GB223877A - Improvements in telephone systems - Google Patents

Abstract

223,877. Western Electric Co., Ltd., (Assignees of Dustin, G. E.). Oct. 24, 1923, [Convention date]. Automatic exchange systems.-A digit-absorbing selector, for use in a multi-exchange system in which some of the exchanges have not reached their ultimate capacity, responds to the first digit it receives, absorbs the next digit without effecting any selective operation, and then hunts automatically for an idle trunk. The absorption of the second digit may take place either on particular levels only or may be irrespective of the level selected by the first.digit. In the 100,000- line system indicated in Fig. 1, comprising ten exchanges reached over different levels of a first or office selector 12, the selector 12 may be one in which the second digit is absorbed only on levels leading to exchanges (for example, that containing the subscriber 7) in which the unnecessary thousands-selecting stage has been omitted. Alternatively, the selector 12 is of standard type, and the incoming selector 13 in the incompletely-developed exchange is of the type in which the second digit it receives is absorbed on all levels. First arrangement, Fig. 3, in which the second digit is absorbed only on particular levels, for example, the third. Upon the seizure of the selector, relays 300, 310 operate and the first series of impulses is repeated to the vertical magnet 341 in parallel with a slow-release relay 320. At the end of the digit, the relapse of relay 320 completes a circuit 312, 326, 321, 394, for relay 330 which locks up over contacts 392, 343, 337, 380, but if the switch has been raised to the third level no circuit is yet completed for the rotary magnet 342. The next series of impulses is therefore repeated by relay 300 to relay 320 in parallel with a slow-operating relay 350 which locks up, but the operation of relay 330 prevents any further vertical movement and the digit is therefore ineffective. At the end of this digit, the relapse of relay 320 completes a circuit 326, 321, 394, 357, 335 for the rotary magnet 342 which, on operating, unlocks relay 330. If the first trunk is busy, relay 330 re-energizes over contacts 392, 343, 361 and the grounded test wiper 329, and the switch takes another step. When an idle trunk is found, relay 370 energizes in series with relay 330 to extend the connection. If the first digit dialled is other than 3, the operation of relay 330 at the end of the digit completes a circuit for the rotary magnet 342 over an extra wiper 345 and a righthand winding of relay 350, and hunting takes place at once so that the second digit will pass to a succeeding switch. Second arrangement in which the second digit is absorbed on all levels. In this case, the wiper 345 and the right-hand winding of relay 350 are omitted, and the operation on all levels is similar to that described in the preceding paragraph for the third level.