GB645084A - Improvements in or relating to oscillation generators - Google Patents

Abstract

645,084. Automatic control systems for oscillation generators. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. March 11, 1948, No. 7463. Convention date, March 13, 1947. [Class 38 (iv)] [Also in Groups XI and XL (c)] In an oscillation generator, particularly for high-frequency heating purposes, the grid bias for the oscillator valve is produced by rectification of the output of a resonant control circuit which is inductively coupled with an impedance which constitutes part of the tank circuit of the oscillator and is so tuned that any frequency changes due to changes in the impedance of the load connected to the oscillation generator produce a predetermined regulation of the output voltage of the oscillator. As shown, the oscillator valve 1 has a tuned output circuit comprising the inductor 7 and variable capacitor 10, a load 9 being connected in shunt with the inductor 7. The control circuit comprises an inductor 14 inductively coupled with the inductor 7 and shunted by a variable capacitor 15 across the terminals of which are connected the anodes of a full-wave rectifier 16, the voltage drop across resistor 13 causing a negative bias to be applied through the resistor 12 to the grid of the oscillator valve. As the temperature of the load varies the resonant frequency of the output circuit will correspondingly vary and if the resonant frequency of the control circuit is the same as that of the output circuit 7, 10, on no load; a variation of the oscillator frequency in either direction reduces the negative bias applied to the oscillator valve and increases the output voltage of the oscillator to counteract any decrease resulting from a change in the dielectric or magnetic constants of load 9. The resonant frequency of the control circuit 14, 15 may also be adjusted to be above or below that of the output circuit on no load so that variation in the oscillator frequency in one direction produces an increase in the output voltage and variation in the opposite direction a decrease. In Fig. 3 (not shown) the oscillator is arranged for induction heating of a magnetic load, the resonant control circuit being tuned so as to reduce the output of the oscillator when the temperature of the load exceeds the point at which the load becomes non-magnetic.