Patent GB-613553-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1946-06-14
Abstract: 613,553. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. June 14, 1946, No. 18010. Convention date, June 11, 1941. [Class 40 (iv)] In a system in which a group selector hunts over a group of trunks marked by a distinctive potential which corresponds with a reference potential numerically selected in the register controller, a second reference current is selected in the register' controller to permit the selector to hunt also over second choice trunks which lead indirectly to the next selecting stage. The various potentials are characterized by their phase, selection control being similar to that described in Specifications 555,530, 563,666 and 565,785. Figs. 1 ... 5 show trunking diagrams of various embodiments. In Fig. 1, the second choice trunks are obtained over some outlets of the group designated by the succeeding digit. In an alternative, Fig. 2 (not shown), the groups are paired, second choice outlets of each being obtained from some outlets of the other. In Fig. 3, a group selector giving access to local trunks and to groups of outgoing junctions has additional outlets to overflow switches OK giving access to additional junctions of the several groups. Fig. 4 (not shown) is similar to Fig. 3, but with overflow switches OK 1 , OK 2  for local trunks and junctions respectively. In Fig. 5, the multiple is split into several parts, each part being accessible to a primary and a secondary selector PGK, SGK and outlets from an overflow group of each primary selector go to different secondary selectors. In one embodiment, Figs. 6, 7, 8, 13, according to Fig. 1 in which all outlets of a group are situated together, the groups being arranged in succession around the arcs of the selectors, both reference potentials are applied in the register controller during the first rotation of the selector switch. Incoming digits are registered on switches SM1 ... 3 in the usual manner, Dir 1 ... 3 directing the digits to the switches and providing an operating earth for Chr. Assuming digit 2 is registered on SM1 reference potentials #2, #3 are connected respectively via its banks b, c to the signal receivers I, II. When XM1 goes off normal relay Ar and power magnet P energize in the selector which hunts for a free outlet marked on its d-terminal by potential #2, whereupon gas valve B 1  in the signal detector I operates followed by Vtr which stops the switch. Relays Ft2, Fhr pull up in turn and momentarily release Chr to extinguish tube B1, after which Vtr reoperates if the selector is still on the outlet. Relay Str pulls up and closes a D.C. test circuit in which Th, Dtr operate and Br in the group selector switches through. Relay Dtr operates Sar and when the former releases on switch through Sar steps switch OM to prepare for the setting of the next selector. All direct outlets busy. The switch passes on to outlets of level 3 and signal receiver II tests for marking potential #3 and operates Vt1r to stop the switch, the A.C. test being repeated and the D.C. test being made as before. Relay Vt1r however operates Vt2r which locks and when Dtr operates Vt3r comes up, instead of Sar, operating V2r and releasing Ft2, Vt2r and chr. Relay Vt3r also operates Or which locks, earths the control electrodes of B2 to immobilize the signal receiver II and applies to the signal receiver I a reference potential #11 characteristic of the last few outlets of the seized switch which lead to alternative outlets of the required group. Relay Vt3r releases with Dtr after the switch through and the seized switch hunts for an outlet marked by #11, seizure and subsequent operation taking place as for a direct outlet. In an alternative arrangement according to Fig. 1, enabling the outlets of the selectors to be distributed in any order, only direct outlets are tested on the first rotation of the selector and both direct and alternative outlets on the second rotation. The last contact of the selector is marked by a potential #11. In the control circuit, Fig. 10 (not shown), a reference current #11 is connected to the signal receiver II during the first rotation of the selector at the end of which the operation of Vt1r, Vt2r connects up additional relays to replace the reference current #11 by that of the alternative outlets. Groups of outlets may be paired as described above, each group of the pair containing outlets giving access to the alternative outlets of the other group of the pair, Fig. 9 (not shown). In the arrangement according to Fig. 3, the circuit of Fig. 7 is modified, Fig. 11 (not shown), by the removal of the right-hand contact set of Or, wire 20 being connected straight to brush d of OM and bank c of SM1 having positions corresponding to local outlets connected to a potential # 12 and the remainder to #11. #12 has a phase not used in group selector outlets so that receiver II will not operate for settings corresponding to local outlets. If all direct outgoing junctions are engaged when the selector reaches overflow outlets marked by #11, signal receiver II operates as described above and the seized overflow selector now hunts under control of signal receiver I which is still marked by reference current from bank b of SM1. Overflow switches for two sets of groups may be provided by marking the levels from which the respective overflow switches are accessible by potentials #11, #12 and connecting the bank c of SM1 accordingly. In the arrangement according to Fig. 5, when the primary selector reaches the first contact of level 11, operation of Vt1r in the control circuit causes the seconddary selector of the succeeding multiple split to hunt for a free outlet of the required group. The circuit for relay Or in this particular embodiment is modified by the inclusion of additional relays, Fig. 14 (not shown), so that if the secondary selector also reaches its eleventh level the second operation of Vt1r operates one of the additional relays to shunt down the switching relay Br in the primary group selector, which then moves to the next free contact of level 11 connecting to another secondary selector having access to a different part of the multiple split.