Patent GB-657684-A (GB)
Title: Telegraph exchange systems
IPC: H04L12/00
Filed: 1948-02-20
Abstract: 657,684. Telegraph exchange systems. WESTERN ELECTRIC CO., Inc. Feb. 20, 1948, No. 5089. Convention date, Oct. 22, 1938. [Class 40 (iii)] In a manual telegraph exchange system employing inter-exchange junctions capable of transmitting only two signalling conditions (marking and spacing), calling signals are transmitted over the junctions as a long marking condition, ringing signals as a series of impulses of substantially unit length and alternately marking and spacing, break-in signals by a similar series of impulses preceded by a spacing condition of predetermined length, and release signals by a prolonged spacing condition. During release operations, junctions are rendered available for further use after release signals have been received even though the plugs from the last connection have not been taken down. The invention is described with reference to a system in which a call is set up from a subscriber, Fig. 1, belonging to a first exchange, Figs. 1-5, over a junction, Fig. 6, to a second exchange, Figs. 7-11, and thence over a further junction, Fig. 12, to a third exchange, Figs. 13-17, containing the wanted subscriber, Fig. 17. The circuits in each exchange are identical as are also the junction circuits and the subscriber circuits and for the purposes of this Abridgment only Figs. 1-7 are shown. Where reference is made to elements in other Figures, the reference numeral of the corresponding element in Figs. 1-7 is indicated in brackets, e.g. reference to relay 809 (209) means that relay 809 of Fig. 8 (not shown) is being referred to but its circuit connections are exactly the same as those of relay 209 in the identical Fig. 2. (In all the Figures of the Specification, the first digit of a 3-digit reference numeral and the first two digits of a 4-digit numeral indicate the number of the Figure and in the identical Figures, the same last two digits are used for the corresponding elements, e.g. relays 209, Fig. 2; 809, Fig. 8; 1409, Fig. 14.)' Calling local operator. Starting key 106 connects source 103 to relay 105 which in turn connects the source to the teleprinter motor 102 and to relay 104. Relay 104 completes a loop to the exchange including the lower winding of relay 112 thereat. Relay 117 operates calling lamp 131 and, if desired, an audible alarm 134, and replaces ground on the lower leg by negative battery to provide increased current for relay 107. Negative potential at the junction of the windings of differential relay 111 marks jack 130 busy to other operators. Reply by local operator. Insertion of plug 204 in jack 130 energizes relays 111, 208, 207 over the sleeve circuit. Relay 208 operates relays 209, 310 which extend the subscriber's line to repeating relays 302, 303. When the operator throws listening key 224, relays 223, 221 operate over lead 419, resistance 418 and key 406 and insert the operator's teleprinter 405 into the line circuit so that communication between operator and subscriber may take place, copies being made at both ends by relays 407, 107. Calling operator at second exchange. If a tested outgoing junction is busy, battery on the sleeve circuit of jack 501 is extended over the tip of plug 315 and lead 422 to operate polarized relay 411 which lights busy lamp 416. If a tested junction is out of order, battery of opposite sign on the sleeve circuit operates relay 410 to sound a buzzer 414 as well as lighting lamp 416. When plug 315 is fully inserted into the jack 501 of an available junction, relays 312, 502 operate over the sleeve circuit and relay 311 connects the tip of plug 315 to relays 320, 321. Relay 502 operates relays 503, 504 and converts the tip of jack 501 to ground, and relays 311, 502 extend the ring circuit to relay 505. Relays 320, 321 operate relay 317 to light lamp 300 in series with pilot relay 401 which lights pilot lamp 400 and, if desired, sounds buzzer 402. Relay 503 connects negative battery to the sleeve of jack 501 to mark it busy. Relays 610, 612 in the repeater circuit 601 are operated to marking position over conductor 512 and the marking contacts of relay 505 and this condition is transmitted over junction 603 and repeated by relay 605 over conductor 713 to relays 714, 706. Relay 714 controls a relay 717 which, due to the provision of condenser 720, has a 0.2 second delay in moving to its left-hand position when its upper winding is de-energized. After this delay, relay 721 is operated to light lamp 722 and to mark the junction busy to an operator wishing to make a call in the reverse direction. Reply by operator at second exchange. Insertion of plug 804 (204) in jack 701 energizes relays 702, 808 (208), 807 (207) over the sleeve circuit. In the cord circuit, relay 808 (208) operates relays 809 (209), 910 (310) which extend the circuit to repeating relays 902 (302), 902 (303). Relay 809 (209) extends the tip conductor to relays 834 (234), 829 (229), the former operating over high-resistance 744 and energizing relay 825 (225). In the incoming junction circuit, relays 703, 704, 727, 728, 717 (to right), 716, successively operate. Relay 705 sends a marking signal back over the junction and relay 514 responds to move relay 517 (similar to relay 717) to its right-hand position. Relays 527, 528, 529, 517 (to left), 516 successively operate, relay 527 connecting negative battery to the tip wire of the cord, releasing marginal relay 320. Relay 321 holds over resistance 544. Relay 316 operates and relay 317 releases extinguishing lamp 300 by which the first operator is informed that she may communicate by her teleprinter with the second operator. Calling operator at third exchange. Insertion of plug 915 (315) in jack 1101 (501) of an available junction operates relays 912 (312), 1102 (502), 911 (311), 920 (320), 921 (321), 1103 (503), 1104 (504), 917 (317) as described above. Relay 917 (317) operates relay 828 (228) which connects positive battery to the incoming tip conductor to energize polarized relay 731. Relays 735, 710 operate and a spacing signal is sent back over junction 603 to relays 506, 514. Relay 514 operates relay 517 to the right initiating a chain of interaction between relay 517 and relays 532 (which has an operating lower winding and a normally-short-circuited locking upper winding), 515, 535 and 534 resulting in the release of relays 527, 529, 516. The release of relay 527 re-connects ground to the tip wire of the cord to operate relay 317 and relight lamp 300. The junction circuits operate as described above and lamp 1322 (722) is lit. Reply by operator at third exchange. The operation is the same as for the reply by the second operator until relay 916 (316) operates and relay 917 (317) releases. The release of relay 917 (317) releases relay 828 (228) causing negative battery to be applied to the tip wire releasing relay 731. Relays 707, 708, 733 (moving to the left with a 0.3 second delay), 709 interact to release relays 735, 710. Relay 708 operates and relay 709 releases to send back a marking signal over junction 603. Relay 514, in responding to the mark, operates relay 530 which releases relay 528. Relay 527, 528, 529 re-operate, relays 320, 317 are released and lamp 300 is extinguished to inform the first operator that she may communicate with the third operator. Connection to called line. If the line is busy or out of order, positive or negative potential on the sleeve circuit will operate relay 1611 (411) or 1610 (410) as for a call to a busy or faulty junction. If the line is idle, relays 1512 (312), 1711 (111) operate over the sleeve circuit. Relay 1712 (112) operates over its upper winding and the subscriber's loop, and relay 1718 (118) connects ground to the tip circuit over which relays 1521 (321), 1520 (320) operate. Relay 1517 (317) operates relay 1428 (228) which connects positive battery to the tip wire to energize relay 1331 (731). Relays 1335 (735), 1310 (710) operate to transmit back a spacing signal. In the incoming junction circuit at the second exchange, relay 708 operates relay 733 to the left, energizing (after 0.3 second delay) relay 709 which connects ringing current 749 to the incoming tip wire and this is repeated back to the first exchange as alternate marks and spaces. The first spacing signal sent back causes relay 514 to move relay 517 (with 0.2 second delay) to the right where it operates relay 532. Relay 515 operates to move relay 517 to the left where it operates relay 536 which again opens the circuit of the upper winding of relay 517. The timing is such, however, that relay 517 is prevented from moving to its right-hand position a second time owing to the arrival of ringing current which intermittently actuates relay 514. The spacing signal sent back from the third exchange passes to the first operator and to the calling subscriber to indicate the progress of the call but may be excluded from the subscriber by operating splitting key 235 controlling relay 215. In the outgoing junction at the second exchange, the response of relay 1114 (514) to the spacing signal causes the release of relays 1127 (527), 1129 (529), 1116 (516) as before. Ground on the tip wire energizes relay 920 (320), and relay 917 (317) operates relay 903 (303) to send back a marking signal. Relay 708 responds, releasing relay 709, and relay 705 repeats the marking signal to relay 514, the operator and the calling subscriber, relays 515, 536 being released. Relay 917 (317) also operates relay 828 (228), energizing relays 731, 735, 710 to send back a further spacing signal. Relay 514 responds to this to bring about the release of relay 527 which causes the lighting of lamp 300 as before. Ringing. (1) By operator at third exchange. Key 1417 (217) operates relay 1504 (304). Relay 1509 (309) operates and locks and connects ringing current from source 1507 (307) over the ring circuit to bell 1708 (108). When the key is released, source 1507 (307) is replaced by source 1508 (308) intermitten