AUTOMATIC TESTING OF RELAY SWITCHING CIRCUITS 1165 



to match each other. Simplified circuit sketches which show the inter- 

 connection of test set and wired unit circuits are provided to enal:)le the 

 1 ester to determine quickly the cause of the failure. 

 I Th(^ C'ard-(^-Matic test set, while performing admirably on the rela- 

 tively simple relay circuits within its range and capabilities, falls down 

 on the more complicated relay switching circuits used in telephone 

 central offices for several reasons. The most important of these are: 



1. A fixed cycle within a maximum of twenty steps with any one 

 coded card. 



2. No provision for alternate or optional circuit conditions on a card. 



3. The only power supplies provided to operate relays are negative 

 24-volt dc and 90-volt 20-cycle ringing whereas telephone office units 

 frequently also require negative 48-volt and positive 130-volt dc as well 

 as positive or negative biased ringing currents for party line ringing. 



4. The increase of either test steps or features would increase the 

 size of the perforated card beyond a practical size. 



THE TAPE-O-MATIC TEST SET 



The experience gained in the design and successful operation of the 

 Card-0-Matic test set led naturally to the exploration of ways and 

 means whereby a more versatile and comprehensive set could be devised. 

 The five hole coded perforated teletype tape was selected as a cheap 

 and flexible programing device. It afforded a means of providing a test 

 cycle of any required length and, since the perforating and reading 

 mechanisms were already available, it appeared to be nearly ideal for 

 its purpose. 



Consideration was given to the following desirable features all of 

 which were incorporated in the design of the new set: 



1. Provision for cross-connecting (under control of the coded tape) 

 any test set circuit to any terminal of the circuit under test for as long 

 as necessary and then disconnecting for reuse in later testing steps if 

 required. This A\'ould greatly extend the range and capabilities of the 

 set. 



2. Provision for several power voltage sources which could be selected 

 as required to meet the normal telephone office voltage requirements 

 of the unit under test. 



3. Provision for alternate or optional tests to be coded into the tape 

 to meet the various circuit arrangements that may be wired into the 

 unit as required by the Telephone Company who is our customer. Such 

 optional test arrangements could be applied by the test set under the 

 control of keys to be operated by the tester as part of the setup at the 

 start of the tests. 



