Patent GB-507132-A (GB)
Abstract: 507,132. Telegraph exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Nov. 4, 1938, No. 32035. Convention date, Dec. 16, 1937. [Class 40 (iii)] One of a number of signalling conditions is converted to impulses of alternating character. A line 10, 11, between a local subscriber, Fig. 2, and an intermediate station, Fig. 3, can transmit three signalling conditions, but a duplex circuit, Fig. 4 (not shown), between the intermediate station and a central station, Figs. 5 and 6, can transmit two signalling conditions only. A break signal from the subscriber is converted at the intermediate station to a series of alternating marking and spacing impulses for transmission to the central station. Recall and disconnect signals, which involve earthing the lead 11, are transmitted to the central station as prolonged spacing signals. Subscriber calling. Moving a key 72, Fig. 2 to the right operates a relay 27, which locks, operates a relay 12 and connects power 28 to motors 30, 31 and a generator set 29 which operates a receiving relay 74 to the right. The relay 12 and the restoration.of the key 72 close the line circuit. This operates a relay 49 at the intermediate station, Fig. 3. The relay 49 operates a relay 50 thus operating a relay 51 which locks, operates a relay 52, transfers the circuit of lines 10, 11 to a relay 57, and releases the relay 49, and hence the relay 50. Current in the line circuit now flows through a relay 59 to move it to marking M. At the subscriber's station the current operates the relay 74 to the left to complete a circuit for a printer magnet 32. The relay 52, Fig. 3, operates a relay 53, earths a relay 56 to operate a relay 60 to the right, interrupts the circuit thus closed, and transfers the circuit of the left-hand contact to a relay 73. The relay 53 earths a potentiometer 174, 71, connects potential to the relay 59 to receive telegraphic signals from the subscriber, extends lines 190, 191 to contacts of a relay 55 and the relay 73 respectively, and prepares a circuit for a relay 54 over the line 190. Current over the line 191 is transmitted as a marking impulse over the duplex circuit, Fig. 4 (not shown), to a line 217 and hence to a relay 232 in the terminal circuit at the exchange, Fig. 5. The relay 232 interrupts the circuit of a relay 233, and, after 0À2 second, a condenser 250 is sufficiently discharged for the relay to move its armature to the left to operate a relay 227 which locks: The relay 227 operates a relay 225 to light an answering lamp 224, prepares a relay 226 to receive telegraphic signals from the subscriber, and operates a relay 234 to cause the relay 233 to move its armature to the right whence a relay 235 is operated. The relay 235 locks, releases the relay 234, and transfers the relay 233 to the marking contact M of the relay 232 to maintain the armature of the relay 233 to the right. Operator answers. The operator inserts a plug 83 of the cord circuit, Fig. 6, in a jack 223, Fig. 5. This operates relays 211, 84. The latter operates a relay 92 and extends the tip of the cord to the armature of a relay 91. The relay 211, Fig. 5, releases the relay 225 to extinguish the lamp, and extends the transmission circuit to the armature of the relay 226. Current in this circuit operates a relay 220 to marking M. This transmits a marking signal over the duplex circuit to the intermediate station where it operates the relay 54 which locks and operates the relay 55. The latter transfers the lower winding of a relay 58 to the armature of the relay 59, and completes a transmitting circuit from the relay 58 over the duplex circuit to prepare the relay 58 to respond to telegraphic - signals. The subscriber can now indicate to the operator the other subscriber with whom he wishes to communicate. The operator inserts a calling plug 101, Fig. 6, in a local called subscriber's jack, Fig. 8 (not shown), a jack similar to 223, or a trunk circuit. Transmitting. The relay 57 at the intermediate station, Fig. 3, does not respond to impulses from the subscriber, Fig. 2, but the relay 59 repeats them over the duplex circuit. The relay 56 follows the signals repeated by the relay 59, moving to the right for spacing and the left for marking. In the left position it maintains the relay 60 to the right, and in the right position interrupts the circuit. A condenser 61 then discharges to maintain the relay to the right for 0À3 seconds, and, since during normal transmission the relay 59 does not remain on spacing for this period, the relay 60 remains to the right. The signals are repeated to the relays 232, 226, at the central station, Fig. 5. The relay 232 interrupts the circuit of the relay 233, but this is retarded by 0À2 seconds and does not release during normal transmission. The relay 226 repeats the signals to a relay 90, Fig. 6, which repeats them to the local subscriber's station. If the operator's printing key 89 is operated, a relay 88 extends the transmitting circuit through the operator's position circuit, Fig. 7 (not shown), to the repeating relays 90, 91 of the cord circuit. Splitting keys enable the operator to communicate with either subscriber. If the operator's transmitting contacts or the called subscriber's teletypewriter contacts are operated, the relay 220, Fig. 5, repeats the impulses to the relay 58 and the subscriber's relay 74 which controls the printing magnet 32, Fig. 2. Break signals. A break key 18 interrupts the line circuit to move the relay 59 to spacing S. This repeats the signal over the above transmission circuit and reverses the bias on the relay 58 to maintain it on marking to ensure the proper transmission of the break signal. The relay 59 also controls the relay 56. At the end of the 0À3 second period, described above, the relay 60 moves to the left to operate the relay 73, which transfers the lead 191 to a source 75 of 20-cycle ringing current. This causes the transmission of alternate marking and spacing currents over the duplex circuit. The preliminary 0À3 seconds part of the break signal moves the relays 232, 226, Fig. 5, to spacing and, after 0À2 seconds, the relay 233 moves to the left to operate a relay 229, which remains operated. This operates a relay 230 and hence the relay 234. The latter moves the relay 233 to the right to operate a relay 231, which locks and releases the relay 234 to interrupt the circuit of the relay 233. Before a second 0À2 second interval, ringing current is received by the relay 232, and the relay 233 is prevented from moving. The relay 230 also interrupts the transmitting circuit to the relay 226 which remains on spacing S. The relay 226 repeats the break signal to the relay 90, Fig. 6, which repeats it to the local subscriber's relay and causes his teletypewriter to operate send-receive contacts to shortcircuit the transmitting contacts. Restoring the break key 18, Fig. 2, recloses the line circuit to the intermediate station where a consequent marking impulse restores the rest of the circuit to the normal transmitting condition. A break or spacing signal may be transmitted from the operator or the local subscriber. This operates the relay 220, Fig. 5, to spacing on the next marking impulse in the relay 226, where it remains during the transmission of the break signal over the duplex circuit. Similarly, the relay 59, Fig. 3, remains at marking during the transmission of the spacing break signal by the relay 58. The break signal moves the relay 74, Fig. 2, to spacing to operate send-receive contacts 20 to receiving and thus interrupt a transmitting distributer 17 and short circuit transmitting contacts 19. Recall. A recall key 16 interrupts the line circuit and earths the conductor 11 to operate the relay 57. This operates the relay 70 to release the relays 51, 55 to restore the circuit to the idle condition, whereupon the relays 70, 51 release. The relay 59 transmits a spacing signal to the repeating relay 226 at the central exchange and to the relay 232, which operates the other relays as described for a break signal. The relay 232, however, remains on spacing (because no ringing current is transmitted) and permits the relay 233 to move to the left and operate the relay 235 followed by a relay 228 which locks. This releases the relays to restore the circuit to the idle condition, and operates a relay 85, Fig. 6, to light a lamp 86 and operate a relay 87, which -locks. Releasing the recall key, Fig. 2, disconnects earth from the line 11 and completes the circuit between the lines 10, 11. The apparatus of Figs. 3, 5 operates as described for initiating a call and the relay 85, Fig. 6, releases. Until the operator's printing key 89 is operated, an interrupter 93 flashes the lamp 86, which is extinguished on the operation of the key. Recall signals may also be sent by moving the line key 72, Fig. 2, first to stop, then to test, and finally back to the line position. Disconnect. The line key 72 is operated to stop to de-energize the subscriber's equipment and connect earth to the lead 11, and is then returned to the line position. The circuits at the intermediate and central stations operate as for a recall signal, but the lamp 86 does not flash. The operator then removes the plug 83 to release the relays 84, 211, which causes the relay 220 to transmit spacing current. A motor stop signal may operate contacts 15, Fig. 2, to release the relay 27 and thus return the circuits to normal as above. Operator calls. The calling plug 101 is inserted in the jack 223 to operate the relays 211, 98, and cause the relay 220 to transmit a marking impulse. Operation of the ringing key 100 causes the relay 220 to transmit alternate marking and spacing currents, which operate on alternating-current relay 63, Fig. 3. The relay 63 operates a relay 65 to move the relay 60 to the right. This operates relay 66, which locks, and interrupts the circuit of the relay 60, which, after 0À3 seconds, moves to the left. This operate