1156 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956 



duction test sets for their exclusive use, adaptable manually operated 

 test sets were first used. These sets required a high degree of flexibility 

 in interconnecting the terminals of the circuit under test to those of the 

 test set and in applying the proper potentials in sequence that would 

 insure putting the cii'cuit through its paces and checking that the switch- 

 ing functions are properly performed. 



It should be stated here that since all apparatus components of these 

 circuits such as relays, transformers, capacitors, inductors and resistors 

 are tested and inspected for their respective electrical and mechanical 

 requirements when manufactured, except in the case of some types of 

 relays which require adjustment to meet their particular circuit recjuire- 

 ments, the testing of switching circuits is largely confined to verification 

 of the circuit wiring with normal voltages. Although marginal component 

 tests are not normally applied, operation tests will, of course, detect 

 defective apparatus components which cause malfunctioning of the 

 circuit. 



MANUAL TEST SET 



Fig. 1 shows a representative manual type test set that was extensively 

 used for wired relay vmit testing before the introduction of the automatic 

 test sets to be described later. On the left side is a pin jack field into which 

 the numbered wires of the connecting cable can be individually plugged 

 in order to connect the test set terminals to the proper terminals of the 

 relay unit under test. The other end (not shown) of the cable is equipped 

 with a contact fiixture arranged to give quick electrical connections to 

 the terminals of the wired relay unit. The plugging of the pins into the 

 proper pin jacks is a feature needed to provide flexibility in a test set 

 arranged to test many types of circuits and is a part of the setup opera- 

 tion for any one circuit. It is a slow and time-consuming operation since 

 each lead has to be identified and plugged into the proper pin jack. The 

 pin plug setup must be taken down and rearranged in order to test any 

 other type of relay circuit. 



The test set is equipped with signal lamps for visual response indica- 

 tions and manually operated keys for the use of the tester in performing 

 the test operations. Separate power cords are plugged into power distri- 

 bution jacks which supply the various potentials commonly used in 

 telephone central oflSces. 



After the initial setup the tester operates the numbered keys and ob- 

 serves the lamp signal responses in accordance with the chart clipi^ed 

 to the front of the test set. Failure to get a particular lamp indication 



