Patent GB-598120-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1945-08-29
Abstract: 598,120. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. Aug. 29, 1945, No. 22191. Convention date, Nov. 10, 1944. [Class 40 (iv)] In a PABX system in which privileged subscribers can set up both local and main exchange cells, the instrument of each subscriber, privileged or otherwise, is provided with a key for local calls and a key for each main exchange trunk. Identical equipment may be provided at each substation. Separate groups of links are provided for local and for main exchange calls and on operation of a key an appropriate local or trunk link is connected to the calling line under the control of an allotter (Fig. 4) including relays common to a number of subscribers and to both groups of links. Incoming calls can be answered by any one of a number of subscribers. The trunk can be held whilst a local call is made to the wanted subscriber who then transfers the call by pressing the corresponding trunk key. The trunk finder link TLF (Fig. 2) for connecting a calling line to trunk No. 1 (wires 381, 382) comprises ten group relays 200 to 210 (only two relays shown), five unit relays 220 to 260, each corresponding to two digits 1 or 6, 2 or 7 ... , 5 or 0 and a subgroup relay 270 which operates only if the units digit is in the group 6 to 0. A group relay, a unit relay and the relay 270 together prepare the connection of the calling line. The local finder link LLF (Fig. 5) is similarly arranged, corresponding parts having reference numerals with the same tens and units figures. The allotter, Fig. 4, comprises ten group relays 400 to 410 and ten unit relays in two groups of five 420 to 460 and 420' to 460<1> respectively corresponding to the digits 1 to 5 and 6 to 0. The group and unit relays of the allotter mark the corresponding relays in the trunk finders TLF and the local finders LLF by group contacts such as 401, 411 and unit contacts such as 421, 461, 421<1>, 461<1>, Each group relay 400 or 410 is followed by an auxiliary relay 400<1> or 410<1> to provide ground, through the keys, for the start relays 280, 580 or for the busy relays B7. Call to main exchange over trunk No. 1. When the hand-set is lifted at station A (No. 11, privileged), line relay 120 (L) marks the calling number 11 on the allotter. If the allotter is free, group relay 400 (group 1) operates through chain contacts 404 to 414 and locks at 403. The unit relay 420 (unit 1) similarly operates over chain contacts 425 and 423 to 464<1> and locks at 424. The corresponding group and unit relays are marked in all the finders. Trunk key TK1 is closed to operate'start relay 280 together with 290 over 190A and 387, whereupon the marked relays in TLF operate and lock. Relay 290 also applies ground to wire 11c to operate cut-off relay 130 (CO) which disconnects 120 (L) thereby removing the markings from the allotter. Slow-to-release relay 480<1> operates over wire 201 to free the allotter relays and to release the allotter for further calls. In the meantime, 300 is operated from the main exchange over the calling loop and 310 follows, holding cut-off relay 130 (CO) and the group and unit relays in TLF. The circuit for A.C. relay 350 is opened at 311 and the connection at the main exchange is obtained in the normal way by dialling. If another privileged caller now presses his TK1, the start ground on wire 190A is extended at 315 (operated) over 389, 682 to operate 610 which connects battery over 681 to operate the caller's busy relay B7 and to apply busy tone as at 141. Station B is not privileged and on pressing TK when the trunk is free, the start ground over 190B, 389 operates 610 to apply busy tone. Local call. When A (No. 11) lifts his handset to call B (No. 10), the allotter is taken into use and the calling line marked on the finders as for a main exchange call. Key LK is operated and applies ground over 181, common start wire 485 and contacts 622 of the first operated relay (i.e. the first free link) of the relays 620, 630, 640 in the distributer (Fig. 6) and conductor 680 of the corresponding finder to operate start relay 580 and relay 590. The line 11A, 11B is extended over 781, 784 to line relay 700 and guard relay 720 energizes to hold the LLF relays and to operate cut-off relay 130 (CO). Impulses dialled by A are repeated by 700 to counting relays, not shown, 760 being operated during each series of impulses and the tens relay 770 and a unit relay, not shown, are operated to connect line 10. If B is busy, ground on wire 10c operates 750 which applies busy tone to the calling line. If B is free, 750 does not operate, but on release of 760, 740 and 130<1> (CO) operate in series, 740 locking and extending 10B to the lower winding of the ringing control relay 730 and applying ringing current from a source GEN to WA at 741. B answers by lifting hand-set and operating the local key to operate 730 and to complete the talking circuit. Incoming call from main exchange and transfers. An incoming call over 381A, 381B operates A.C. relay 350 which is followed by 360 to close a circuit for the signals SL individual to the line which signals appear at a number of substations. Contact 363 is closed to enable a non-privileged subscriber to set up a connection to the trunk concerned. Any subscriber answers the call by pressing the corresponding key TK to set up a connection to the trunk. Relay 300 operates and is followed by 310. If the call is for B and is answered by A, A then presses key HK to operate 320 over 11D and to hold the trunk at 321. At the same time, 300 releases, 310 following after an interval and 330 followed by 340 lights the hold lamp HL and changes over 337 to enable a restricted subscriber to answer. A sets up a local call to B who picks up the held trunk by pressing the corresponding TK which mechanically releases the LK operated to answer the local call from A. The distributer, Fig. 6, comprises a number of relays 620, 630, 640, associated with a local finder and connector link. When the finder relays are marked by raising the hand-set at A, the start circuit controlled by LK passes over contact 621 of the first operated (i.e. free) relay 620 to start relay 580 of the associated finder LLF. When A is connected through to B, both contacts 592 and 722 are opened by release of 590 and operation of 720, 620 releases and extends the start circuit to the next finder. When the finders have all been used and released in turn, 600 is energized and operates 620, 630, 640 once again for another cycle, as the contacts 722 fall back on termination of the calls. If all the links are engaged when a local key LK is pressed, ground over 621, 631, 641 operates 610 to operate the caller's busy relay B7.