Patent GB-339279-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1929-08-27
Abstract: 339,279. Automatic Telephone Manufacturing Co., Ltd., Paulett, W. H., and Gillings, C. Aug. 27, 1929. Automatic exchange systems.-In an automatic telephone system a plurality of step-by-step switches, e.g. group selectors, are provided with common control equipment which is associated with a switch by a hunting switch on the switch being taken into use. Alternatively, the hunting switch allots idle common control equipment to an idle switch prior to the switch being ta.ken into use, the connection of the controlling equipment with the switch enabling the switch to be seized. Associating common controlling equipment with selector upon the switch being taken into use. When the switch, Fig. 1, is seized relay K is operated over the calling loop to mark, by disconnection of earth potential, a contact in bank 3 of the finder switch FS and energize the "start" relay S. Relay S operates the self-driving stepping magnet DM and the switch FS is driven until the marked contact is engaged and the short-circuited relay KF is operated. Relay KF connects impulse relay A to the lines, opens the "start" circuit and extends the " start " lead to the next idle finder switch FS. Operation of relay A energizes relay B which over wiper 4 connects holding potential to the test lead PR and at b4 busies contact engaged by wiper 3 to other switches. Dialled impulses operate relay A which operates the vertical stepping magnet V of the selector over wiper S. The stepping circuit includes slow release relay C which operates relay G to prepare the circuit of the rotary magnet R. The pause following the dialled impulses allows relay C to release and operate the rotary magnet R one step after which the selector wiper continues to rotate until absence of earth in the test bank of the selector prevents re-energization of relay G and further rotation of the selector and allows the short-circuited relay H to operate. Relay H busies the test wiper of the selector and extends the calling line. Switching through the calling line releases relays A, B, K and the common equipment is released. All trunks busy. If no idle line is found during rotary motion, the selector takes up the 11th position and cam contacts S1, S2 are operated. Contacts S1 release relay H, and S2 earths test wiper to operate a common overflow meter. Relay BB also is operated upon release of relay H to apply busy tone to the line at contacts bb1. Release. When in response to a busy signal calling subscriber releases, relays A, B release to restore relay K and thereby operate the restoring magnet Z of the selector. When the receiver is replaced at the end of a normal call the last switch is released and earth is removed from test wiper to release relay H and cause operation of the releasing magnet Z. Allotting idle control equipment to idle switches. In the arrangement shown in Fig. 2, a distributor D associates all common control equipments with idle group selectors. So long as an idle control set is not associated with a selector, relay KD is operated. Relay KD operates relay KF over wiper 10 provided a short-circuit is not established over wipers 9, 11 by wiper 1 of finder FS engaging busy contacts. Relay KF operates relay S over wiper 1 to remove the guarding earth on PR and energizes relay SD which releases KD to energize stepping magnet. DM2 of the distributor D. The distributor continues to step until all the control relay sets are associated with idle selectors, i.e. until all the KF relays operate to energize common relay CH which prevents further operation of relay KD and magnet DM2. Assuming the selector shown is taken into use relay K connects line relay A across the loop circuit and releases relay S to guard the connection and hold relay KF operated. Relay A is impulsed by the dialled impulses and operates the vertical stepping magnet V. Rotary hunting of the selector is effected in a. manner similar to that previously described until operation of relay H. switches through the calling lines, releases K to restore the comon equipment, busies the engaged contact in bank 1 of finder FS and releases relay A which by the release of relay B energizes relay C and operates stepping magnet DM1, which causes release of relay KF, and consequently relay C to release magnet DM1 and thereby step the finder on to the next contact. If these contacts correspond to a busy selector magnet DM1 is again operated over wipers 1, 11. 9 and further stepping takes places until relay KF is energized. In the event of the distributor D engaging the contacts of a busy control set, relay SD is operated to cause a further step. If all group selectors are in use relay CH is operated to release relay KD and thereby prevent continuous hunting. Hunting is also prevented in a similar manner when all control sets are in use