Patent GB-451362-A (GB)
Title: Improvements in telephone systems and automatic switches for esutherein
IPC: H04Q3/00
Filed: 1935-02-04
Abstract: 451,362. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, TAYLOR, R., 30, Oulton Road, Wavertree, and BAKER, G. T., 31, Wharnecliffe Road East, all in Liverpool. Feb. 4, 1935, No. 3629. [Class 40 (iv)] In a bidirectional final selector having two sets of wipers in which wiper-switching is dependent on the route over which the selector has been seized, the two routes of access comprise the same negative and test wires with separate positive wires, and one positive wire includes the wiper-switching relay which is arranged to operate during the interdigital pause, being short-circuited at other times. If seized from a double-wiper group selector in a 4000-line exchange, the first digit chooses a set of wipers of the group selector and also determines the positive wire to be used. Alternatively, the final selector may be seized from two different groups of group selectors or from different levels of the same group selectors. The final selectors described with reference to Figs. 1, 2 (not shown), and Figs. 3, 4 are of the kind described in Specification 391,123 in which release is brought about by continuance of the rotary movement, and that shown in Figs. 3, 4 is adapted for P.B.X. hunting. Call to an ordinary line. Line, release and dialling relays A, B, C energize upon seizure, and the tens digit is repeated to the vertical magnet VM in series with C, the energizing winding of which is short-circuited when the selector moves off-normal. Relay E pulls up when C falls back at the end of the digit, transfers the impulse circuit to the rotary magnet RM and re-operates C by removing its short circuit. The short-circuit about wiperswitching WS is removed by E until the first rotary step is taken to enable this relay to pull up in series with A and lock if the selector is seized over the lower positive wire + 2. Relay C, the energizing winding of which is short-circuited during the rotary movement, falls back at the end of the units digit and disconnects E, and the wanted line is tested during the release period of the latter. If the line is idle, switching relay H energizes, and when E is back, J energizes and completes the ringing circuit, while C re-operates. Upon reply, ring-trip relay F pulls up followed by back-bridge relay D, the loop including a current-limiting resistance BR. The connections of line relay A are reversed, and E reoperates, locks and disconnects J, during the release period of which booster battery is applied to the test wire. Relay E is then unlocked. If the line is busy, H is inoperative and G energizes and sends back busy tone and flash. Upon release, relays A, B, C, F and H fall back and the rotary magnet RM operates in a self-interrupting circuit to advance the wipers clear of the bank, whereupon they drop and return to normal. Earth is removed from the test wire to free the preceding switches when B falls back and is re-applied when C falls back until the final selector reaches normal. Seizure during the unguarded period does not affect release since B can only energize in the normal position. P.B.X. hunting. Assuming that the wipers are set on the first line of a P.B.X. group and that this is busy, HS energizes over one of wipers P2 and connects G (upper winding) in series with H. When E falls back and C re-operates, a fresh circuit dependent on G is made for the rotary magnet RM which controls G (lower winding) at its interrupting springs. When an idle line is found, G holds in series with switching relay H which then releases G, HS. If all the lines of the group are busy, relay G (lower winding) energizes on the last line and disconnects HS which sends back the busy signal. The rectifier MRA prevents holding of G by metering battery.