROSS CONNECTING FIXTURE 



DEVICE / CIRCUIT 



> /TERMINALS 



I I f 



TEST CABLE 



PORTION OF 

 RELAY CKT 

 UNDER TEST 



Fig. 3 — Simplified circuit sketch for automatic test operation. 



