AUTOMATIC TESTING OF RELAY SWITCHING CIRCUITS 1161 



)usines.s offices to furnish the flexibiHty needed in answering and trans- 

 ferring calls. These s3^stems are used where the number of telephones 

 served does not warrant the use of a regular PBX switchboard. 



These circuits are relatively simple but their large scale pi'oduction 

 warrants the use of high speed automatic test sets to perform the test 

 functions and to indicate circuit trouble. 



Fig. 4 shows the operating position of the Card-0-Matic* test set 

 which was developed to test such unit assemblies. The keys shown are 

 used to initiate and control the automatic operation of the test set and 

 in trouble shooting. They are not to be confused with those that per- 

 form the actual testing functions described previouslj^ for the manual 

 test set. The lamps pro^'ide indications of the progress of the tests and 

 of the positions of the watching relays which are also needed to aid in 

 determining the point of circuit failure. The meter type relay in the 

 upper left corner of the operating panel provides a sensiti\'e checking 

 de\'ice for audio freciuency tests through the \'oice transmission circuits. 

 The telephone dial affords a simple means of generating any recjuired 

 number of pulses for operating stepping selectors on some types of units. 

 The terminal field in the lower front of the cabinet gi\^es the tester access 

 to the circuit terminals of both the unit under test and the test set for 

 his use in analyzing and locating faults. The upper cabinet was a later 

 addition and contains the multi-contact rela3\s needed to permit testing 

 units with more than one circuit. The row of push buttons are used to 

 select the circuit to be tested. 



Fig. 5 is a rear ^'iew of the set that shows the perforated insulating 

 card from which the set derives its name. The coded card controls the 

 sequence of test operations and is hung on pins over the field of 1,000 

 spring plungers (20 X 50) as a part of the setup operation for a particu- 

 lar relay unit. Closing the door and screwing up the hand wheel, which 

 is necessary to provide the force required to depress the plungers, will 

 ground those which coincide with holes in that particular card. 



Cross-connection setup of the test leads is achieved by the use of a 

 plug-board such as is commonly used for quick change over on perforated 

 card type business machines. Fig. 6 shows the plug board being inserted 

 into the transport mechanism. The relatively large number of terminals 

 are retjuired because each of 60 test leads must be capable of being 

 patched in to an equi\'alent number of terminals on a maximum of ten 

 different circuits. Not all of our test sets are equipped with the upper 

 cabinet since most key units have only one circuit and on these a simpler 



* Patent No. 2,329,491. 



