부산대학교 도서관

Electrolytic conductivity (EC) sensors are widely used in diverse industries, including: pharmaceuticals, food, power, manufacturing, and environmental monitoring. This article presents an overview and analysis of EC sensors used in these industries from the lowest to the highest range of conductivities and in applications, where there are strong requirements for accurate and traceable conductivity measurements of water and electrolyte solutions. Included are reported sensor designs based on two- and four-electrodes with parallel plates, coaxial cylinders, van der Pauw configurations, planar and miniature configurations, and contactless inductive or capacitive coupling. A comprehensive list of exact analytical formulas for computation of cell constants for the configurations is provided. The advantages and disadvantages of using frequency domain or time domain measurement schemes in these sensors are discussed, and the reader is guided to select the suitable method of sensor calibration among the methods available, computing uncertainty budgets, ensuring traceability to the International System of Units (SI) and compliance with standards, such as Pharmacopeias. Finally, trends in the development of EC sensors and the related challenges in relation to calibration and compliance with standards are presented. This article also introduces the reader to the EC cell of a sensor, which can be modeled by solving the Poisson–Nernst–Planck equations or using appropriate equivalent circuit diagrams. It is stepwise described how the models can be extended to include effects such as electrode polarization and steric effects of ions, and it is illustrated by means of an ideal EC cell, where guards eliminate fringe fields, that the simplest equivalent circuit with a single resistor and a single capacitor models electrolytic sensor data very well in the lower range of electrolytic conductivities.