Patent GB-395346-A (GB)
Title: Improvements in or relating to telephone systems
IPC: B60B33/06
Filed: 1932-01-11
Abstract: 395,346. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool. Jan. 11, 1932, No. 820. Convention date, Jan. 10, 1931. Addition to 366,143. [Class 40 (iv).] In a system of the kind described in the parent Specification in which, when all the normal A and B finders of a group are busy, overflow finders giving access to first selectors over secondary finders are taken into use, the following modifications are provided. (1) The secondary finders are two motion switches, are allotted by a chain circuit, Fig. 6, with a number of points of entry and arranged to give preference to the finder SF in which the calling finder OF appears on the first level, and hunt simultaneously with the primary finders. (2) Overflow finders OF, Fig. 5, in a number of different groups are multipled to a single set of terminals in the banks of the secondary finders SF. (3) Separate allotters are used for the normal and overflow finders. (4) The subscribers' line relays are of the so-called 3-pole type described in Specification 272,872 and cannot be operated by a ground on either or both line wires, and the finder test relays are of the same type and are arranged as polarized relays to prevent their operation by booster battery. Ordinary finder. Line relay 201, Fig. 2, makes marking and starting circuits for the preselected finder FA, Fig. 1. 163 in the common control circuit energizes 164 which energizes the start relay 106 and vertical magnet 109. 106 polarizes the switching relays 104, 105. The magnet interacts with the common stepping relay 166 until the vertical wiper 262 finds the marking ground whereupon a holding circuit is made for 166 over the lower winding of the change-over relay 165 which locks. The rotary magnet 108 then interacts with 166 until a calling line is found whereupon 104 or 105 pulls up in series with the cut-off relay 202, cuts the drive, switches through and kicks off the allotter. If two calling lines are found simultaneously, 104 and 105 are both energized but only 104 is locked. The driving magnet 161 releases 164 to release the remaining common relays and then continues to drive the allotter until wiper 147 finds a dead terminal. Overflow finders. When the last A-finder switches through, 162 falls and when the last B-finder switches through, 262 falls. When 162, 262 are both released, 290 falls, extending the start circuit to the overflow group, in which a primary finder OF, Fig. 3, selects the calling line in the same way as an ordinary finder. In this case however 303 (which otherwise corresponds with 106) energizes the starting relay 433 in the nearest idle secondary finder SF, Fig. 4, and puts a bridge across the talking wires to hold SF if it finds first. Vertical and rotary magnets 437,436 interact in turn with stepping relay 434, the change-over being looked after by 345. When the calling finder is reached the switching relay 430 or 431 pulls up in series with 304 in the primary finder. 304 opens the locking circuit of 303, holds switching relay 301 and the cut-off relay pending the relapse of 303 and then falls back. The transfer relay 432 is energized by 430 or 431 to extend the starting circuit, and remains looked while there is ground on the starting wire to prevent interference, when the finder becomes idle, with a call in process of being set up. When however all the transfer relays are operated, 471 pulls up and unlocks those belonging to idle finders. Faulty operation of finder. Start relay 163 energizes over one winding the differential relay 167 which sets the weighted springs 187, 188 into vibration. Later, the change-over relay 165 connects up the other winding of 167 instead of the first and 167 falls and pulls up again to set the springs 187, 188 vibrating again before 168 has had time to operate. On the relapse of the start relay, 167 is cut off. If the change-over relay fails to pull up or the start relay fails to fall back, 168 pulls up, lights a signal lamp and releases the busycommon relay 162 to enable the A subscribers to use the B-finders. Testing. Springs 113 provide a means for identifying the wiper set in use, the common lamp 175 glowing when the springs are operated if 104 is not energized. Springs 192 are for routining, their operation so that all are connected together causing the A-finders in turn to move to an extreme position on the 5th level and then drop back, and their operation so that only the upper pair make contact releasing 162 and causing the B-finder to operate in a similar manner. If the central spring is isolated, the A-half group is withdrawn from service.