GB552945A - Overload protection on x-ray control apparatus - Google Patents

Abstract

552,945. Protective cut-out arrangements. GUNSTONE, A. C., and LAMBERT, R. A. Feb 9, 1942, No. 1688. [Class 38 (v)] An X-ray tube 20 having separate controls for presetting the filament current, tube voltage, and time of exposure, has means for preventing operation of the tube when the three settings selected by the operator are such as would result in damage to, due to overloading of, the tube. The filament is energized by a transformer 4 in series with a tapped resistance 17 controlled by a multi-way switch 5. The tube-voltage is derived from a transformer 3 which is energized by a tapped autotransformer 1 under control of a contactor 8, the tapping of autotransformer 1 being selected by a switch 2. An auxiliary transformer 16 having a tapped secondary has its output adjusted by a switch 6 which is mechanically coupled to switch 5, the arrangement being that, due to the coupling with 5 and to switch 2, the voltage output of 16 is proportional to the tube-input. The output of 16 is connected across a tapped resistance 9, the control switch 10 of which is mechanically coupled to the setting-member 11 of the exposure-timer 12. Part of the resistance 9 applies a bias voltage to the grid of a gas-triode valve 13 having in its plate-circuit the operating winding of a switch 14 controlling the energization of the coil of contactor 8 and an indicating lamp 21. The exposure is initiated by manual switch 15 and automatically stopped by the timer 12, which is preferably of the type employing a condenser/resistance device connected to the grid of a gas valve. For every value of input selected by regulators 2, 5 there will be a limiting time of exposure, and the resistance taps are so selected that, if 11 is preset so that this time is exceeded, the resulting bias blocks the valve 13 and opens switch 14 to prevent energization of contactor-coil 8, at the same time lighting lamp 21. The operation is thus left to the discretion of the operator and the tube can be used to give maximum efficiency without endangering its life. A further regulator 7 is coupled to 5 and 6 so as to provide an additional autotransformer voltage with increase of loading and neutralize the effect of " regulation."