Patent GB-349256-A (GB)
Title: Improved call finding arrangements in automatic telephone systems
IPC: H04Q3/00
Filed: 1930-04-25
Abstract: 349,256. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, and DIXON, R. G., 162, Westmount Road, Eltham Park, both in London. April 25, 1930, No. 12794. [Class 40 (iv).] In a call finder system in which a finder hunts first for a marked group and then for a line in that group, if two finders are hunting for different calling lines, the second finder does not enter the group over which the first finder is testing. Two arrangements are described; in one, the second finder continues its group hunt if it reaches a marked group over which a finder is already searching and, in the other, the second finder pauses on the group marking terminal until the first finder has switched through, when it either enters the group or passes on dependent on whether the second calling line is or is not in that section. All finders cut into and test over the last group and return to normal if the eleventh contact in that section is reached. The finders, which, as described, are bi-directional 200-point switches with two sets of wipers, are taken into use over a relay chain starting circuit which is so arranged that if a later finder in the chain is hunting when an earlier finder is freed, the chain is maintained to the later finder. A system, in which the order in which the finders are taken into use is dependent on the level calling, is also described. When a call originates the group marking relay 17 (not shown) energizes, marking the required level in vertical bank NP1 and energizing B, Fig. 1. The vertical magnet VM energizes and steps the wipers, offnormals n change over extending the start circuit over n2 and C energizes. The vertical magnet VM and relay C interact until the marked level is reached when C holds over its second winding and B releases, changing over to the rotary magnet RM. Magnet RM steps the wipers, changing over contacts nr, and B reenergizes. C and RM now interact, and when the calling line is reached either D or E pulls up, from battery on the calling line, stopping hunting and switching the line through. B releases but the switching relay is held from earth returned by the seized selector switch. When the switching relay releases ZM energizes to restore the switch. During rotary search windings (II) and (III) of Care energized each time C operates but these windings being in opposition have no effect at this time. If a second finder had been hunting over the marked level the earth on NP1 would have been extended over nr2 and V2 of that switch to NP2, and consequently, when the finder reached the group, opposing windings (II) and (III) of C would have been energized, releasing C which recompletes the circuit for VM to move the switch on. The tenth level is permanently earthed in NP1 and is not multipled in NP2 and consequently, on reaching this level, all finders cut in and search. The eleventh contact in all levels is connected to E (II) and if this contact is reached E energizes and B releases. As no earth is returned however from a succeeding switch E releases and restores the finder to normal. In the embodiment shown in Fig. 2, when a call originates M (not shown) energizes and S pulls up. B operates and VM steps the wipers, changing over the offnormals n and energizing C (II) which interacts with VM. When a marked level is reached C holds over winding (1) and, if another finder is searching in that level, earth is encountered by V2 (extended from NP1 by the wipers of the searching switch). Hunting stops but S remains energized from V2. When the searching switch finds the calling line its B relay releases removing the earth from NP2. If the second calling line is in that level earth is still found on NP1 holding C. Otherwise C releases and VM continues to step the wipers until the marked level is reached. When C holds up, S de-energizes, operating the rotary magnet RM and interaction between C and RM moves the wipers until the marked line is reached when D, or E, energizes as before, switching the line through. If more than one finder is waiting to enter a group that finder on which the S relay releases quickest enters the level first. The relay E connects a buzzer to the test jack T to indicate which set of wipers is in use should a tester plug be inserted in the jack T. Should the finder illustrated be engaged when a call originates, the start circuit is extended over SL2 to the next finder. Relay F energizes and holds, in this circuit, shorting n2, and preventing interruption of the start circuit should the finder illustrated be released whilst the second finder is hunting.