Patent GB-165796-A (GB)
Abstract: 165,796. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Madsen, F. T.). July 3, 1920, [Convention date]. Automatic and semi-automatic exchange systems.-Two-way trunks between main and branch exchanges terminate at both ends in selector repeaters, and at the main exchange are also connected to jacks, the arrangement being such that in the normal condition of the circuits, as shown in the Figures, the selector at the incoming end of a trunk, for a call in either direction, can only be operated by the main-exchange operator, but by making certain simple alterations in the circuits this restriction can be removed and a call in either direction can be set up completely by the calling subscriber. The alteration necessary for this purpose consists in disconnecting a pair of terminals 96, 97 and connecting a pair of terminals 94, 95, these terminals forming part of the repeater set E, Fig. 2, at the main exchange. Certain special lines at the branch exchange are not directly accessible to local subscribers ; to obtain connection with such a line a subscriber must call the main-exchange operator, who then completes the desired local connection over the branch-exchange connector belonging to the trunk over which she was called, this trunk remaining engaged during the connection although not carrying talking currents. Interexchange dialling takes place in all cases over a simple circuit including the two sides of a trunk 50, 51 in parallel. The branch exchange is assumed to have a capacity of 100 lines. Calls to branch exchange originated by mainexchange operator. The operator plugs into jack J energizing relay 68 in the sleeve circuit in series with her impulse sender. Relay 68 energizes relay 67, which grounds the busy wire 56<1> to light lamp L<@> and energizes relay 101 to cut off the trunk frcm its incoming selector. At the same time a simplex impulse circuit is closed by contacts 91, 88 over wire 93 and the two sides of the trunk in parallel to energize relay 15, which energizes relay 14 and closes a circuit 37, 27, 9 for controlling the branch exchange connector, to which number-impulses are now repeated by relays 68, 15. When the called subscriber answers, relay 19 is energized over the wires 8, 10 and the called line and energizes relays 12, 13. When the called subscriber disconnects himself, relays 19, 12, 13 de-energize in turn, and in the interval preceding the relapse of the sluggish relay 13 ring- ing current from a generator G is connected across the trunk 50, 51 to give the operator a disconnect signal. The connection is released when the operator takes down her cord. Calls to branch exchange originated by main exchange subscribers. The calling subscriber obtains access to an idle trunk over selector terminals 52, 53, 54, energizing relays 66, 65. Relay 65 grounds the busy wire 56', energizing lamp L<2> and relay 101, and lights the outgoing call lamp L. The simplex trunk circuit is completed over contacts 85, 83 and wire 93, but since contact 85 is short-circuited by the wire joining terminals 96, 97 the calling subscriber is unable to transmit impulses to the branch exchange. He can be freed from this disability by disconnecting terminals 96, 97 and can then set up the connection without the aid of the operator. As it is, the operator answers the signal L by plugging into jack J, energizing relays 68, 67, so as to transfer the simplex circuit 93 to the control of sleeve relay 68 at contact 91, and completes the connection as before described. She may then withdraw the plug, leaving the connection under control of relay 66. Calls from branch exchange to main exchange. The branch exchange subscriber raises his connector to its tenth level, on which it acts as a selector to find the terminals 2, 3, 4 of an idle trunk, whereupon relay 19 is energized and energizes relay 17, which energizes relays 12, 13 and completes a simplex trunk circuit through relay 16 and wire 36. Relay 62 is energized at the main exchange over wire 93 and energizes relay 61, which grounds the busy wire 56<1> and energizes the incoming call lamp L<1>. Relays 61, 62 prepare a circuit 71, 74, 94, 95, 73 to bridge the condenser in the repeating-coil R<1>, so that if terminals 94, 95 were connected, the line relay of the incoming selector would be energized and the calling subscriber would be able to set up the connection unaided, his impulses being repeated by relays 19, 62 to the incoming selector. In that case, a relay 18, Fig. 1, would be energized during each set of impulses to substitute a resistance 38 for the upper winding of relay 19 in the calling circuit (producing a control circuit less susceptible to line leakage than a circuit having both windings of the line relay across the line) and to substitute resistance 38 for relay 16 in the simplex circuit (preventing operation of the local connector over wire 9). As it is, however, terminals 94, 95 are disconnected and the calling subscriber is unable to operate the main-exchange switches. The operator answers the signal L<1> by plugging into jack J, energizing relays 68, 64, and having ascertained that a main-exchange connection is required plugs an idle cord into an auxiliary jack J<1>, energizing relay 63, which connects relay 62 in parallel with itself in the sleeve circuit and completes a bridge 71, 74, 77, 73 across the repeating-coil condenser so as to energize the line relay of the incoming selector. Relay 62 controls this circuit in response to impulses in the sleeve circuit of jack J<1> to set up the wanted connection. When the calling subscriber disconnects himself, relays 12, 13 operate as before described to give the operator a supervisory signal, and she then releases the connection by withdrawing the plugs from jacks J. J<1>. Special calls local to branch exchange but requiring intervention of main-exchange operator. The, special lines may be connected in the tenth level of the incoming connectors at the branch exchange. A branch exchange subscriber desiring connection to such a line calls the main-exchange operator as described in the preceding paragraph, and the operator plugs into jack J. Relays 12, 13, 16, 17, 19, Fig. 1, and 61, 62, 64, 68, Fig. 2, are now energized. Impulses are produced in the sleeve circuit of jack J and are repeated by relay 68 in the simplex circuit 90, 79, 83, 93 to control relay 16, which repeats them over wire 9 to control the incoming connector. The calling and called lines both receive current through relay 19. Disconnection is signalled to the operator by relays 12, 13 as before described, and the connection is released by withdrawing the plug frcm jack J.