Forced-air heater control system and method

A forced-air heater control system for an electric heater having at least one electric heating element disposed within an air duct carrying forced air from an upstream position to a downstream position, said at least one electric heating element supplied with electrical power via a power control switch, the control system comprising:

• an upstream temperature sensor and a downstream temperature sensor, said upstream and downstream temperature sensor being a thermistor or a resistive temperature detector (RTD), said respective temperature sensors being disposed equidistant from said at least one electric heating element within said duct and close enough to sense radiant heat from said heating element, and each said temperature sensor having a respective electrical output;
• a control circuit accepting as inputs said respective electrical outputs of said temperature sensors, said control circuit including means for obtaining a difference between the output of said upstream temperature sensor and the output of said downstream temperature sensor, said control circuit generating a difference signal which represents convection heat sensed by said downstream temperature sensor, said control circuit including means for generating a pulse width modulated signal based upon said difference signal;
• a communicative coupling between said control circuit and said power control switch such that said pulse width modulated signal controls are applied to said electrical power supplying power to said at least one electric heating element, said power control switch controlling said at least one electric heating element in said forced-air heater control system.

A method of controlling a forced-air heater system having at least one heating element disposed within an air duct carrying forced air from an upstream position to a downstream position, said at least one electric heating element supplied with electrical power via a power control switch, the method comprising:

• sensing the heat in the air duct at equidistant upstream and downstream locations relative to said at least one electric heating element, said sensing including radiant heat sensing from said heating element;
• comparing the heat sensed at said equidistant upstream and downstream locations to obtain a difference signal;
• and
• enabling said power control switch to supply said electrical power when said difference signal is below a predetermined value, wherein said power control switch controls said at least one electric heating element in said forced-air heater control system.