Patent GB-281584-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1926-08-26
Abstract: 281,584. Standard Telephones & Cables, Ltd., and Haigh, L. B. Aug. 26, 1926. Automatic and semi-automatic exchange systems.-Link circuits each comprising a linefinder and a selector which are preselected by a distributing switch contain one relay only in addition to those normally forming part of a selector, and are characterised in that (a) the said relay which controls the hunting of the linefinder is energized, when the calling line is found, in a circuit independent of the finder wipers (b) when the connection is extended beyond the link circuit, only one relay remains energized therein (c) when an operator is wanted to extend a call, a special number is dialled so that a calling device individual to the caller at a manual board is operated over wipers of the selector and line-finder, and when the operator answers, the link circuit is released, (d) a spare distributor-switch is provided for a group of such switches and is substituted for anyone thereof by the depression of a key individual to it. Line-finder and distributor When the calling subscriber lifts his receiver, relay L Fig. 1 energizes, grounding the wire D multipled to the final selector banks and removing earth from the release trunk conductor P. Relay S Fig. 2 now operates over the common lead from earth at L9.8. The line-finder switch LF, Fig. 3, is now stepped in a circuit battery, magnet ROT1, RL, back contact of key DK. S(11-12), G(12-11), back contact of key DK, H, K1, (11, 12), Fig. 3, release trunk to earth, until the calling line is found. Relay K1, Fig. 3, shortcircuited during hunting, now energizes [battery, ROT1, K1, (2, 1), SGL, key DK, S (5, 6), G (6, 5) earth], energizing relay H over the calling loop. Relay B Fig. 3 now operates from battery over the supervisory lead SUL, and the subscriber's cut-off relay K, Fig. 1, energises over the private wire P, disconnecting relay L, Fig. 1, which in turn releases relay S, Fig. 2, relay K1, Fig. 3, remaining energized in a locking circuit. The sleeves of the subscribers' multiple jacks at a manual switchboard, normally earthed through relay winding C (1, 2), are now connected to battery through winding C (3, 4) to busy the line. The distributor is now stepped on to an idle group selector 8 [ground B (8, 9) Fig. 3, SOL, key DK, B (11, 12), Fig. 2, key DK, ROT2, battery], and relay G, Fig. 2, is operated in parallel thereto to prevent interference, with the selectors. Group busy. Relay K1, Fig. 3. closes contacts 16, 17 in series with similar contacts in the remaining selectors. When all are busy, relay B of the distributor operates, opening the start lead at B (5,6). and the distributor stepping circuit at B(11,12). Contacts H (8, 9) replace K1 (16, 17) during the selector operation. Dialling signal and group selector. Ground at K1 (15, 14) starts the dynamotor to give dial tone [lead DTN (5, 7), A (3, 4), K1 (7, 6), calling loop, K1 (9, 10), A (1, 2) earth]. At the first set of impulses the selector wipers are stepped up [earth, H (6, 5), A (6, 5), B (6, 7). X (1, 2, C (1, 2), V (4, 2), battery] and relay G1 operates [G1 (1, 2), N (4, 3), C (5, 7), B (11, 14] and locks up over the off-normal contacts N and interrupter contacts R (1. 2). Relay C releases, and closes a circuit for rotary magnet R, which shifts the wipers one step into the bank, and re-energizes relay G1 If the selector is on a busv trunk, relay G1 operates from ground at the wiper P, and the wipers are stepped on as before until a free trunk is found. Relay H now operates [battery. G1, N (4, 3), R (1, 2), X (6, 7), H, B (11, 10), earth]. Relays B, Fig. 3, and K1 release, and the calling loop is switched through, so that relav A releases. Call to operator. A single, digit is dialled, so that the group selector hunts over grounded contacts in a special level to an eleventh contact, normal post springs NP, and cam springs X being operated in turn. Relay H is shorted and further stepping obviated. A calling-party's lamp at the manual board is now lighted [ground, B (10, 11), X (5, 7), H (14, 15), P. Fig. 3, line L, Fig. 1, lamp battery], and ring- back tone is sent over NP (3, 2). When the operator plugs in, relay C (1, 2), Fig, 1, operates from battery in the cord-circuit, disconnets the automatic apparatus, and grounds the private wire D. Relays A, B, Fig. 3, release, cutting out the lamp, and energizing release magnet Z. Relays K1 K release, thus freeing the calling party's line. Auxiliary allotting switch. One spare switch SD is provided for each two ordinary allotting switches. This switch has twice the number of contacts in each level and a fifth wiper, and the test wipers of the ordinary switches are connected in different levels, the remaining contacts of which are earthed. Change-over is effected by one of two keys DK.