Thermal cut=out for protection of electric blanket - uses thermistors at either end of element, linked by conductive strip wound over element to detect current imbalance arising from faults

摘要

The thermal cut-out circuit is used to protect electric blankets against overheating, having a resistor and thermistor in close proximity to a thermostat which opens if the temperature rises to a set value. Two such circuits are used, one at each end of the element, and they are connected in parallel with the heating element via a conductive strip wound over the length of the element. The heating element (1) is supplied from the AC mains (2,3) through thermostat contacts (4,5) at each end of the element. NTC circuits (6,7,8,9) are placed adjacent to the contacts and give off heat which opens the contacts and recloses them when the control enclosure (10,11) has cooled. If a local hot spot occurs due to element damage or insulation failure, the resulting current imbalance leads to operation of one of the thermostats.