Patent ID: 7268859

Claim:
A liquid metering device comprising: a conduit including a lumen adapted to permit liquid to flow through the conduit, a portion of the conduit having a wall adjacent the lumen through which light may pass; a liquid heater adapted to heat a portion of the liquid at a first position along the conduit; a light source adapted to generate at least one beam; a beam splitter adapted to split the at least one beam into a first beam and a second beam directed along respective first and second beam paths, wherein at least one of: (i) the first beam path passes, with respect to a first side of the conduit, all the way through the conduit and all the way through the lumen at a second position along the conduit and the second beam path does not pass through the lumen of the conduit, wherein the first beam has a same frequency exiting the lumen as compared to entering the lumen, and (ii) the first beam path crosses the lumen at the second position along the conduit and the second beam path does not enter the lumen of the conduit and does not enter the wall of the conduit wherein the first beam has a same frequency exiting the lumen as compared to entering the lumen; a device adapted to combine the first and second beams after the first beam has at least one of passed all the way through the lumen and crossed the lumen, respectively, such that the first and second beams undergo a degree of interference; and an optical detector adapted to detect an intensity variation of the combined first and second beams caused by a heated portion of the liquid passing through the first beam.