Patent GB-549334-A (GB)
Title: Improvements in telephone systems
IPC: H04Q3/58
Filed: 1941-05-13
Abstract: 549,334. Semi-automatic exchange systems. ASSOCIATED ELECTRIC LABORATORIES, Inc. May 13, 1941, No. 6172. Convention date, May 16, 1940. [Class 40 (iv)] In a system wherein a small number of subscribers' lines, which may be party-lines, terminate at a switching centre which is connected to the exchange by a single trunk, the identity of a calling line is signalled to the exchange by characteristic calling current. Where there are only two lines connected to the switching centre the magneto current goes unchanged over either wire of the trunk, whilst where there are three lines two conditions are obtained by transmitting the positive or negative half-cycles over one wire. The connection of any line to the trunk is effected by the application of positive or negative potential to either wire at the exchange. Switching centre connected directly to operator's position.-In the arrangement shown in Figs. 1, 2, the switching centre 10 terminates three subscribers' lines 11, 12, 13, which may be party-lines on which code ringing is employed, and the trunk 31 terminates at the exchange in three jacks 265-267 individual to the lines 11-13. Magneto calling current from the line 11 energizes relay R110, which extends the positive half-cycles by way of rectifier 114 over the upper wire of the trunk 31 to operate relay R210. Similarly, calling current from the line 13 energizes relay R100, which extends the negative half-cycles by way of rectifier 105 over the upper wire to operate relay R200. Relays R200, R210 are polarized by rectifiers 203, 213 in parallel therewith. Calling current from the line 12, however, goes directly over the lower wire of the trunk and operates relay R220. Relays R200, R210, R220 control calling lamps 268-270 associated with the jacks 265-267. Sleeve relays R230, R240 connect negative to the upper and lower wires of the trunk, whereas sleeve relay R250 connects positive to either wire according to the condition of R230. At the switching centre, relays R120, R130, R140, which are polarized by rectifiers 105, 114, 146, respond to. these conditions and connect the appropriate line or lines to the trunk. The sleeve relays also complete the operator's talking connection through repeating coils 260. The operator may ring the connected line by actuating ringing key 275 or 279, according to a code if necessary, but if the calling subscriber is on another of the lines 11-13 she first asks him to hang up or alternatively -removes the calling plug temporarily to release the corresponding connecting relay. On a revertive call, the operator does not need to take any action beyond plugging in. A ring-off signal operates a drop 272 in the cord-circuit. In a second arrangement shown in Figs. 7, 8, the switching centre 70 terminates two lines 14, 15 and calling current goes directly over one wire or the other of the trunk 55 to operate relay R810 or R820. Connecting relays R700, R710 are controlled by sleeve relays R830, R840 by the application of current to one wire or the other. Switching centre connected to operator's position by way of tandem exchange.-The trunks 31, 55 terminate at the finder and connector banks at the tandem exchange and are associated with individual circuits, Figs. 3 4 and Figs. 6, 5 (not shown). Each finderconnector link 970, 1170, Figs. 9, 10, 11, is connected to an operator's position, Fig. 12, at the central exchange over a trunk 45. Relays R300, R320, R340 respond to calling currents over the trunk 31, as in Figs. 1, 2, and control relays R310, R330, R350 which apply potentials to the trunk wires to operate the appropriate connecting relay at the switching centre 10. Start relay R400 energizes and causes an assigned finder 970 to rotate into engagement with the trunk, whereupon switching relay R920 pulls up in series with cut-off relay R410. If the calling line extends to a paystation, however, R400 remains locked over a strap 426a. Switching relay R1030 extends the connection to the trunk 45 and makes a simplex circuit for relay R450 in series with differential relay R460 to the repeating coils 1080. Relay R1060 operates momentarily until R1050 pulls up and connects up R1240, which causes the lighting of lamp 1283 and the return of a ringing signal to the calling party. When the operator plugs in, switching relay R1230 completes a talking connection, holds R1250 and connects up R1220 after an interval determined by a vibrating armature. A simplex circuit now exists over the trunk 45 for relay R940 in series with differential relay R950, and the former connects up R930, R1160. One limb of this circuit is made, however, before R1220 pulls up, so that R950 energizes temporarily and controls R1000 to extend a tone signal to the operator in the case of a paystation line. Actuation of dial key 1285 energizes R1210 and inserts the dial 1284 in the simplex circuit to control relay R940 which repeats impulses to set the connector 1170. Relay R1030 restores at the first step, and relay R1100 pulls up over wiper 980 since the call emanates from a switching centre and makes a fresh circuit for R450, R460. Assuming first that the connector is set to an ordinary subscriber's line, relay R1130 energizes if it is busy and gives busy tone to the operator when dialling relay R1140 falls back. On the return of dial key 1285, the slow-release of R1210 opens one limb of the simplex circuit momentarily to energize R950, which through R1000 causes the operation of R1010, extending the busy tone to the calling line. The operator may replace her talking connection by throwing key 1292 momentarily, whereupon R950 again energizes and this time effects the re-operation of switching relay R1030, busy tone being cut off. If the wanted line is idle, switching relay R1110 energizes on the relapse of R1140 and the operator rings by means of key 1291, a path for ring-back tone being made by R1010 when dial key 1285 is restored. Finally, switching relay R1030 re-operates under the control of key 1292 and completes a 3-way talking circuit. When the operator unplugs in response to a ring off signal, the opening of the simplex circuit on the trunk 45 brings about the release of the finder-connector link, whereupon the disconnection of R450 effects the release of the trunk circuit. Revertive call (both subscribers connected to the same switching centre).-Since the connector is set by dialling to the same position as the finder, relay R1120 energizes over wipers 979, 1180, operating switching relay R1110, unlocking R1100 and opening the busy tone circuit. Relay R1070 energizes over wiper 1182 and puts the simplex circuit of R450, R460 under the control of R940 for the repetition of a second dialled digit to pairs of counting relays R360, R362 &c. Relay R390 energizes and locks at the first impulse, disconnecting the original signalling circuits from the trunk 31, and when dialling relay R420 falls back, a circuit is made for another of relays R310, R330, R350 (the one corresponding to the calling line being already up), and a signal is sent to connect the wanted line to the trunk at the switching centre. The return of dial key 1285 effects through R950, R1000 the operation of R1010, which disconnects R1070, and in addition R460 is operated momentarily by the opening of one limb of the simplex circuit therethrough to connect up R470, R480. The operator rings and then throws key 1292, which brings about the operation of switching relay R1030 and a second operation of R460 to release R470, R480 and unlock R390. The latter reconnects the original signalling circuits to the trunk 31 to restore the connection of the calling line at the switching centre. Call to switching centre from ordinary subscriber's line at tandem or central exchange.- In either case, the connector is set under control of the operator's dial. Switching relay R1110 energizes in series with cut-off relay R410 and makes over the connector wipers the simplex circuit for R450, R460, which is brought by R1070 under the control of R940 for the repetition of the second digit. The connection is completed in the manner described 'in the preceding paragraph.