Patent GB-305691-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1927-11-02
Abstract: 305,691. Standard Telephones & Cables, Ltd., (Polinkowsky, L.). Nov. 2, 1927. Automatic and semi-automatic exchange systems.-Relates to backward signalling arrangements, such as are described in Specification 261,109, in which the switches at a calling automatic exchange are controlled by closures and openings of a low resistance loop at a called automatic exchange. If the calling exchange were a manual one, these signals would cause repeated operation of the calling subscribers meters, and, according to the invention, their repetition to a calling manual exchange is prevented. In one arrangement, relays Uar, Ubr, Fig. 1, associated with the junction are initially operated to open the metallic circuit over the junction when the manual operator plugs in, and are subsequently maintained operated over the B-position at the automatic exchange. When the junction is switched through at the B-position, these relays are held over a bridge which at this time exists at the incoming group selector. The opening of this bridge before the reply of the called subscriber releases the relays and completes the metallic circuit over the junction. In another arrangement, the circuit of the incoming group selector are altered by means of a cross-connecting frame so thai the bridge is not given. First arrangement, Figs. 2 and 3, with the arrangements enclosed in dotted lines at the left of Fig. 2 replaced by Fig. 1. The inset, Fig. 2<A>, shows alternative connections for the relays Lgr, Ctr at the B-position and the following description should be read in conjunction therewith. The operation of these relays connected according to Fig. 2 is, however, substantially the sarde. When the manual operator plugs into the jack of an outgoing junction, Fig. 1, relay Uar energizes over its right-hand winding and is followed by Ubr, Ucr. Relay Ucr locks over the sleeve and closes the b-wire. Relay Ubr opens the loops around the condensers in the speaking wires and connects the windings of Uar to the wires so that relay Lgr at the B-position at the automatic exchange pulls up in series with Uar and_lights lamp GL. The B-operator then sets up the call in known manner over an incoming group selector, Fig. 3, and subsequent switches. When selection is completed, sequence switch R, Fig. 3, is in position 10. The sequence switch at the succeeding selector removes battery hitherto connected to test terminals c and releases Gtr which closes a circuit over cams E, O for Glr to cause R to move to position 13. In the meantime, the wanted line is tested and a loop placed across the speeding wires at the succeeding selector energizes relay Cs2r over cams L, J so that R stops in position 13. On entering position 12, ground over cam N was connected over the third wire to relay Ctv ut the B-position and the junction was switched through to the incoming selector where a bridge (cam I, terminals 6, 4, relay As2r, terminals 3, 4, contacts of Glr, terminals 15, 12, impedance B1, 11, 1 and cam K) had been placed across the junction. Uar, Fig. 1, remains operated over this brdge and maintains Ubr. Relay As2v opens the release circuit over 2, 5, Gtr (left), cam G to battery. If the wanted subscriber is engaged, the circuits remain in this condition until the manual operator withdraws the plug, whereupon Ucr falls back and releases As2r which completes the release circuit. If the wanted subscriber is free, the loop at the succeeding selector is opened and Cs2r releases. Sequence switch R now moves to position 14, and thence to position 16 when Cs2r re-energizes over the called loop. Energization of Cs2r closes the circuit of Glr which opens the previously traced bridge and releases Uar, Ubr, Fig. 1. After leaving position 15, the circuit of Glr is opened at O so that the bridge closes again and operates the supervisory relay of the manual operator's cord. Second arrangement. The apparatus shown in Fig. 1 is not used and the manual operator's cord is arranged as shown at the left of Fig. 2, the cross connections at the frame in Fig. 3 being altered as shown at A or B according as to whether supervision, is over the a- or b-wire. The following description applies to the connections shown at B. Relay As2r operates at the same moment as in the first arrangement but, instead of operating over a bridge, it operates over the awire, cam I, terminals 6, 4, relay As2r, terminals 3, 9, 10, contacts of Glr, terminals 15, 13, cam P, terminals 14, 8. The corresponding circuit over the b-wire and balancing impedance B1 includes the condenser shown below cam C so that the manual operator's supervisory relay is not operated. When sequence switch R moves to position 15 on reply of the called subscriber, a bridge is closed over cam 1, relay As2r, cam P, impedance B1 and cam K. The supervisory relay operates and the call is metered. If the line is very long, the bridge may be repeated at manual exchange by a relay Ls2r, Fig. 4.