A New Non-Intrusive Optical Technique to Measure Transparent Liquid Level and Volume

We report here a novel optical technique for the continuous measurement of the level and the volume of transparent liquids in a cylindrical container. This measurement technique is based on the principle of liquid level induced modulation in the solid angle of a divergent light beam incident on liquid surface. This technique has advantages of being a very sensitive and non-intrusive way of measurement. The proposed technique has been experimentally tested with clean water, colored water, diluted glycerin, and pure glycerin by using liquid containers having 100-, 250-, and 500-mL capacity. Measurement results provide the highest sensitivity in the case of a container having smallest diameter. The proposed system is capable of measuring the liquid level and volume with approximate resolutions down to 3.2 μm and 6.2 μL, respectively, in the case of a 100-mL container. The sensitivity is found to decrease with the increasing diameter of the container as well as with the decreasing optical transparency of the liquids, but increase with the increasing refractive indices of transparent liquids. And this technique has an appreciably larger dynamic range of measurement, good linearity, and repeatability in the measurement responses.