| 摘要 |
An electrically powered heating panel comprises a resistance heater 1 and a current supply means 2 for supplying current to the heater. The heater comprises a first heating element 6 connected in series with a second conductor 8, which may also be a heating element. The first and second elements lie in close proximity to one another and are separated by a layer of relatively low melting point insulating material such as polyethylene. A third heating element 7, is connected in series between the first and second elements. A sensing element 9 lies in close proximity to the third heating element to detect current leaking therefrom. The sensing element is connected to means sensitive to the leakage current and operable to regulate the current supply to the heater. A fuse F1 is provided to cut off the current supplied to the heater in the event of it exceeding a predetermined limit. The arrangement is such that should the heater begin to overheat the insulating layer between the first and second elements the layer will melt at at least one location along their lengths. This causes a short circuit which bypasses the third heating element 7 so that the current flowing through the heater increases to at least the predetermined limit and blows the fuse. <IMAGE> |
