Patent GB-654311-A (GB)
Title: Improvements in automatic telephone switching systems
IPC: H04M15/04
Filed: 1948-08-13
Abstract: 654,311. Automatic exchange systems. WESTERN ELECTRIC CO., Inc. Aug. 13, 1948, No. 21395. Convention date, Aug. 22, 1947. [Class 40 (iv)] In a system in which the digits employed to set switches to connect a calling line to a trunk are not normally registered means is provided operable in response to a connection between a line and a trunk to indicate the number of digits so employed and their individual values. As shown, trunks are accessible from first, second, or third selectors, and in some cases (e.g. trunk T1) may be reached in all three ways. The sleeve conductor of each trunk which can be reached in only one way is directly connected to one element of each of a plurality of diode gas tubes, the number of tubes in each case being one more than the number of digits dialled to reach the trunk. Where a trunk such as T1 may be reached in more than one way the sleeve conductor of each appearance is connected through one winding of a relay (SR1, SR2, SR3) to the sleeve conductor of the trunk, a front contact and the other winding of each relay being connected to the group of tubes individual to the appearance. In each group of tubes, one tube (the upper in Fig. 3) is used to indicate the number of digits dialled to reach the trunk, its other elements being connected to the corresponding one of bus-bars D1, D2, and D3 ; and the other tubes indicate the values of the respective digits dialled, one element of each being connected to a corresponding one of bus-bars A1 ... A10; B1 ... B10 ; or C1 ... C10. Recovery circuits each comprising two triode gas indicating tubes for each bus-bar and a pulsing tube are provided, three such circuits being shown. Tubes I1 to I6 are three pairs of indicating tubes and P1 the pulsing tube of the first circuit, indicating tubes (not shown) being provided for all the other busbars. An impulser, which may be of the type disclosed in Specification 650,774, is arranged to raise the potential of the pulsing tube control grids in turn to fire them cyclically. The cathode of each pulsing tube is connected to the anodes of the first tubes of all the pairs of indicating tubes in its recovery circuit, so that when a pulsing tube fires positive potential is applied to the first tube anodes of that circuit. Assume that station S (Fig. 1) originates a call to trunk T3. To initiate the recovery of the digits dialled to reach the trunk, relay TR3 is operated by any suitable means whereupon positive battery is applied to sleeve 50 of the trunk ; start relay ST3 (Fig. 2) is also operated and a trunk-finder, say F1, connects the cathode of P1 to the sleeve 50. When P1 next fires a positive pulse is transmitted over the sleeve whereupon N6, N7 and N8 fire and extend the pulse to bus-bars D2, A2 and B2. The pulse on D2 is applied to the starting electrodes of tubes 13, 19, and I15 but as only I3 has positive potential connected to its anode (P1 firing) it alone fires and is followed by 14. Relay RL1 operates (and holds as I4 remains conducting) indicating that two digits were dialled. In like manner, the pulses applied to A2 and B2 affect two other pairs of tubes (not shown) and two relays similar to RL1 are operated to indicate that the digits dialled were " 22 ". In the case of trunks such as T1 accessible over more than one route operation of the TR relay brings up the SR relay individual to the appearance seized and this relay extends the sleeve conductor to the relevant group of tubes. Since the pulsing tubes do not fire simultaneously the digits dialled by different stations to reach different trunks may be recovered simultaneously by employing a different recovery circuit for each call.