Patent GB-383747-A (GB)
Title: Improvements in or relating to intercommunication telephone systems
IPC: H04M3/58
Filed: 1931-11-21
Abstract: 383,747. Intercommunication systems. ERICSSON TELEPHONES, Ltd., 67, Kingsway, London, and HUNT, W. E., Ericsson Telephone Works, Beeston, Notting- ham. Nov. 21, 1931, Nos. 32292/31 and 13316/32. [Class 40 (iv).] In an intercommunication system having access to exchange lines, a station when connected to an'exchange line is able to communicate with a station to which it otherwise would not have direct access. The invention may be applied to fully secret systems but is described in connection with a system in which a station cannot normally make connection with the calling station of an established local connection. A station connected to an exchange line may set up an interim connection to another station or may bring one or more stations into the exchange connection. A main station obtains access to an exchange line whether idle or engaged, some stations obtain access only to idle exchange lines, while other stations obtain access to idle exchange lines only at the discretion of an operator at the main station. A standard station circuit is readily adaptable to either kind of station. Station apparatus comprises a key such as LK1 for connecting to each other station, an exchange key EK and common contacts CK operated when any key is depressed. The keys are latched in the depressed position and depression of one station key releases a previously operated station key and partially releases the exchange key for a purpose to be described later. Two keys pressed simultaneously remain latched and all keys are released by replacement of the receiver. Depression of a key slightly beyond the latched position closes the calling circuit which includes contacts 12, 13 of the common set CK. Alternative arrangements are described for enabling the system to operate in conjunction with various types of main exchange. Local calls. The receiver is removed from cradle CS and key (say LK1) of the desired station is fully depressed to bridge the two right-hand springs. A calling circuit is thus completed over CS (14); LK1 at the calling station, the B line, contacts 16 of the unoperated cradle switch at the wanted station to its buzzer BZ. When the called party replies, relay F at his station operates over both windings in series, connects him to the calling line and feeds battery to both parties. If the wanted station is engaged, its calling circuit is open and if it is engaged as a called party, its relay F will already be operated so that the new connection is established immediately. If it is engaged as a calling party, its relay F is not already operated and will not now operate since common key contacts CK 20 are open at calling stations, but the calling circuit will pass over F (i), CK 21, common wire K to the buzzer BZ at the new calling station to give the busy signal. Relay F does not operate in this circuit. Call to central battery exchange. It will be assumed that terminals 1, 2 are strapped (as shown). The receiver is removed and exchange key EK is depressed, but not into the calling position in which 10, 11 are bridged. Relay E operates over the D wire, locks up and connects the calling party across the exchange line AX, BX. The call is set up in normal manner, the stations of the intercommunicating system being provided with dials if the exchange is automatic. The calling station cannot normally be called by a local station since it is disconnected from its home line. Relay E also operates relay G to disconnect the D wire to prevent another ordinary station obtaining access to the exchange line. If a station attempts to do so, its buzzer BZ is operated over the C wire. Conference facilities. Another local station can be communicated with during an exchange call by pressing the appropriate key such as LK1. This releases key EK and its contact b but contacts a remain latched in the operated position so that the exchange line is disconnected from the local station but is looped over RS3 to hold the line. If the required local station is free- or engaged as a called line in a local call, the local connection is completed as previously described. If it is engaged as a calling line, the previously described circuit over its relay F (i) is completed but as the buzzer at the calling-station is short-circuited by relay E, F now pulls up to complete the local connection unless the wanted line is engaged on another exchange line in which case its relay E would already be operated to prevent the connection. To resume the exchange conversation, the exchange key EK is again pressed, the local key being automatically released thereby. If the exchange key is held down while the local key is pressed, both local stations are brought into communication with the exchange. Any number of local stations may thus be brought in. To terminate such local connections, the local keys may be restored by a special release key or by an unwired local key, or it may be arranged that the exchange key releases local keys if slightly depressed beyond its normal latched position. Transferring exchange calls. A station (say A) engaged in an exchange call may transfer it to another station (say B) by setting up a local call to B as described in the preceding paragraph whereupon the party at B, informed of the exchange line in use, presses the corresponding exchange key. The line tests engaged and operates the buzzer at B which is heard at A and the party thereat replaces his receiver and restores the operated keys. Relay E at A and relay G fall back, and a circuit is completed over the D wire for relay E at B which connects station B to the exchange line. Graded service. As has been seen, the station with circuits as shown cannot obtain access to an engaged exchange line. By strapping terminal 2 to 3 instead of 1, relay E is operated by key EK independent of the condition of the exchange line and this circuit may be used at a main station to reach another station engaged in an exchange call for the purpose of offering a trunk call. If terminal 2 is strapped to 4 the station cannot get direct access to the exchange line and to call the exchange he must call a local main station. The party at the main station tells the other local party to press an exchange key and presses key PB thereby completing a circuit for relay E at the other local station. Incoming exchange calls. Ringing current energizes CR which operates indicator I and a common bell BL. The party at the main local station answers and transfers the call as previously described. Modified circuits for exchange lines. Figs. 6 and 7 show circuits for exchanges having central signalling battery and local speaking batteries, Fig. 6 being suitable for leg signalling and Fig. 7 for loop signalling. 'For calls to the exchange, G operates as described for Fig. 5 and completes the outgoing loop, local speaking battery being fed over repeating coil RC. When the call is cleared at the local station, G falls back and connects grounded positive battery to the lower leg in Fig. 6 or merely opens the loop as in Fig. 7. Incoming ringing current energizes CR in each case. In the case of a magneto exchange the circuit shown in Fig. 8 is used, local instruments being fed by a separate battery LB at the repeater RC. To call the exchange, key EK, Fig. 1, is fully depressed to the ringing position, whereupon E, Fig. 1, and both G and H, Fig. 8, pull up, pole-changer PC is started up and sends out ringing current to the exchange. To clear, the local party again depresses EK fully to send out ringing current. Main stations may have engaged indicators for exchange lines operated by relay G and other stations may have such indicators operated over the C line and a press key.