Patent GB-746942-A (GB)
Title: Improvements in or relating to telephone or like systems
Inventor: BAKER GEORGE THOMAS
IPC: H01H67/26
Filed: 1952-05-27
Abstract: 746,942. Automatic exchange systems. BRITISH TELECOMMUNICATIONS RESEARCH, Ltd. May 21, 1953 [May 27, 1952], No. 13436/52. Class 40 (4). Information for operating a switch in a crossbar system is registered on a magnetic drum arranged during each cycle to control the appropriate magnets of a plurality of switches. Construction of cross-bar switch. Fig. 1 shows one cross-point with its associated operating mechanism. Projections 13, 28 are normally free of continuously reciprocating bars 5, 25. However, when coupling magnet 4 operates it attracts its armature 6 so that the bar 5 rocks the projection 13 and bridge bar 32 to the left. Momentary operation of a select magnet 27 rocks spring-mounted finger 22 counter-clockwise in a similar manner so that the finger is inserted between bar 32 and spring 31 at the selected cross-point. Release of magnet 4 then restores bar 32 to close the contacts 30, which are thus maintained closed without any magnets energized. The cross-point is released by momentary operation of coupling magnet 4. Automatic exchange system. General description. The system described caters for 40 subscribers with two cross-bar switches of the type just described, one used as finder and the other as connector. Control is by a high-speed storage device of the magnetic drum type, such as is described in Specifications 717,687 and 717,689. The magnetic drum has three tracks, a register track with a portion assigned to each subscriber, a transfer track which is normally empty and may be used by any subscriber, and an address track. Each track has 40 sections each of 4 blocks of 5 unit areas. TZ, TY, TX pulses are used corresponding to the subscribers' numbers, the various blocks, and areas, respectively. The register track has an auxiliary reading head RH<1> (not shown) one group in advance of the normal reading head. Dialled digits are entered on the part of the register track assigned to the calling subscriber and are transferred to the transfer track where they are compared with the numbers on the address track until correspondence is found. If the called party is free connection is made over a pre-selected bridge circuit and the equipment connects to the calling party over a similar mechanism. Registration of calling and called numbers. When a subscriber closes his loop a pulse on lead PA energizes memory circuit M10 at time positior TX1, TY1 to enter a busy dot in position TX5, TY4 of the corresponding part of the register track, M10 then restoring. The called number is then entered in binary form into blocks 72, 73 of the calling party's section of the track in the manner described in Specification 717,689. If the distributer D, Fig. 15, is free it marks lead STL so that when the auxiliary reading head encounters the busy dot in block Y3, M1 operates (STL, SL<1>, TX1, TY3). When the transfer track is free M2 operates to clear the transfer track and transfer thereto the dialled digits over,leads AT, BT, these digits being repeated all round the track. M1 also writes a busy dot in position X1, Y2 of the transfer track, while M2 marks the calling party's section of the register track at X3, Y4. At the next scan M3 is operated by the busy dot (SLT, TX1, TY2) to initiate comparison of the digits on the transfer track with the various combinations of digits on the address track. M3 is repeatedly reset until correspondence occurs when it operates M4 (TX1, TY4) which inserts a busy mark at X5, Y4 in the called party's section of the register track (lead B) if it was previously free. If the called party is already busy M4 makes a corresponding dot in the transfer track (lead BT) and the busy dot on the register track has already caused the auxiliary reading head to operate M5 (SL<1>, TX5, TY4). M3, M4, M5 are then reset during the scanning of the fourth block Y4. If the called number is free, however, M6 operates and pulses lead PU to cause the final selector to connect with the called line in a manner described later. M6 is then reset. When the auxiliary reading head encounters the dot at X3, Y4 marking the calling party's section of the register track, M7 operates but is reset if the called party is busy (SLT, TX5, TY4). In this case M8 also operates to clear the transfer track, M8 being reset at the next scan. However, if the called party is free, potential on lead STF operates M9. Operation of line-finder and connector. Each cross-point, Fig. 12, has eight pairs of contacts corresponding to four subscribers, selection of two pairs being effected by relays WA, WB. Gas tubes DT1-DT12, Fig. 13, are controlled by a 10-point cyclic counter C followed by two binary counters S1, S2 controlling relays WA, WB so that select magnets SM1-SM10 and relays WA, WB in combination can select one of the 40 paths through the line-finder according to which subscriber's section on the drum is operative. If the called party is free, M6 pulses lead PU to strike tube NT, Fig. 15, and the appropriate tube or tubes of the set DT1-DT12 but the related SM magnet and WA, WB relays do not pull up due to resistance R10. Distributer D has preselected an idle bridge circuit and ST now pulls up to prevent D hunting, to energize relay A which operates B to busy the bridge circuit, and to energize bridge magnet BM2 of the connector switch. Contacts BMC then operate BP to energize the appropriate magnet or magnet and relays in the selector switch (not shown) connected in series or parallel with the corresponding select magnet SM1-SM10 or select magnet and relays WA, WB in the finder. This select magnet earths lead SM1 to operate SP which restores the bridge magnet BM2 to trap the operated select finger and close the cross-point. BM2 releases BP which releases the select magnet and operates CA. Release of the select magnet restores SP to energize CO, so operating bridge magnet BM1 of the finder switch and marking lead STF. Ringing current is applied through relay F to the called line. When the called party answers F locks up and completes the speaking circuit. The finder switch operates in a similar manner, the marking of lead STF operating M9 as already described to cause operation of the select magnet corresponding to the calling party. When conversation ends the control circuit re-operates the bridge magnets momentarily to release the connection. Specification 747,010 also is referred to.