Patent GB-310800-A (GB)
Title: Improvements in or relating to telegraph concentrators
IPC: H04L12/00
Filed: 1929-04-19
Abstract: 310,800. Associated Telephone & Telegraph Co., (Assignees of Lomax, C. E.). April 30, 1928, [Convention date]. Central station apparatus.-A sending station, by breaking a normally closed circuit, sets in operation at a central station or concentrator a set of wipers which hunt for a disengaged receiving apparatus and effect a connection therewith. Each sending station Y has individual to it at the central station a hunting switch S with three wipers 10, 20, 30, switching magnet D, and magnets C, E, V. The contacts of the switch S are respectively connected to receivers, of which No. 1 and and No. 5 are shown, and the contacts of all the switches S individual to different sending stations are multiplied, as indicated by arrow heads. Idle condition. In the idle condition the magnets A and C are energized via winding C, key L, polarized relay B (which is not energized in view of the direction of the current) and keyboard K. Sender calling central station. To make a connection the operator at station Y breaks the above circuit by depressing key L, thus deenergizing magnet C. If receiver No. 1 is disengaged, magnet E is energized via contact C-2, wiper 20, earth at R, and magnet D. Magnet E then holds on through contact E-2, breaks the circuit of switching magnet D at E-4 so that subsequent message signals will not disturb the connection, and holds open the circuit of magnet C at E-6. It also closes the circuit ot magnet F via contact E-2, wiper 10, battery negative at F, earth, switch R. wiper 20 and contact C-2. Magnet F cuts in at F-1 the signal lamp W and magnet G which starts the receiver-motor T. At the same time the receiver printing-magnet H and keyboard are connected to line via wiper 30 and contact E-5. At the transmitting station the restoration of key L energizes the polarized magnet B, since the line circuit now terminates on battery positive at H; relay A is consequently short-circuited via B-1, so that transmitter motor M and signal lamp X are out into circuit at A-1. Signalling then takes place from the keyboard K. Clearing of line. The line is eventually cleared by the operation of switch R, which breaks the circuit of magnet E and thus restores all parts to normal. Hunting for disengaged receiver. When the busying switch P at receiver No. 1 has been operated, earth is connected via lead 12 to the first contact of the top bank of switch S. Switch E is thus short-ciruited so that it remains unaffected when the contact C-2 is closed by a call. The switch magnet D is therefore energized and the switch S hunts till the wiper 10 finds a contact which is not earthed. All receivers busy. If all the busying keys P are depressed or all the magnet F energized the circuit of the magnet U is closed and an " all trunks busy " meter is actuated over the line TB. At the same time the switch-stepping magnet D is cut out at U-2 and since the magnet B fails to be energized the signal lamp X- at the sending station does not light up. Selection of sending station by central station operator. The central station may have a connector switch (not shown) with banks of contacts to two of which leads 21, 22 are connected. When magnet V is energized via this selector, switch S is disabled since magnet C is disconnected from the contact V-1 but kept energized via contact. V-2.