| 摘要 |
<p>560,791. Automatic control systems for heating by high frequency current. BRITISH INSULATED CABLES, Ltd., WALTON, G. H., QUALE, J.C., and JONES, P. Oct. 14, 1942, No. 14399. [Class, 38 (iv)] Temperature. The energy supplied by a highfrequency valve oscillator to a body such as a travelling sheet of dielectric material passing between electrodes 2 is controlled by a thermal detector 3 which causes a change in the magnitude and/or phase of the 'grid voltage of a control valve 14, preferably -gas or vapour filled. As shown in Fig. 2, the detector 3 is a resistance in a Wheatstone bridge comprising also a temperature-determining adjustable resistance 4 which is supplied with a.c. at 5. Any unbalance voltage is amplified and applied through a circuit 10 to the grid of a rectifying control valve in the anode circuit of valve oscillators 17, the output of which is coupled by condensers 19 to the electrodes 2; the circuit 10 determines the phase relation between grid and anode volts of the valve 14. In alternative arrangements (1) the amplifier supplies its voltage through transformers and rectifiers to the grids of two valves reversely connected in parallel in a phase shifting circuit to produce changes in phase of the grid volts of valve 14; (2) the detector 3 is a gas-filled envelope, the expansion of which varies two resistances in a circuit such as 10 to shift the phase of the voltage applied to the grids of two back-to-back valves in series with a transformer supplying through rectifier the anodes of the oscillator valves, or the phase shifted voltage may be applied to the grid circuit of a control valve varying the flow of rectified current in a cathode bias resistance of the oscillators (3) the detector 3 may be a bimetallic spiral, adjusting a potentiometer furnishing a voltage to the amplifier of Fig. 2, or a number of thermocouples in series furnishing a variable bias voltage in the grid circuit of the amplifier.</p> |
