A Device for Measuring the Electrical Conductivity of Liquids Using Phase Sensitive Detection Technique

The quantification of electrical conductivity in fluids is integral to various applications, including water engineering, biomedical, and industrial sectors. This study introduces an innovative methodology harnessing phase-sensitive detection to assess conductance, thereby nullifying the coupling capacitances' interference between the probe cell's metallic electrodes. The devised electronic conditioning circuit incorporates a 1 kHz sinusoidal voltage source, an admittance-to-voltage converter, a lock-in amplifier, and a microcontroller/LCD interface. Calibrations were performed over two ranges, 1 mS/cm and 20 mS/cm, utilizing precise combinations of resistors, capacitors, and adjustable resistors. The experimental findings were juxtaposed with a standard commercial conductometer across various solutions - calibration solutions, electrolyte solutions (NaCl, KCl, CaCl2, MgSO4), and different water treatment room solutions at a hemodialysis center (Carbon filter, water softener, Reverse osmosis, Dialysate). The relative error in the measured conductivity was derived, with a maximum value of 1.45% noted. This error margin is inferior to those reported by many commercial conductivity meters, suggesting improved accuracy of our method.