Patent GB-933038-A (GB)
IPC: H05G1/70
Abstract: 933,038. Supply systems for X-ray apparatus. WATSON & SONS (ELECTRO-MEDICAL) Ltd. May 28, 1962 [June 2, 1961], No. 19978/61. Class 38 (4). A supply arrangement for a pair of X-ray tubes 1, 2 provides adjustment of the ratio of the tube currents so that the total tube current does not alter, provision also being made for adjustment of the total current and the tube voltage and for compensation of the spacecharge effect, the regulation of the high voltage transformer and the variation in supply voltage. The tubes 1, 2 are supplied through a rectifier bridge 19 from a high voltage transformer 6 whose primary winding is connected to an autotransformer 5 through an exposure timing switch 17, a voltage selector switch 12 and a bank of contacts 14 forming part of a tube current selector switch. This switch has further contact banks 13, 15 connected to a resistor chain 16 and the secondary winding of a transformer 20 arranged to compensate for the spacecharge effect. The secondary of transformer 20 is connected through tapped resistors 22, 23 to the primary windings of transformers 7, 8 whose secondaries supply the filaments of the tubes 1, 2, the primary windings being connected to autotransformer 5 through the secondary winding of a current transformer 10 shunted by a resistor 11 which is adjustable to provide compensation for variation in the voltage of the supply 3, 4 when the resistance of this supply is 1 ohm (adjustable to this value by the resistor 9). In operation the tube voltage is set by switch 12 and the total current by switch 13, the ratio of the tube currents being varied by simultaneous adjustment of resistors 22, 23 which are so arranged that in their extreme positions only one or other of the tubes 12 is operative. Adjustment of switch 14 provides compensation for the regulation of the transformer 6. Resistors 22, 23 may be continuously variable instead of tapped. In a modification, Fig. 2 (not shown), the secondary of transformer 20 is connected to the movable contact of a potentiometer resistor whose ends are connected through resistors and a doublepole changeover switch to the primaries of transformers 7, 8, operation of this switch disconnecting transformer 8 and connecting transformer 7 directly to the transformer 20. In another modification, Fig. 3, the total tube current is controlled by tapped resistors 41, 42 adjustable by ganged switches 43, 44, and the ratio of tube currents is determined by the setting of potentiometer resistor 40. Switches 36 . . . 39 provide for work requiring only a single tube. The circuit of Fig. 3 may be modified by connecting the movable contact of potentiometer 40 through a selector switch to tappings on autotransformer 5, this switch being coupled to switches 43, 44 to provide voltage regulation compensation upon adjustment of the total current. Potentiometer 40 may be replaced by a tapped resistor or a tapped inductor, Fig. 4 (not shown). If it is desired to operate tubes having very different characteristics, the circuit of Fig. 3 may be modified as shown in Fig. 5 where the total current is controlled by tapped resistors 47, 48 and the division of current by adjustable resistors 49, 50 coupled. together in the reverse sense. Resistors 49, 50 may be tapped or may be replaced by a pair of variable inductors, Fig. 6 (not shown), or by a transductor with double control windings. The arrangement may be extended to operate three X-ray tubes by providing a second current distribution control means and using the first control means to distribute current between one tube and the second control means, which distributes current between the remaining two tubes.