Patent GB-191202320-A (GB)
Title: Improvements in Automatic and Semi-automatic Telephone Circuits.
Filed: 1912-01-29
Granted: 1913-02-28
Abstract: 2320. Siemens Bros. & Co., [Siemens & Halske Akt.-Ges.]. Jan. 29. Automatic and semi-automatic exchange systems ; metering systems.-In systems in which a local call is interrupted in favour of a trunk or other preferred call, by circuit-changes effected by the trunk or other operator, the call relays and registers, which would usually be brought into operation when a call is commenced or ended, are prevented from being actuated. In the systems described, the local connexion is released by directly grounding the test lead of the wanted subscriber, thereby, if the subscriber is the calling party in the local call, short-circuiting the cut-off relay of his preliminary selector so that it returns to normal when the cut-off relay is again energized. If the subscriber is the called party in the local call, his cut-off relay remains energized, but an additional relay in the connector is shortcircuited and brings about the release of the connexion. In the system shown in Figs. 4, 5, and 6, the invention is described as applied to a system in which a local call is established through a preliminary selector VW, Fig. 4, group selector GW, and connector LW, Fig. 5, and is interrupted by a trunk operator through a special connector FLW, Fig. 6. A second system is described which closely resembles that described below. Preliminary selector. When a subscriber T removes his receiver, his line relay R<33> energizes the rotary magnet D<33>, which is cut off by the test relay Tr<33> as soon as an idle group selector is found. The test relay is first energized over the contacts r, i1 and the test lead c1, but locks up over contacts t1, i2, thus short-circuiting its high-resistance winding so as to mark the test lead c1 of the group selector, and also the subscriber's own test lead cf, engaged. The test wiper of the preliminary selector normally rests on a contact e so as to connect the test lead cf to the test relay. In a modified arrangement, the subscriber's line relay has two additional windings. Group selector. The group selector is then adjusted to select an idle connector by means of its line relays A, B, vertical and rotary magnets H, D, side-switch magnet S, and test relay P in the manner described in Specification 6654/10. The side-switch is shown in its fifth or conversation position. Connector. The wiring of the connector also closely resembles that of the connector in the prior Specification, the principal differences being the provision of a relay P3, connected to the test lead in the fourth and later positions of the side-switch, the relay P3 controlling the circuit of the line relay B2. The connector is raised and rotated by the vertical and rotary magnets H2, D2, and the sideswitch is brougbt into its third position as described in the above mentioned Specification. Busy test. The test relay Y is connected by the arm s17 to the test lead c55 and if the called line is idle, the relay Y and cut-off relay Tr55 energize in series. The side-switch magnet S2 is thus energized over contact y2 and interrupter U. Supply of ringing current. In the fourth position of the side-switch, the relay Y de-energizes and closes the circuit of the ringing-relay L over arm s23. The first call lasts until a slowly-moving interrupter U1 sends a further impulse through the magnet S2, moving the switch into its fifth position in which the ringing-relay L is earthed through an interrupter Co. In the fifth position of the arm s16, the relay Y is connected to the subscriber's b-line, so that when the subscriber replies current flows from the battery through an inductance Dr, arm s18, called sub-station, arm s16, and relay Y to ground. The closing of contact y1 sends a further impulse through the magnet S2, thus moving the side-switch into its sixth or conversation position. Normal release and metering of completed calls. During a conversation, the relay P3 is energized over the test lead c55 and maintains a circuit for the relay B2 over the calling line. When the calling or called subscriber hangs up his receiver, the relay B2 or Y, as the case may be, is de-energized so that a further impulse from the interrupter U passes over contact 12 or y2 to the magnet S2, thus moving the side-switch into its seventh position, in which the arm s19 connects the battery and relay Q to the test lead c3, thereby energizing the relays Q, Fig. 5, and P, Fig. 4. The relay Q brings the magnet S2 into a holding-on circuit, whilst the relay P connects the magnet S over the arms s<11>, s6 to the interrupter U, thus moving the side-switch of the group selector into its sixth position in which the metering-relay Z is connected over the arms s<11>, s6 to the a-side of the talking circuit, so that current flows through the relay Z, lead a2, as, arm s15 in its seventh position, contact 11, and relay B2 to earth. The relay Z is thus energized and short-circuits a resistance w1 in the test lead c1, thus increasing the current sufficiently to actuate the meter magnet ZR<33>. In the sixth position of the side-switch the magnet S, Fig. 4, is connected directly to the interrupter U, so that the next impulse causes the side-switch to move into its seventh and final position, in which the arm s7 connects the release magnets M, N to the back contact of the relay B, so that the group selector is released if, or as soon as, the calling subscriber replaces his receiver. In the seventh position the circuit of the test lead c2, c3 is broken, so that the relay Q, Fig. 5, is de-energized and opens the circuit of the magnet S2, which moves the connector side-switch into its eighth position, in which the arm s21 prepares the circuit of the release magnets M2, N2, which circuit is completed at y2 when the called subscriber replaces his receiver. In the seventh and eighth positions of the arm s15, the relay B2 is connected in circuit with the relay A2, thus opening the contact 12, so that the release of the connector cannot be effected by the calling subscriber only. Operation of trunk connector. The trunk connector shown in Fig. 6 is provided with means whereby the trunk operator is informed whether the line wanted for a trunk call is free, or engaged in a local call or in a trunk call. This is effected by using two test relays P4, Ps of different sensitiveness, which control the connexion of the tone signalling transformers FV, OV, Fr, to the speaking trunk. The connector is positioned by intermittently earthing the a-lead, these impulses being repeated by the relay As to the vertical and rotary magnets H3, D3. The side-switch magnet S3 is controlled by the relay B3, which is energized by applying battery potential to the b-lead. Trunk connector busy test. In the third position of the side-switch the relays P4, P5 are connected to the test-wiper cp. If the wanted subscriber is idle, both relays are energized over the test lead cg, c55, Fig. 5, contact e, normally engaged by the test wiper of the preliminary selector, high and low resistance windings of the cut-off relay Tr55 and contact k2 to ground. The relay P4 short - circuits its high resistance windin g so as to mark the lead c55 engaged. The excitation of both relays connects the tone transformer Fr to the relays As, B3, and the operator is thus informed that the wanted subscriber is free. If the wanted subscriber is engaged in a trunk call, the test lead is directly earthed by the arm s27 of some other trunk connector, so that neither of the relays P4, P5 are energized, the tone transformer FV being then connected in circuit. If the wanted subscriber is engaged in a local call, his test lead c55 is earthed over a relay P3 if he is the called subscriber, or over the low-resistance winding of his cut-off relay Tr55 and contact k if he is the calling subscriber. In each case the potential on the test lead is such as to energize the relay P5 but not the relay P4, thus connecting up the tone transformer OV. Release of the local connexion. To prevent the trunk operator from interrupting an existent trunk connexion, the side-switch magnet S3 is dependent in its third position upon a contact controlled by the relay P5, which is energized except when the wanted subscriber is engaged in a trunk call. If the wanted subscriber is not engaged in a trunk call, the operator moves the side-switch into its fourth position by energizing tt e relay B3, thus establishing speaking communication with the local subscribers over arms s25, s26. After informing them of the impending interruption of the local connexion in favour of a trunk call, she brings the side-switch into its fifth position in which the arm s27 directly earths the test lead cg. If the wanted subscriber was the called subscriber in the local call, this produces no change in the subscriber's circuit, relay Tr55 remaining energized, but the relay P3, Fig. 5, is short-circuited, and opens the circuit of the relay B2, which energizes the magnet S2, thus bringing the connector side-switch into its seventh position. The relay Q, Fig. 5, then energizes in series with the relay P, Fig. 4, and brings about the release of the connexion as previously described. The interrupted call will not, however, be metered owing to the interruption of the circuit of the metering-relay Z at the contact of the relay P3. If the wanted subscriber was the calling subscriber in the local call, the low-resistance winding of his cut-off relay Tr55 is earthed over contact k and is consequently short-circuited when the arm s27, Fig. 6, moves into its fifth position. The relay Tr55 is thus de-energized and allows the preliminary selector to return to normal, when the relay Tr55 is again energized by current over the contact k2, relay windings, and arm s26 to ground. The local connexion is thus interrupted at the preliminary selector so that the call is not metered. The selectors and connector are released as before.