Patent GB-671679-A (GB)
Title: Improvements in or relating to telephone switching systems
IPC: H04Q3/00
Filed: 1949-06-29
Abstract: 671,679. Automatic exchange systems. WESTERN ELECTRIC CO., Inc. June 29, 1949 [June 29, 1948], No. 17205/49. Class 40 (iv). A substation is provided with means for connecting either a telephone set or a numbersending device to line in accordance with signals, e.g. polarity reversals received from the exchange. The number-sending device is of a type which sends two brief impulses separated by an interval characterizing the digit and runs continuously to send repeatedly the whole of the wanted number until polarity reversal from the exchange acknowledges receipt of the number. Line finder action. The substation equipment may be either as shown at 510 or 550, Fig. 5, the connection of the number-sending device being effected either by the relay 516, rendered operative to currents of one polarity only by rectifiers 518, or by the polarized relay 556. The subscriber (say 550) first sets his number-sending device and then lifts the handset. Ground is then applied around the subscriber's loop to the upper control electrode of the gas tube 613 whose consequent discharge is however limited by the resistor 627 so that the hold magnet 612 of the primary switch 610 does not operate at this time. Its change in anode potential however causes tube 618 to fire and bring up relay 619 which connects negative potential to the left-hand grids of valves 620 ... 621 connected in lock-out circuit which ensures that only one valve can fire. Assuming 621 fires, it energizes the select magnet 623 in series with 720 which is associated with one set of junctor circuits 730 ... 731. Relay 720 applies potential from potentiometer 1020 to the control gaps in tubes 710 ... 711 whose left-hand electrodes are also connected in a lock-out circuit so that only one fires, say 710, thereby bringing up (amongst others) the select magnet 643 of the secondary switch 640. When select magnet 623 comes up it short circuits resistance 627, thereby permitting tube 613 to discharge fully and bring up the hold magnet 612. Magnet 623 also brings up hold magnet 646. The subscriber is now connected via the primary and secondary switches 610, 640 to the junctor circuit 730. Seizure and setting of register controller. When tube 621 fired it brought up 1013 which primed valves 1155 ... 1157 in the respective register-controllers. Only one of these, say 1155, discharges, due to a lock-out circuit and brings up the select magnet 910 of the register connector switch,. whose hold magnet 912 operates over the junctor circuit and the primary and secondary switches to earth at the primary select magnet contact. The subscriber's loop is thereby connected to the register-controller to bring up 1154 and 1152 therein. The last earths the S-wire to maintain the hold magnets and applies a pulse to gas tube 1015 which fires momentarily to remove H.T. from all the gas tubes whose consequent extinction releases the corresponding select magnets. Relay 1154 also brings up 1510 and releases 1542 to enable the digit receiving equipment, Figs. 13, 14, and connect the subscriber's loop thereto. The polarity applied to the speaking wires at relay 1154 is now such as to cause the subscriber's polarized relay to connect up the digit sending equipment. The digit sending equipment then sends out the wanted subscriber's number repeatedly, each digit being represented by the interval between two pulses (each of a duration of 1 m/s.). After the whole designation is sent a "blank" interval at least equal to twice the maximum time required to send a digit elapses prior to the repetition of the number. In order to allow for transients each digital interval is caused to be greater than 3¢ milliseconds, the receiver being disabled for this period immediately after the reception of the first impulse. The impulses are fed via the limiter, Fig. 13, to the amplifier 1428 and the code detector 1411 to the " blank " interval timer 1425. When this operates immediately prior to the reception of a number the code start circuit 1426 enables the digit detector 1429 which, when it receives its first or " start " pulse, conditions the circuit 1431 to start the timing multivibrator 1432, and steps the circuit 1433 controlling the circuit 1434 which steers the first digit to the binary counter 1413. The start pulse also operates the circuit 1430 which disables the digit detector for 3¢ milliseconds. Meanwhile the timing multivibrator 1432 feeds seven ¢-millisecond pulses via the switching circuit 1437 to the counter 1436 which after it has counted off the seven pulses actuates the circuit 1435 to cause 1437 to transmit any further impulses via the digit steering circuit 1434 to the counter 1413. The second or " stop " pulse of the digit actuates.circuit 1431 to stop the operation of 1432. The next digits will be received in registers 1414, 1415, being directed there by the steering circuit which is stepped on reception of each start pulse. The number of pulses received should be twice the number of digits to be dialled. These pulses are counted at 1418 and if their number is incorrect the recycle circuit 1422 passes a pulse to relay 1513 which momentarily inserts an inductance in the battery supply to the counting and switching circuits to reset them so that they may receive the number afresh. 1514 operates a " recycle " meter. If the number of pulses received is correct the circuit 1421 transmits a pulse to relay 1516 which releases 1510, brings up 1512 to disable the code detector 1411 and operates 1518 which inserts an inductance in the H.T. supply to restore the circuits 1431, 1418. The settings of the register circuits 1413 ... 1415 are transferred to relay sets A1 ... A8, B1 ... B8, C1 ... C8. Relay 1516 also operates 1169 which brings up 1012 and 661, the former operating after a slight delay to pulse the valve 1015 and operate 1017 to extinguish any of the gas tubes which may have been fired while 1012 was operating. Relay 1012 also prevents the control circuits from responding to a further incoming call. If a call was already incoming when 1169 operated 1013 would be operated in the H.T. circuit of valves such as 621 and 1012, and 661 would not operate until 1013 was released. Relay 1012 also causes tube 1163 to fire and connects the marking wires from contact trees of the A, B and C relays to the marking circuit, Fig. 12. Tubes 1163 ... 1164 in the different register circuits are connected in a lock-out circuit so that only one register may use the marking circuit at any instant. Selection and release of register. The marking circuit is so arranged that with marking potential on one hundreds (2), one tens (1) and one units (1) lead will produce a potential on a lead (211) sufficient to fire the valve 616 corresponding to the wanted line. Relay 1165 brings up 1167 which grounds lead 1115 to bring up 718, 722 in the junctor circuit, and relay 917 and select magnet 915 in the tertiary switch, Fig. 9. Relay 718 connects the subscriber's loop to 719, battery thereat being so poled as to disconnect the number sending device and connect up the telephone set. 719 in operating supplies holding ground for the primary and secondary hold magnets 612, 646 and disconnects 1154 which partially restores the register. The operation of 917 marks all the idle paths leading to the cathodes of valves such as 620 associated with all the subscriber's lines via the select magnets such as 641 of the secondary switches, contacts of relay 661 and back through hold magnet contacts of the secondary switches to the select magnets of the primary switches. The firing of 616 causes the firing of 618 which in turn through relay 619 conditions the tubes such as 620, 621 of which owing to the lock-out arrangements only one, say 620, fires. Select magnet 622 and relays 820, 1013 energize in series, but the first is slow to operate and meantime 820 has grounded one side of the select magnet in switch 647 corresponding to 641. When 622 operates it brings up the hold magnet similar to 646 but associated with 649 and short circuits 627 to bring up the hold magnet in 614. Completion of the secondary cross-point contacts then operates hold magnet 930. This in turn brings up 724 which connects up ringing current and applies a pulse to the release circuit associated with tube 1015 to remove H.T. from all the gas tubes and so release the select magnets. In the register circuit, 1167 has interrupted the battery supply to the marking circuit and with the extinction of 1163, relay 1165 releases and brings up 1517 which releases the connection between the junctor and the register. Relay 1517 brings up 1519 which inserts an inductance 1552 in the H.T. supply to restore the counters 1413 ... 1415, and the other circuits 1421, 1422 and 1417. Circuit 1421 releases 1516 which releases the register. Relay 1165 in releasing opens the circuit of the lower winding of the differential relay 717 which now operates through current in its upper winding and releases the hold magnet 912 of the register connector. When the called subscriber answers ring-trip relay 723 releases 722 which brings up the called subscriber's supervisory relay 721. Both this and the calling subscriber's supervisory relay 719 apply holding ground to the S-wire to hold the connection. If the called subscriber is busy the cathode of 616 is at ground potential and the tube does not fire. As a result no circuit to the junctor circuit is set up and 724 does not operate so that busy tone is reverted. Inter-exchange and tandem calls. Where calls have to be routed through several tendem exchanges the digit receiving equipment, Fig. 14, would be arranged to respond only to those digits necessary for routing the call through the exchange. Thus in a call from one exchange via a second exchange to a subscriber on a third exchange, the first exchange might register only a first portion of the digits, the second exchange only a second portion of the digits and the