GB478652A - Improvements in or relating to automatic switch controlling circuits for automatic telephone or like signalling systems - Google Patents

Abstract

478,652. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., and RICHARDS, I. T. July 21, 1936, No. 20179. [Class 40 (iv)] A group selector having two sets of wipers hunts over the selected level with one set of wipers in response to all digits except o and 7, and in response to those digits drops back and responds to a second digit before hunting, one set of wipers or the other being effective according as the first digit is 5 or 7. The invention is applicable also to final selectors. The group selector described is of the kind disclosed in Specification 391,151 which upon release continues its rotary movement to an extreme position. The drop-back movement however takes place over the setting path by operation of the vertical magnet in the manner described in Specification 399,815. Line and release relays A, B energize upon seizure and connect up dialling relay C (left winding) in series with the vertical magnet VM. Dialling tone is transmitted inductively through the centre winding of line relay A. Impulses are repeated to the vertical magnet VM in series with C (right winding), B being short-circuited at each impulse, and relay H pulls up at the first step and short-circuits C (left winding). Assuming the digit received is other than or 7, the relapse of C at the end of the train completes a selfstepping circuit for the rotary magnet RM and places H under the control of test wiper P1, so that it falls back when an idle line is reached and cuts the drive. Relay C (left winding) reoperates, switches through and again connects up H, which is subsequently held from the succeeding switching stage to control release. If no idle line is found, switch through takes place in the eleventh position which is wired to line relay A and a busy signal is transmitted over eleventh step springs S. If the selector is set to the 7th level, post springs NPA are operated, and relay H falls back after a single rotary step, since this level is unwired in the PI bank. Relay DR energizes and connects up the vertical magnet VM, which removes the rotary detent and allows restoration of the wipers. At the same time wiper-switching relay DA operates and locks, so that after a second digit is received hunting takes place over the upper set of wipers. If the selector is set initially to the 5th level, post springs NPA, NPB are operated and drop-back occurs in a similar manner, but relay DB operates in place of DA so that the lower set of wipers remain effective.