Patent ID: 8541716

Claim:
Heater control apparatus for controlling power to a heater that has an AC powered heating element which produces heat when connected to an AC power source, said heater control apparatus comprising: A. A first temperature sensor and a second temperature sensor positioned in close enough proximity to the heating element to sense heat produced by the heating element; B. A heater controller comprising: (i) an AC power circuit extending between an inlet connector in the heater controller and an outlet connector in the heater controller, wherein said inlet connector is connectable electrically to an AC power source and said outlet connector is connectable electrically to the heating element to provide AC power to the heating element via the AC power circuit; (ii) a high-limit power switch in the AC power circuit between the inlet connector and the outlet connector of the heater controller that is capable of opening and closing the AC power circuit; (iii) a high-limit control circuit that is connected to the high-limit power switch in a manner that causes the high-limit power switch to open the AC power circuit in response to a temperature sensed by the first temperature sensor exceeding a high-limit temperature parameter and that causes the high-limit power switch to close in response to the temperature sensed by the first temperature sensor not exceeding the high-limit temperature parameter and a power sequence condition; (iv) a controllable process power switch in the AC power circuit between the inlet connector and the outlet connector of the heater controller that is capable of opening and closing the AC power circuit to control the AC power provided at said outlet; and (v) a process control circuit that is connected to the process power switch in a manner that causes the process power switch to open and close the AC power circuit in response to comparison of the temperature sensed by the second temperature sensor with a preset desired set point temperature.