Design and validation of an inline conductometric measurement instrument for hydroponic nutrient solutions

Inline monitoring of electrical conductivity (EC) is essential for process control in hydroponic nutrient management systems. Accurate EC measurement requires stable excitation, robust signal conditioning, and reliable compensation for temperature effects inherent to electrolyte solutions. This study presents the design, calibration, and validation of an inline conductometric instrument integrating EC and temperature sensing within a compact device. The measurement system employs an AC-excited two-electrode probe, ratiometric signal acquisition, and embedded temperature compensation. The instrument was developed for continuous operation and industrial integration via a TCP Modbus interface. Performance was evaluated through laboratory calibration using reference conductivity standards and field validation in an operational hydroponic farm. Measurements showed strong agreement with a commercial reference instrument (Greisinger G 1409), with deviations remaining within the combined uncertainty limits of both systems. The results demonstrate that the proposed instrument provides stable and reliable inline EC measurement suitable for continuous monitoring and control applications. Although focused on hydroponics, the presented design and validation framework may also apply to a broad range of inline conductivity measurement tasks beyond hydroponics. • Design of an inline conductometric measurement system for hydroponic solutions • AC-excited two-electrode probe with integrated temperature compensation • Calibration and uncertainty evaluation using traceable conductivity standards • Experimental validation against a commercial reference instrument • Industrial RS-485 / TCP Modbus interface for continuous operation