Zone melting dia. control - using capacitor parallel to heating coil tuned to higher harmonic for actual value signal

摘要

Control signal in the rod dia. control unit of a zone melting appts. is produced by connecting a variable capacitor in parallel to the induction heating coils. This forms a resonance circuit which can be tuned to a harmonic of the fundamental frequency of the high-frequency generator. Any frequency changes in this particular circuit, due to inductivity changes of the heating oil, are used as the output quantity for the prodn. of the actual value for the rod dia. control. Arrangement results in a much better sensitivity than when inductivity changes of the heating coil alone are used for the control.