Patent GB-191213971-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1912-06-15
Granted: 1913-06-16
Abstract: 13,971. Automatic Telephone Manufacturing Co., [Automatic Electric Co ]. June 15. Automatic exchange systems. - Some subscribers of an automatic branch exchange are disabled from trunking to the main exchange while others are free from this restriction. For this purpose the lines 49, 50 at the outgoing end of the trunk are controlled by a relay 96, belonging to an impulse-repeating set F, and the energizing-circuit of the relay 96 is arranged to include a winding 15 of the calling subscriber's line-switch C. This circuit is of too high resistance for the complete energization of the relay 96, except in the case of those subscribers to whom trunk service is permitted and whose line - switches have the windings 15 shunted by resistances 103. The operations when a branch-exchange subscriber A makes a trunk call are as follows. When the subscriber lifts down his receiver, he is connected by a line-switch C, operating as described in Specification 1419/10, to a selector E, of which one level of terminals is allotted to trunks such as 49, 50, while the rest give access to local connectors. The first set of current-interruptions sent by the subscriber operates the vertical magnet 38 to raise the selector to the trunking level, and the side switch then moves to second position. The rotary magnet 39 is now energized over the side-switch arm 41, the springs of an interrupter relay 88, and the upper springs of the relay 47, and moves the wipers 35, 36, 37 on to the first set of trunk terminals. The side-switch magnet 42 is energized by the rotary magnet at the contact 89 and closes the circuit of the interrupter relay 88, which opens the circuit of the rotary magnet. If the first trunk is busy, the side-switch magnet remains energized over the side-switch arm 40 and testwiper 37, and the relay 88, which is now opencircuited at the contact 89, de-energizes and again closes the circuit of the rotary magnet to effect a second step. When an idle trunk is reached, the side-switch magnet is de-energized and moves the side switch to its third position, cutting out the rotary magnet 39 and completing the circuit of a relay 46, which cuts out the line-relay 45 and continues the line to the wipers 35, 36. The line-relay 91 of the repeater set F is now energized and energizes the slow-release relay 94, which completes a holding-circuit for the selector relay 46 and for the holding-winding 15 of the line switch C from ground G<8>, through the relay 96, test-wiper 37, side-switch arm 40, &c. If the subscriber A is one of those who are not provided with a resistance 103 in shunt to the winding 15, the armature of the relay 96 is only attracted so far as to join the springs 104, 105, and a circuit is closed from the signalling device M', through the springs 104, 105, 106, springs 110 of the relay 91, inductance 111, springs 98, 97 of relay 117, to the upper line-wire, and back over the lower line-wire and the lower winding of the relay 91. The subscriber thus receives a signal that he is attempting an unauthorized connexion. If, however, the subscriber's lineswitch has a shunt 103 to the winding 15, the armature of the relay 96 is fully attracted, breaking the above signal circuit by separating the springs 106, 105, and closing contacts 99 and 102. The wires 49, 50 are now connected through contact 99, inductance 111, contact 110, and contact 102, and the subsequent series of current interruptions are repeated to the main exchange by the line relay 91 opening the contact 110. During each series a slow-release relay 117 is energized, which short-circuits the inductance 111 and disconnects the lines 49, 50 from the condensers of the repeater set. At the main exchange the connexions are completed by selectors like the selector E and by a connector organized as in Specification 1421/10. Specification 26,301/06 is also referred to.