GB616795A - Improvements relating to high frequency electrical heating - Google Patents

Abstract

616,795. Automatic control systems. MITTEL MANN, E. July 30, 1945, No. 19513. Convention date, July 21, 1944. [Class 38 (iv)] [Also in Group XL (c)] In a high-frequency heating apparatus, in which a high-frequency generator feeds a reactive heater through a coupling device, the voltage across the resonant circuit controls means for adjusting the coupler. The power output of the high-frequency oscillator G, Fig. 3, is adjusted to an arbitrary level by setting resistance G1 in the common cathode lead of the oscillator valves, the indication of the valve voltmeter V being brought to the point O. The material H to be heated is inserted between the electrodes and the coupling condensers C2, adjusted until the valve voltmeter indicates the value M. The potentiometer P may be ganged to the resistance G1 to render the indications independent of the power level at which the adjustment is being made. One or other of the thyratrons F5 and F6 fed from the secondaries of the transformer F9 is fired if the amplitude of the high-frequency oscillations varies from the predetermined value causing the motor F4 to vary the coupling condenser C2 and restore the amplitude to the optimum value. Various methods of coupling the load to the oscillator are described (see Group XL (c)). In a modification, Fig. 7, an inductive heater H6 is employed, the coupling being varied by slugs C8 driven along the axis of the coil G9 by a. screwed shaft C10. A coil V4 coupled to the coil G9 produces a D.C. potential across the resistance. V6 to provide negative bias for the valve V7, the bias of valve V8 being derived from a potentiometer V9 connected across the power supply. If the bias potential applied to valve V7 varies from normal, the potential of the anodes of valve V7, V8 varies and causes one of the thyratrons F15, F16 to fire and the motor F20 to run and adjust the coupling to nullify the variation.