| 摘要 |
Apparatus and a method for externally determining the level of a mass of flowable material such as liquid or granular material contained in a closed or sealed container includes an elongated strip of material coated or imbedded with cholesteric liquid crystals which vary chromatically with variations in temperature. The elongated strip is applied to the outer surface of the wall of the container in heat conducting relationship thereto and extends along the height of the container. The container is exposed to a temperature change either natural, such as that which occurs at sunset and sunrise, artificially induced, such as dousing with water at a temperature different from the ambient temperature of the container or by energizing a heater element at the wall of the container adjacent the elongated strip. Because of the difference in the rate of heat conduction of the void volume and the filled space of the container, the container wall experiences a temperature gradient which is most pronounced at the interface of the contents. The temperature of the container wall changes abruptly at the surface of the contents. This change in temperature is readily discernible visually because of the abrupt change in color of the elongated strip at the material interface thus permitting an observer to readily detect the level of the contents in the container.
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