GB769063A - Improvements in or relating to x-ray apparatus - Google Patents

Abstract

769,063. X-ray apparatus. PHILIPS ELECTRICAL INDUSTRIES, Ltd. May 26, 1955 [May 29, 1954], No. 15221/55. Class 98(1) In X-ray apparatus having a safety circuit to prevent the high voltage from being switched on in the event of a failure of' the filament current supply, the working contact of an electromagnetic relay is included in the control-circuit for high voltage and the energization of the relay is controlled by the sum of two voltages, which are approximately in phase opposition, one being a constant voltage and the other voltage varying with the filament current. As shown in Fig. 1, an auto-transformer 7 has tappings 8 whereby a variable voltage can be applied to the primary winding 6 of a high tension transformer 5, the secondary winding 4 of which is connected to the X-ray tube 1. Contacts 12, 13 of a high-voltage control relay 14 are included in the supply leads 9, 11. The autotransformer 7 also supplies the primary winding 20 of a filament transformer 19 through a fuse 22, a variable filamentcurrent resistor 21 and a variable resistor 23. A voltage proportional to the filament current is developed across the resistor 23, while a fixed voltage, approximately in phase therewith is developed across a part 24 of the winding of the transformer 7. These voltages are connected in opposition across a rectifier bridge 27. The output of the rectifier bridge is connected to the winding of a relay 26, having contacts 29 in series with the winding of relay 14. When the voltage derived from the filament current is substantially equal to the fixed voltage; relay 26 is not operated and contacts 29 are closed, so that relay 14'may be energized from a supply 16, 17 on closure of a switch 15. If desired, the rectifier bridge 27 may be omitted the voltages being connected in phase opposition to two windings of the differential relay. Alternatively, the voltage output from the rectifier bridge 27 may be applied to a switching valve such as a triode or a gas filled discharge tube. A condenser 36 may be connected in parallel with the primary winding of the filament transformer 19, in order to reduce the reactive component of its zero load current.