Increasing the accuracy of level-based volume detection of medical liquids in test tubes by including the optical effect of the meniscus

A novel system for liquid volume detection is reported in this paper. The system uses two lasers with different wavelengths to scan the entire height of tubes. By detecting the shape and position of the meniscus that is formed at the liquid-air interface, the volume of liquid in a tube of known geometry can be determined. To increase the accuracy of this level-based volume detection, the shape of the meniscus must be considered. The optical effect of the meniscus in such a system was modeled and its effect on the volume detection simulated. A laboratory prototype was built and the biggest difference between the measured power of the transmitted light through the meniscus and the simulated data was less than 8%.