Patent GB-343460-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone exchange systems
IPC: H04M7/10
Filed: 1929-11-15
Abstract: 343,460. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., Columbia House, Aldwych, London. -(Hatton, W. and Dahl, R.; 46, Avenue de Breteuil, Paris.) Nov. 15, 1929, No. 34948. [Class 40 (iv).] In a system in which if a calling subscriber fails to hang up, the distant end of a two-way junction is released by a thermal relay in the link circuit at that end and subsequently the outgoing end is released by a thermal relay in the originating link circuit the junction may be seized at the distant end for a call in the opposite direction without interfering with or being interfered with by the forcible release of the (original) outgoing end from the previous connection. Operation of link circuit to select junction. When the calling line is found, Lt, Lt<1>, Lb, A, E, As and Se are operated and dialling tone goes back over normal contacts of the marker SM which, when moved off by the first digit, starts the selector SMS1. If the digit is greater than 5, SMS2 (not shown) is started and SMS1 stopped. Terminals representing junction groups in the banks 4 and 5 of the marker are connected to the wires A. The selector is stopped on an idle junction of the marked group by Jt which pulls up in a circuit including wipers c1, e1 of SMS1 and 4, 6 of SM, and if dialling-relay Lm has fallen back, energizes Mc, whereupon As, Se drop. Junction circuit at outgoing end. C, Lm, Lb, A, B, Is are operated and the normal bridge through Ic is broken. Shortly afterwards Lm falls energizing Tl which connects battery and ground through Cs to the outgoing side of the junction. Cs holds Lb. At the first dialled impulse, Tl falls substituting an impulsing bridge for Cs and energizing Co which locks up. Lm is energized during dialling and holds Lb. Junction circuit at incoming end. When Cs is connected to the junction at the originating office, 1c starts the finders of idle links and energizes B to busy the junction to the connectors, and when the junction has been found, Co cuts off Ic. Operation of link circuit to select line. The marker-wipers 4, 5, if the tens digit denotes a line, are on terminals connected to the wires B and consequently the selector stops at the beginning of the marked group and energizes Tc instead of Mc so that the units impulses go direct to the selector magnet. At the beginning of this digit, Pb pulls up followed by Hs, Rc and at the end Pb, Hs fall in succession. In the interval Ft is connected up and if the line is idle locks and rings the line. When the called party replies Rg unlocks Rc which completes the talking circuit. Normal release. The calling party releases Is at the outgoing end and Tl, Cs, Lb, A and Co fall back. B holds up and the full resistance of C is included in the test circuit so that Jt falls and releases Mc and the link is restored to normal after which B is released. On the release of Tl at the ougtoing office As in the incoming office is released and the link and junction circuits there are restored to normal. Back release by thermostats. When the called party hangs up, Cs connects up Th and in 30 seconds the latter, provided it has not been cut off by the release of A from the calling end, connects battery to wiper e to operate Br in the incoming end junction circuit. Br holds Co but short circuits E which releases the link circuit at the terminating office. The thermostat is thus cut off and releases Br whereupon Co, B fall back. On the relapse of E, Cs in the outgoing end junction circuit is released and is followed by Lb, A, Tl, Co. B, however, holds up and the full resistance of C is thus cut into the test circuit to release Jt, Mc in the originating link circuit as in normal release. In this case, however, since the calling party has not cleared, As pulls up and connects up the thermostat which after 30 seconds forcibly dissociates the calling party from the link and operates his fault relay. C and B in the junction circuit are then released. It will be observed that during this period B holds the junction busy to connectors but does not prevent its seizure by a finder in case a call arrives from the other end in which case Ic and afterwards Co will be operated. These relays do not interfere with the forced release but simply provide alternative circuits for B. It is also to be noted that if the calling party hangs up, and the junction is seized again for a call in the same direction, in the interval between the operation of Th at the distant end and its release, Cs at the outgoing end is operated over a loop provided by Br at the other end so that Lb, A are not released.