Patent GB-191229356-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1912-12-20
Granted: 1913-12-22
Abstract: 29,356. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. Dec. 20. Automatic exchange systems and apparatus. -A subscriber's individual switch or prelirninary selector C, Fig. 1, is arranged so that after a connexion has been released the wipers 22, 23, 24 remain on the terminals of the trunk through which the connexion was made, and the same trunk, if disengaged, is taken into use when the subscriber calls again. A constructional form is shown in Fig. 3. When the subscriber A, Fig. 1, lifts down his receiver, a circuit is closed over his line-wires 15, 16 through the line-relay 18, which closes a circuit through the winding 75 of a differential relay 17. If the trunk on which the wipers 22, 23, 24 are resting is idle, the relay 17 becomes energized and disconnects the line 15, 16 from the relay 18 and connects it through the common segments b, Fig. 3, and the wipers 22, 24 to the trunk wires 212, 213. The relays 41, 40 of the selector D then become energized in the usual manner and a holding circuit for the relay 17 is closed over the wire 87, wiper 23, wire 90, and springs 73, 74, 101 and 102. If however the trunk 212, 213 should be engaged, the relay 17 will fail to become energized, the effect of the winding 75 being neutralized by the winding 89, which receives current from the grounded wire 87 through the wiper 23, wire 90, and springs 73, 72. A branch of this circuit passes through the interrupter springs 21 to the stepping-magnet 20, which rotates the wipers 22, 23, 24 until an idle trunk is found, whereupon the winding 89 is open-circuited. The relay 17 then becomes energized and connects the line 15, 16 to the appropriated trunk. The connexion to the wanted subscriber is completed over circuits which are the same as in Specification 1421/10, the called subscriber's individual switch being put out of action by the energization of his cut-off relay 19, which disconnects his line relay from the line wires. When the connexion is released, the de-energization of the relay 40 opens the holding-circuit of the relay 17, which disconnects the line-wires 15, 16 from the wipers 22, 24, which remain on the terminals of the trunk 212, 213. In the modified arrangement shown in Fig. 4, the preliminary selector is provided with a two-position side-switch 190 ... 194, and the wipers 176 ... 179 are connected through slip-rings and brushes 180 ... 183. The operating magnet 185 has two windings 188, 189 and two armatures 186, 187. The winding 188 affects only the armature 187, which serves to release the side-switch from its first position by depressing the catch 208, but the winding 189 operates also the armature 186, which propels the selector. Both armatures also control groups of springs, as shown. The sideswitch is restored to its first position by a slowrelease magnet 210. The operations are as follows. When the calling subscriber lifts down his receiver, a circuit is closed over the linewires 15, 16 through the winding 188. The magnet 185 attracts its armature 187, and if the trunk 212, 213 is idle the side-switch trips at once to its second position, in which it (a) connects the line-wires 15, 16 to the wipers 176, 177, (b) connects ground G<17> to the wire 211 to mark the calling subscriber busy in the connector banks, (c) connects ground G<17> to the wiper 179 to mark the trunk 212, 213 busy to other switches, and (d) connects the restoring- magnet 210 over the wiper 178 to a circuit in parallel with the release magnet of the first selector. If, however, the trunk 212, 213 is already engaged, the terminal on which the wiper 179 rests is grounded, and as soon as the armature 187 is attracted a circuit is closed from the wiper 179, through the springs 222, 221, 224, 225 and the winding 189. The magnet 185 therefore attracts its second armature 186, and as the circuit of the winding 189 is thereby broken at the interrupter springs 222, 221 this action is repeated and the switch driven forward until an idle trunk is reached. As long as the switch is being propelled, the magnet 210 is energized from ground G<18> and holds the side-switch in its first position. When the wiper 179 comes to an ungrounded terminal the winding 189 is open-circuited, and shortly afterwards the magnet 210 releases its armature, allowing the side-switch to move to its second position. When the connexion is released, the magnet 210 is energized in parallel with the first-selector release magnet and restores the side-switch to its first position, the wipers 176 ... 179 remaining on the terminals of the trunk 212, 213 until the subscriber calls again.