Patent GB-367509-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1931-01-02
Abstract: 367,509. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, and DIXON, R. G., 162, Westmount Road, Eltham Park, both in London. Jan. 2, 1931, No. 236. [Class 40 (iv).] In a small system suitable for ten subscribers employing a single connecting circuit and a set of relays for selecting the wanted line, a common call wire becomes connected to one of the calling subscriber's speaking wires when the dial is moved off-normal to effect the operation of a common call relay and the line relay, whereupon the calling circuits of all the subscribers are opened until the conversation is terminated. In one arrangement the calling line is extended by the line relay to the connecting circuit, and the other end thereof is connected to the called line over contacts of the selecting relays, while in a second arrangement both lines are connected by their line relays to the connecting circuit which includes a single feed relay, the set of relays serving to mark the called line. First system, Fig. 1. No action takes place until the subscriber moves his dial off-normal, when ground on the call wire cw is extended over the lower lir.e wire to line relay L(I) and call relay C(I and II). The latter energizes and short-circuits its winding I, allowing relay L to pull up and connect the line to feed relay A, which operates and connects up relays B, BA, BB. Relay L(II) holds locally, and ground is removed from the call wire cw. Relay D energizes until the first impulse is received to connect up relay Z and to hold relay C, which being slow to release is subsequently maintained at back contact a2. Impulses are now repeated at contact a1 to the chain of relays U .. Y which operate one at a time, each preparing the circuit of the next and opening the locking circuit of the previous one. The sixth impulse operates relay U again, and since relay Y does not relapse until the end of the impulse, relay Z is unlocked and falls back. Relay C falls back at the end of the train and connects the ringing circuit to the wanted line over contacts of the chain relays and relay Z. The ringing circuit comprises two relays R, RR which interact to supply reversals of current to the line. Ring-back tone is sent to the calling subscriber. On reply ring cut-off relay TR pulls up and completes the connection, feed relay D being connected to the called line. Relay TR, which falls back last when release occurs, at contact tr5 prevents the operation of any other line relay until release is complete. Second system, Fig. 2. Call relay C and line relay L operate as in Fig. 1, connecting the calling line to feed relay A, and relays B, BA, BB pull up. Relay C holds over front contact a1 until impulsing begins, and is then maintained during the train at back contact a2. Impulses are repeated at contact a1 to the set of relays V .. Z which operate in various combinations to mark the wanted line. Relay C then falls back since one or more of relays W, Y, Z are operated in each combination and closes the ringing circuit which comprises two interacting relays R, RR as in Fig. 1. On reply, line relay L of the called party energizes over the loop, locks and completes the connection, both parties being fed with current over relay A. Should the wanted line be in a looped condition due to a fault for example, relay C remains operated over the loop after impulsing is finished and prevents ringing. The absence of ring-back tone informs the calling party that the connection is unobtainable.