Patent ID: 7688433
Filing Date: 2010-03-30
Classification: G01C

Abstract:
1. Apparatus comprising: a. a vessel containing liquid having a reflective surface and an index of refraction which changes with temperature, b. a lens situated in an optical path between the reflective surface and a focal plane of the lens, c. a point source to emit light through the lens toward the liquid surface, d. a two-dimensional array of detector elements located such that light reflected from the reflective surface passes through the lens onto the detector elements, each detector element producing a value corresponding to amplitude of incident light, e. a processor responsive to the values produced by the detector elements to calculate a center of gravity of the image formed on the detector elements, wherein the calculated center of gravity is dependent on inclination of the vessel, and f. a sensor producing a signal dependent on ambient temperature, wherein the processor is responsive to the signal for applying a temperature correction which compensates for changes in the index of refraction of the liquid when calculating the center of gravity of the image formed on the detector elements.