Patent GB-162297-A (GB)
Abstract: 162,297. Automatic Telephone Manufacturing Co. Ltd., (Assignees of Jacobsen, E.). April 26, 1920, [Convention date]. Automatic exchange systems.-When a calling line A at a branch exchange is extended by its line switch C to a first selector D, a switch C' associated with the selector D seizes an idle trunk 140, 141 to the main exchange. The impulses for the first digit operate the selector D and also a first selector at the main exchange. If the level to which these selectors are raised corresponds to a connection within the branch exchange, the trunk 140, 141 is at once released and the succeeding sets of impulses are forwarded to a. second selector and connector in the branch exchange over a local trunk such as 98, 85, 99; but if the first digit represents a main-exchange connection the selector D takes only a single rotary step, and subsequently acts as a repeater for repeating succeeding impulses over the main-exchange trunk 140, 141. Means are provided for giving a busy signal if all the outgoing trunks are busy when a call is made to the main exchange. Local call. When the selector D is seized, the line relay 52 energizes slow-release relay 53, which grounds wires 33, 110, energizes the polarizing-winding of relay 56, and energizes relay 58, which locks itself through a back contact of the rotary magnet 59. Relay 52 also bridges the wires 111, 112 through windings of relays 55, 56 so as to energize relay 102, which locks itself to wire 110 and connects the stepping-magnet 103 of switch C' to the test wiper 122. The switch C<1> advances until it finds the ungrounded test terminal of an idle trunk 140, 141, whereupon the switching-relay 101 is energized, disconnecting trunk wire 111 from relay 102, and energizing relay 130, which h grounds the trunk test terminals and disconnects ground from the starting-wire 133 of the group of switches C<1>. Ground will still be connected however to this wire at some other point, such as 142, as long as any of the mainexchange trunks are idle. The first set of impulses are repeated by relay 52 to the vertical magnet 61 and also over the trunk 140, 141 to the first selector at the main exchange. A slowrelease relay 54, energized in parallel with magnet 61, short-circuits the lower windings of relays 55, 56 to give the impulses a clean path over the trunk 140, 141. At the termination of the impulses, relay 54 relapses, and the rotary relay 57 and rotary magnet 59 co-operate in known manner to find an idle trunk in the selected level. At the first energization of magnet 59 the locking- circuit of relay 58 is opened, but this relay remains energized over wiper 92, the terminals engaged by this wiper being all grounded in the levels serving the second selector of the branch exchange. When the test wiper 91 reaches the ungrounded terminal of an idle trunk, the switching-relay 50 is energized and disconnects relay 52. Relay 53 then relapses, disconnecting ground from the wire 110 so as to de-energize relays 101, 102, 130, and in the momentary interval before the relapse of relays 102, 130 (which are of slowrelease type) ground is connected to magnet 103 to step the switch C<1> to the terminals of the next trunk. Call to main exchange. The operations are the same as those already described until the moment when the selector D takes its first rotary step, whereupon the relay 58 becomes de-energized, because all the terminals of the selector D in levels corresponding to main-exchange connections are blank. The circuit of the rotary valve 57 and switching relay 50 is thus opened at contact 80, bringing the rotary movement at once to a stop and leaving the line relay 52 in circuit, so that succeeding impulses are repeated at 'contact 69 over the trunk 140, 141. When the call is completed and answered, the reversal of current in the trunk 140, 141 energizes the polarized relay 56, which energizes the reversing relay 51. Busy signal when all trunks are engaged. If all the main-exchange trunks are busy there will be no ground connections to wire 133 and no circuit will be closed through relays 102, 55, 56 when relay 52 is energized. The switch C<1> therefore will not be set in motion, and when relay 58 relapses a circuit will be closed from the busy tone machine Q through the back contact and upper winding of relay 55, so that, by induction in the lower winding of the same relay, a busy tone will be impressed on the calling line. Non-numerical switching-arrangements. The Specification as open to inspection under Sect. 91 (3) (a) describes the circuits of a line switch of the no-normal type organized like the switch C<1>, so that when released it steps forward to the terminals of the next trunk to the one which it has just been occupying. In a system having first and second non-numerical switches, the second switches may be organized in this way, the first being of the usual type. This subjectmatter does not appear in the Specification as accepted.