Patent GB-281779-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1926-09-11
Abstract: 281,779. Siemens Bros. & Co., Ltd., Grinsted, W. H., and Lyden, T. Sept. 11, 1926. Automatic exchange systems.-for interworking between an exchange working with loop impulsing and supervision, and one with leg impulsing and supervision, means are provided in connection with calls in either' direction for transforming the control from one kind to the other. For calls from the leg-system exchange to the loop-system exchange, the outgoing selectors, Fig. 1, at the former may be of ordinary type, whilst the incoming selectors, Fig. 2, at the latter receive leg impulses and transmit loop impulses and on the other hand receive loop supervisory signals and send back leg supervisory signals. Alternatively, the outgoing selectors at the leg-system exchange may be modified, as in Fig. 4, to repeat leg impulses to local switches and loop impulses to the loop-system exchange the incoming selectors at the latter being of standard type. As a further alternative, the outgoing trunks may be provided with leg-loop repeaters, Fig. 9, the selectors at both exchanges being standard. For calls from the loop-system exchange to the leg-system exchange, the outgoing trunks may be provided with loopleg repeaters, Fig. 3, or the incoming selectors, Fig. 6, at the leg-system exchange may be modified to receive loop impulses and transmit leg impulses and to receive leg supervision and transmit loop supervision. With the latter arrangement, ordinary outgoing repeaters may be employed or two-wire or three-wire trunks without repeaters. Various combinations of the arrangements for working in the two directions may be employed, the transforming apparatus being situated either all at one exchange or for one direction in one exchange and for the other direction in the other exchange. Call from leg-system exchange to loop-system exchange; outgoing selector, Fig. 1, transmitting leg impulses. Relay A energizes over its winding 1 and test wire c, and causes relays V, D to energize and lamp PL to light., When the switch moves off normal, relay E operates over contacts v1, a2, d1, k3, extinguishes lamp PL, and locks up. At the end of the digit the relapse of relav D completes the rotary-magnet circuit, andwhen an idle trunk is found, test relay T operates over windings 1 and 2, short-circuits its winding 1, and energizes relay C, which switches through and connects a third winding 3 of relay T to the test wire. Further impulses are repeated by relay A over coil RA, contact a3, and the b-wire. When the called party replies, relay Y operates over the a wire and completes the metering circuit by connecting low-resistance winding 1 of relay A over contacts e3, y2 to the c-wire. Contact y1 short-circuits relay E, which relapses to terminate the metering impulse. If all outgoing trunks are busy, relay T energizes over its winding 3 and the eleventh test terminal, and a busy signal is connected to the a-wire. Incoming selector, Fig. 2, transforming leg. to loop impulses. Relay A operating over the bwire, energizes relay B and lights lamp EL. Impulses incoming over the b-wire are repeated over contacts a1, b3, s1 h1, and relay C to the vertical magnet VM, and at the end of the digit rotary hunting takes place in the usual manner under the control of a stepping relay G. The operation of the test relay H completes a loop through the left-hand winding of polarized relay E over the outgoing a. and b-wires, and further impulses incoming over the b-wire, are repeated over this loop at contact a2. Relay D operates during the digit to remove relay E from the loop. When the called subscriber replies, relay E responds to current reversal over the loop and connects battery to the incoming b-wire to operate relay Y, Fig. 1. If all outgoing trunks are busy, springs s1 - - s3 operate, and busy tone and flash signals are transmitted in known manner. Outgoing selector. Fig. 4, transmitting' loop impulses. For local calls and for calls, to other leg-system exchanges, the operation of the selector is substantially the same as that described with reference to Fig. 1. On levels 2 - - 6, 9, however, corresponding to calls to loop-system exchanges, a relay SR operates over an additional vertical wiper x, and replaces battery connected to coil RC and earth to relay Y by a loop containing coil RC. winding 1 of relay L, and contacts sr5, l1. Succeeding impulses are repeated over this loop at contact a3, relay D operating during impulsing over contacts a2, sr4, t5, to give a direct loop over contacts sr3, d3. When the called subscriber replies, polarized relay L energizes, removing a short-circuit from relay Y, which completes the metering circuit and shortcircuits relay E. Leg-loop repeater, Fig. 9. Relay A operating over the b-wire removes a short-circuit from relay N, which energizes over the c-wire and completes an outgoing loop over winding 1 of relay Y, coil RB, and contacts d2, a2. Impulses incoming over the b-wire ,are repeated over the loop at contacts a<2>, relay D energizing during each digit to short-circuit relay Y and coil RB. When the called subscriber replies, polarized relay Y operates over the loop, connects coil RB<1> into the loop, and connects battery over coil RA to the a-wire to give a supervisory signal at the legsystem exchange. When relay A releases, the opening of the loop releases the switches at the distant exchange, but relays N, D remain operated until earth is moved from the c-wire at the preceding selector. Loop-leg repeater, Fig. 3, Relay A operating over the incoming loop repeats impulses at contact a1 over the b-wire in series with coil RB, whilst the operation of relay Y over the a-wire when the called party replies is transmitted back as a loop supervisory signal by the reversal of the connections to relay A. Call from loop-system exchange, to leg-system exchange; incoming selector, Fig. 6, transforming loop impulses to leg impulses. The outgoing selectors at the loop system exchange are of known type, and the inter-exchange trunks may be two-wire with an ordinary repeater, two-wire without a, repeater, the connection being held by a relay in series in the a-wire, or three-wire, the selector show in Fig. 6 being adapted for the latter arrangement. Relay A operating over the loop energizes relay V, which connects earth to the c-wire to operate a holding relay at the outgoing end. Incoming impulses are repeated at contact a1 to the vertical magnet VM, after which relay D relapses and hunting takes place as usual. Succeeding impulse trains are repeated at contact a<3> over the outgoing b-wire. When the called subscriber replies, battery connected to the awire energizes relay Y, which reverses the current in the incoming loop by replacing the line relay A by an oppositely-connected relay AA. Contact y1 short-circuits relay E, which relapses and the talking circuit is completed over contacts e3. When the calling subscriber hangs up, relays AA, V release, but earth is maintained on the test wire until off-normal contacts k2 are opened.