Patent GB-312120-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1928-02-20
Abstract: 312,120. Standard Telephones & Cables, Ltd., Baker, J. H. E., and Wright, E. P. G. Feb. 20, 1928. Automatic exchange systems.-A group of numerical switches of the Strowger type is provided with a. common set of controlling relays connected in multiple to all the switches of the group, and operatively associated with a particular switch only during the setting of the switch. The invention is described in its application to a group selector and to a connector. In the case of the group selector, the common control set may include relays by means of which certain digits are absorbed, or are effective in connecting up a second set of wipers. Specification 276,442 is referred to. Group selector, Fig. 1. Relay K energizes over the loop, locks to the incoming test wire and extends the loop to the line relay 1 of the common apparatus, which energizes and connects up release relay 2, grounding the test wires of all the selectors of the group. Dialled impulses are repeated by relay 1 to the vertical magnet V, series relay 3 energizing at the first step and connecting up relay 6. When relay 3 falls back fit the end of the train, the rotary magnet R operates and disconnects relay 6 which in turn disconnects the magnet R. If the first trunk is busy, relay 4 energizes over the test wiper, and interacts with the rotary magnet R until an idle line is reached. Test and switching relay H then energizes in series with relay 4 which is now inoperative, disconnecting line relay 1. Relay K falls back when release relay 2 relapses, and switching relay H is held over the test wiper in series with the rotary magnet R. On release, release magnet Z operates over a back contact of relay H. If no idle line is found, in the 11th position, relay 5 energies over cam springs S, and connects up busy flash through relay 1, release relay 2 being held during the periods when this relay is de-energized. Modification for absorbing a particular digit, Fig. 2. In response to the particular digit, springs NP1 are closed, and when series relay 3 falls back, relay 7 energizes, locks and connects up the release magnet Z to restore the selector. Relay 8 then energizes and the selector responds to a second train of impulses, relay 6 being connected up by series relay 3 as in the case of an ordinary selector. Modification for connecting up a second set of wipers in response to a particular digit, Fig. 2. Springs NP2 are closed in this case, and relays 8, Q energize in series and lock independently, and the release magnet Z restores the selector. Relay 7 then energizes, and the selector is ready for operation in the ordinary way, but with the second set of wipers connected up. Connector, Fig. 3. Relay K energizes over the loop, locks to the incoming test wire and extends the loop to line relay 1 of the common apparatus, which energizes and connects up release relay 2, grounding the test wires of all the connectors of the group. The first train of impulses operates the vertical magnet V, relay 3 being energized in series, and two-step relay 7 then energizes fully to connect in the rotary magnet R, which responds to the second train. If the wanted line is busy, two-step relay 5 energizes fully when series relay 3 falls back, and connects up busv flash through relay 1, release relay 2 being held during the periods when this relay is de-energized. If the wanted line is free, ringing relay 4 energizes when relay 3 falls back, and ringing current is sent out over ring cut-off relay 6. ring back tone being conected back through relay 1. Upon reply, relay 6 energizes, locks and connects up switching relay B of the connector, which disconnects relay 1, and the common apparatus is released. Feed relays A, D energize over the calling and called loops, and the former locks relay B while the latter reverses the current in the calling loop for metering purposes. On release, release magnet Z operates over a back contact of switching relay B.