A high-precision measurement technique for evaluating alcohol concentrations using an optical metrology system based on a position sensing detector

This study develops a high-precision, non-destructive optical metrology system based on a position sensing detector for measuring the refractive index of a liquid solution such that its alcohol concentration can be derived. A series of experiments are performed to measure the refractive indices of samples of known alcohol concentrations in the range 0–99.5%. The experimental results indicate that the refractive index and the alcohol concentration are related by a quadratic function. According to this mathematical function, the refractive index of a sample with an alcohol concentration of 95% is n95%=1.36442. The measured value of the refractive index of the same sample is found to be nalcohol-95%=1.36587. The deviation of just 0.00145 between the two sets of results confirms the accuracy of the analytical prediction method. For a sample with a known alcohol concentration of 37%, the error between the analytically predicted concentration value and the actual value is found to be less than 0.7%. Overall, the results confirm that the proposed system provides a low-cost, straightforward and highly precise approach for measuring the alcohol concentration of liquid samples.