GB617100A - Improvements in or relating to telecommunication exchanges - Google Patents

Abstract

617,100. Electric indicating systems. STANDARD TELEPHONES & CABLES, Ltd. May 10, 1946, No. 14200. Convention date, April 15, 1941. [Class 40 (i)] [Also in Group XXXIX] In a signalling system, different potentials, each characteristic of a different indication, are applied at one end of a signalling wire or wires and the same range of potentials is applied sequentially at the other end, and an interposed detector responds when a minimum difference of potential of predetermined magnitude and polarity exists between the ends of the wire. As applied to the control of a selector by a register controller, the register S, when set, applied, by means of wiper a, an appropriate potential over contacts of Ar, Br and Cr to one end of the primary winding of transformer T. The other end is connected to the wiper g of the selector switch, which is self-driven by magnet SM. At each step, a pulse of current passes through the transformer winding, owing to the difference in potential between the ends of the line, but only when wiper g is connected with a potential sufficiently positive with respect to wiper a is the pulse of sufficient magnitude and of correct direction to fire cold cathode tube L. The circuit is such that when this occurs, wiper g rests on the contact corresponding to that indicated by wiper a. The firing of the tube L allows anode current to flow through relay Gtr which breaks the stepping circuit and operates Ar. The latter relay breaks the anode circuit and releases Gtr, but maintains the stepping circuit open. A protective arrangement is incorporated which operates if, owing to a faulty circuit, wiper g stops on a terminal beyond the correct one, by testing whether the tube will still fire if the potential is reduced by one step. Bank contacts bare multipled to contacts of bank a, contact 1 in b being connected to contact 2 in a and so on. When wiper g stops and. Ar operates Br operates in series with it and a new anode connection to tube L is now taken to a point of potential equivalent to one contact back. If the tube again fires, Gtr operates Cr, which locks, extinguishes the tube and gives a fault indication. In this Figure the rectifiers R1, R2 reduce any reverse voltage surge which might tend to trigger valve L, while R3 provides a low resistance path for any such voltage which might nevertheless appear across the transformer T. The potentiometer P is used to adjust the initial setting of the triggering voltage.