INTERTOLL TRUNK CONCENTRATING EQUIPMENT 323 



control f>;ap breaks down (which is minimum ()3 volts for this tii])c) R 

 is the value of resistance in ohms, and (' is the ^'alue of the capacitor in 

 farads. The timing circuits measure an inter\al of about 0.8 seconds 

 which is sufficient to ])ermit the distant end of any trunk, whicii has just 

 been released, to restore to normal. When the timing interv^al is com- 

 plete the GUARD TIME relays release, the: direction of selections is re- 

 versed, and selections are resumed. 



Direction of Selection Control 



Two directions of selection are provided for both incoming and out- 

 going trunks to (1) by-pass incoming and out-going trunks which are in 

 trouble, (2) to guard against blocking due to a single trouble in the 

 controller itself. (See Fig. f2.) The directions of selection are controlled 

 by two combinations of relays, plus three other relays controlled by these 

 combinations. The aow and aoz relays control the outgoing directions of 

 selection. With these relays in the unoperated condition the outgoing 

 trunks will be selected in the low to high order and with them operated 

 selections will be made in the high to low^ order. The outgoing trunks, in 

 the normal course of events, are served starting with lowest or highest 

 numbered trunks and proceeding to the highest or lowest numbered 

 trunk depending upon the direction of selection at the time. When the 

 last trunk has been selected the direction is reversed by either operating 

 or releasing the aow and aoz relays depending upon the status cjuo ante. 

 In case a short time-out is due to failure to close the crosspoint the direc- 

 tion of selection of outgoing trunks is reversed immediately. It is also 

 reversed whenever a long time-out occurs, whatever the cause. 



The AW and az relays form the combination which controls the in- 

 coming direction of selection. Controlled by them are the control 

 relays ci and C2 associated with the low to high and high to low direc- 

 tions respectively. With the aw relay unoperated the ci relay is operated 

 and the direction of selection is from low to high. With the aw^ relay 

 operated the ci relay is released, the C2 relay is operated and the direc- 

 tion of selection is from high to low. The incrmiing direction of selection 

 is reversed under the following conditions: 



1. When the outgoing direction is reversed upon the last outgoing 

 trunk being selected the incoming direction is also reversed if and when 

 there are no more incoming trunks within the gate waiting to be served. 



2. When a short time-out occurs due to the faihu'e of the end relay 

 to operate or failure of continuity check. 



3. When a second failure to close crosspoint occurs. 



4. When a long time-out occurs. 



