Patent GB-377965-A (GB)
Title: Automatic telegraph switching system
IPC: H04L12/00
Filed: 1931-04-30
Abstract: 377,965. Telegraph switching systems. INTERNATIONAL COMMUNICATIONS LABORATORIES, Inc., 67, Broad Street, New York, U.S.A.-(Assignees of Vernam, G. S. ; 196, Clinton Place, Hackensack, New Jersey, U.S.A.) April 30, 1931, No. 12734. Convention date, July 23, 1930. [Class 40 (iii).] In a telegraph system in which each of a number of subscriber stations is connected to a central station over an individual line circuit, and in which a small current normally flows over each line circuit during idle periods from a source at the central station, switch means is provided at the central station operable in response to an increase of the line current controlled from the subscriber's station, for extending the line circuit to an idle operator's position at the central station. The subscriber may obtain, by dialling, a connection to an operator position at the central station, selected in accordance with the class of telegraph service he wishes to utilize or to be forwarded from the central station. The apparatus at a subscriber station is shown diagrammatically in Fig. 2. Connection from a subscriber to a selected central station operator. On the operation of a key 54, Fig. 2, at a subscriber station the closure of contact 56 shunts the high resistance winding 59 of a polarized relay 58 and increases the current to operate the line relay 436 at the central station. Battery 437 is connected to test terminal 543 and group relay 554 is energized placing ground on the vertical level segments corresponding to the calling line. The bank multiple is " slipped " over the levels so that the vertical marking is placed on different levels for the different line finders to limit the amount of vertical hunting. The relay 554 places ground on the start lead 553A to energize relay 512 of a " first preference " or " home " switch on the corresponding relay of a subsequent finder. Stepping relay 525 is operated and energizes the vertical magnet 522 with which it interacts until the wiper 507 has been stepped up the vertical bank 506 to find the grounded terminal 508, 509 .. of the calling line, when relay 515 operates and prevents further vertical stepping. Relay 515 also transfers the stepping circuit to the rotary magnet 523 with which it interacts until the terminal of the calling line has been found. Assuming that the terminal 543 is associated with the calling line, cut-off relay 438 and relay 532 are operated in series and the telegraph line 51<1> is switched through terminal 547 to line 551 and over the contact A of relay 532 to the selecting circuit 600, Fig. 5. If the calling line had been associated with test terminal 545, relay 501 operates in addition to relay 532 to switch the telegraph line at its contact 501 B. When the line is extended to the selecting circuit 600, Fig. 5, relays 603, 608 operate and resistance 607 is such that an increased current flows through the lamp 70 of the subscriber to indicate that he may dial to select his connection to a desired group of printers at the central station. The selecting impulses are passed over contacts A, B of relays 603, 608 respectively to the rotary magnet 616 and a relay 617 which opens the circuits from the arms 618, 619 of the rotary switch leading to further line finders. After the first step, the impulsing circuit of the rotary magnet 616 is completed over contact B of operated relay 617, which releases at the end of the impulse train to establish circuits over the selected contacts for a group of secondary line finders to establish the connection to an idle printer of the selected group. Switch arm 618 applies potential from battery 602 to test terminal 625, and arm 619 operates group relay 701B of the line finders 700B, which, by means of a relay chain similar to that shown in Fig. 4, enables the first idle line finder to search for the marked terminal. The relay chain is provided with manually controlled switches which disconnect the line finders associated with unoccupied printer positions. When the calling line has been found, relay 601 operates, switches the line through to the secondary line finder from which the lines 751, 851 lead to the printer contacts 802 and to a relay 803 controlling the printing magnet 825. At the same time relay 809 completes an operating circuit for the lamp 812 which indicates to the operator that a circuit has been completed to his printer. The incoming message operates a relay 804 which at contact 826 controls a local circuit through the printer magnet 825. Release of connection. The operator breaks the connection by opening contact 810 which subsequently releases relay 601 and effects the operation of the release magnet 614 of the selector switch. Relays 536A, 532 of the line finders are released and release magnet 527 restore the switch to normal. Cut-off relay 438 is released, and the reversed current through relay 58 at the subscriber station opens the contact A to break the circuit of the relay 67 which on falling off opens the operating circuit of the subscriber's motor 73. The calling subscriber may stop his motor by operating key 54 to close contact 61, energizing control relay 72 which breaks at contact B the circuit of the control relay 67. If the subscriber operates his release key before the central station operator has completed his transmission, the operation of switch 806, Fig. 5, operates relay 58 to open the circuit of the release relay 72, and on the return of switch 806 to its normal position, relay 58 is again de-energized to close the circuit of control relay 67. Establishment of connection from central station to a desired subscriber. Calling and preselector operations. The operator moves his switch 121 to close contact 130 thus operating a relay 205 of a first selector 200 individual to him. Relay 205 operates a slow-release relay 210 grounding the release lead 224 and preparing a circuit for the vertical magnet 213 through relay 212 in series. On the first vertical step, off-normal contacts 219, 220 are closed. At the end of the impulse train, relay 212 releases, and completes a stepping circuit for the rotary magnet 217 which interacts with relay 216 operated on the closing of contacts 219, 220 to step the wipers 225, 227, 229 until wiper 225 finds an ungrounded terminal associated with a free group selector. If no free selector is found, the rotary magnet opens contact 203, breaking the circuit of a switching relay 201, and closes contact 204 shunting the high-resistance winding of relay 205 to illuminate a " busy " lamp 126 at the operator's position. Group selector. If a free group selector 300 is found, relay 201 operates, switching through the telegraph line at contact F and the second selector is stepped vertically by the second impulse train to hunt in a rotary direction to find an outlet to a free final selector 400 or to transmit a busy indication as described for the first selector 200. Final selector. When a free final selector is found, relays 401, 406 are operated, preparing the impulsing circuit for the tens digit to the vertical magnet 413. When relay 412, operated in series with vertical magnet 413, releases, the impulsing circuit is transferred over the off-normal springs 411 to the rotary magnet 424 and a relay 417 in series, which operates and at its contact D<1> closes for the impulse circuit a shunt path round contact D of relay 416 which, if operated, as the wiper passes over a grounded busy terminal, would nullify the calling connection. If the called line is busy, relay 416 opens the circuit of the switching relay 421 and shunts the high resistance winding 402 of the relay 401 so that current through the lamp 126 at the central station is increased, and the operator releases the established connection to the final selector. If the called line is free, bank terminal 428 is not grounded, and battery 437 is connected through cut-off relay 438 and winding 422 of the relay 421, which operates, and at contact D extends the line through contact B of relay 438 to the polarized relay 58 at the subscriber's station. Through connection. On the establishment of the connection, the central operator moves his key 121 to the " through " position, closing contact 136 which from battery 101 reverses the line current to release polarized relay 58 which over its contact A completes a circuit for a control relay 67 bringing, the motor 73 into operation and completing the printing circuit over the receiving magnet 53 and the transmitter 52. Release of connection. The subscriber may stop his motor as described for the inward connection, and if this is effected before the central station operator has terminated his transmission, key 121,. Fig. 3, may be moved to close contact 128, operating polarized relay 58, Fig. 2, and then returned to the " through " position to operate again relay 67. The connection through the selectors is released by moving key 121 to open contact 130 thereby releasing relays 401, 406 and opening the locking circuit of relay 421 and energizing the release magnet 426. Relays 201 of the first and second group selectors release and energize the release magnet 221. The release of relay 421 opens the circuit of the cut-off relay 438, and negative potential from battery 433 operates relay 58, which releases control relay 67 and opens the circuit of the motor 73.