Patent GB-375441-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/58
Filed: 1931-03-30
Abstract: 375,441. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., (formerly AUTOMATIC TELEPHONE MANUFACTURING CO., Ltd.), Strowger Works, BELAS, F. T., 27, Arlescourt Road, and McCLEW, J. W., 26, Arlescourt Road, West Derby, both in Liverpool. March 30, 1931, No. 9642. [Class 40 (iv).] At a satellite exchange, a discriminatorselector having two sets of wipers discriminates by means of a vertically-moving wiper, alternative circuits being employed to effect discrimination as desired in accordance with the numbering scheme after the first digit or after the second digit when the first digit is one which causes the selector to drop back. Calls to an adjacent exchange as well as local calls are set up over the discriminator-selector, and the circuits are such that the discriminating digit in certain cases causes the selector to drop back and to respond to the next digit. First arrangement, Figs. 1, 2, and 3A, with discrimination on the first digit, which is absorbed for local calls but not for adjacent exchange calls. Line and release relays A, B energize, causing the operation of relays JD, MD, J, and the switch JFS hunts for a main exchange junction. Dialling tone is applied at the main exchange or locally if no idle junction is found, and the first digit is repeated to the vertical magnet VM and over the junction. Local calls are designated by the digit 6, and when dialling relay C falls back, the release magnet ZM operates over vertical wiper VW and wire 8 and restores the wipers. Relay LD now energizes, being no longer short-circuited over springs N2, locks, disconnects relay JD to release the junction and opens the holding circuit over the junction. The vertical magnet VM responds to the second digit, and the rotary magnet RM operates by interaction with stepping relay G which is controlled by busy ground on test wipers P1, P2 in such a way that the upper set of wipers has preference. The connection is extended by switching relay HA or HB. On the reply of the called party shunt-field relay D responds and relays MD, J fall back in turn to effect metering. If the call is one to an adjacent exchange, designated by the initial digit 8, relay LD energizes directly over its locking winding and rotary hunting takes place at once over the eighth level. Calls to an operator are routed in a similar manner. If the first digit designates a main exchange call, as soon as relay C falls back the rotary magnet RM energizes to move the wipers one step, but relay LD is not operated. Relay HA energizes to provide for metering if the call is successful or to give a busy signal if the switch JFS has stopped in its last position due to all junctions being busy. The connection is completed over the main exchange switches. When release occurs a pair of relays JA, JB serve to hold the junction for an interval pending the restoration of the distant switches. Second arrangement, Fig. 3B, with discrimination on the first or first and second digits, the first being absorbed for local calls in the latter case. If the initial digit is other than 8, the call is routed to the main exchange as in the first arrangement above. If the initial digit is 8, the release magnet operates to restore the wipers, and relay DA energizes and locks to change over the discriminating circuits. The second digits 1, 2 designate local and adjacent exchange calls, and in response to these digits relay 1LD operates to release the junction and initiate rotary hunting over the appropriate level. For any other second digit, relay 1LD does not operate, and the call is completed over the junction. Third arrangement, Fig. 3C, with discrimination on the first or first and second digits, both of which may be absorbed. An initial digit other than 6 always routes the call to the main exchange. The initial digit 6 causes the wipers to drop back and operates relay 1DA to change over the discriminating circuits. For local calls designated by the second digits 1 .. 5 relay 1LD operates and unlocks relay 1DA and rotary hunting takes place at once over the appropriate level. The operation is similar for the second digit 8, which designates an adjacent exchange call. For a local call having the second digit 9, however, the numbering scheme requires that it shall be absorbed, and accordingly relay 1LD energizes in series with relay 1DA and connects up the release magnet. Relay 1DA falls back and rotary hunting takes place after the receipt of the third digit.