Patent GB-353508-A (GB)
Title: Improvements relating to telephone systems
IPC: F16K3/08
Filed: 1930-04-25
Abstract: 353,508. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, and CHRISTIAN, D. A., Morven, Charlton Road, Charlton, both in London. April 25, 1930, No. 12796. [Class 40 (iv).] In a system with offices in a chain, idle incoming junctions are maintained in association with idle outgoing junctions so that there is normally a waiting free route from end to end of the chain. In the system described, the first digit designates the wanted office and operates a two-motion selector to select a right or left junction or a local trunk. The second digit which is the same (say 0) for all calls, is wholly absorbed if the call is local but for inter-office calls is repeated in part over the junction, each impulse (except the first) causing an incoming junction to be switched through to the preselected outgoing junction. The number of impulses repeated is determined by a counting switch marked by a vertical wiper on the selector. At the terminating office, failure to receive an impulse causes the preselector to move away from the outgoing junctions and hunt for a local trunk. Some offices in the chain may be manual. Reference is made to a system, not described in detail, in which the offices have no group selector stage but make use of link circuits with common control circuits. In such a system the connectors give access on two adjacent levels to right and left junctions and are arranged to move opposite one of these levels on seizure, the first digit being recorded by a discriminating switch in the control circuit and causing the selector to hunt in one or other outgoing level or drop back. An incoming call is preferably steered to a connecting circuit with which an idle control circuit is already associated. Originating office. The first digit is repeated to the vertical magnet VM, Fig. 2. On the relapse of D at the end of the digit, L having been energized on the first impulse and remaining locked up, a driving circuit is made for the rotary magnet RM. When an idle junction (or local trunk) is found, T marks it busy, locks itself and energizes C. If the call is local S pulls up immediately over normal terminals of the translating switch AS and the vertical wiper VS with the result that the next digit, during which C remains energized in spite cf the operation of E on the first impulse, is wholly absorbed. Otherwise, the next digit, shorn of the first impulse by the arrangement of contacts e<2>, a<2>, is repeated over the junction and to the magnet DM of the translating switch until the latter finds the terminal marked by the vertical wiper, whereupon S renders the remainder of the digit ineffective. Intermediate offices. At the end of the first impulse of the second digit, PL, PR at the adjacent exchange are operated, and the next impulse thus energizes PT to seize the preselected junction. At the end of the impulse, pl2 operates PL, PR at the next office. Final office. This office receives no impulse so that PQ is enabled to pull up to drive the hunting switch in search of an incoming selector. Two-way working. Apparatus BWEL, BWER shown in detail in Fig. 4 is arranged between each junction and its preselector. On an incoming call ETR operates in series with Y or PY at the preceding exchange (which however cannot operate in this circuit) cuts off COR and busies the junction to the local first selectors and the preselectors. SR is energized by PR, releases ETR and itself marks the junction busy. Outgoing calls energize COR to switch the junction direct to the group selector or incoming preselector. Metering. When the called party replies, Y completes a metering circuit over the third winding of the line relay and the test wire, the circuit being broken shortly afterwards by the relapse of L. Metering could however be variable in accordance with the position of the selector.