Patent GB-323794-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone exchange systems
IPC: H04Q3/00
Filed: 1928-10-10
Abstract: 323,794. Standard Telephones & Cables, Ltd., and Wright, E. P. G. Oct. 10, 1928. Automatic exchange systems. - A switch is moved by an impulse train a number of steps greater than the number of impulses and then moves automatically to a further position determined by the initial setting. The invention is described as applied to marking switches. The switch shown in Fig. 1 is common to a number of group selectors and is dialled to one of the positions 1 - - 0 marked below the terminal row D, and then moves automatically to the corresponding one of the positions 1 - - 0 marked above the row, and hunts for an idle trunk. The switch is of double wiper simultaneous hunting type but has only one marking wiper M. The selector has two wipers M1, M2, 180‹ apart and wiping over the same row of marking terminals, one or other wiper being selected according to which wiper set of the marker has been connected up. The talking and test wipers of the selector are double ended, the ends wiping over different rows. The next digit, if it arrives before the selector switches through, goes over line wipers on the marking switch. The marking switch, Figs. 3, 4, which is common to a group of connectors, Fig. 2, in response to the tens digit goes to one of the positions 1 - - 0 marked below the row D and then to the corresponding position 90....78 marked above it and is then stepped by the units digit in the ordinary way. A relay energized if the tens digit is odd connects up the marking wiper M2 in place of M1, and the test wiper T2 in place of T1. If the line is busy, the marker sends back a busy signal. If it is idle the connector is driven to the line and ringing current is sent from the marker circuit. Group selector. When the selector is seized, K pulls up to connect up the marker circuit in which line and release relays 1, 4 pull up. At the beginning of the 1st impulse, dialling relay 3 pulls up, and at the end, the driving magnet R is energized over 2.4, I, 1.4, 3.4, 4,2, and moves the switch one step. Each subsequent impulse, owing to the connections of the I terminals, causes it to move 4 steps, 1 at the beginning, 2 independently off the line relay, and 1 at the end. To ensure that this step is made in spite of the premature arrival of the next impulse, the line relay, at the end of each impulse, locks itself over the interrupter springs on R. On the relapse of the dialling relay, 2 pulls up sluggishly and makes a driving circuit for Rover the off-normal row N. If the digit is 5, 7 or 9, 6 pulls up before 2 to mark the positions 5, 7, 9 indicated above the row D by connecting them to relay 5 and remove this marking from the others. When the switch reaches the nearest terminal so marked, i.e. the beginning of the group corresponding to the digit dialled, 5 stops it, by releasing 2, and energizes 9 which releases 5 and makes a new driving circuit for the switch. When wiper T1 or T2 finds an idle trunk, 71 or 72 stops the switch and energizes 81 or 82 which switches through, makes a driving circuit for R1 of the selector and connects 5 to its wiper M1 or M2. When the selector reaches the marked trunk 5 stops it and energizes H which locks up and switches through. 1 was released by 81 or 82 and 4 which held temporarily in parallel with the driving circuit of R<1> now falls back, releasing K and the marking switch relays and homing the marking switch. All trunks busy. If the marking switch finds the trunks reached over the last terminals in a group busy, 5 pulls up over wiper D, stops the switch and energizes 2 to send the busy signal. Connector. When the connector is seized, K, 1, 4 pull up and the marking switch responds to the first digit in the same way as the group selector marking switch except that it takes 4 steps for the 1st as well .as for the subsequent impulses. If the digit is odd, 7 pulls up to connect up the 2nd marking and test wipers and if it is 5, 6, 9 or 0, 2 pulls up to mark the 5,6 90 positions instead of the <3>4 <7>8 positions by connecting them to 5. On the relapse of dialling relay 3, W pulls up, locks itself and drives the marker to the nearest of the positions so marked where it is stopped by 5. It is then stepped by the units digit. If the line is busy, 6 pulls up over T1 or T2 to send busy tone from BT and remains locked on the relapse of 3. If not, the relapse of 3 energizes 7 over T1 or T2. 7 locks over its lower winding grounds the marking wiper of M1 or M2, and unlocks 5 to drive the connector. When the marked line is reached 5 pulls up over wiper C in the connector and wiper M1 or M2, energizes 2 (which if operated before was unlocked by the dialling relay) to complete the ringing circuit over F. When the called party replies F pulls up, locks itself and energizes B which energizes BB. BB connects up the line relay A and back bridge relay D and releases K to restore the marker. The connection of A reverses the direction of current flow in the calling loop. After the relapse of K, B is held by A until the end of the connection.