Patent GB-197093-A (GB)
Title: Improvements in or relating to telephone exchange systems
IPC: H04Q3/00
Filed: 1922-02-24
Abstract: 197,093. Western Electric Co., Ltd., (Western Electric Co., Inc.). Feb. 24, 1922. Automatic exchange systems.-In a call-finder system in which a group of subscribers' lines served by a group of finder switches is divided into subgroups, means are provided whereby no subgroup can succeed in establishing more than one connexion until all calls simultaneously made in other subgroups have received attention. The invention is described as applied to a system in which the subscribers' lines are divided into groups of 300 lines, each served by a group of finder switches 200, 205 - - 225, Fig. 2, of the panel power-driven type having fifteen sets of brushes, each brush-set having access to twenty subscribers' lines. Each group of finder switches is divided into two half-groups A, B, and each brush-group of twenty lines is divided into two half-groups of ten lines, the multipling being so arranged that lines which appear as first-choice lines in the lower half of a brush-group in one group of finder switches A, appear as second choice lines terminating in the upper half of the corresponding brush-group in the other half-group of finder switches B, and vice versa. The lines are normally served by the half-group of switches in which they appear as first choice lines, but if these switches are all busy, an idle switch of the other half-group is taken into use. A first and a second choice line in the first two brushgroups only of the finder switches are shown in Figs. 1 and 2. Assuming a line 100 in the subgroup terminating in the lower half of the first brush group of the finders A, calls, the line relay 103 closes a circuit for a relay 105 common to this sub-group. The relay 105 locks up, energizes a relay 145 over conductors 114, 148, and completes a second circuit over conductors 115, 116 for the left-hand winding of a relay 110 which locks up over its right-hand winding in a circuit including the starting relay 146, which disconnects the left-hand winding of the relay 110 and completes a circuit 119, 150, 151, 152, 213 for the starting relay 209 of the first finder switch .200. The relays 145, 146 are common to the major group of 300 lines, whilst the relay 110 is common to the first brush group of 20 lines. The starting circuit for the relay 146 extends to the lower brush groups over a series circuit 117, 158, 162 including the inner righthand armatures of the brush group relays 110, 139, 144, so that when simultaneous calls occur in two or more brush groups the upper brush group is always given preference. If the first finder switch is busy, the starting circuit closed by the relay 146 will extend over contact 213 top to the starting relay of the next finder. Should all the finder switches in which the line 100 appears as a first choice line be engaged, a circuit is completed for the left-hand winding of a relay 203 to earth over the outer left-hand armatures of the busy relays 208 of all the finders in the half-group A. The starting circuit is thereby extended from the conductor 152 to a relay 204, which closes a starting circuit to the finders in the other half-group B over the lead 251. In a similar manner, when a line, which appears as a first choice line in the half-group B, calls, the starting circuit is extended over the lead 155, and if all the finders in this half-group are busy the relays 206, 201 are energized and a starting circuit is closed to the half-group A. Assuming, however that the first finder 200 in the halfgroup A is idle, the relay 209 locks up over its left-hand winding and closes a circuit for the updrive power magnet 236, the relay 110 having meanwhile completed the circuit of the common brush tipping magnet 237 and energized a brushgroup relay 111, which locks up and closes circuits for the right-hand windings of further brushgroup relays 108, 109. Relay 109 responds and interrupts the circuit of the relay 145, but the relay 108 remains inert, the flux created by its right-hand winding only being sufficient to hold its armatures once they have been attracted. When the centering brush 239 engages the segment 240, the right-hand winding of the relay 110 is short-circuited over the lead 117, its relapse de-energizing the tripping magnet 237 and connecting the lead 117 to the starting wire of the next brush group. On the tripped wipers 222 - - 226 reaching the calling line, the stopping relay 212 is energized in series with the left-hand winding of the relay 108 over the wiper 226 and the lead 113, the relay 209 deenergizing and disconnecting the power magnet 236 when the brushes are properly centred and the brush 239 engages an insulator segment. The sequence switch magnet 218 is now energized, and on advancing out of its normal position closes a circuit from battery over conductor 249, brush 224, and conductor 112, for the cut-off relay 104. Relays 103, 105 are now de-energized, the former opening the circuit through the left-hand winding of relay 108, which however is held energized until the circuit over its right-hand winding is interrupted on the relapse of the slow-release relay 111, which also opens the circuit through the right-hand winding of relay 109. After conversation, the finder 200 is restored in wellknown manner. If simultaneously with the line calling, a line, say the line 130, in the second brush group calls, the line 100 will be given preference as already described, but on the energization of the relay 109 following the response of relays 110, 111, the group relay 145 will not de-energize, since an alternative circuit 156, 148 is completed by the sub-group relay 135. When the calling line 100 has been found and the relay 111 relapses, the right-hand winding of the relay 109 is disconnected, but this relay remains energized over its left-hand winding, conductor 147, and the armature of relay 145, thereby holding open the circuit through the lefthand winding of relay 110 and preventing this relay from re-energizing should another call exist in the first brush group. The simultaneous call in the second brush group will therefore proceed, and if no call simultaneously exists in some other brush group, on the response of relay 137 the group relay 145 will relapse, open the holding circuit of the relay 109, and permit the relay 110 to energize and initiate the waiting call in the first brush group.