GB492225A - Improvements in regulating systems for electric discharge devices - Google Patents

Abstract

492,225. Automatic regulation. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 10, 1937, No. 30881. Convention date, Nov. 13, 1936. [Class 38 (iv)] The cathode of a discharge device, such as an X-ray tube supplied with A.C. is maintained at a substantially constant temperature, despite variations of the A.C. potential, by an intermittently conducting device, such as a grid-controlled discharge tube, adapted to modify the instantaneous flow of current to the cathode during a half-cycle in response to supply potential variations. A discharge potential is impressed across the electrodes 10, 11 from the A.C. supply lines 15, 16 through transformer 14. The cathode heating circuit is also supplied from the lines 15, 16 through transformer 18. The primary of this trans - former is, however, short circuited during part of each halfcycle by a grid-controlled discharge tube 20. The control grid 24 is connected through a resistance 25 to a non-linear circuit including a resistance 27, a condenser 28 and a saturable reactor 29. The phase angle between the supply voltage E and the grid voltage E0 accordingly varies with variations in the value of E whereby the discharge tube 20 may be rendered conductive at a definite point in each half-cycle corresponding to the voltage E, as shown at t in Fig. 3. The reactor 29 may be adjustable. In a modification two discharge tubes 20 are provided to deal with both the positive and negative half-waves, the control grids being supplied from a commutator driven by a synchronous motor, the angle of lag of which relative to the supply varies with changes in the supply voltage.