GB532287A - Improvements relating to telephone systems - Google Patents

Abstract

532,287. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and COLLEY, E. Aug. 24, 1939, No. 24383. [Class 40 (iv)] In a selector which hunts for an idle outlet marked by battery on the test terminal, the test relay is operated before the hunting motion and is released by differential action when an idle outlet is encountered. In Fig. 1, test relay H energizes and locks over winding (i) upon the operation of dialling relay C, and when the latter falls back and closes the self-interrupting circuit of the rotary magnet R, winding (ii) of H is connected to the test wiper P. To ensure quick release by current flow over wiper P, winding (ii) has more ampere-turns than winding (i) and the relay may have a nickel-iron core. On the relapse of H, relay C re-operates, switches through and again connects up H, which holds to ground fed back over wiper P and maintains C. The selector restores when H, C fall back by resumption of its rotary motion. In the modification shown in Fig. 3, test relay H energizes over winding (ii) and locks over winding (i), and is subsequently released by current in the reverse direction through winding (ii). Other arrangements, Figs. 2, 4 (not shown), are described in which the selector is marked idle by the absence of ground on the test wire instead of by the presence of battery, as in Figs. 1, 3.