Patent GB-152063-A (GB)
Title: Improvements in or relating to electric selective signalling and like systems
IPC: H04M1/70
Filed: 1919-06-04
Abstract: 152,063. International Electric Co., and Baldock, F. R. June 4, 1919. Party-line systems and apparatus.-An electric selective signalling system particularly applicable for party-line, train-dispatch, and mine telephone systems comprises a selector switch at each station adapted in its selected position to close a circuit through a relay which connects the talking-set to line, the relay being also operable from the station itself when the selectors are in neutral position. The stepping and ringing current may be supplied from a control station or by magnetos at each out-station. Means are provided for calling the control station from an out-station, and thereby obtaining communication with other lines. Fig. 1 shows the circuits for two party lines AB, A<1>B<1>, each having control stations E, E<1> with intermediate cord circuits C. When subscriber No. 1 desires to call another station, say No. 2, on the same line, he depresses the key K1, thus energizing relays QB and 3 at the control station and supplying intermittent current from the pole-changer X to the line B through the contact 4. This current steps round all the selectors S, the circuit therefor being from line B, line 5, contact 6, arm 7, and stepping-magnet 8, to earth. At the calling-station this current also passes through contact 6<1>, springs 6<2>, 6<3> closed by the depressed key K1, winding 13 of relay N, bell I, to earth. The energization of the caller's relay N closes a hold-on circuit 15 at the contact 14, and also connects the receiver to the line 5 at the contact 17. When the caller removes his receiver from the hook 19, it completes its connexion across the lines 1, 5 at the springs 18, 19. As the selector switches rotate, the arms 7 at all stations are lifted off the contacts 6, 6<1> and the stepping- magnet 8 is transferred from line 5 to line 1. The caller then releases key K1 and presses key K2, thus energizing relay QA and connecting the source X of intermittent current to the line A, and thence to all the magnets 8. The caller watches the indicator on his own selector, and when it reaches the wanted number, he releases the key K<2> and depresses K1, thus supplying ring- ing current over line B, line 5, selector contact S, relay N, and bell I. This circuit is made only at the wanted station, and the energization of the relay N at that station connects the instruments to line. No other subscriber on the line can listen in, because all the selectors are moved from the neutral position and a subscriber is therefore unable to energize his own relay N by pressing his key K1, as the circuit therefor is broken at the contacts 6, 6<1> When the conversation is finished, the hanging up of the receivers momentarily short-circuits the hold-on coil 15 of the relays N at contacts 20, 21, and thus disconnects the instruments at the contact 17. The selectors are then stepped forward to neutral position by depressing the key K2. Operation of the keys K1, K2 by a third party produces a noise in the telephones across the line which may be utilized as a signal that the line is wanted for an urgent call. Suitable contacts may be provided on the selectors for enabling all the stations to be rung simultaneously. When magnetos are used at each station instead of a central pole-changer X, one magneto terminal is earthed, and the other connected to the key. When the key is not depressed, the magneto current is supplied to the line 1, and when the key is depressed the current is switched on to the line 5. The key also operates contacts 6<2>, 6<3>, as shown in Fig. 1, but the second key is dispensed with. When a subscriber desires to call a station on another line, he first calls the control station energizing the relay N0 and lighting a lamp L, The operator plugs in the jack J, opening the circuits of the lamp L and winding 15 and connecting the lines A, B to the cord circuit C. The key K3 is moved to the left and the operator hears the required number, and plugs into the jack J<1> of the wanted line. The key K3 is then thrown to the right, and the key K4 to the left. The latter key K4 acts in its left-hand position like the keys K1 at the out-stations, and in its righthand position like the keys K2. The required station on the line A<1>, B<1> is thus selected and rung. The operator then restores key K<4> to the normal speaking position and listens for the called party's answer. The key K<3> is then returned to normal and the parties are connected.