Current time control for heater resistor - forms modulated control pulses by superposition of PWM signal on two-point control state signal

摘要

The heat dissipated in a heating resistor is controlled by varying the a.c. current using a power control element switched in accordance with the full wave timing principle. The control element consists of two antiparallel thyristors switched on by synchronised control pulses from a pulse-width modulated pulse generator at the instants of polarity changes of the a.c. current. A pulse modulator is used which widens the width of a rectangular signal when the heater resistor temperature rises and lengthens the on - period of the power control element. Suitably modulated control pulses for the power control element with a switching sequence determined by the two point control, are generated by superposition of the PWM signal on a signal representing control state of the two-point control.