ELECTRICAL HEATING APPARATUS PROTECTED AGAINST AN OVERHEATING CONDITION

摘要

An electrical heating apparatus such as an electric blanket includes a resistance heating wire embedded in the blanket together with a single heat sensitive conductor also embedded in the blanket and disposed in a thermally responsive relation to the heating wire. The heat sensitive conductor has a positive temperature coefficient electrical impedance which is continuous along its entire length. As an overheating condition arises in the blanket this is sensed by the heat sensitive conductor which is being monitored by a controller to reduce or cut off current to the resistance heating wire as necessary. The invention makes it a practical proposition to monitor all heated portions of the blanket with the elimination of all discrete temperature sensing elements.