Heater wire with integral sensor wire and improved controller for same

Abstract

An improved heater wire and electro-thermal controller suitable for use in electric heating appliances such as electric blankets and heating pads. The heater wire is formed with a first conductor for heat generation and a second conductor for sensing. The first conductor and second conductor are wound as coaxial spirals with an insulation material electrically isolating the two conductors. The two spirals are counter-wound with respect to one another to insure that the turns cross, albeit on separate planes, several times per inch. With the conductors thus formed, if the insulation separating the conductors fails, the first and second conductors will come into electrical contact to facilitate detection of this hazardous condition. The controller of the present invention includes an electronic control unit a sensor input circuit, a heater driver circuit and a user interface circuit. The heater driver circuit is operatively coupled to the first conductor and provides a heater voltage in response to a signal received from the electronic control unit. The sensor input circuit is operatively coupled to the second conductor, measures a resistance and voltage associated therewith, and provides a signal to the electronic control unit in response thereto. The electronic control unit is responsive to signals received from both the user interface circuit and sensor wire input circuit and controls the heater driver circuit accordingly.