Patent ID: 7612311

Claim:
In a plasma processing system, a method for controlling an electric heater, the method comprising: a) receiving a setpoint temperature; b) comparing said setpoint temperature with a load temperature, said load temperature representing a temperature measured for a load that is most recently measured; c) generating a duty cycle command responsive to said comparing; d) updating said duty cycle command using a cumulative duty cycle error after step c); e) quantizing said duty cycle command to a PWM (Pulse Width Modulation) signal after step d), said PWM signal comprising a plurality of on pulses and a plurality of off pulses; f) employing said PWM signal to trigger a solid state relay (SSR) circuit, thereby energizing said electric heater responsive to said PWM signal; g) interrupting said SSR circuit in accordance with a predefined interval that is less than a 60 Hz AC cycle; and h) accumulating a duty cycle error into said cumulative duty cycle error after step d), said duty cycle error being a difference between said duty cycle command after said updating and an ideal duty cycle command, wherein said steps a) through h) are repetitively performed.