Patent GB-333928-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1929-05-22
Abstract: 333,928. Automatic Telephone Manufacturing Co., Ltd., and Gillings, C. May 22, 1929. Automatic exchange systems.-Relates mainly to the circuits of two-directional finder switches which are controlled by marking in each direction of motion, and which may have two sets of wipers. In the arrangement of Fig. 1, the same stepping relay G interacts with the vertical and rotary magnets VM, RM of the finder and with the rotary magnet R of the associated group selector, while the change-over relay T of the finder performs the functions of the release relay of the selector. In another arrangement, a stepping relay of the shunt-field type is provided for double-hunting. In the arrangement of Fig. 6, a differenteial wiper-connecting relay S is employed. The finders are arranged in three groups, those of the A and B groups being 100- point switches with a single set of wipers or with two sets of wipers hunting on five levels only, and those of the C group, which are employed when all those in the A or B groups are in use, being 200-point switches arranged for doublehunting or with a wiper-discriminating relay. Preselection of the finders is effected by means of allotting switches or by means of relays controlling chain starting circuits. Finders and allotters, Fig. 1. The finders of the A and B groups have their two sets of wipers arranged five steps apart, only one bank being used, or alternatively the two sets of wipers are arranged as usual, and the five upper levels are not used. On the initiation of a call, line relay LR energizes, marking the test terminal of the line and connecting earth to the start wire of the sub-group to operate relay AX and mark the vertical test terminal in bank VA. Relay AD energizes and closes circuits over wipers of the allotter FA1 to start a finder of the A group, in which line relay A and stepping relay G energize over wipers of the allotter, and the latter interacts with vertical magnet VM until vertical wiper VW reaches the marked level, when relay T pulls up and transfers the stepping circuit to rotary magnet RM, with which the stepping relay G then interacts. The calling line is marked by battery through cut-off relay CO, and test relays HA, HB are connected to test wipers P1, P2 so that one or other pulls up when the line is reached, and opens the energizing circuit of relay G. The test wire is grounded by relay T until the switching relay H of the selector S operates, the usual release relay being dispensed with. Cut-off relay CO energizes, line relay LR being held in series, and line relay A is connected to the calling line. The first train of impulses are repeated by relay A to the vertical magnet V of the selector S in series with relay C, and relay G reenergizes at the first vertical step, and when change-over relay C falls back, interacts with the rotary magnet R to effect the hunting movement. Relay AE energizes when test relay HA or HB operates and disconnects relay AD, and magnet DM1 of the allotter FA1 receives an impulse over wiper 18, and continues to advance the allotter until the nest idle finder is reached. If a finder is set in operation by a subscriber momentarily lifting his receiver, it steps vertically to the 5th level in the case of the A and B groups or to the 10th level in the case of the C group, and then rotates until it is clear of the bank terminals, when relay H energizes and connects up relay AE to restore the finder and to cause, the allotter to preselect the next idle finder. Modified finder. In another arrangement, stepping relay G is of the shunt field type, one winding being connected to each of the test wipers PI, P2 during the rotary movement, and the windings being connected in parallel during the vertical movement. It does not, however, control the hunting motion of the selector S. All finders of a group busy. Relay AB is operated as long as there are idle finders in the A group over parallel circuits. When the last idle finder is set in operation, relay AB remains held temporarily until relay AD falls back, and then relapses and prepares a circuit for relay AY, which by connecting up wiper 23 in place of wiper 18 causes the allotter FA1 to preselect an idle finder in the C group. Relays BB, BY in a similar way control the allotter FA2 to preselect an idle finder in the C group. If all the finders of the C group are in use as well as all those of either or both of the A and B groups, relay CB relapses and connects up either relay AZ or BZ or both. If a call is made when both these relays are energized, an overflow meter OM is operated. Relays AB, BB, CB control meters for recording the number of times all the findors of each group are in use, while relays AZ, BZ prevent unnecessary operation of the allotters FA1, FA2 when no finders are available. Assuming all the finders in the A and B groups to be in use, if a subscriber in sub-groups 1-5 calls, relay AX energizes and completes the circuit of relay AY, which locks, connects up relay AD, opens the circuit of relay BY to prevent its operation by a call initiated in sub-groups 6-10 and extends the sub-group marking wires to the five lower vertical bank terminals VC. Relay BY energizes in the case of a call in sub-groups 6-10 with similar results, except that the five upper vertical bank terminals VC are permanently connected to the corresponding terminals of bank VB. Arrangement of finders. In the arrangement described above, a finder of the C group must take more than five vertical steps to reach a calling line in sub-groups 6-10. This may be avoided in most cases by arranging the finders of the C group in two sub-groups (11-IS and 16- 20) in which the connections between the upper and lower halves of the vertical banks are reversed as in Fig 2, and reversing the order of choice by the allotter FA2 as regards each of the B and C groups respectively. Finders with only one set of wipers may be employed in the A and B groups, and in this arrangement when a finder of the C group is set in operation the sub-group marking wires may be extended to the vertical bank by relay AY or BY. Alternatively, the finders of the C group may have two vertical wipers corresponding to the two sets of wipers and two vertical banks multipled respectively to the vertical banks of the finders of the A and B groups, a wiper discriminating relay being energized or not according to the allotter by which the finder is taken into use; relays AY, BY are dispensed with, since there is no harm in two finders hunting simultaneously in different subgroups. The finders of the C group in the arrangement of Fig. 1 may be provided in this manner with two vertical wipers co-operating respectively with the upper and lower halves of the vertical bank. A simplified arrangement is referred to in which the C group is dispensed with, all the positions in the banks of the allotters being occupied by the finders of the group, and a spare allotter is provided for use if an allotter becomes faulty. Finders with relay preselection, Figs. 6, 7. A separate start relay AX is provided for each subgroup of lines, and this relay upon energization connects up line relay A of the preselected finder, and marks the apprcpriate vertical bank terminal. The circuits of the finder differ from Fig. 1 in regard to the test arrangements. A differential relay S (lower winding) energizes over test wiper P1 as the first rotary step, locks and connects test relay H to test wiper P2. If the calling line is encountered by test wiper P1, the shortcircuit around the upper winding of relay S is removed, and it relapses by reason of its windings being in opposition, connecting test relay H to test wiper P1. Relay H energizes with the usual results and also closes a circuit for relay HR which locks and extends the starting circuit at hr3 to the next finder. It will be seen from Fig. 7 that the starting circuit for each group of finders takes the form of a closed circuit to which earth may be connected at various points by the start relays such as AX. The finders are divided into sub-groups corresponding to the subgroups of lines, and slip multipling is employed between the levels of the sub-groups as in Fig. 8, so that the finders of each sub-group are first choice as regards calling lines terminating in their first level, second choice as regards calling lines terminating in their second level, and so on. Relays AB, BB, CB are adapted to energize when all the finders of the corresponding group are in use, and relays AY, BY control points in the starting circuits of the finders of the C group, which become effective when the start relays such as AX, BX are energized. Relays AY, BY cannot both be operated at the same time.