Patent GB-339493-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1929-12-09
Abstract: 339,493. Coventry Automatic Telephones, Ltd., and Moss, B. F. Dec. 9. 1929. Automatic and semi-automatic exchange systems.-In a private branch exchange, calls to and from the main exchange are established over a link circuit terminating at one end in a line finder and also in a plug and at the other end in a junction finder. A calling subscriber becomes connected to an idle link circuit on dialling the single digit 9 or 0 by means of circuits completed at the first selector, which then releases, and, if the main exchange is automatic, a call thereto may be set up either by the P.B.X. operator or by the subscriber himself. An incoming call from the main exchange is extended auto. matically to an idle link circuit and is completed by the operator by means of the plug of the link circuit. A local call may also be completed over a link circuit by the operator when the subscriber dials 0. Alternatively the operator may connect a link circuit to a local line by dialling into the local switches. If desired the dialling of O may light a lamp common to a group of lines, and the connection of the line to the link circuit may be initiated only when the operator presses a key associated therewith. Outgoing call initially controlled by operator. The calling party dials' 0, and post springs are operated in the selector 4 to connect earth to wire 13 to energize relay ER, Fig. 3, which closes a circuit over wiper 19 of the assigner for relay C. Magnet 12 now advances the line finder into engagement with the calling line, which is marked over wire 10 by earth at post springs 9 of the selector 4. Test relay G energizes, connecting up relay QA and lighting lamp 29. Relay QA locks relay G, connects up line relay A and release relay B of the link circuit and applied direct earth to wire 7 to short-circuit relay 5 in the selector 4, thereby effecting release of the latter and of the line finder 3. Earth is connected to wire 30 to mark the link circuit busy and the assigner advances into engagement with the next idle link circuit. Relays ER, C fall back on release of the selector 4. The operator throws speaking key 31 to energize relay SR which connects up the operator's set over wires 32, 28. Should the calling party hang up after giving the wanted number, he may be recalled by means of ring-back key 22, 27, relay QA being held meanwhile over a contact of relay SR. To set up a main exchange connec- .tion, the operator throws key 38 to energize relay CT which starts the junction finder hunting for an idle junction, magnet 39 being connected to wiper 40. Test relay QB energizes when this is found, and connects up relay S which completes the line circuit to the main exchange. If the main exchange is automatic, the call may be completed by the operator by means of her dial 33 or by the calling subscriber, impulses being repeated by line relay A. The winding RC is short-circuited during impulsing at dial springs 47 or at a contact of relay C. The operator withdraws from the connection by restoring key 31, which disconnects relay SR. Release is under control of the calling party. Outgoing call set up directly by calling party. The calling party dials 9 in place of 0, and post springs are operated in the selector 4 to energize relay DO, Fig. 3, in place of relay ER. The operations proceed as already described with the exception that relay CT energizes over wiper 48 of the assigner immediately after relay C, consequently relay G does' not lock when relay QA pulls up, and lamp 29 does not light. The line finder and junction finder hunt simultaneously. Incoming call. Ringing current applied at the main exchange operates relay L, which locks and earths wire 53 to energize relay JR in the assigner, which locks and closes a circuit over wiper 54 for relay PB and lamp 55. Magnet 39 is connected to wiper 56 and the junction finder hunts, for the calling junction. Test relay QB energizes, connects up switch relay S and connects earth to wire 30 to advance the assigner. The operator throws speaking key 31 to energize relay SR, which unlocks relay PB and connects the junction to her set over wires 32, 28. The operator completes the call by inserting plug 56 in jack 57, first making the usual tip and sleeve test, whereupon the subscriber's cut-off relay energizes to earth at the jack springs, and earths the sleeve circuit to energize relay T, which lights lamp 64. The subscriber is rung by means of key 58, 62, and upon reply, line relay A pulls up and extinguishes lamp 64. The operator withdraws by restoring key 31. If the wanted line is engaged, the operator may break into the existing connection by inserting a special plug which does not operate the auxiliary springs. Local call set up by the operator. The subscriber dials 0, and a link circuit is taken into use and lamp 29 is lighted as described in the second paragraph above. The operator then completes the connection as described in the preceding paragraph. All link circuits in use. In this case all the multiple earth connections to wire 15 are removed by relays such as QA or QB, and the assigner remains in its first position until a link circuit becomes idle. The operator may ascertain at any time which link circuits are in use by operating key 65 in the assigner, whereupon lamp 67 lights in those link circuits. Faults. If fuse 68 blows, relay T energizes and marks the link circuit busy. Graded service. Certain subscribers may be debarred from making outgoing cadls directly by providing an extra relay in the selector 4 which prevents the normal operation when 9 is dialled and connects a tone to the line. Certain subscribers may be debarred from making or receiving calls to the main exchange in any circumstances by means of an individual relay which connects up a tone or other signal when the operator attempts to set up such a call. When the dialling of 0 serves only to light a lamp common to a group of lines, subscribers entitled to similar service are grouped together.