Patent attributes
An improved control device and method is usable with flexible heating wire having a conductive core with a Negative Temperature Coefficient (NTC) layer and a helically wound heater conductor within an insulative outer sheath. The conductive core is coupled to a control circuit, a phase shift relative to the AC power supply being indicative of the temperature of the wire. The nonlinear nature of the NTC layer enhances the detection of local hot spots anywhere along the length of the wire. Precise temperature measurement is achieved by measuring the time differences between two zero crossings and the power to the heater compensates for abnormal use such as bunching of the heater wire. The control of the heater wire is particularly suitable for use with appliances such as heating pads and electric blankets.
