Patent GB-342735-A (GB)
Title: Improvements in or relating to exchange systems for interconnecting telegraph apparatus
IPC: H04L12/00
Filed: 1929-11-06
Abstract: 342,735. Telegraph exchange systems. STANDARD TELEPHONES & CABLES, Ltd., McWHIRTER, E. M. S., FLINT, J. G., and CHAPMAN, S., Columbia House, Aldwych, London. Nov. 6, 1929, No. 33854. [Class 40 (iii).] In an automatic exchange system for type-printing telegraph apparatus, connections are effected selectively by means of said apparatus, the completed connection comprising a two-wire path. A modified type-printing receiver at the exchange effects the connection between two subscribers in response to the designation of the called subscriber sent by means of the calling subscriber's transmitting apparatus. Subscribers' typeprinting telegraph apparatus M1, M2, M6 are connected at the exchange to relays Al, B1, A2, B2, A6, B6 respectively and to connecting links of which only three are shown, said links each having relays P, X denoted by 1P, 1X, 2P, 2X &c. and relays 1L1, 1L2 &c. one for each of the subscribers M1, M2 &c. A receiver TM, modified so that it operates a relay system instead of a printer, connects the calling subscriber to the called subscriber, after a fresh connecting link has been found, by closing the appropriate contact TM1, TM2, ... Calling operation. Subscriber M1 calling subscriber M2 with first connecting link engaged. Subscriber M1 presses the key K1. Relay A1 operates through battery, winding Al, winding D1 key K1, contact of A1, contact of relay B1, earth, and completes a holding circuit to earth on its lowest upper contact. Since the first connecting link is engaged and the contact 1x1 is open the operated bottom contact of the relay A1 completes a circuit for the relay 2L1 from earth, bottom contact of relay B1, bottom contact of relay A1, bottom winding of relay 2L1, contact 2x1, contact of TM, resistance, battery. The relay 2L1 operates and energizes the relay 2X from battery winding of relay 2X, operated contact of 2L1, operated contact of relay A1, to earth. Relay 2X operates and closes a holding circuit for relay 2L1 from earth, left contact of relay 2X, winding of relay 2P, contact of 2L1, upper winding of 2L1, to battery. The relay of 2P does not operate as the resistance of the relay 2L1 is too high. Subscriber M1 is then in series with the modified apparatus TM, from earth, winding M1, key of M1, operated contact 2L1, lower operated contact of relay 2L1, contact B1, apparatus TM, to battery. Instead of printing the designation of the required subscriber the mechanism TM operates the appropriate contacts, TM2. A circuit is then completed for the relay 2L2 from battery, resistance, operated contact of relay 2X, unoperated contact of relay 2P, winding of relay 2L2, contact TM2, unoperated contact of relay A2, contact of relay B2 to earth. Relay 2L2 operates and closes a holding circuit as in the case of relay 2L1. Relay 2P now operates and closes circuits for the relays B1, B2 which operate, thus disconnecting the apparatus TM and connecting the subscriber's apparatus M1, M2 in series from earth, apparatus M1, contact of relay 2L1, contact of relay 2L2, apparatus M2, contact of relay A2, operated contact of relay B2, resistance, battery. At the same time the relay D1 operates owing to the added currents of the two windings of the relay A1 and feeds tape to the machine M1, thus signalling the completion of the connection. Clearing operation. Release is effected by opening the key K1, which de-energizes relay A1, thereby releasing the relay 2X which in turn de-energizes the relays 2P, 2L1, 2L2 and hence the relays B1 and B2 thus returning the system to normal.