Patent GB-234556-A (GB)
Title: Improvements relating to automatic and semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1924-02-29
Abstract: 234,556. Siemens Bros. & Co., Ltd., and Christian, D. A. Feb. 29, 1924. Automatic exchange systems; metering.-In a forward loop impulsing system in which the battery feed for impulsing is located at the originating end of a two-wire junction, a supervisory signal, e.g. the metering signal, is sent back by bridging a low-resistance winding or relay across the distant incoming end of the junction. Three arrangements are described. In the first, the impulse relay is provided with high and low-resistance windings, the former receiving the impulses and the latter being bridged across the trunk, on the reply of the called subscriber, to operate a marginal supervisory relay at the originating end. In the second system, the low-resistance winding is connected across the junction during impulsing as well as on the reply of the called subscriber, the supervisory relay being prevented from operating, or the meter circuit being opened, during impulse transmission. According to the third arrangement two relays are used in place of a single impulse relay having high and low-resistance windings. The originating end of the junction may be at a manual operator's position. First arrangement, Figs. 1 and 2. A first selector, Fig. 1, serves a two-wire junction leading to an idle incoming selector, Fig. 2, in the usual manner, the impulse relay AA at the incoming selector being energized over its high-resistance winding 1 by current fed forward over the a and b-wires through the windings of a supervisory relay Y and a retardation coil RA at the first selector. Owing to the high-resistance of the winding 1 the relay Y does not resopnd. The relay AA energizes the release relay VA and the change-over relay DA, and on the next impulse series being dialled the first selector impulse relay R repeats them at armature a3 to the incoming selector impulse relay AA, which repeats them at armature aa1 to the vertical magnet VM<1>. At the first vertical step, relay LA energizes and locks up, and the relay DA is maintained over back contact aa2 of the impulse relay AA, so that on the termination of the impulse series the change-over relay DA relapses, and closes a hunting circuit for the rotary magnet RM<1>. When an idle trunk is engaged, the test relay TA locks energized, switches through the wipers, and opens the hunting circuit. Subsequent digits are repeated at contacts aa3, and when the wanted party answers, a supervisory relav YA energizes over the called loop in series with a retard RA<1>, opening the circuits of relays LA, DA, and at contact ya2, connecting the low-resistance winding 2 of relay AA across the two-wire junction. The reduction in the resistance of the forward loop causes the response of the supervisory relay Y, Fig. 1, which prepares a circuit for a relay S of a delayed metering device, similar to that described in Specification 200,928. A common cam alternately applies earth to the wires 10, 11, and on the grounding of wire 10 the relay S energizes, locks up, and prepares a circuit for relay Z, which is subsequently completed over the wire 11. closing the meter circuit over the test wire. Second arrangement, Figs. 1 and 3. When the incoming selector, Fig. 3, is taken into use the impulse relay AB is energized over a forward loop including its high-resistance winding 1, but on the energization of the relay LA at the first vertical step, the low-resistance winding 2 is substituted and receives the remaining impulses. At the end of the impulse series the relay DA relapses and re-connects up the high-resistance winding 1. The supervisory relay Y, Fig. 1, responds during impulsing, but the delayed metering device prevents metering. If delayed metering arrangements are not provided. metering may be prevented during dialling by including a back contact of the slow release relav D in the metering circuit, or alternatively the a-wire may be disconnected from the relay Y and connected direct to earth during impulsing by a contact of relay D. When the called subscriber replies, relay YA responds and the low-resistance winding 2 is permanently bridged across the junction at contact ya2, causing the response of the supervisory relay Y, Fig. 1, which brings about metering as described in the previous paragraph. Third arrangement, Figs. 1 and 4. When the incoming selector, Fig. 4, is taken into use, the high-resistance relay AH and the low-resistance winding 1 of relay AL energize over the forward loop, but the relay AH only responds, closing an independent circuit over the winding 2 of relay AL. Relay AL causes the energization of the release and change-over relays VA, DA. At the first impulse series, the high-resistance relay AH interrupts the circuit of the low-resistance relay AL, which closes the vertical stepping circuit. On the first vertical step, relay LA responds and short-circuits the relay AH, so that the winding 1 of the relay AL becomes effective for subsequent impulses. On the cessation of these impulses, the relay DA relapses, the short-circuit is removed from relay AH, and the first condition is restored. During subsequent trains of impulses, on the first relapse of relays AH, AL, relay DA reimposes the shunt across relay AH. On the reply of the called party, the supervisory relay YA directly bridges the low-resistance winding 1 of relay AL across the junction, causing the response of the supervisory relay Y, Fig. 1, at the first selector.