Patent GB-284756-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1926-11-01
Abstract: 284,756. Automatic Telephone Manufacturing Co., Ltd., Passmore, W. O., and Flenley, A. E. Nov. 1, 1926. Automatic and semi-automatic exchange systems.-In a private branch exchange, internal connections are set up by the subscribers over selectors, but for calls to the main exchange, an operator is reached by dialling " O," the selector rotating to the 11th contacts normally used for a busy signal, and when she replies, the seized switches are released, and the connection completed over her cord-circuit if the subscriber is entitled thereto. If the subscriber is not entitled to outside calls, the sleeve relay of his jack is of high resistance so that a marginal relay in the cord cannot operate to complete the speaking circuit even if the operator sets up the connection. For calls between P.B.X.'s over tie-lines, the subscriber dials a special number so that a special repeater is reached, and the wanted subscriber or the other operator is reached by dialling. The repeater is normally a connecting link between an incoming selector and the tie-line, but when it is reached by a subscriber the incoming selector is disconnected therefrom. The operator may answer or make a call over the tie-line through the repeater, the sleeve relay being of high resistance to prevent non-entitled subscribers obtaining outside calls over the tie-line. The cord-circuit is reversible, either end being used for answering. Call between extensions. When the subscriber in the P.B.X. lifts his receiver, his line relay 11, Fig. 1, operates over leads 1, 2, and the line switch hunts for a free selector. Relay 3 is also energized over armature 12, applying battery to busy the subscriber's calling jacks J1. J2 on the manual board. When a free selector S is found, relay 15 energizes to connect the line through. Dialling tone is sent back from lead DT and the connection is set up as usual. Successful outgoing exchange call. The subscriber dials " O," so that the selector S moves to the 11th contacts in the tenth level, operating post-springs 29 and cam-springs 30, 31. Relay 25 operates, connecting up ring-back tone RB, lighting call lamp 10, and disconnecting busy tone BT. The operator plugs into answering jack J3, and relays 5, 101, 103, Fig. 3, energize in series. disconnecting relay 3, Fig. 1, call lamp 10, and the selector S, so that the selector and lineswitch release. The operator ascertains the required connection by means of speaking key K2, and plugs into the required trunk, relay 112 only operating in series with the high-resistance trunk sleeve relay. The call is completed either manually or by means of dialling and ringing keys K3. K4. Unsuccessful outgoing exchange call. The relay 5 of a non-entitled P.B.X, subscriber is of high resistance, so that when the operator answers, only relay 101 operates in series therewith, so that the speaking connection remains open at armature 104. Connection over tie-line to another P.B.X. The subscriber obtains access over selector S, Fig. 1, to the repeater, Fig. 2. Relays 61, 64 energize and a loop is formed for tie-line 53, 54, [53. armature 63, right-hand winding of impedance 60, 59, lower winding of polarized relay 71, 70, 65, 54]. Relay 75 is also energized to busy jack J4 and to disconnect the leads 86. 87 leading to an incoming selector. The subscriber now dials the number of the wanted subscriber, and, on reply, relays 71, 56 operate due to reversal of line current, so that the whole of impedance 60 is cut in and the talking circuit is completed. If the calling subscriber does not know the number he requires, he dials " O " to call an operator in the manner described above over an incoming selector at the other P.B.X. Incoming call over tie-line. A loop is placed over leads 53, 54 to seize an incoming selector over leads 86, 87. Relay 79 operates over lead 88 to busy the repeater to the subscribers and to jacks J4. The connection may now be set up automatically. If, however, " O " is dialled, the incoming selector earths lead 89 to light lamp 90. upon which the operator plugs into jack J5, and sets up the connection manually, relay 82 being operated to complete the talking circuit. Outgoing call over tie-line by operator. The operator plugs into jack J4, energizing relay 82. and dials the required subscriber or the other operator. The Provisional Specification states that for a call to an operator, ring-back tone could be connected to the first contacts of the 10th level, and the lamp 20 lighted by operation of springs 29, relay 25 being dispensed with.