Patent GB-365032-A (GB)
Title: Improvements in automatic and semi-automatic telephone plants
IPC: H04Q3/00
Filed: 1930-07-08
Abstract: 365,032. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON, 33, Kungsgatan, Stockholm. July 8, 1930, No. 20684. Convention date, July 9, 1929. [Class 40 (iv).] Selectors used for both ordinary and preferred calls are adapted for the latter purpose by a preliminary setting to a particular position in which the test circuits are so changed that an existing ordinary connection may be interrupted. The particular position may be an additional position, e.g. one reached by dialling eleven impulses in which case the preferred-call operators will have special impulse senders ; or alternatively one of the ordinary positions of the selector may be reserved for this purpose and in this case in order to prevent the establishment of a preferred call by an ordinary subscriber a signal is sent back to an earlier point in the connection to prevent the completion of the connection except in the case of a call from an operator. In the system shown calls from a subscriber A and a toll operator EP, Fig. 1, are extended over a repeater and junction FL to a final selector, Fig. 2, at another exchange. The final selector is of the type described in Specification 259,562, [Class 40 (iv), Telephones &c.], comprising a single magnet CM connected at both its ends to battery and a series of interlocking armatures operated in succession in response to impulses by the successive application of ground to a series of tappings 1 .. 0, each armature on operation closing a set of contacts KS and on release changing over springs OK to transfer the impulse circuit to the next tapping point. The digit 0 is employed for adapting the selector circuits for breaking-in and when the selector is set to this position a signal is sent back over the junction FL which signal for a call from a subscriber A causes the shortcircuiting of the impulse-repeating contacts 1 of relay RA, Fig. 1. In systems employing two-directional selectors, the change-over of the test circuits is effected by a preliminary setting in the first direction, the selector being then released, or if the first position in the first direction is used as the special position release need not be effected. Preferred calls ; adapting final selector for breaking-in. Relay RA operating over circuit 6 energizes relay RK and completes a bridge across the junction FL including the upper winding of relay RD which operates relay RQ. Relay Aa, Fig. 2, operates over this bridge energizing relays K, D. Relay JBR energizes over the wire c from the operator's position EP and energizes relay SBR over resistance r1 at the same time making the junction busy to the group selector GV. The operator then dials the special digit 0, the impulses being repeated by relay RA over the junction to relay Aa. During the impulsing, relay RW energizes to short-circuit the upper winding of relay RD. The release of relay Aa at the first impulse energizes relays I, B, and at the end of the impulse the release of relay I connects ground over circuit 23 to tapping 1 of magnet CM causing the first armature to be attracted. Relay B is held and relay C operated over circuit 21. At the next impulse the operation of relay I releases the first armature which switches over springs OK1. Relay B releases but relay C remains locked over circuit 22. At the end of the impulse ground is connected over circuit 26 and springs OK1, OK2 to the second tapping 2 causing the second armature to be attracted. The remaining impulses operate in a similar manner and at the end of the tenth a circuit 27 is completed for relay JA which operates and energizes relay JE. After a pause, relays D, C, JA, release, relay D re-energizes and relay JE remains locked. Relay JA whilst operated short-circuits the conductors of junction FL releasing relay RD and energizing relay RY which connects the upper windings of relays Ra, Rb in series. Both operate and complete a circuit for relay RB which short-circuits. the impulse-repeating contacts 1 of relay RA. This operation is however ineffective in the case of a call from the operator since relay RB is unable to lock up owing to the operation of JBR but releases when JA releases. Establishing preferred call; called line free. The final selector is set in a similar way in response to a further digit and when relay D releases relay P operates and relay JG is connected over circuit 40 to the c-wire of the wanted line. If the line is idle relay JG energizes connecting up relay JD which removes a short-circuit from relay G and this also energizes connecting-up ring-back tone RJ over the called-side feed relay Ac. When relay C relapses relay JE is unlocked and ringing generator RG1 is connected over relay R to the called line. When the called party replies relay R operates unlocking relay P, and feed relay Ac energizes over the called loop energizing relay JF and releasing relay R. Whilst energized, relay R connects earth to the b-wire of junction FL releasing relay RD and energizing RY which connects Ra and Rb to the bwire. Relay Ra operates and energizes relay RM which connects earth to the b-wire of trunk EFL to operate a supervisory signal before the operator. Release. When relay Ac falls back, the upper winding of relay Aa is disconnected from the a-wire and the release of relay RD causes relay Rb to operate over the b-wire completing a circuit for relay RC which opens the a-wire from the operator. At the final selector, relay Aa releases and opens the circuit of JF but before this releases relay P reoperates. When JF releases the called subscriber is again rung so that the operator may converse with him. Release is effected by the operator opening the line circuit to relay RA. Called line busy. If the wanted line is busy in a toll call the c-wire will be directly earthed so that neither of relays JG, G will energize but a busy signal BT will be connected over relay Ac. If the wanted line is busy in a local call, relays JG, JD operate but not relay G. When relay C releases relays JA, JB operate and relay R is energized releasing relay P. Relay JA short-circuits the junction wires to transmit back a signal which is repeated by relay RB over the a and b wires to the operator. The operator may now speak to the wanted party over front contacts of relay JB. If the call is accepted she dials a digit of any value causing the release of relays JB, JE, and the completion of a circuit 72 for relay G which operates to directly earth the test wire so releasing the existing connection. Relay Ac operates and relay R sends back an answering signal. Ordinary call. Since relay JE is not energized, test relay JG is not connected up but testing is effected by relay G which only responds if the wanted line is idle. Ringing takes place in a similar manner but from a different source RG.