| 摘要 |
An apparatus for sensing whether a liquid with a turbulent surface and contained within a vessel has fallen to a level where the liquid is substantially expended. The apparatus includes a light source for emitting light, a light sensor which is sensitive to the light emitted by the light source and which outputs a signal proportionate to the amount of light sensed, and logic for determining from fluctuations in the signal output by the light sensor when the liquid has fallen to the level in the vessel where the liquid is substantially expended. The fluctuations in the signal are caused by randomness in reflections of the emitted light due to the turbulence of the surface of the liquid. Where the vessel has a closed top and the liquid initially fills the vessel, the logic additionally uses the magnitude of the signal from the light sensor to determine when the liquid has fallen to the level where it is substantially expended. The magnitude of the signal is employed to distinguish between a condition in which the vessel is full and the turbulence of the surface of the liquid is dampened by the closed top of the vessel and a condition in which the level of the liquid has fallen to approximately the level where the liquid is substantially expended.
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