Patent GB-253595-A (GB)
Title: Improvements in telephone systems
IPC: H04Q3/00
Filed: 1925-03-17
Abstract: 253,595. Standard Telephones & Cables, Ltd., (formerly Western Electric Co., Ltd.), and Hartley, G. C. March 17, 1925. Automatic exchange systems ; metering; party l i n e systems. - In a two-party-line system of the kind in which a reverting call is made by dialling a special number and thereby taking into use. a relay group which upon the calling subscriber hanging up impresses ringing current alternately on the two line wires, only successful calls are metered, metering being prevented if the ringing current is cut off by the calling party again lifting his receiver. The relay group may be called by a faultsman to test the bell at an ordinary station, in which case also metering is not effected. The two parties on a line are distinguished by one of the substations, hereafter called the substation X, being of the standard kind, and the other, referred to as the station Y, having a switch-hook which momentarily grounds both line wires when the receiver is removed or replaced. When the reverting- call relay group shown is taken into use, the line relay A and a relay G are energized over the calling loop. The relay A energizes a relay B which locks over its grounded armature, but the relay G is differentially wound and does not respond. If the substation X is calling, when the receiver is replaced, the relay G remains unoperated, but if the substation Y is calling, the momentary ground on the negative wire when the receiver is put up causes the response of relay G, which locks over its right-hand winding to the grounded armature of relay B. In either case the relay A relapses and closes parallel circuits over its lefthand contacts for relays C, II, which disconnect the relays A, G from the calling line. Relay C also closes the ringing circuit from the lead RL, over relays E ,F, and contacts of relay D, which is intermittently energized (over an interrupter lead connected to the left-hand armature of relay B) to project the ringing current alternately over the two line wires to ring alternately the substation bells which are connected respectively from the two line wires through condensers to earth. The relays E. F are not responsive to alternating current. If the subscriber X removes his receiver to trip the ringing current, the relay F does not respond since it is differentially wound and is energized over both its windings, but if the subscriber Y trips the ringing, it is unbalanced by the monetary ground at the substation and locks up over its left armature. In either case, however, the two-step relay E operates its light spring armature 6 and locks over it. The relay E disconnects ringing current, reconnects relay A to the loop and restores the control of relay B to relay A. The relay C falls away sluggishly, and during its relapse the release and metering wire RT is connected over the righthand armature of relay B and the outer left hand armatures of relays C, E, to the outer right-hand armature of relay F. If now either relay F or G is energized (signifying that one of the parties has called and the other tripped the ringing), booster battery is connected to outer right armature of relay F and the wire RT to meter the call, but if both or neither are energized (that is, if the originating party tripped the ringing or if a faultsman called the revertive relay group from an ordinary station to test the bell thereat), ground, is connected to the lead RT and the call is not metered. When the last party hangs up, relay A relapses and restores the relay group.