Patent GB-213218-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1923-11-05
Abstract: 213,218. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Stehlik, R. F.). March 19, 1923, [Convention date]. Automatic exchange systems with call-finders and finder-allotters common to a group of lines have means for re-starting a finder which stops on a non-calling but faulty line and for starting a finder allotter over an auxiliary circuit when its normal starting circuit is defective. The finders are provided with two-step marginal relays which operate partially to prepare the driving circuit and fully to interrupt it when the calling-line is found. An alarm is given if the starting circuit of a finder is defective. The finders F and finderallotter FA are rotary switches of no-normal type and operate on the release of their stepping magnets. Normal operation. Subscriber A on making a call operates his combined line and cut-off relay 14 partially so that armatures 17. 19 move to their working position. Ground on the starting wire 29 energizes two-step relay 63 partially so that it attracts its armatures 70, 71. Stepping magnet 61 now operates over its self-interrupting contacts and wiper 25 until the ungrounded terminal 22 of the calling line is reached, whereupon the upper winding of relay 63 being no longer short-circuited receives current in series with magnet 61 and relay 63 operates fully, switches the line through to the group selector E and the test wiper 25 from itself to relav 62 and locks itself to the release wire 76. Relay 62 energizes immediately in series with the cut-off winding of relay 14, locks up under control of relay 63 and extends the release conductor 76 back to wiper 25. Relay 14 energizes fully, locks up to the release wire and disconnects itself and ground from the calling loop. The grounding of release wire 76 energizes relay 33 and the stepping magnet 34 of the finder allotter, which steps on until wiper 43 finds the ungrounded terminal of an idle finder, whereupon relay 33 releases. Release is effected by the removal of ground from the wire 76. Relays 14, 63 fall back, the latter releasing relay 62. Re-starting a finder that stops on a non-calling faulty line. When relay 63 energizes fully, a local circuit is made for stepping magnet 61, but on normal operation this circuit is broken by relay 62 before it becomes operative. If now subscriber A is non-calling but terminal 22 is ungrounded owing (say) to dust on armature 17, relay 63 operates fully, but relay 62 does not (armature 17 being un-attracted). Stepping magnet 61 energizes, releases itself and relay 63 and moves the wipers one step. Relay 63 re-energizes partially over the starting wire 29, and the finder now operates in the normal way. Starting the finder-allotter when the normal starting circuit is defective. Relay 62 on operating completes a circuit for a slow-to-operate relay 32, but in normal operation this circuit is broken immediately by relay 33 which energizes from ground on the release wire. If for any reason the group selector E fails to return ground to energize the stepping magnet and relay 33, relay 32 pulls up and energizes them. Relay 33 releases relay 32, which releases the stepping magnet, and the wipers are moved on and hunt for an idle finder. The finder now taken into use is started over wire 29 (relay 14 being still partially operated) and operations proceed in the normal way. Alarm arrangement when the starting circuit of a finder is broken. Relay 30 which energizes as soon as the starting wire 29 is grounded completes a circuit for the common alarm signal 35 if owing to a break in the starting circuit, relay 31 fails to operate.