Patent GB-247647-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1924-11-17
Abstract: 247,647. Automatic Electric Co., and Lomax, C. E. Nov. 17,1924. Automatic exchange systems.-A subscriber's line terminates at the exchange in two branches over one of which his line is adapted to be extended to any line in the exchange, and over the other of which his line may be extended to a limited number of lines required at frequent intervals. The invention is described as applied to an automatic exchange system in which a subscriber A, Fig. 1, who is afforded special service, in addition to being provided with the usual impulse transmitter whereby he may establish connection with any other subscriber over one branch of his line and a train of switches such as C, E, H, Fig. 2, is provided with a set of keys K, Fig. 1, by means of which an individual switch b, Fig. 3, associated with the second branch 149, 150, may be operated to extend connection to any one of a limited number of lines which may 'be frequently required. The switch S is a single motion switch of the no-normal type and advances its wipers on retraction of its stepping magnet. Assume that the privileged party A desires to call a substation A<1> to which direct service is given, and that the key K<9> is individual to this substation. The subscriber A depresses the locking key K<9> without removing his receiver, thereby grounding a particular combination of three (viz. 39, 41, 45) of the seven-control conductors 39 - - 45 extending from the substation A to a relay group R<1> - - R<7>, Fig. 2, at the exchange, and energizing the relays R<1>, R<3>, R<7> in series with a switching relay 135, which grounds the test wire 138 and the conductor 152 and transfers the talking conductors 36, 37 from the branch leading to the subscriber's line switch C to the branch 149, 150 extending to the switch S, Fig. 3. The relays R', R<3>, R<7> apply ground to the thirteenth contact in the bank of the wiper 202, Fig. 3, over the conductor 109, and a relay 210 energizes over the grounded conductor 152, and closes parallel circuits for the stepping magnet 212 and a slow relay 211. The magnet 212 opens the circuit of the relay 210 which in turn de-energizes the magnet 212, which advances the switch wipers and again energizes relay 210. The alternate operation of the relay 210 and magnet 212 continues until the wiper 202 engages the grounded thirteenth contact, over which a relay 207 is energized, which opens the circuit of the relay 210. If the wanted line is idle, on the relapse of relay 210, the relay 215 energizes, locks up over its lower winding, grounds conductor 142 to energize the cut-off relav of the called line switch C<1> and mark the called line busy, connects ringing current from a generator G<1> to a special bell 95, Fig. 1, at the calling station to indicate that the desired connection has been established, and connects ringing current from a generator G to the called line. When the called party answers, a ring cut-off relay 225 locks over its lower winding, transfers the called line to the feed relay 227, and applies a special tone from an interrupter T to the called line to advise the called party that the call is from a special substation and that he must hold the line until the calling party answers. The relay 227 opens the circuit of the calling party's bell 95 to inform him that the called subscriber has answered. The calling subscriber then removes his receiver and draws talking current through the feed relay 230. which disconnects the identity tone T. If the wanted line is busy, ground on the test wiper 203 energizes busy relay 232 which locks up on the relapse of slow relay 211, and applies busy tone from the machine B to the calling line. As the bell 95 will not be rung, the calling subscriber will eventually remove his receiver and hear the busy tone. If the wipers of the switch S happen to be on the wanted line when the corresponding key K is operated, relay 207 is energized at the same time as relav 210 and opens the circuit of the last-mentioned relay before the stepping magnet is energized. When the key K is restored at the end of the conversation, relays R', R', R', 135 relapse. Relay 135 re-connects the calling line to the line switch C and unlocks relays 215, 225, which restore the circuits of the switch S to normal.