GB251385A - Improvements in or relating to trunk offering final selectors for use in telephone systems - Google Patents

Abstract

251,385. Standard Telephones & Cables, Ltd., and Lowry, L. P. Feb. 25, 1925. Automatic and semi-automatic exchange systems.-A trunk-offering connector if the wanted party is idle rings him at once and if he is busy connects him to the operator's set. If the call is accepted both parties in the local connection hang up and the party wanted for the long distance call is immediately re-rung by the connector which on his reply completes the connection in the usual manner. Signals are given to the operator at each stage of the connection by a relay K which also sends the ringing current. Selection of wanted line. Line relay A and release relay B pull up, and the tens digit is repeated to the vertical magnet VERT. Springs ON change over and at the end of the digit series relay C switches over the impulse circuit to the rotary magnet ROT which then receives the units digits in parallel with relay G. Busy test and signal. If the line is busy, relay E pulls up over the test wiper P, followed on the relapse of relay G by relays H, K. Relay H locks itself to a local ground and relay E to the test wiper. Relay K disconnects the ringing circuit, completes a talking circuit (without a feed battery on the called side) and reverses the connections of the line relay to signal the operator. Ringing current and signal. If the call is accepted, the local subscribers hang up. Relay E falls back, sends forward ground to energize the cut-off relay over B10, E6, H10 and releases relay K. After an interval relay K restores the normal connections of the line relay to indicate that the line is now idle, and. completes the ringing circuit over ringing trip relay F. Ring-back tone is sent over H14 and a small tone condenser. When the call is answered, relay F extends the line back to the feed relay D which re-energizes the reversing relay K. If the wanted party is idle to begin with, relay E does not pull up and on the relapse of relay G ground is forwarded to the cut-off relay over the upper winding of relay H. Relay H pulls up its light armature 5 to complete its locking circuit in which it is energized fully, and ringing current is sent out as just described. Release. This is controlled by the operator and may take place at any stage. When the called party hangs up, relay D releases relay K to give a signal to the operator who then takes down the connection whereupon relays A, B. F, H fall back and the release magnet RLSE is operated in series with a common alarm relay (not shown).