Patent GB-321983-A (GB)
Title: Improvements in and relating to automatic and semi-automatic telephone exchange systems
IPC: H04Q3/00
Filed: 1928-08-23
Abstract: 321,983. Standard Telephones & Cables, Ltd., and Wright, E. P. G. Aug. 23, 1928. Automatic exchange systems.-A group selector for dealing with large groups comprises two permanently associated single-motion switches one or other of which hunts in a desired group according to the value of the first or first two digits, the discrimination being effected in a control switch of the group-marking type common to a group of selectors. The associated switches have two sets' of wipers and corresponding wipers of the two switches are connected in parallel, a common pair of switching relays being employed. As described, switch 1 has access to groups designated by the digits 21-20, while switch 2 has access to two groups designated respectively by the digits 5 and 9. The digit 1 is without effect, and any other digit results in the sending of a busy signal. When it has been determined that switch 2 is to be used, that is, as soon as the third impulse is received, this switch starts its hunting action, first over the group denoted by the digit 5, and then, if and when a sixth impulse is received, over that denoted by the digit 9. The selector is used in conjunction with finder-switches in tandem controlled by an allotting-switch as described in Specification 317,521. Upon seizure, relay O energizes over wiper C of the alotting-switch, and when connection is made with the calling line, relay K energizes over wiper B, and associates the selector with the control switch. Line relay 1 and release relay 4 energize disconnecting relay O and connecting up slow-release relay 3 over wiper SC1. Impulses are repeated to magnet Rover 2 (1), 1 (3), 1 (4), and relay 3 falls back at the end of the train. If only a single impulse is received, relay O energizes over wiper SC2 and closes the restoring circuit for magnet R. If the digit received is 2, relay 6 energizes over wiper SC2, locks and completes the restoring circuit, but when the normal position is reached, relay 21 pulls up and locks. In response to a second digit, as soon as the control switch moves off-normal, magnet R1 of switch 1 operates over 3 (K), 2 (2), 3 (E), 3 (F), 3 (9), 1 (8), and when the group marked by wiper SC4 in the bank of wiper 1C is reached, relay 8 energizes, cutting the drive and connecting up relay 7. On the relapse of relay 3, magnet R1 is again connected up to hunt for an idle line, test relays E, F being connected to test wipers 1AT, 1BT. One of these relays energizes when an idle line is found and connects up the corresponding switching relay HA or HB, whereupon relays 4, K, 8, 7, 2 release, energizing relay O to restore the control switch, which is then available for use in other connections. If the first digit received is greater than 2, at the third impulse, a circuit is closed for magnet R2 or switch 2 over 7 (K), 1 (F), 1 (E), 4 (9), SC5, 5 (2), and the group designated by the digit 5 is marked by wiper SC3 in the bank of wiper 2C, so that hunting takes place in that group, relays 8, 7 being energized to connect test relays E, F to test wipers 2AT, 2BT. If the actual digit received is 5, when relay 3 falls back, provided an idle line has been found, switching relay HA or HB energizes over 1 (4), 1 (3), 6 (2), SC2, 3 (8), 8 (K) or 2 (E), 2 (F), 11 (K). If however the digit is greater than 5, the seized line is dropped, relays 8, 7 and E or F being released, and the group designated by the digit 9 is marked by SC3, so that hunting now takes place in that group, the connection over a seized idle line being completed when the full 9 impulses have been received. If the digit received is 3, 4, 6, 7, 8 or 0, on the relapse of relay 3, relay 9 energizes over wiper SC2 and connects up busy tone. If an idle line has not been found when relay 3 falls back, relay 9 energizes partially, closing contact 2 (9), and if all the lines of the wanted group are busy, relay 8 relapses when the last line is passed and relay 9 energizes fully to give a busy signal. If no impulses are received, either for the first digit or for the second digit if the first is 2, relay HA becomes energized after an interval by means of relays 5, 7, and an alarm signal is operated.