| 摘要 |
<p>An electric immersion heating element for a water boiling vessel has associated therewith a single thermal sensor which protects the element against overheating due to its being switched on when dry and also serves to switch off the element when water boils in the vessel. The heating element is of traditional construction with a sheathed wire-wound element proper affixed to a head plate and with a hot-return portion of the element proper affixed to the head plate to enable the element temperature to be sensed on the opposite side of the head plate, but the element sheath and the head plate are formed of stainless steel (or another material having a low thermal conductivity as compared to copper or brass), the fixation of the element hot return portion to the head plate is by means of a spot weld (or another highly localized fixation), an enclosure is provided on the element head in the region thereof whereat the element hot return portion is affixed and is arranged so that water fills the enclosure when the vessel is filled but is expelled therefrom by steam generated by water boiling in the vessel, and the single thermal sensor is arranged to be in close thermal contact with a highly localized area of the head plate corresponding to the location whereat the element hot return portion is affixed thereto on the opposite side thereof.</p> |
