Patent GB-456750-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1935-05-13
Abstract: 456,750. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, TAYLOR, R., 30, Oulton Road, Wavertree, and BAKER, G. T., 31, Wharnecliffe Road East, all in Liverpool. May 13, 1935, No. 14054. [Class 40 (iv)] During the rotary movement of a two-co-ordinate finder associated with common control-apparatus, the calling line is marked by a connection extending through the common apparatus to the rotary magnet, the completion of the circuit over the test wiper when the line is reached causing the rotary magnet to be energized continuously to terminate the movement. The system shown includes normal or first-choice finders directly linked to group selectors and overflow or second-choice finders associated with secondary finders. The system is such that if a faulty secondary finder is unable to complete a connection both the primary and secondary finders are released and another primary finder associated with a different secondary - finder group is taken into use. An idle overflow primary finder is only taken into use when there is an idle secondary finder in the group having access to that primary finder. Routine-testing means is provided for testing the normal and overflow primary finders and the secondary finders, the arrangement for the overflow finders being such that during the test the normal finders are busied but they are again rendered available if all the overflow finders become busy. In the drawings, the chain dotted lines represent the connections for a normal primary finder and the broken lines with circles those for an overflow finder. Normal operation. A calling line relay L operates one of the group relays SA .. SE which in turn operates start relay ST in the first control circuit PC1. Relay LK operates over wiper R2 to resistance battery YA in the allotted finder, removing a short-circuit from relay VR which then operates in series with magnet PAM and completes a circuit over wiper R3 for relay HA. The line relay of the associated selector operates over the b-wire, lead SM, and wiper R4, and holding ground is placed on lead P. Vertical magnet VM operates in a self-interrupting circuit over wiper R7 and when the marked level is reached relay VT operates over the lower vertical wiper VW and operates relay RS which shortcircuits HA. Rotary magnet RM then operates in a self-interrupting circuit from ground on alarm lead 10 and when the calling line is reached a holding circuit for the magnet is closed over wiper R8, relay P, wiper R7, upper vertical wiper VW, relay K, wiper P1 or P2, relay HA or HB, to ground on wiper R3. Relay P releases ST, and relay G, which is then connected to wiper R2 interacts with magnet PAM to preselect an idle finder. If a further call comes in before one has been allotted, a self-interrupting circuit is substituted to save loss of time. Overflow conditions. When all regular finders are busy, relay RFB releases energizing RFZ which changes over from wiper R2 to R1 so that the overflow finders are tested, the test circuit including lead SS and relay DS in a secondary control group. Relay DS operates DR which completes a driving circuit for magnet SAM but if the allotter has already selected an idle secondary finder, relay DK operates completing a driving circuit over wiper SA3 for the finder magnet SAM, and operating FR which causes the associated selector to be seized. The primary finder in use is marked over lead SM and when the marked contact is reached relays FK, SK operate to switch through the secondary finder, and relay G in the primary allotter operates to release LK. In the secondary allotter, relay GG interacts with magnet SAM to preselect an idle secondary inder. When the calling subscriber hangs up, magnet RM rotates the primary finder to the end of its bank vhere it drops under gravity and hen restores rotarily. When all overlow primary finders are busy, battery s removed from the grid of valve VAA which then operates relays OFB, OFZ o disconnect the allotters and to ubstitute overflow meters. If all econdary finders of a group are busy, relay OB releases, FB operates and ground is placed on lead SS to nark busy to the primary allotter the primary finders associated with the group. If the secondary group seized s unable to complete the call due to a blown fuse, battery is removed from ead SS to release relay LK in the primary allotter'so that a new primary finder associated with a different econdary group will be selected. Routine testing. Keys KRT, Fig. 1, one for each level cause the coresponding level to be marked and each finder to be set in turn to that evel over which it then rotates to eleventh contacts which are wired to he upper bank VB in different ways so that the operation of one or other or both of the relays HA, HB is ested. To routine the overflow inders, key KT also is thrown ausing the operation of relay RFZ vhich makes the normal finders non-selectable. If all overflow finders become busy, however, relay OFB is operated by valve VAA to shortircuit RFZ and restore the normal inders to service. The secondary finders are tested by throwing a key KST which at KST1 marks last contacts in the finder banks and at KST2 closes a start circuit for one or other control set SC1, SC2. Specifications 391,123 and 429,767 are referred to.