Patent GB-396887-A (GB)
Title: Improvements in or relating to intercommunication telephone systems
IPC: H04M3/62
Filed: 1932-05-09
Abstract: 396,887. Intercommunication systems. ERICSSON TELEPHONES, Ltd., 67, Kingsway, London, and HUNT, W. E., c/o Ericsson Telephone Works, Beeston, Nottingham. May 9, 1932, No. 13315. [Class 40 (iv).] In an intercommunication system, an extension station is normally connected to one intercommunicating station (home station) by a two-way line and may be called direct by any intercommunicating station. For outgoing calls, the extension calls the station to which it is connected, and the operator at that station requests the wanted station to call the extension. The invention is described in connection with the intercommunication system described in Specification 383,747, the intercommunication apparatus being omitted from the present drawings. Modifications of the exchange line arrangements of the prior Specification are also described. Calls outgoing from extension. As shown, terminal T at the extension, Fig. 1, is grounded, positive battery being assumed grounded, but T may alternatively be connected bv a third wire to positive battery at the home station, Fig. 2. A1, B1 and A2, B2 are pairs in the multiple cable individual to the extension and home station respectively for incoming calls. Calling key RB operates relay U (upper), Fig. 2, which connects ground from RB to conductor B2 in the multiple cable, the buzzer (not shown) at the home station being connected between B2 and battery if this station is disengaged. The calling key is released and the receiver at extension is removed whereupon U re-operates over both windings in series over switch-hook SH. The extension is now connected to conductors A2, B2 which, when the home station replies, are connected to the home instrument as described in the prior Specification, speaking battery for both stations being fed over relay U. If a station other than home is required, the home attendant calls the wanted station from which the extension is called as described in the next paragraph. Calls to the extension. The calling station attendant operates a key to connect his instruments to conductors A1, B1 so that V operates over the calling loop, disconnects U, connects conductors A1, B1 to the extension line, and operates buzzer BY at the extension over conductor 29, contacts of key XK and the righthand winding of V. The station and extension are fed with battery over V. If a station calls the extension during a conversation between extension and its home station, this conversation is not cut off since contacts v1, v2 are bridged by condensers QA, QB. Exchange facilities. If the extension desires an exchange connection, the home attendant throws key XK to connect the extension to the exchange line AX, BX. Should another station now call the extension, ground connected at the calling station to B1 passes over V to common conductor K to the buzzer at the calling station to give the busy signal as described in the prior Specification. If the exchange is central battery, subsequent opera tions occur as described with reference to Fig. 5 of the prior Specification except that an indicator N, Fig. 2, is now provided in the calling loop and operates M which energizes G in the said Fig. 5 to prevent another station calling the exchange. If the exchange is automatic, dialled impulses from the extension intermittently release N but M holds. When the extension receiver is hung up, the indicator releases to. inform the home attendant who restores XK. If the exchange uses central battery for leg signalling but not for speech, the equipment shown in Fig. 3, is provided conveniently at the home station but it may be at any station other than an extension. Key XK operates indicator N over the calling loop and left-hand windings of coil RC, Fig. 3. Relay M pulls up and operates G which completes the circuit on the outgoing side of RC. If the exchange uses loop signalling, the equipment, shown in Fig. 4, is provided which operates similarly to Fig. 3 for outgoing calls. In the case of a magneto exchange, the equipment shown in Fig. 5, is provided. If an intercommunication station calls, G, H pull up and polechanger PC sends out calling current all as described in the prior Specification. If, however, the extension calls, H and PC are not operated and the exchange is called by magneto MG at the extension after XK at the home station has been thrown. The extension is fed over retard FR. All calls incoming from the exchange are answered by the station at which the equipment of Fig. 3, 4 or 5 is situated. If this is not at the home station, a call for the extension is first transferred to the home station, which calls the extension and then throws key XK. If key XK is left thrown, e.g. during the night, calls from extension pass directly to the exchange and incoming calls operate the extension bell W in addition to the indicator I, Figs. 3, 4, 5, which normally operates a bell BL. The bell BL may be disabled by switch NS.