GB722330A - Improvements in or relating to protective circuits for x-ray tubes - Google Patents

Abstract

722,330. Switching and supply systems for space-discharge apparatus; protective arrangements. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Dec. 12, 1951 [Dec. 15, 1950], No. 29111/51. Class 38 (4). A protective circuit for a diagnostic X-ray tube 15 supplied over a high-voltage transformer 4 is provided with means for applying a sub-normal voltage to the transformer primary winding 5 before an exposure and until the tube discharge current reaches a prescribed value, and for thereafter applying the normal voltage to the primary winding subject to the control of protective means dependent directly or indirectly upon the said discharge current. This provides that the full tube voltage shall not be applied until the cathode 13 is sufficiently emissive, and as shown the means comprises an auxiliary winding 21 on a regulating autotransformer 3 which supplies the primary winding 5 from A.C. mains terminals 1. Also as shown, the protective means comprise a first relay whose winding 22, serially connected in the transformer primary circuit through relay contacts 20 which are closed by actuation of a control switch 18 to position I, closes its contacts 23 when the discharge current reaches its prescribed value to prepare a circuit for the winding 10 of a further relay. Actuation of switch 18 to position II further prepares the circuit of winding 10 whose contacts 8, 9 and 27 respectively complete the normal voltage circuit and break the sub-normal voltage circuit of primary winding 5 for a prescribed exposure period determined by a time switch 24. In the circuit shown the tube is supplied over a rectifier 12, but in another embodiment, Fig. 2 (not shown), this is omitted, and a modified form of protective means which embodies a gridcontrolled discharge tube is connected on the secondary side of the transformer 4.