Patent GB-139701-A (GB)
Abstract: 139,701. Automatic Telephone Manufacturing Co., (Automatic Electric Co.). May 30, 1919. Automatic exchange systems; phantom - circuit systems. - Phantom circuit working over telephone trunks terminating in automatic switching-mechanism is facilitated, as regards the balancing of the circuits, by the use of tuned alternating-current relays to control the automatic switches, the alternating currents for operating these relays being passed in parallel through all four of the trunk conductors. General arrangement. In the system illustrated, the automatic switches at each end of two-way trunks are controlled by an operator at the other end. The four trunk wires are shown at 101 - - 104, the apparatus associated with the ends of the real trunks at M<2>, M<5>, M<4>, M<7>, and the apparatus associated with the phantom circuit at M<3>, M<6>. It will be seen that, at each exchange, the middle point of the trunk circuits (a point between the repeater coils 113, 114 at one exchange and between the coils 119, 120 at the other exchange) is connected to a three-branched circuit, each branch of which includes a condenser and inductance (such as 56, 57) and an AC relay (such as 52). When a key (such as K<4>) is pressed, a relay (such as 51) is energized which cuts out the A.C. relay and connects in its place an A.C. generator (such as 80); the current from this generator flows through the A.C. relays in the other two branch circuits at the same exchange, and also over the four trunk wires in parallel and through the A.C. relays in the three branch circuits at the other exchange, but the only relay energized is the relay at the other end of the particular trunk circuit to which the generator belongs; for example, the generator 80 will only energize the relay 152, 81 will only energize 153, and so on. For this purpose, the generators belonging to the different trunk circuits give currents of different frequencies (for example, generators 80, 180 may have a frequency of 200 cycles, 81, 181 may be 300 cycles, and 82, 182 may be 400 cycles), and the capacities and inductances in the different branch circuits are arranged to give resonance at the frequencies of the corresponding generators, so that the current in the resonant branch circuit as very large compared with that in the other branches. The A.C. relays have three limbs, two of which are wound with low-resistance windings in parallel, one of the windings having a condenser in series with it, and the local circuit formed by the two windings and the condenser may also be tuned, so as to increase the resonance effect. In a modified arrangement, this local resonance effect is relied on exclusively, the three branch A.C. circuits at each exchange being replaced by a single series circuit which includes the three A.C. relays and three transformers connected to the A.C. generators. The operators numerical impulse-sender S, Fig. 2, produces interruptions in the A.C. circuit, and the resulting de-energizations of the selected A.C. relay control the automatic switches of the corresponding trunk circuit through a repeaterset, such as E, Fig. 4. Calls over the same trunk circuits can also be dealt with manually; for example, the operator at the first exchange can, by means of ringing-key K<3>, Fig. 1, operate a dropsignal 162, Fig. 3, whereupon the operator at the second exchange plugs into jack T'; in this case, the trunk circuit is disconnected from its automatic switching-equipment bv a sleeve relay 150. Control of automatic switches by operator. It will be supposed that automatic switches are to be controlled over the trunk 103, 104 from left to right. When the operator presses key K<4>, Fig. 2, relay 51 is energized (and locks itself under control of sleeve relay 50) and generator 80 is connected to the A.C. circuit through the impulse-sender S, energizing relay 152 as described above. Relay 152 bridges a condenser in the outgoing side of repeater R<4>, so as to energize relays 210, 211 of the repeater set E, Fig. 4. Relay 211 bridges the outgoing circuit 242, 243 through an inductance 215, and relay 210 energizes a slowrelease relay 213. Relay 213 puts a busy potential on the sleeve of jack J' and open-circuits sleeve relay 150, so that if an operator, for supervisory purposes, disregards the busy test and plugs into jack J', relay 150 is not energized and the connexion between the trunk circuit and the repeating-set E is not broken. By means of the relays 152, 211, the interruptions in the A.C. circuit caused by the impulse-sender S are repeated as interruptions in the circuit 242, 243 so as to control the two-wire selective switches in the well-known way. At the first interruption, relay 214 is energized and energizes relay 212, which locks itself and disconnects the drop-signal 162. Relay 214 disconnects the outgoing conductors 242, 243 entirely from the incoming conductors 240, 241 during the passage of impulses. When all the impulses have been sent, key K<4> is opened, so as to free the sender S for use on other circuits; but a shunt path is closed at another contact of key K<4> to keep the A.C. generator circuit closed until the eventual de-energization of relays 50, 51 when the connexion is taken down. Specifications 26301/06, 1419/10, 29654/10, 2270/14, and 2543/14 are referred to.