Patent GB-191401970-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1914-01-24
Granted: 1915-01-25
Abstract: 1970. Automatic Telephone Manufacturing Co., and Sperry, A. B. Jan. 24. Automatic and semi-automatic exchange systems.- In a system in which connexions may be set up either by calling subscribers or by exchange operators, and in which the same connectors serve for completing both kinds of call the connector circuits are modified so that when the call is set up by a subscriber, the calling and called lines are supplied with current from feeding-bridges at the connector, in the usual way, but when the call is set up by an operator, these bridges are automatically cut out and a clean metallic circuit is extended through from the operator's position to the called line. The invention is specially applicable where the operator has to establish toll-line calls. The discrimination between the two kinds of call is effected at the connector by a relay 24, Fig. 3, controlled over the third-wire circuit 49, 43, which termimtes in a ground connexion 42, Fig. 1, in the case of a call established by an operator, but not in the case of a call established by a subscriber. In the system illustrated, ringing-current is supplied from the connector, and the relay 24 is energized only when the called subscriber replies, but according to the Provisional Specification the relay 24 may be energized immediately the connexion with the wanted line is completed, the line being rung in this case directly from the operator's position. Specifications 1298/10, 29,654/10, 19,253/12, and 5249/13 are referred to. Junction line busy signal. To extend a call from a subscriber A, Fig. 1, to a subscriber A<1>, Fig. 3, an operator plugs a cord C into a junction line leading to an idle selector D, Fig. 2, and operates her number sender, 5, Fig. 1. A relay 36 in the sleeve circuit lights the junction line busy lamps 40 and connects ground at 42 to the third wire of the trunk. Group selector and connector. In response to the first series of impulses, the selector D, Fig. 2, operates as described in Specification 10,376/12 to select a connector E, Fig. 3, the connexion being switched through by the relay 51, which is energized in a branch from the third wire circuit 43, 49. The second and third sets of impulses operate the connector in the usual way to select the wanted line. Busy test and signal. If the line is engaged, the private magnet 23 is kept energized in the usual way over the wiper 16 and side-switch arm 21 to lock the side-switch in its second position, and the busy relay 25 is energized and connects the audible busy signal Q to the calling line through the interrupter 26. In the intervals between the supply of busy tone current, the interrupter 26 connects the line 48 to battery through a resistance 27, intermittently energizing the supervisory relay 91, Fig. 1, which flashes the lamp 39. Supply of ringing- current. If on the other band the wanted line is idle, the side switch moves to its third position and energizes the relay 74. The wanted line is now connected through the interrupter 30 alternately with the ringing-generator 28 and with ground G". The ringing-circuit includes the right-hand winding of the self-lockiug ringing- cut-off relay 29, which does not respond to the alternating ringing-current but is energized by the direct current which flows when the called subscriber answers. Disconnexion of bridge circuits at connector. The relay 29 opens a short-circuit across the lefthand winding of the differential relay 24 and closes a contact in the circuit of the right-hand winding. If the connexion had been set up by a subscriber on the automatic exchange, current would now flow in series through the two windings of the relay 24, and the relay would fail to energize, but since the connexion has been set up by an operator, the lefthand winding is short-circuited over the wires 49, 43 and contact 42, Fig. 1, and the relay therefore becomes energized. The line 47, 48 is thus switched directly to the wipers 15, 17, the normal feeling-bridges through the relays 65, 66 being entirely disconnected. The release relay 32 is now de-energized, but the circuit of the release magnet 20 is held open by the relay 24. Supervisory signals : release. The called subscriber is fed with current through the supervisory relay 91 and inductance 90, Fig. 1. When he hangs up his receiver, the relay 91 de-energizes and lights the lamp 39, and the operater withdraws the plug P<1>. This de-energizes the relay 36, which open-circuits the reliy 24, which de-energizes and closes the circuit of the release magnet 20. Signalling failure of calling subscriber to clear his line. In the case of connexions set up by subscribers on the automatic exchange, release is effected in the usual way when the calliog subscriber hangs up his receiver, and a lamp 96 is lighted if he delays doing so after the called subscriber has hung up.