GB660977A - Improvements in and relating to the operation of x-ray apparatus - Google Patents

Abstract

660,977. Control systems for space discharge apparatus. GENERAL RADIOLOGICAL, Ltd., and QUITTNER, V. Nov. 16, 1949, No. 29331/49. Class 38 (iv). An electronic switching system for an X-ray tube 3 which permits control of the energization of the tube from a low-tension D.C. source 30 comprises a coupling transformer 24 having its primary 25 connected through a control switch 31 to the source 30 and a well-insulated secondary 26 connected between the cathode 15 and grid 16 of a control valve 14, the ratio of transformation and time constant of the transformer circuit being made such that the ride or fall of the primary current is prolonged so as to produce a voltage across the secondary of magnitude above the minimum necessary to render the tube 3 conductive and for the maximum desired duration of exposure. In the arrangement shown, upon closing switch 13 a decreasing negative voltage is applied to the grid of valve 14, rendering it non-conductive, whereupon a positive bias is applied to auxiliary valve 10 from resistance 21, and valve 10, receiving its energy from battery 19, then conducts and neutralizes the negative voltage from a high-tension source 18 applied to the grid 8 of the main switching valve 6 allowing it to conduct and permit high-tension current to flow through the X-ray tube 3. For kinematography purposes a rotary switch 32 is included in the primary circuit and synchronized with the film so as to make contact whilst the film is in the gate. Suppression of oscillations at the instant of switching may be effected by shunting a resistance 27 or a condenser 28 across the secondary 26 whilst a resistance 29 connected across the primary 25 reduces the voltage appearing across the primary. When the circuit is opened. The desired time constant is preferably obtained by working the transformer core along the steepest portion of its magnetization curve. The exposure may be effected by opening the switch 13 by reversing the necessary transformer connections (Fig. 4, not shown) and timing of the exposure may be obtained by simultaneously opening the circuit between a battery and condenser across the latter of which is connected a potentiometer resistance having part connected between the cathode and grid of a gas-filled valve shunted across switch contacts 31 so that the precharged condenser, holding off the valve, discharges through the potentiomter to a voltage value at which the valve conducts and completes the circuit between the switch contacts. Specification 637,082 is referred to.