GB792112A - Improvements in or relating to the control of alternating current electric supply circuits - Google Patents

Abstract

792,112. Switching systems for X-ray apparatus. WATSON & SONS (ELECTROMEDICAL). Ltd. Feb. 2, 1956 [Fob. 2, 1955], No. 3065/55. Class 38 (4). A circuit arrangement for effecting closure of an X-ray contactor 19 at a zero voltage point in the A.C. supply wave comprises a half-wave rectifier 3 and normally-open contacts 4 of a control relay 5 connected in series with the operating coil 1 of the contactor and a " prepare " switch 6 across an A.C. source 2, the relay being actuated, upon operation of an " exposure " switch 11, by a voltage pulse supplied to its winding from a peaking transformer 9 over a rectifier 13 which is so poled that the contacts 4 close during a half-cycle when rectifier 3 is non-conducting. Energization of contactor coil 1 is thus initiated at the commencement of the next half-cycle. Closure of contacts 19 follows a half-cycle later, as the operating time of the contactor is arranged to correspond to half a cycle. The contactor subsequently holds in, over an auxiliary contact which now short-circuits the rectifier 3, until relay 5 is released. In the form shown, the relay is polarized and is released by returning switch 11 to its " off " position to bring into circuit a further rectifier 12 which reverses the polarity of the pulses applied to the winding. In another arrangement an unpolarized relay is employed which, when operated, closes auxiliary contacts for short-circuiting rectifier 13 so as to retain the relay energized until the energization circuit is interrupted by the opening of a simple make - and - break " exposure " switch. The peaking transformer 9 is supplied through a resistor 7 by which the phase of the operating pulse applied to the relay is controlled. A phase change circuit, such as described in Specification 792,111, [Group IV (a)], may be incorporated, so that energization of the contactor may be initiated at the beginning of a half-cycle of either polarity. Specification 601,811. also is referred to.