Patent GB-491878-A (GB)
Title: Improvements in automatic switches for use in telephone or like systems
IPC: H04Q3/42
Filed: 1937-03-11
Abstract: 491,878. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., BEALE, C. E., and RICHARDS, I. T. March 11, 1937, No. 7219. [Class 40 (iv)] In a group selector, in the event of all the outlets of a selected group being busy, the busy signal is withheld for a predetermined period which is timed by an individual timing device and the selector may seize any line which becomes idle during that period. The invention is applied to a third trunk selector giving access to long-distance junctions, the wanted group being determined by the third digit keyed by the operator, and the selector is of the bidirectional type described in Specification 391,123 in which normal release is effected by renewed operation of the rotary magnet. In the first arrangement in which a group is confined to a single level, the selector hunts repeatedly over the group at timed intervals, while in the second arrangement in which a group comprises several levels, the selector waits in the set position until an outlet becomes idle before hunting. First arrangement, Figs. 1, 2. Line relay A energizes over the loop while CS energizes over wire S and connects up release relay B and dialling relay C, whereupon the vertical magnet VM responds to impulses in the usual manner. Assuming that hunting is to take place over the whole group, differential relay DF responds to the unbalancing of the loop in the register-sender, the operator having keyed the fourth digit 1, and connects up TA (middle winding) and AR, and the latter locks. The slow release of C closes a selfinterrupting circuit for the rotary magnet RM in parallel with the left winding of test relay TA, which is maintained over its right winding and wiper P as long as busy outlets are passed over. On an idle outlet, TA falls back and connects up H, HX to effect switching through. Relays A, CS, B relapse, while C reoperates in order to control subsequent release. In the 11th position, if no idle outlet has been found, TA falls back and the operation of cam springs S connects up C, SR, and the latter extends earth over wiper PS to light a busy lamp associated with the group. Relay A falls back when the register sender releases, but CS, B, AR remain operative, and TA energizes in a fresh circuit. A circuit is made for relay SO which operates after a period determined by a dashpot and connects up RL, which disconnects SR and short-circuits C, so that after an interval the vertical magnet VM operates to effect rotary release in the manner described in Specification 391,123. Relays RL, SO now relapse and the hunting operation is repeated. A switch SS advances one step at each operation of RL and, after a predetermined number of searches have taken place, CO energizes over a connection between its bank and terminal 13, opens the circuit of SO and applies busy tone to relay A and busy flash to wire S. If an idle outlet is found in the course of a re-search, the switch SS immediately homes by interaction with CO. Selection of a subgroup or of a particular outlet. The release of C after the vertical movement connects up CR, E to transfer the impulsing circuit to the rotary magnet RM, which now responds to the fourth digit keyed by the operator. At the end of the digit, C, CR relapse in turn, connecting HS momentarily to wiper P1 and making a circuit for test relay TD which is already connected to wiper P. Relay HS energizes to battery if the outlet is the first of a subgroup and locks locally, while if this outlet is idle, TD energizes and connects up H, HX, whereupon C reoperates and disconnects E, HS. If, on the other hand, TD is short-circuited over wiper P1, the relapse of CR disconnects E, and the re-operation of C closes a fresh circuit for the rotary magnet RM, which now interacts with G (upper), a test circuit over TD and G (lower) being made at each step. When an idle outlet is reached, G holds in series with TD which connects up H, HX as before. If the whole subgroup proves busy, on the last outlet G holds to earth over wiper P1, and on the relapse of HS busy tone is sent back. If the outlet selected by the fourth digit is not the first of a subgroup, HS is inoperative and E is held after the relapse of CR, so that TD remains connected to wiper P, and operates when the outlet becomes idle. The increased resistance connected to wire S darkens the supervisory lamp when switch through occurs. Second arrangement, Figs. 3, 4. Relays A, CS, B, C energize as in the first arrangement, and, after the vertical setting is complete, the response of differential relay DF to the unbalancing of the loop brings about the operation of TA and AR, the latter connecting up AX. Relays GF, RC are now connected to the two vertical wipers VW. The left-hand bank contacts of the levels comprising the group are multipled to battery as long as an idle outlet exists, while the right-hand bank contacts of the levels containing idle outlets are individually connected to earth, except for the last level of the group, the bank contact of which is earthed permanently. If there is an idle outlet therefore, GF operates and short-circuits its high resistance winding to prevent operation of the GF relay in any other selector. If there is an idle outlet in the first level of the group, RC operates and the relapse of C makes a selfinterrupting circuit for the rotary magnet RM, and test relay TA falls back when an idle outlet is reached, as in the first arrangement above. If however there is no idle outlet in the first level, the relapse of C makes a selfinterrupting circuit for the vertical magnet VM which is maintained until a level is reached on which RC operates, whereupon hunting takes place over that level. Should all the outlets become busy during the vertical search (due to seizure of two-way junctions from the distant end), the selector hunts over the last level to the 11th position in which CO energizes over cam springs S and connects busy tone to the loop and busy flash to wire S. If GF fails to operate, the selector remains in the set position for a predetermined period for an outlet to become idle. This period is timed by a switch SS which is controlled by time pulses over wire 14 and which, on reaching a position wired to terminal 13, closes a circuit for CO to give the busy signal. The operator may set the selector on a particular outlet by keying the appropriate third and fourth digits as in the first arrangement above: