Patent GB-426224-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1933-12-18
Abstract: 426,224. Automatic and semi-automatic exchange systems. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and SUGGARS, L. C., c/o General Electric Co., Stoke, Coventry. Dec. 18, 1933, No. 35542. [Class 40 (iv)] In a small private branch exchange at which main exchange junctions terminate in hunting switches 3S, incoming and outgoing calls may be set up by an operator whose position is equipped with keys EK, JK individual respectively to the subscribers' lines and to the junctions. A subscriber requiring an outgoing call dials a digit which causes his line to be extended to the operator's position, the answering of the call by means of the key EK releasing the local switches. The operator sets up the wanted call by dialling over an idle junction, and a further action on her part causes the switch 3S to connect to the calling line. Alternatively, privileged subscribers may set up outgoing calls by dialling a digit which automatically seizes a junction and sets the switch 3S on the calling line. On an incoming call, operation of the key EK of the wanted subscriber causes the switch 3S to hunt for his line. For night service when the operator's position is unattended, each junction may be arranged to extend incoming calls automatically to a particular subscriber by operation of a key NS which starts the switch 3S and marks the line of the subscriber in question. Local call. Start relay P of an idle finder 2S is connected up over ST2 upon operation of common line relay J, the calling line being marked at g1 by the partial operation of twostep relay G over the loop. When the line is found, switching relay Q pulls up, extending the start wire to the next idle finder and connecting G in series with T. Line relays J, M are effective alternately and control different groups of finders over start wires ST1, ST2, the change-over being effected by relay N, which is of the same general construction as that shown in Specification 208,075, [Class 40 (iv)]. When connected up by J, it is locked mechanically by an auxiliary armature which is withdrawn by the operation of its second winding when M subsequently energizes on the next call. In the connector, which is of the type described in Specification 235,771, [Class 40 (iv)], line and release relays A, B energize and two trains of impulses are effective, relay C being up during both trains and Z being up during the second train, and the call is completed in the usual manner. The connector remains off-normal after release until it is next taken into use. Main exchange call set up by the operator. In response to the digit O, the connector is set to a position in which relay MB operates, sending back ringing tone and lighting the calling subscriber's lamp EL. The operator throws the corresponding key EK, connecting up relays DO, EF to connect her set to the line, the finder-connector link being released by the short-circuiting of relay T. The key JK of an idle junction is thrown, resulting in the operation of relays UU, NN, X, W and O, and the dial IS is operated to set up the desired call, CO which loops the junction being shunted by auxiliary springs BO. Operation of the junction connect key JC through the medium of RR causes the switch 3S to connect to the calling line, which is marked by key EK. Switching relay EE pulls up and extends the calling line to line relay AA which holds X. The junction engaged lamp GL lights and the operator restores keys JC, EK and JK. Upon release, AA and EE fall back, freeing the junction, and lamp GL is extinguished. The operation of the hold key HK when the key JK is restored enables the operation to control release by maintaining the junction loop independently of AA, holding relay X and connecting up lamp CL to give a clearing signal when AA falls back. Main exchange call set up by the subscriber. In response to the digit 9 the connector is set to a position in which relay MA operates. Busy tone is supplied over lead 24 if all the junctions are busy. Otherwise relay U, Fig. 4, of a free junction energizes over lead 25 and causes the switch 3S to hunt for the calling line, which is marked over lead 16 in bank 3S4. The junction engaged lamp GL lights, and the circuit of UU is opened. Relay Y energizes and connects up switching relay EE, which causes the calling line to be extended to the junction, over which further trains of impulses are repeated by AA, CC being up during each train. If release is unduly delayed, the operator may break down the connection by means of key ER, which disconnects EE and causes the switch 3S to step on. Incoming call. Ringing current operates relay W which lights the calling lamp CL and transfers the start lead 25 to the next idle junction. The operator throws the junction key JK to connect up relay UU, which extends the junction to her circuit and operates X. The key EK of the wanted line is thrown together with the junction connect key JC, which by means of RR causes the switch 3S to connect to the wanted line marked in bank 3S5 by the key EK, whereupon switching relay EE energizes and lights lamp GL. The operator restores key JC and rings by operating key RB. Upon reply AA operates and extinguishes lamp CL. Keys EK, JK are restored, supervision being given by lamp GL. The operator may hold the connection by means of key HK as described above, or may enter the connection for monitoring or toll-offering by means of keys EK, TO. A subscriber accepting a toll call is re-rung by means of key RE. Night service. When the operator's position is unattended, each junction is associated with a particular subscriber's line by means of key NS. The lead between points X is then omitted, but local and outgoing calls can be set up without interference. Relay W when energized by ringing current operates NC which initiates hunting of the switch 3S for the associated subscriber's line which is marked in bank 3S5 by the opening of contact nc1. Switching relay EE operates QA and connects FE to wiper 3S3. If the line is idle, FE energizes and applies ringing current, and FN operates upon reply and completes the connection. If the line is busy, ringing tone is applied over key NS to inform the subscriber of the waiting call, which is completed when the existing call is released. Should the calling party hang up before the call is answered, W remains looked, but is released after a definite period by a time delay circuit.