Patent GB-184551-A (GB)
Abstract: 184,551. Western Electric Co., Ltd., (Western Electric Co., Inc.). May 5, 1921. Automatic exchange systems.-In a selector of the multiple-brush power-driven type in which the brushes move in one direction over bank contacts arranged in panel form, each group of terminals over which hunting takes place is provided with a set of multipled overflow terminals with which the brushes engage when all the outgoing trunks of the group are busy. These overflow terminals are not marked busy when the brushes come to rest upon them, so that any other set of brushes also engaging its multipled set of over-flow terminals is also stopped thereon, thus preventing a wrong connection from being set up by a set of brushes passing on to hunt in the next group of terminals having a different numerical significance. A special commutator strip included in the circuit of the test brush consists of conducting segments electrically con. nected together but arranged with gaps between the segments, so that an auxiliary brush on the main brush shaft closes or opens the circuit which marks the selected set of terminals busy according as the brushes are resting upon a set of terminals leading to an outgoing trunk or upon the overflow terminals. The invention is described with reference to a second group selector, Fig. 2, to which a subscriber 100, Fig. 1, has obtained connection through a manual exchange 102 leading to an automatic exchange operator and a first group selector 106, 107, 108, the required number having been set up on an operator's keyboard set and transferred to the register-controller shown diagrammatically at 116, 117. Normal operation of the sytem when an idle line in the selected group is available. When the brushes 106, 107, 108 of the first selector have seized an idle second group selector, the line relay 201 energizes in a circuit 263, 207, 106, 116, 107, 209 to drive the sequence switch 200 into its 2nd position in which the up-drive magnet 211 is energized to raise the brush shaft 246 to determine the tripping of the proper set of brushes. The movement of the grounded brush 221 over the commutator strip 213 causes the intermittent short-circuiting of the fundamental circuit 106, 107 and after the required number of impulses has been sent back, the opening of the fundamental circuit at the relay 117 of the register de-energizes the relay 201 to stop the brushes and drive the switch 200 into its 3rd position. The relay 201 again energizes over the fundamental circuit to drive the switch 200 to its 4th position in which the up-drive magnet 211 is energized to raise the selected set of brushes 227, 228. 229, which are tripped by the magnet 210, to the desired group of terminals B, under the control of the brush 222 and commutator strip 215 which intermittently short-circuits the fundamental cricuit. At the end of this series of impulses the opening of the fundamental circuit at the relay 117 de-energizes the relay 201 to move the switch 200 to its 5th position in which the relay 201 energizes in a local circuit over contact 203 to drive the switch 200 to its 6th position. If the first trunk on which the brushes are standing is busy, the test terminal 232 is earthed and the relav 201 remains energized over a locking circuit 208, 216, 223, 229 and earth to energize the up-drive magnet 211 which raises the brush to hunt for an idle line in the group B, the relay 201 remaining energized as long as earth is found on the test terminals 232, a holding earth circuit, being supplied between the positions of contact with the test terminals by means of the commutator strip 214 and brush 220. When an idle trunk 250, 251, 252 is reached, the relay 201 de-energizes and (1) stops the brushes, (2) marks the test terminal 252 busy over a circuit 266, 208, 216, 223, 229 and (3) drives the switch 200 into its 7th position in which the earth connection 266 is replaced by earth at contact 205. Relay 201 now energizes and locks up over contacts 206, 114, driving the switch 200 into its 8th position in which the talking circuit is completed over contacts 207, 208. Release. When the calling subscriber hangs up, the manual exchange signals the automatic exchange operator who presses her release key to release the first group selector. The opening of the locking circuit of the relay 201 de-energizes the relay to drive the switch 200 to its 18th position in which the down-drive magnet 212 is energized. When the brush shaft reaches its normal position, the brush 222 engages a conducting segment 255 to drive the switch 200 to its 1st position. Operation when the selected group contains no idle trunk. If no idle trunk is found during the hunting operation of the brushes in the 6th position of the switch 200 as above described, the brushes continue to advance on to a set of overflow terminals 233, 234, 235 which are marked idle and stop the brushes. In this position of the brush shaft 246, the brush 223 rests on a gap between two conducting segments of the overflow commutator strip 216 and the circuit for earthing the test terminal is therefore open and the circuit terminal 235 is not marked busy, so that any other set of brushes 240, 241, 242 reaching the multipled overflow terminals 243, 244, 245 will also be brought to rest. A signal of the busy condition of the group may be given to the operator and the connection released in known manner. If it be desired that two or more groups A, B should have the same numerical significance so that the, brushes after finding no idle line in the group B shall proceed to hunt in the group A, the test terminals of the overflow sets may be marked busy by manually-operated keys 256, 257.