AUTOAIATIC TESTING OF RELAY SAVITCHING CIRCUITS 1159 



system is at best a slow and laborious one which is subject to human 

 error. Wages for testers are determined not primarily on their ability 

 to operate keys and check the indications of lamps but on their skill in 

 analyzing and clearing trouble conditions. If some quick and automatic 

 means could be devised to make the initial cross connection setup, apply 

 the potentials in the proper sequence under control of some programing 

 device and check the circuit responses at each step a real advance in 

 speeding up tests and reducing human errors would be accomplished 

 Such an automatic set ideally should have improved response indications 

 to aid the the tester in locating circuit troubles when the test set stops 

 on the failure of meeting any test requirement. 



THE AUTOMATIC TEST SET 



The key and visual lamp indicating functions of the manual test set 

 can be replaced by relays in an automatic test set which perform these 

 operations if they are under control of suitable programing and advanc- 

 ing circuits as shown in Fig. 3. Here the "signal" relays operate through 

 the contacts of the relay under test and their operating positions are 

 checked by the "watching" relays whose contact closures must match 

 those of the signal relays. The series path through the contacts of all 

 signal and watching relays is called a chain lead. The program circuit 

 establishes the positions of the watching relays to meet the expected con- 

 ditions prior to operating the key relay and then any lack of continuity 

 through the chain lead caused by failure to satisfy test conditions halts 

 the progress of the tests under control of the advancing circuit. At this 

 point additional contacts (not shown) on the signal and watching relays 

 may be used to light signal lamps to convey information to the tester 

 as to which portion of the circuit failed to operate properly. 



For quick setup a pre-wired multi-contact adapter plug may be used 

 as a cro?s-connection device to permit establishing the proper test con- 

 nections to the unit under test. One will be required for each type of 

 relay circuit to be tested. These, together with some means whereby 

 the sequential operation of the programing circuit can be controlled, 

 constitute the essential features of an elementary automatic relay switch- 

 ing circuit test set. How these basic features can be extended into prac- 

 tical embodiments will be explored further below. 



THE CARD-O-MATIC TEST SET 



Key equipment relay units are small switching circuits used as cir- 

 cuit building blocks to provide the desired optional features in conjunc- 

 tion with the key boxes or key-in-base telephones often seen in small 



