GB870070A - Improvements relating to ratchet type selector switches - Google Patents

Abstract

870,070. Automatic exchange switches. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Feb. 9, 1960 [Feb. 26, 1959], No. 6751/59. Class 40 (4). In a stepping circuit for a ratchet-operated selector switch, the energizing coil of the electromagnet of the switch is connected in the collector-emitter circuit of a transistor which is connected as a blocking oscillator by virtue of a regenerative feedback coupling, in the form of a feedback coil magnetically coupled to the energizing coil, provided between the collectoremitter circuit and the base circuit of the transistor. An electromagnet DM operates the ratchet mechanism of the reverse drive step-bystep switch RS, DM having an energizing coil C1 in the collector-emitter circuit of transistor T. A feedback winding C2 is connected to the base of the transistor from a positive potential large enough to keep the transistor " cut off " under normal conditions. If a negative pulse e.g. from an electronic or ferrite core gate circuit, is fed via network C, R to the transistor, the base potential falls and the transistor begins to conduct. The current through energizing coil C1 rapidly increases due to the regenerative action through the feedback coil C2 until magnetic saturation of the coils is reached, when current in C1 ceases until the flux linking C2 dies away. RS is switched one step and, if only one pulse is transmitted, will go no further. Alternatively, the switch may be self-stepped to a marked contact. On closure of start contact st negative potential is extended over normally closed contact sh to the base, thus stepping the switch, which continues stepping until the marked contact, which is grounded, is reached. The switch may be homed by reconnecting negative potential to the previously marked contact and opening sh. Since the operating signal does not pass through either of coils C1, C2 the signal path may be made non- inductive and hence could be of considerable length, and also wiper W2 may be of the non- bridging kind.