AUTOMATIC TESTING OF RELAY SWITCHING CIRCUITS 1173 



also apparent that several paths can be found that will satisfy any one 

 switched connection. Paths are assigned in sequence by a series relay 

 loop circuit. The entry point on this circuit is changed periodically to 

 distribute wear on the relays and switch cross points. 



Although only one lead for the switched circuit is shown for each 

 cross point in Fig. 12 there are actually four leads through corresponding 

 pairs of contacts through each cross point. The remaining leads are 

 associated with the holding and signalling functions of the switch. 



The block schematic (Fig. 13) shows the principal functions which 

 must be included in an automatic test set of this sort. A somewhat more 

 detailed schematic is presented in Fig. 14 in order to show the functions 

 of the forty test features 0-39. These are tabulated in Table I. 



The coding of the two letter combinations in the tape must follow a 

 defuiite sequence in order that the machine may recognize and act on 

 the information it receives. This sequence is as follows: 



1. Code FW to stop the tape at the end of the reset cycle after which 

 tests will proceed w^hen the start button is pressed. This is the first code 

 on all tapes. 



2. Codes to set up crossbar switches to connect each circuit terminal 

 to its proper test set terminal and the proper termination. Knock down 

 or release codes may also be sent. 



3. Codes to operate or release "Kej^" relays. These relays are shown 

 without windings in Fig. 14. 



4. Codes to operate or release the watching relaj^s associated with 

 the "Signal" relays which are shown with windings in Fig. 14. 



5. Codes to operate or release relays controlling the lamps associated 

 with relays in the circuit under test to aid in trouble shooting. 



6. Codes to delay the timing out interval up to a maximum of ten 

 seconds. 



7. Code FJ which checks the matching of all signal and watching 

 relays through the chain circuit for satisfaction of all test conditions 

 being applied. 



In addition to the above, additional codes can be inserted after each 

 FJ test signal to stop progress of the test to permit the tester to perform 

 some required manual operation. After completion of this step he presses 

 a button associated with that operation and the test proceeds. Option 

 codes can also be inserted at the beginning and end of each testing step 

 to permit bypassing of that part of the tape if the corresponding option 

 keys are operated at the beginning of the test. A common knock down 

 code FR can be inserted at any time to release all connections and re- 

 lays for a quick disconnect and make all test set features available for 



