Patent GB-655974-A (GB)
Title: Automatic switching arrangement
IPC: H04Q3/00
Filed: 1947-12-23
Abstract: 655,974. Automatic exchange systems. CLAESSON, P. H. E., and GRUNDIN, I. W. Dec. 23, 1947, No. 34073. Convention date, Nov. 14, 1946. [Class 40 (iv)] In inter-exchange working after an idle junction to the wanted exchange has been seized and the signals indicative of the wanted party have been sent thereover, the junction is released and when the wanted party has been reached the called exchange initiates the seizure of an idle junction to the calling exchange and the connection thereto of the switching circuit to which the calling party is still connected. As shown in Fig. 1, traffic at calling exchange A has access over a group selector GV to an intermediate relay set MR and an intermediate selector MV which performs the non-numerical selection of an idle relay repeating set REP associated with a line L to the wanted exchange B. A transmitting register RES, and a receiving register REM are associated by register selector REV. Selector MV also performs the numerical selection of the relay set MR when a connection is re-established, and non-numerical selection of an idle intermediate relay set for incoming traffic. Similar apparatus at exchange B are designated by similar references letters with a prime sign. The transmitting register RES receives dial impulses from the calling party and re-transmits them as code signals comprising either positive or negative pulses, or voice-frequency signals of different frequencies, which may, if desired, modulate the carrier wave in a carrier wave system. At exchange B, the code signals are received in receiving register REM<SP>l</SP> and are re-transmitted as dial impulses to the local switch train. Detailed description, Figs. 4-15. A subscriber of exchange A desiring to call subscriber 13001 at exchange B, dials the number and is in known manner connected to a group selector GV, Fig. 4, which is driven to an idle intermediate relay set MR in which relay 402 pulls up. Relay 701 of the register selector REV follows, locks in series with 711 and initiates the sequential operation of relays 715 to 724 so that the test wires of the transmitting registers RES (Figs. 8, 9) are connected in turn to test relay 713. The test wire of an idle register (say that connected up by 715), carries negative potential to which 713 operates, thus disconnecting the succeeding relays 716 to 724 and operating select magnet 733, followed by bridge magnet 735 of a cross-bar switch to associate the intermediate relay set with the register. Relay 401 pulls up, 402 releases and during the release period of 701 a signal characteristic of the particular intermediate relay set is sent to the register. This signal is received by a relay group comprising 802, 803 and 804 connected to the a-wire and 805, 806 and 807 connected to the b-wire. Relays 804 and 807 operate only to a strong current (e.g. 50 ma.); 803 and 806 to a medium current (e.g. 20 ma.) ; and 802 and 805 to a weak current (e.g. 5 ma.), so that by choosing different resistances for connection to the a- and/or b-wires by each of the start relays, e.g. 701, of the intermediate relay sets, one or more of the relays 802 to 807 is operated to indicate the relay set concerned. Assuming, in the present case, that a weak negative potential is applied to the a-wire and none to the b-wire relay 802 only is operated. Relay 801 follows and transfers the a- and bwires to relay 808, which operates and brings up 809. The operation of 403 releases 701, whereupon 808 falls away. The calling party now dials the wanted number. The first impulse causes the operation of select magnet 815 and digit relay 810, 814 coming up in series with 815 at the end of the impulse. The second impulse operates 816; 812 releases 815 and assuming the first digit to be 1 (2 impulses), 810 falls away. Relay 811 and bridge magnet 825 operate, the latter closing a contact group corresponding to the first digit; and relays 816 to 811 are released. The remaining digits are received in like manner, bridge magnet 830 marking the last digit and bringing up relay 405 which locks in series with 501 of the intermediate selector MV, and operates the select magnet 502 corresponding to the intermediate relay set. Relays 515 to 524 are operated sequentially to find an idle relay repeating set to exchange B. If the first set is idle (minus on test wire), test relay 514 operates over winding I, stops the hunting and brings up bridge magnet 532, thus connecting the a- and b-wires of the repeater to the sending register RES. Relay 902 of the register operates in series with 606 and 607 of the repeater, relay 609 staying down as its windings act in opposition to one another. Operation of 607 starts up a tone generator and charges condenser C so that a positive pulse is modulated on the tone frequency and transmitted to exchange B, where it causes polarized relay 1210 (Fig. 12), to close its upper contacts and bring up 1205, followed by 1203, 1201, 1200, and 1208. The intermediate selector MV<SP>1</SP> taken into use performs either numerical or non-numerical selection of an intermediate relay set MR<SP>1</SP> under control of the signal combination received by relays 1325 to 1328. On the operation of 1200 condenser C<SP>1</SP> (Fig. 12) is charged to initiate the transmission of an answering signal to exchange A to which relay 610 responds by closing its upper contacts, thus operating 605 followed by 603 and 602. The consequent battery reversal releases 902 in the sending register RES, whereupon 904 and 908 operate and positive battery is applied to the a- and b-wires to the relay repeating set REP in which 609 responds. Condenser C is thus short-circuited until 903 relapses followed by 908 and 609, whereupon a positive current pulse is transmitted under control of 607. Relay 1210 responds to this pulse and positive potential is applied to the a-wire, thus bringing up 1328 and 1330. When 1330 relapses 1312 pulls up and relays 1315 to 1324 commence hunting for an idle intermediate relay set MR<SP>1</SP>. Test relay 1313 responds to the idle relay set (say the first) followed by select magnet 1302. Relays 1501 and 1512 in the register selector are operated and relays 1515 to 1524 commence hunting for an idle receiving register REM<SP>1</SP> under control of test relay 1514. Assuming the first register to be idle, select magnet 1534 and bridge magnet 1535 are operated, where-  upon bridge magnet 1332 pulls up and 1200 falls away, thus reverting a negative pulse to exchange A, causing polarized relay 610 to close its lower contacts. Relay 604 is energized and brings down 603 so that 602 relapses and restores the normal polarities on the a- and bwires whereupon 902 re-operates. In the receiving register at exchange B 1031 operates in series with test relay 1514, and relay 1030 which follows energizes bridge magnet 1535 and releases 1031. The re-operation of 902 brings up 907, 909, and 916, and 905. Retransmission of wanted number from exchange A. The wanted party's number is then re-transmitted by RES under control of the cross-bar switch (Fig. 8). On the first operation of 905, 912 comes up and brings up 910 over contact 7-8 of select magnet 816. Relay 916 releases 909 and energizes 915. Negative potential is thus connected via the a-wire (Fig. 9) to 607 and 609 (winding I), and with 905 up, 908 down, 609 operates, thus short-circuiting condenser C. Relay 906 is operated by 905 which then relapses, whereupon 911 energizes in series with 912 and the negative potential is removed from the a-wire. The consequent release of 609 recharges C and a positive pulse is transmitted. Relays 905 and 906 continue to interact and on the second operation of 905 negative potential is again applied to the a-wire, and 913 comes up, followed by 908 under control of the cross-bar switch (Fig. 8). The second operation of 906 causes a second positive pulse to be sent to line and also brings up 909 which stops the transmission of pulses and energizes 917. Relays 910, 911, 912, 913, 908, and 909 fall away, and 905 re-operates to initiate the transmission of the second digit. With 908 down, the a- and b-wires are both open-circuited and the subsequent release of 607 discharges C and a negative pulse is sent to line. The operation of 909 under control of 826 and 818 (not shown), releases 905 and prevents operation of 906. Relay 607 then re-operates and recharges C to send a positive pulse. The transmission of the third and succeeding digits takes place in a similar manner under the control of 827 and the succeeding bridge magnets. When 909 comes up at the end of the sixth digit it is followed by 922 which releases 909 and then locks in series with 915. The consequent operation of 905 initiates the sending of a signal characteristic of the intermediate relay set in use. Two positive pulses are sent as described for the first digit above, and then 905 again re-operates and initiates a third pulse. Relay 911 releases and brings up 914 which re-operates 909 to stop the transmission, it being assumed that the relay set is No. 2 (code + + +).  The operation of 901 then opens the loop to the repeater (Fig. 6), whereupon 607 releases and a negative pulse is sent to line. Relay 601 then falls away, the repeater is disconnected, and bridge magnets 532 and 735, and relays 401 and 903 are released. Relay 402 operates to the calling loop and holds the group selector pending the reply of the called party. Reception of wanted party's number at exchange B. The polarized relay 1210 responds to the first positive pulse of the first digit and closes its upper contacts, thus operating 1205 which connects positive potential to the a-wire (1208 up) and over the cross-bar switches of MV<SP>1</SP> (Fig. 13) and REV<SP>1</SP> (Fig. 15) to relays 1101  (winding I) and 1103. Relays 1103 and 1105 are two-step relays which operate their " a " contacts when energized by a weak current and their " b " contacts for a strong