GB1334790A - X-ray control system with film darkening - Google Patents

Abstract

1334790 X-ray tubes CGR MEDICAL CORP 20 Oct 1971 [27 Oct 1970] 48791/71 Heading H2H An X-ray tube 5 connected to a transformer 12 having a rectified sine wave output is caused to emit radiation for a selected period of time which is arranged to occur symmetrically of the midpoint of a half-cycle of the sine -wave in order that when the tube is used at its maximum loaded value (max kV and mA), with a cine camera 20, the maximum amount of film darkening (which varies as V<SP>4</SP>) may be obtained. The tube is normally rendered non-conductive by means of a-grid bias supply 18, but operation of the cine camera motor causes a pulse generator 24 to emit a pulse of predetermined length after a predetermined delay to actuate a grid modulator switch 28, thus short circuiting the supply 18 and allowing the tube to operate. The delay and the pulse length are chosen so that the pulse is symmetrically disposed about the midpoint of the sine wave, the input to transformer 12 being automatically synchronized to the cine camera drive motor input; the sine wave output 42a, 42b, 42c, Fig. 7, is passed through a filter 15 so that, when the tube is operational, the tube input is as much like a square wave 42d as possible so as to maximize the film darkening, to avoid voltage deviations and to protect the transformer secondary. Circuits are described for the filter 15, the pulse generator 24 and the grid modulator switch 28 (Figs. 2-4, not shown), wherein the delay and the pulse length are determined by appropriate setting of circuits involving respective monostable multivibrators, and the switch 28 comprises a plurality of cascade-connected transistors.