Patent GB-377772-A (GB)
Title: Improvements in telegraphic intercommunication systems
IPC: H04L12/00
Filed: 1931-05-20
Abstract: 377,772. Telegraphy. SIEMENS & HALSKE AKT.-GES., Siemensstadt, Berlin. May 20, 1931, No. 14915. Convention date, July 5, 1930. [Class 40 (iii).] An exchange line or other main line terminates in a main subscriber's station which has extensions to a small number of substations. An in-coming call can be transferred to a sub-station by depression of a key at the main station, but outgoing calls and clearing signals are effected by substations without the assistance of the main station. Several substations can be connected to the main line simultaneously for conference working. The main line L1' L2 terminates in the receiving relay ER and transmitting contact sr of the main station. Exchange or distant station calling main station. The switching-on relay U0 of the main station is in the idle state energized as shown, the armature er resting on its marking contact z. When a call is received by the receiver relay ER, armature er cuts out relay U0 whose armatures U01, U02, U03 prepare the main station apparatus while the armature U04 cuts in the indicators SZ0, SZ1, .. at the main and substations. The slow-release relay V0, energized via U01, U02, closes its contact V01 to start the motor and opens its contact V02 to maintain the de-energization of the switching- in relay U0. The transmitting relay SR is energized via U01, U03 so that armature sr now rests on its spacing contact t, and messages can thereafter be sent to the exchange line L1 by means of transmitter contact s0. Received signals are passed by armature er to receiving magnet EM, which controls a printer. Calling a substation. A substation NSt1 is called by the main station which puts it into communication with the exchange line L1, L2 by closure of the key NT1 individual to it. Contacts u11 .. u13 are closed and prepare the apparatus at substation NSt1, while contact U14 cuts in the indicators SZ0, SZ1 ... By the time when the calling key NT1 is released its place has been taken by armature h12 of motorcontrol relay H1, which holds on the connection. Meanwhile the telegraph apparatus at the main station is put out of action by relay U0, which is energized through contact U15 of relay U1, unless this effect is prevented by manual opening of key FT0. Similarly, the parts U2 NT2, U21 .. U2. serve a further similarly constructed substation. Main station or substation calling exchange or distant station. The system being in the idle condition as shown, one of the calling keys FT0, FT1 . , is opened. Switching-in relays U0. U1 .. consequently release and prepare the local circuits as in the case of an incoming call. Armature sr moves to its spacing instead of its marking contact and so effects a call. Dial-switches may be provided for calling an automatic exchange. Clearing. Clearing is effected by opening of the clearing key ST0 or ST1 .. at the main station or one of the substations. The corresponding relay V0 or V1 .. releases, and armature V01 or V 11 .. effects stoppage of the motor M0 or M1. At the same time the sending relay SR releases and armature sr comes to rest on its marking contact z. The receiver armature er at the distant station consequently cuts off the relay U0 at that station and its sending relay SR comes to rest in the marking position, thus sending a return signal to relay ER at the station shown. Armature er comes to rest on its marking contact and completes the circuit of relay U0 or U1 .. when key ST0 or ST1 .. is released. Relay U0 or U1 .. on pulling up maintains the idle condition of the station as shown.