Patent GB-215109-A (GB)
Abstract: 215,109. Aitken, W. Feb. 6, 1923. Automatic exchange systems; manual exchange systems.-In a small automatic private branch exchange, in which loop alternating-current ring- ing is employed, a subscriber's line, on making a call, is connected to an idle one of a number of connection-circuits with which is temporarily asso-- ciated an idle relay impulse-responder which operates to mark the wanted line, whilst simultaneously with the marking operation, a relay associated with the connection-circuit operates and so controls the test leads of all the connection-circuits that connection takes place between the called line and the connection-circuit to which the calling line is connected, the two lines being in parallel with one feed-relay common to both. Each line has a ringing-relay included in the marking-circuit, whilst the usual subscriber's line is made insensitive to ringing-current and acts as a ring-cut-off relay. The impulse-responder comprises a single chain of counting relays and includes an " impulse-clipping " relay which operates in parallel with each counting-relay and breaks, or puts a resistance into, the circuit of the next relay, so preventing any one impulse from operating more than one counting-relay. Outgoing calls to the main exchange are effected by dialling a particular digit which operates a counting relay at the end of the chain, the locking circuit of this relay including the operating winding of a connecting relay corresponding to the next idle outgoing trunk, which is thereby connected to the connection-circuit associated with the calling line, the impulse-responder being released. Incoming calls are established manually by means of a cord-circuit, in the sleeve circuit of which is included a relay which remains energized after the connection has been released at the main office but permits the trunk cut-off relay to de-energize and free the trunk, so that another call may be made on the same trunk. even though the local plugs may not have been taken down. In the system described in detail, relays are employed throughout the P.B.X., but a modification is referred to in which the connections between the subscribers' lines and the connection-circuits are established by providing each line with a 25-point rotary switch, the marking-circuit in this case effecting the starting of the called party's switch to hunt for the connection-circuit in use. Local call; connection to idle connection-circuit and seizure of idle impulse-responder. When the left-hand subscriber removes his receiver, his line relay R1 completes circuit 2 for relay R2 of the first connection-circuit (assumed to be idle). Relay R2 operates to connect the calling line to the connection-circuit, in series with the impulse relay R3. Guard relay R4 closes the locking circuit 5 for relay R2, in which circuit the cutoff relay R5 energizes, whilst relay R6 opens circuit 2 to mark the connection-circuit busy and prepares the control circuit 7 of the next idle connection-circuit. Relay R8, energizing in circuit 8, tentatively associates the first idle impulse-responder (shown on the right of the Figure) with the connection-circuit. Selection of wanted line (No. 22). The first impulse of the first digit is repeated by relay R3 over circuit 9 and operates relays R9<1>, R9<11>, in parallel. These relays are similarly adjusted so that both pull up together, relay R9" being adjusted to open its contact y and lock up over circuit 10, an instant before it closes contact x, so that when the latter contact is closed to extend the impulse circuit to relay R18, the presence of resistance r prevents relay R18 from operating. As soon as the first impulse passes over circuit 9, relays R9, R13, R11 operate, the latter closing the circuit of relay R14 which locks up in series with relay R15, causes the exclusive seizure of the impulse-responder by opening circuit 8, and pre-selects the next idle impulse-responder by closing circuit 17. The second impulse is repeated over circuit 9 to operate counting-relay R18 in parallel with relay R9<1> which clips the impulse as before. At the end of the first digit, relay R9 de-energizes and closes circuit 19 leading to a relay R19' which forms part of a " marker " comprising a multiple relay unit of the kind described in Specification 181,134. Marginal relay R19 does not energize in this circuit, but relay R19<1> locks up and connects its armatures to the multiple bars 1 - - 6. The impulses of the second digit are repeated over circuit 21 and operate relay R18 again. Relay R20 being now operated, the relapse of relay R21 at the end of the digit completes circuit 24 which includes bar 2 of the marker and extends to and marks the wanted line. Relays R19, R24 energize in this circuit the former closing circuit 25 in which " admitting " relay R25 operates and re-connects ground to circuit 2 whilst opening circuit 7, so that relay R29 energizes in circuit 29 to connect the wanted line to the connection-circuit. The release of relay R22, which was operated during the final series of impulses and caused relay R26 to lock up, completes circuit 28 in which relay R28 operates to unlock all counting-relays and restore the impulse-responder to normal. Ringing arrangements. Ringing relay R24, operated in marking-circuit 24. connects ringing- lead 31 in series with line relay R31 to the substation line. When the called subscriber replies, line relay R31 energizes to trip the ringing and to unlock relay R24 which, on de-energizing, causes the cut-off relay R33 to energize in the locking-circuit of connecting-relay R29. Both subscriber's lines receive talking-current over the common feed-relay R3. Busy signal. The operation of the cut-off relay R33 opens contact 24<1> so that, in the case of a call to a busy line, the marking circuit is not completed, relay R19 does not energize, but relay R34 operates in circuit 34 and connects up busy tone over circuit 36. Call to main exchange. In the example shown, this is effected by dialling the digit 8 causing the operation of counting relay R37 which locks over circuit 38 in series with the operating-winding of the connecting-relay R38 of the first idle outgoing trunk 39. Relay R38 connects the trunk 39 to the connection-circuit in use, and energizes relay R40 which extends circuit 41 of the next connection-circuit to the corresponding connecting-relay R41 of the next trunk. The holding winding of relay R38 is shunted by a resistance or a condenser and is included in one wire of the loop. The closure of contact 42 of relay R37 operates relay R28 and the impulse-responder is released as before. Incoming call established manually. Upon the insertion of a plug A into the jack J<11> of an incoming trunk 44, relay R46<1> energizes in series with cut-off relay R46 and prepares circuit 47. Plug B is then inserted in the jack J<1> of the wanted line, relay R48 operating in the sleevecircuit and relay R49 in the talking-circuit. At the end of the conversation, the freeing of the connection at the main office causes the de-energization of relay R49 which completes circuit 47 in which relay R47 operates and lights clearing lamp L50. Relay R47 also maintains relay R46<1> energized whilst disconnecting relay R46 so that the trunk is free for another call, although the local plugs have not been taken down. Disposition of impulse-responders and markers. The Provisional Specification refers to a larger system for example, for 400 lines, in which there are seven impulse - responders available amongst four groups of lines, there being one responder to each group, an additional one to each pair of groups, and the remaining one in common to all four groups. A number of markers may be common to a number of impulse-responders, and, in a further modification, the hundreds relays may be associated with each responder whilst the tens and units relays are used in common, there being, for example, three sets to seven impulse-responders. The Provisional Specification also refers to Specifications 178,783 and 204,118.