Control apparatus for induction heating system

Claim 1

IN AN INDUCTION HEATING SYSTEM OF THE TYPE WHEREIN AN OSCILLATOR CIRCUIT IS ENERGIZED BY A POWER SUPPLY EMPLOYING AT LEAST ONE CONTROLLED RECTIFIER HAVING A CONTROL ELEMENT, WHEREIN SAID OSCILLATOR CIRCUIT PRODUCES HEAT ENERGY FOR A LOAD, AND WHEREIN SAID HEAT ENERGY AND THE ELECTRICAL ENERGY OUTPUT OF SAID OSCILLATOR CIRCUIT TEND TO VARY, THE COMBINATION THEREWITH OF CONTROL APPARATUS COMPRISING (A) MEANS COUPLED TO SAID OSCILLATOR CIRCUIT FOR DERIVING A FIRST D.-C. SIGNAL RESPONSIVE TO THE AMPLITUDE OF SAID ELECTRICAL ENERGY OUTPUT OF SAID OSCILLATOR CIRCUIT, (B) MEANS ADJACENT TO SAID LOAD DERIVING A SECOND D.-C. SIGNAL RESPONSIVE TO THE AMPLITUDE OF SAID HEAT ENERGY, (C) MEANS COMBINING SAID FIRST AND SECOND D.-C. SIGNALS TO OBTAIN A THIRD D.-C. SIGNAL, (D) MEANS RESPONSIVE TO SAID THIRD D.-C. SIGNAL FOR DERIVING AN A.-C. ERROR SIGNAL HAVING A MAGNITUDE AND PHASE DEPENDENT ON THE AMPLITUDE AND DIRECTIONS OF THE VARIATIONS IN SAID HEAT AND ELECTRICAL ENERGY (E) MEANS INCLUDING A DISCRIMINATOR CIRCUIT RESPONSIVE TO THE MAGNITUDE AND PHASE OF SAID ERROR SIGNAL FOR DEVELOPING A D.-C. CONTROL SIGNAL HAVING A POLARITY AND MAGNITUDE DEPENDING ON THE MAGNITUDE AND PHASE OF SAID ERROR SIGNAL, AND (F) MEANS TO APPLY SAID D.-C. CONTROL SIGNAL TO SAID CONTROL ELEMENT OF SAID CONTROL FRECTIFIER TO CONTROL ITS TIME OF RECTIFICATION IN A COMPENSATORY MANNER WITH VARIATIONS IN SAID HEAT AND ELECTRICAL ENERGY OUTPUT.