Patent GB-139554-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M9/00
Filed: 1919-01-13
Abstract: 139,554. Shrivell, H. G. Jan. 13, 1919. Intercommunication systems; electric selectors.-The talking sets of the calling and called parties are connected in series with each other. and with the battery in the same circuit, over the home lines of the two parties. The talking circuit is connected to the common battery by the depression of a key, or the operation of a relay, at the called station when the called party replies to the call. In one system described, a switch at the called station automatically finds the calling- line. In the arrangements shown in Fig. 1, stations 1, 3 have manual selectors S<1>, S<3> for selecting the called and calling stations, whilst station 2 has pushes 36 for selecting a station to be called, and a step-by-step selector 30 operated by a magnet 32 for automatically finding the calling- line. Connexion between stations 1, 3 with manual selectors S<1>, S<3> for selecting called and calling stations. To call station 3, party 1 moves his switch S' to contact 3 and moves the key K<1> to its calling position, thereby closing a circuit through an indicator I<1> at his own station and bell G<3> at station 3. If the called line is free, the interruption of this circuit by the bell intermittently energizes the indicator I<1>; but if the called line is in use, the indicator I<1> is energized continuously over the home lines of the two stations engaged in the connexion. If the wanted line is free, the calling-party removes his receiver and releases the key K<1>, thereby connecting his talking set R<1>, T<1> across the home line 1 and the line 3 of the called station. The called party removes his receiver, moves key K<3> into the answering position, and rotates his switch S<3> until it .engages the calling-line, whereupon a circuit is closed through winding 13 of indicator A<3>, talking set at station 3, line 3, talking set at station 1, line 1, switch S<3>, and winding 23 of indicator A<3>. Current is thus supplied to both stations through the indicator A<3> at the called station, the talking currents passing through the condenser C. A receiver of the non-polarized type may be used. Connexion between stations 1, 2, of which station 2 has selector 30 for automatically finding' the calling-line. To call station 2, party 1 moves his switch S' to contact 2 and moves, key K<1> to its calling position, thereby closing a circuit through indicator I<1> at his own station and bell G<2> at station 2. Both parties then remove their receivers, and the called party depresses his answering-key K<2>, thereby completing a circuit for the magnet 32, which interrupts its own circuit and rotates the selector 30 until the wiper 31 engages the terminal of the calling-line, whereupon a circuit is closed over lines 1, 2 and both windings of the relay 37, which opens the circuit of magnet 32 to arrest the selector, and shortcircuits a resistance 26 to mark the line busy. If the station 2 originates a call, the depression of the key corresponding to the wanted line completes a circuit through the indicator I<2> and the bell at the called station, the talking circuit being completed when the key is partly released. In a modified system, the answering-key K<2 >is replaced by a relay, the circuit of which is closed at the called station when the subscriber removes his receiver. The circuit of the relay includes in series normal contacts of all the station-selecting keys, such as 36, Fig. 1, so that the circuit of the relay is opened at the calling-station by the depression of any key. According to the Provisional Specification, the same selector may be moved manually to select the wanted line, and automatically by a magnet to find the calling- line. Construction of selector. The motor magnet 32, Fig. 2, drives the ratchet-wheel 48 by a pawl 49 having an extension which interrupts contact 35 in the magnet circuit. The terminals 46 are mounted in the path of the wiper 31 on an insulating-ring 45 supported on pillars from the base-plate 42.