GB598350A - Improvements in or relating to electric supply systems for x-ray apparatus - Google Patents

Abstract

598,350. Supply systems for X-ray apparatus. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Nov. 5, 1943, No. 18420. Convention date, July 4, 1942. [Class 38 (iv)] To indicate or prevent X-ray exposures under conditions which would result in the tube being overloaded, a wattmeter is so connected to the tube supply circuits that the deflection of its pointer is representative of the proposed power input to the tube. The scale of the meter may thus be calibrated to read maximum permissible exposure times-as determined by the tube rating charts. A voltage component dependent upon the setting of the timer may also be applied to the meter which is then in the form of a wattmeter relay for preventing energization of tube if proposed exposure time would result in overload. As shown in Fig. 1, a tube 120 is energized through a rectifier bridge 119 and high-tension transformer 112 from an auto - transformer 103 connected to supply mains 101, the period of energization being controlled by a timer 121 which actuates a contactor 114 in the supply to the primary winding of the high-tension transformer. The output voltage-adjusting switches 107, 108 of the auto-transformer are connected to the '' voltage " coil 133 of a wattmeter 130 through a resistor 136, the '' current " coils 131, 132 of the meter being energized by a transformer 137 connected to the supply 101 and including in its secondary circuit a resistor 138, the value of which is varied with the proposed anode current of the tube. The deflection of the pointer 134 of the meter is thus proportional to the proposed power input to the tube and the meter scale may be graduated to show directly maximum permissible exposure times. Resistor 136 may be variable in order that the meter may carry a number of different scales for varying sizes of target spots. In the modified arrangement of Fig. 4, the " voltage " coil 233 of a wattmetric relay 230 is energized by the difference of the voltages across the tube-voltage adjusting switches 107, 108 and a portion 251 of a potentiometer 250, the arm 252 of which is ganged with the moving element 224 of the timer 221. The potentiometer is supplied from a tapped transformer 260 fed from supply 101 and having its tap-selecting switch 263 ganged to the moving arm of the variable " current " coil resistor 239 which may be associated with a " tube current " selector switch. The output voltage of the potentiometer is thus dependent upon the proposed tube current and exposure time. The graduation of the potentiometer resistance and of the transformer tappings is such that at overload conditions the potentiometer output voltage balances the voltage across adjusting switches 107, 108 so that the pointer of the relay is undeflected. In this condition contacts 237, 238 of the relay are closed, thereby energizing a contactor 244 having normally closed contacts 243 in the primary circuit of the high-tension transformer and thus interrupting the supply to the latter. Transformers 237, 260 may have a common core.