Patent GB-633775-A (GB)
Title: Improvements in or relating to control arrangements for x-ray apparatus
IPC: H05G1/44
Filed: 1947-05-21
Abstract: 633,775. X-ray exposure timing apparatus. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. May 21, 1947, No. 13660. Convention date, June 1, 1946. [Class 98 (i)] [Also in Group XL (b)] In an X-ray device of the type wherein a photographic exposure of the X-ray screen is made, the operational time of the X-ray tube is controlled photo-electrically to take account of differing brightnesses of the fluorescent screen as a result of different depths of subject being examined. As shown the image of the subject 9 produced on the fluorescent screen 8 is photographed by a camera and simultaneously projected by a lens system 13 on the cathode of a photo-multiplier 14, whose output controls the charging of a condenser 24 which switches off the X-ray tube when the voltage across it and a resistor 19 reaches a predetermined level. Detailed operation.-Resistance 29 controlling one of the stage voltages of the multiplier tube is first set manually in accordance with the film being used. Auto-transformer 46 feeds further transformers 40 and 57 heating the high voltage rectifier 50 supplying the dropping network 27 of the electron multiplier 14, and rectifier 60 supplying a glow tube stabilized voltage to operate the relay and alarm circuits. Relay 64 first operates and the subject is then positioned before the screen 8 and the manual exposure switch 106 closed. This completes circuits for relays 22 and 70 already prepared by relay 64. Relay 70 closes relay 86 which supplies the primary of the transformer 91 operating the X-ray tube 94 and actuates relay 85 a little later to short-circuit a surge absorbing resistor 92. Operation of relay 22 removes a short circuit from the timing condenser 24 and as soon as the screen 8 starts to fluoresce the electron multiplier conducts to charge condenser 24 through a resistor 19 at a rate proportional to the light flux incident on the tube 14. The total voltage across the resistor and condenser is used to fire a glow tube 32 which actuates relay 80. The resistance 19 compensates for the time taken for the relay 80 to drop out it adds to the voltage across the glow tube 32 due to the condenser 24, a voltage proportional to the intensity of the image on screen 8 so that for high intensities which require low exposure times, the glow tube 32 fires before the condenser 24 has developed by itself the triggering voltage ; as a result a short exposure time is not unduly increased by the drop-out time. Operation of relay 80 de-energizes relays 85 and 86, cutting- off the supply to the X-ray tube. If it is desired to make a large radiograph, a cassette containing intensifying means is positioned on the hood 7. Manual rotation of a screen 124 into a position in front of the camera 10 positions a switch 18 to a different timing circuit and switch 28 to a different stage voltage adjusting resistor 126. Safety arrangements.-If the low voltage fails so that glow tube 32 cannot operate, relay 64 de-energizes to de-energize relay 70 which de-energizes relay 86 to terminate the exposure. A safety timing condenser 73 is provided to switch-off the apparatus after a predetermined time in the event of failure of the normal timing arrangements ; condenser 73 commences to charge as soon as relay 70 operates and on attaining a predetermined voltage fires a glow tube 122 operating a normally unoperated relay 19 de-energizing the X-ray tube and operating an audible alarm 102.