Patent GB-990544-A (GB)
Title: A telephone line concentrator system
IPC: H01L27/06
Filed: 1961-07-20
Abstract: 990,544. Automatic exchange systems. WESTERN ELECTRIC CO. Inc. July 20, 1961 [July 22, 1960], No. 26280/61. Heading H4K. In a concentrator system individual concentrators one per substation are provided, each of which can effect, under control of a central office, connection of the individual substration concerned to any one of a plurality of trunks extending from the central office to all the individual concentrators. The concentrator system is described incorporated in a conventional No. 1 cross-bar system. As shown, two speech trunks 27, 28 extend from the central office (Figs. 3, 4) to individual concentrators 120, 121, 122 (Fig. 2) associated with substations 21, 22, 23 respectively. In addition, each concentrator is connected to a unique pair of the four number group leads NG1 to NG4 via rectifiers such as 29, 210, and to a common return number group lead NGR via a rectifier such as 233. Originating call.-When subscriber 21 goes off-hook, current flows from the - 15 v. source 312 via lead NGR, the calling loop, leads NG1, NG2, and resistances 361, 353 to the - 34 v. sources 311, 313. Transistors 31 and 32 thus conduct, bringing up 3NG1 and 3NG2, followed by 3NG1-A and 3NG2-A, the former relays locking up in series with the respective transistors. Relay 3CO disconnects operating ground from the remaining 3NG- relays, and the energization of the line relay 3L1 (individual to substation 21) causes conventional operation of the No. 1 cross-bar equipment. When the line link primary select magnet 4SEL is operated in the usual way, a trunk mark relay 4MK1 comes up in parallel therewith, disconnects the holding source 350 and grounds leads NG1, NG2 via resistors 361, 353, respectively. Transistors 31 and 32 are thus turned off, but 3NG1 and 3NG2 hold to source 317 under control of 4MK1; which also applies direct ground to NG1, NG2, - 78V. to the ring conductor of the trunk 27, + 20V. to its tip conductor, and - 34V. to NG3 and NG4. This results in the point X of concentrator 120 being at ground potential while in the other concentrators it is at - 34V, so that the crosspoint 216 breaks down to the 78 volts applied between 237 and 238, it having the characteristic shown at 246. The resulting negative pulse passes via resistance 236 and capacitor 239 to point Y, the potential of which drops to about - 70V., whereupon the cross point 215 breaks down. A balanced connection between substation 21 and trunk 27 is thus provided, and current flow over the trunk and loop forward biases transistor 413 to bring up 4CK (verifying crosspoint closure), which is followed by 4RL whereupon 4MK1 and 3NG1, 3NG2 release in turn. Current then flows from 417 to forward bias 416 and operate 4SUP1. The resulting potential holds the crosspoints conducting and back biases the number group lead rectifiers to isolate trunk 27 from these leads, apart from the path via resistance 235 which is connected to a balanced point on the loop and introduces negligible crosstalk. A Zener diode 243 in series with a resistance 244 is connected across the substation loop. With the subset off-hook the voltage drop across resistances 229 and 230 prevents 243 from conducting, but when the dial contacts open, 243 (with the full voltage across it) passes sufficient current to maintain the crosspoints conductive during the dial impulses. At the exchange, relay 4SUP1 repeats the impulses to the line link. On release of the district junctor (not shown) at the end of the call the polarity on trunk 27 is reversed by the relapse of 4TH1 and the crosspoints 215, 216 are thus opened. Terminating call.-The terminating marker (Fig. 4) operates relays 3TS and 4HG1, line link primary select magnet 4SEL, relay 4MK1, line hold magnet 4LH1, and relay 3TL (individual to the wanted line), whereafter it releases. Relay 3TS transfers transistors 31 to 34 from the leads NG1 to NG4 to corresponding leads connected to contacts of relays 3TL1 to 3TLn of which that of 3TL grounds leads 1 and 2 to switch on transistors 31 and 32. As on an originating call this results in operation of 3L1 individual to the substation 21. The leads NG1 and NG2, and the tip and ring conductors of trunk 27 are marked as before with similar results, the subsequent operation of 4RL bringing down 3TS. A 1000 c.p.s. ringing tone generator 453 in series with a conventional 20 c.p.s. ringing tone generator 452 is connected to the trunk 27, condensers 433, 434 and transformer 43 attenuating the 20 c.p.s. signal, whereas the 1000 c.p.s. signal operates a horn ringer at the wanted substation. The answer is detected by operation of 4SUP1. All trunks busy.-When all trunks are busy the announcement trunk 340 may be connected in series with return lead NGR to advise would-be callers of the situation. A subscriber may then dial "O" over NGR, NG1 to NG4 to the register 342 and gain access to an operator to whom he may speak. Extra facilities.-A conference call may be set up over the leads NGR, NG1 to NG4. Teleprinters 21a to 23a may be connected in parallel with the subsets to receive messages over leads NGR, NG1 to NG4 from transmitter 376. Specifications 530,085 and 753,014 are referred to.