Patent GB-237852-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1924-04-24
Abstract: 237,852. Automatic Telephone Manufacturing Co., Ltd., and Ostline, J. E., (Automatic Electric Co.). April 24, 1924. Semi-automatic exchange systems. - In a system which includes repeaters, a busy lamp at a calling operator's position is caused to flash by the application of tone current or booster current to one of the line conductors if the wanted line is busy or otherwise unavailable, or if all the outlets are busy at any stage of the connection. This lamp also flashes when the operator throws her dialling key. An arrangement is also described in which a calling subscriber may signal a called operator by operating his switch hook. Specification 9593/13 is referred to. Manual-to-automatic repeater MAR, Figs. 1, 2. When the operator plugs into the jack J<1>, relays 200, 203 energize, the former lighting lamp L<2>, and the latter connecting up relay 205 and closing a bridge circuit across the trunk wires 228, 229 including winding I of shunt field relay SFR. Relay 205 connects up winding II of relay SFR. The operator's dialling key DK connects up interrupter F to flash lamp L<2>, and applies tone to her induction coil through relay P. Dialled impulses are repeated forward at contact 219, relay 204 operating at the first impulse to provide a direct bridge. If all the outlets are busy at any selector, busy tone current is connected to wire 229 and operates vibratory relay 207 to remove a short-circuit about relay 206, which connects up interrupter I to flash lamp L<2> through relay 201. In the case of a completed call, relay SFR operates upon reversal of line current and connects up relay 201 to extinguish lamp L<2>. In the modification when busy tone current and booster current are connected alternately to wire 229, vibratory relay 207 and condenser 209 are replaced by a marginal relay. Automatic - to-automatic repeater AAR and connector FS, Figs. 6, 7, 8. In the connector, relays 289, 288 energize during the last train of impulses, connecting up the upper winding of a two-step busy relay 287, which now attracts only armature 308. If the called line is busy, switching relay 290 fails to energize, and relays 289, 288 fall back, the latter removing a short-circuit from the lower winding of relay 287 so that it operates fully, closing a new circuit for relay 288 which connects busy tone and booster battery BT to wire 280. Bridge relay 266 in the repeater AAR therefore energizes, and repeats back booster battery over wire 262. Shunt field relay SFR<1> repeats back reversal of line current in the usual way. In the case of a faulty or unavailable line. battery is removed from the cut-off relay, and relay 287 is caused to operate as before, but relay 288 does not energize again since there is no ground on the test wiper, so that booster battery and number unavailable tone NUT are connected to wire 280. Interrupters X, Y are connected up as shown in the tone apparatus. Repeaters R<3>, R<2>, Figs. 9, 10. The repeater R<3> is suitable for use in any type of connection and has a relay 456 for repeating back a booster busy current, and means for repeating forward operations of a subscriber's switch hook. Line relays 453, 454 and release relay 450 energize, closing a bridge across the outgoing trunk, which is replaced by a direct bridge at the first impulse when relay 451 energizes. The repeater R<2> is described fully in Specification 233,007. Opening of the calling loop releases relays 453, 454, connecting relay 452 to wire 515<1>. The circuit of line relays 516, 517 is opened, but relay 517 remains locked at contact 525 and holds up the selector S<1>. Release of relay 516 connects battery to wire 515<1> and operates relay 452, which holds the switches C, S independently of releaserelay 450. Opening and closing of the calling loop now causes lamp SL to flash through relays 454, 516, 523. Relay 519 initiates release when the operator removes her plug.