Patent GB-187736-A (GB)
Abstract: 187,736. Western Electric Co., Ltd., and Deakin, G. Aug. 3, 1921. Automatic and semi-automatic exchange systems.-In a private branch exchange system, the switches used for establishing a local connection are automatically released in response to a digit denoting a main-exchange connection, and other automatic apparatus is brought into operation to connect the calling line to an idle trunk leading to the main exchange. The invention is described with reference to a system of the reverting-impulse type in which a calling line 100, Fig. 1, is connected over a call-finder LF, Fig. 2, to an idle register set, Fig. 3, the connection being completed, in the case of a local call, by a connector FS. The register set, in response to the digit O corresponding to a main-exchange connection closes a circuit for a relay 114, Fig. 1, which releases the switch LF and closes a starting circuit for call-finders JLF, Fig. 4, one of which connects the calling line to an idle outgoing trunk 420, 421. The trunk 420, 421 is adapted for two-way working, incoming calls from the main exchange being extended by an operator over the jack 413 and the cord-circuit shown in Fig. 5, this circuit also providing alternative means, in case of emergency, for setting up outging main exchange connections manually. At night, any P.B.X. subscriber may be permanently plugged through to the main-exchange trunk. Local calls, Figs. 1, 2 and 3. The line relay 110 places a selectable potential upon the terminal 234 over a circuit 110<b>, 114<d>, 122, and closes a circuit 110<a>, 114<f> for the starting-relay 129 which closes starting circuits 121, 221, 240, 241 for all idle call-finders LF having access to the calling line. When the brushes 235 - - - 238 reach the terminals 231 - - - 234 of the calling line, test relays 243, 244 operate to stop the brushes and. move the sequence switch 200 to its 4th position in which the register-choosing switch 290 connects the catling line to idle register set, the completion of this operation being indicated to the calling subscriber by a dialling tone from an interrupter 350 and transformer 355. The calling subscriber then dials the wanted number which is transferred to the register set, and the connection is completed in known manner over the connector FS. Calls to main exchange, Figs. 1 and 4. In response to the digit O corresponding to a mainexchange connection the register closes a circuit over contacts 321, 322, 210, 212, 238, windings 115, 116 of relay 114 and the front contact 112b of the cut-off relay 112 which has energized over the circuit 114<b>, 233. Relay 114 energizes over this circuit and breaks at its contact b the usual holding circuit for the call-finder LF which thereupon releases and with it the register set. Relay 114 also places a selectable potential upon the terminal 404 in a circuit 110<b>, 114<c>, 120 and completes a circuit 110<a>, 114<e> for the starting-relay 130 which closes starting circuits 123, 423, 411<b>, 413<a>, 414 for all idle call-finders JLF. The power-magnets 414 rotate the brushes until one set 405 - - 408 reaches the terminals 401 - - 404 of the calling line when the test relay 415 energizes in a circuit 110<b>, 114<c>, 120, 404, 412b, 413d. As soon as the brushes are correctly centred a relay 410 energizes to stop the brushes and complete a circuit for the holding magnet 418 in series with the relay 411 which switches through the calling line 100 to the outgoing trunk 420, 421 and completes a circuit 411d, 403 for the cut-off relay 112. When the through connection is completed relay 425 energizes in series with the calling line and the line relay 430 at the main exchange to lock up the relay 411 and to light a supervisory lamp 426 to indicate that the trunk is in use. The calling subscriber operates his dial 101 or converses with the operator according as the main exchange is automatic or manual. The connection is released when the calling subscriber hangs up, the relapse of relay 425 unlocking the relay 411 which breaks the through connection and initiates the release at the main exchange. In order to prevent two call-finder switches JLF from making simultaneous connection with the calling line, the relay 415 is made marginal so that two such relays cannot remain energized in parallel, and one or both will de-energize before the slow-acting relay 411 has energized. Incoming calls from main exchange. A relay 435 bridged across the trunk 420, 421 over back contacts of the jack 413, responds to ringing- current transmitted over the trunk from the main exchange and energizes a relay 412 which lights a lamp 438 to signal the operator, and breaks the circuit of the power-magnet 414 to prevent any movement of the brushes 405 - - - 408. The operator inserts the plug JP of a cord circuit, Fig. 5, in the jack 413, learns the desired connection by means of her listening key LK, inserts the plug SP in the jack 102 of the wanted subscriber 100, and operates her ringing key RK. Relay 501 completes the connection and, on the called subscriber replying, supervisory relay 502 extinguishes the lamp SL. Outgoing calls to main exchange set up by operator. In case of emergency, the cord circuit shown in Fig. 5 may be employed to set up main-exchange connections manually over thejacks 102, 413, a relay 504 providing a bridge for the line relay 430 at the main exchange, whilst a dialling key DK permits the connection of an impulse dial 505 for use by the operator when the main exchange is automatic. Provision for night service. Any P.B.X. subscriber may be disconnected from the automatic apparatus shown in Figs. 1, 2, 3 and 4 and directly connected to the trunk 420, 421 by a cord provided with two plugs connected by three plain conductors.