Patent GB-388815-A (GB)
Title: Improvements in or relating to automatic switches for use in telephone or like systems
IPC: H04Q3/00
Filed: 1931-09-04
Abstract: 388,815. Automatic exchange systems. ASSOCIATED TELEPHONE & TELEGRAPH CO., 1033, West Van Buren Street, Chicago, U.S.A. Sept. 4, 1931, No. 24867. Convention date, Sept. 8, 1930. [Class 40 (iv).] In a final selector, the wipers are spaced two steps away from the bank and take a preliminary step automatically at the end of the vertical movement to operate contacts which transfer the impulse circuit to the rotary magnet. The group selector in the system described is of the kind in which the changeover relay serves as the rotary stepping relay. In both switches the release magnet energizes only momentarily to restore the wipers, the double-dog being latched until the normal position is reached. Group selector. When line relay 10 energizes, release relay 15 pulls up in series with change-over relay 20 (inoperative) and connects the vertical magnet 22 in series with itself. In response to impulses, release relay 15 is intermittently short-circuited, thus being slow to release, and allows the vertical magnet 22 to operate, while change-over relay 20 energizes at the first impulse and remains held by virtue of its circuit through relay 15 until the end of the train. Upon relapsing, relay 20 connects up the rotary magnet 41 which advances the wipers one step, whereupon a fresh circuit for relay 20 is completed over rotary off-normal contacts 37 and contact 42 of the rotary magnet to the test wiper 32, so that it serves as the rotary stepping relay. When an idle final selector is found, switching relay 25 being no longer short-circuited energizes and locks in series with relay 20 independently of contact 42, with the usual results. Final selector. Line and release relays 60, 63 energize and impulses are repeated to the vertical magnet 98, while relay 80 in series with release relay 63 pulls up at the first impulse as in the group selector. Relay 75 energizes over vertical off-normal contacts 97 and perpares a circuit for the rotary magnet 99, which is completed when relay 80 falls back, relay 75 being held meanwhile. The rotary magnet 99 advances the wipers a preliminary step to operate rotary off-normal contacts 101, whereby relay 75 is disconnected and the rotary magnet 99 is connected to the impulsing circuit. The final train of impulses are now effective, relay 80 being energized meanwhile and connecting relay 75 to test wiper 93. If the wanted line is busy, relay 75 energizes and locks as soon as relay 80 falls back, and a busy signal is sent. If the wanted line is idle, relay 75 does not operate, and switching relay 85 energizes when relay 80 falls back. Ringing takes place and ring cut off and back-bridge relays 70, 55 operate upon reply in the usual manner. Release. The release magnet 95 energizes when release relay 65 falls back, and a latch 115 holds the double-dog and operates contacts 96, thereby disconnecting the release magnet 95 and extending the release ground to slow-acting alarm equipment SAE. When the switch shaft returns to normal, the double-dog is unlatched and contacts 96 are restored. The release of the group selector is controlled in a similar manner.