JPS57106913A - Temperature control circuit for electric heating device - Google Patents

Abstract

PURPOSE:To exercise accurate temperature control without causing fluctuation of detected temperature even if the hygroscopicity of a heat-sensitive element varies, by inserting a correcting circuit between a filter circuit and a switching circuit. CONSTITUTION:A correcting circuit K is inserted between a filter circuit 11 and a switching circuit 13. A circuit K consists of a current detecting circuit 19 which detects a current flowing through a heat-sensitive element 5 by a voltage signal corresponding to the impedance of the element 5 sent from the circuit 11, a reference voltage detecting circuit 20 which detects the output of an oscillating circuit 9, a phase detecting circuit 21 which detects the dielectric loss angle sigma of the element by the output signals of the circuits 20 and 19, an impedance detecting circuit 22 which detects the impedance of the element 5 on the basis of the output signal of the circuit 19, an arithmetic circuit 23 which receives the combined detection value of the dielectric loss angle sigma from the circuit 21 and a detection value Z from the circuit 22 and then outputs the temperature of a heater 3 corresponding to the detection value, and a voltage level correcting circuit 24 which inputs a voltage level signal, corresponding to the temperature value from the circuit 23, to a trailing comparing circuit 14.