Real-time conductivity monitoring of industrial lubricating oils using an interdigital electrode sensor

Purpose To effectively monitor quality of lubricating oil, the purpose of this paper is to design a novel conductivity sensor with interdigital electrode (IDE sensor), which can accurately and stably monitor conductivity of lubricating oil. Design/methodology/approach A reliable calibration curve was established by preparing a series of sample blends composed of 100# gear oil and varying concentrations of additives. The operational stability of the sensor was assessed through repeated measurements on the same oil samples. Furthermore, the practical applicability of the developed IDE sensors was validated by direct comparison with standard offline laboratory conductivity measurements. Findings The rigorous calibration confirmed a strong positive correlation between the sensor output voltage and the conductivity of the oil. The sensor demonstrated excellent operational stability, exhibiting only minimal voltage deviations during repeated measurements of identical oil samples. It achieved high accuracy, with relative errors ranging from 1.8% to 9.4% compared to standard offline laboratory conductivity measurements. Furthermore, the practical applicability of the IDE sensor was successfully validated in an industrial environment, where its on-site conductivity readings from in-service gear oil closely aligned with offline diagnostic results. Originality/value The proposed IDE sensor integrates significant stability, accuracy and in-service reliability, representing a meaningful advance in lubricant monitoring technology for engineering applications.