Liquid Signature Analyzer Based on Fiber‐Capacitive Drop Analysis

An instrument called the liquid signature analyzer (LSA) has been developed for liquid property studies. The LSA is based on fiber‐capacitive drop analysis and produces a liquid drop fingerprint (LDF) which shows the variation of the coupled light signal inside the drop along with the drop formation. The LDF reflects multiple properties of the tested liquids and it is unique under certain conditions. A fiber‐capacitive drop sensor is designed through which a satiated and uniform drop is formed. A micro‐flow feeding pump, actuated by a single stepper motor and controlled by the computer software, is devised to ensure that the drop is slowly delivered under quasi‐equilibrium conditions. Modulation and demodulation are used to exclude the possible influence of ambient light in the fiber signal processing circuit. Three methods are presented in capacitive signal measurement; they are frequency modulation, differential frequency method, and transformer bridge method. A computer interface for the LSA has been established and software for data acquisition and preliminary image processing was programmed.