AUTOMATIC TESTING OF INTERTOLL TRUNKS 939 



watt, relay (m) in the amplifier-rectifiei- will release. The control circuit 

 then releases relay 10 also to remove the 10 db pad before it proceeds 

 to the next step. If the test power level remains one milliwatt or higher 

 after the 10 db pad is inserted, relay (m) remains operated. The control 

 circuit then locks relay 10 in its operated position to retain the 10 db 

 pad before it proceeds to the next step. In the next step, pad control 

 relay 5 is operated to insert the 5 db receiving pad. The 5 db receiving pad 

 will then be rejected or retained, as described above, depending upon 

 which position relay (m) takes after the 5 db pad is inserted. This 

 process continues until all 9 individual receiving pads have been tried in 

 descending order ending with the 0.1 db pad. When this process is com- 

 pleted, the combination of the 9 pad control relays which remain locked 

 in the operated position determines, additively, the receiving pad loss 

 and consequently, this combination is related directly to the trunk loss. 

 At the originating or control end this combination of operated relays will 

 be translated to the measured loss of the intertoll trunk being tested, 

 when the results of the measurement are recorded. The method of trans- 

 mitting the measured loss from the far end to the originating end is 

 discussed later. 



The transmitting and check pads shown in Fig. 4 are a separate set 

 of pads also controlled by the pad control relays. At the start of the test 

 the total loss in these pads is 19.9 db. Whenever a pad control relay 

 operates to insert a receiving pad, it removes an equal loss from the 

 transmitting pads. Therefore, when the receiving pad adjustment is 

 finished, the loss remaining in the transmitting pads will be equal to the 

 loss of the trunk. Also, the sum of the losses in the two sets of pads is 

 always 19.9 db regardless of the trunk loss being measured, provided all 

 pad components and all pad control relay contacts are in perfect order. 

 This condition permits a precise accuracy check to be made, as discussed 

 later. 



Whenever the control circuit leaves pad control relay 4 or 0.4 in its 

 operated position to retain the 4 db or 0.4 db pad, the subsequent 2 db 

 and 1 db or 0.2 db and 0.1 db pad control relays are disabled. There will 

 will then be no action as the control circuit passes through the 2 db and 

 1 db or the 0.2 db and 0.1 db steps. This limits the maximum receiving 

 pad loss to 19.9 db, which is the maximum range of the automatic meas- 

 urement. This range amply covers the range of losses of intertoll trunks 

 in a usable condition. Loss measurements attempted outside the range 

 of to 19.9 db will cause failure of the built-in checks, mentioned later, 

 and will result in an alarm at the control end of the trvuik. 



