A conductivity-based sensor for detecting micro-water in on-line oil analysis

Molecular water in lubricants causes unavoidable damage in mechanical tribo-systems. To illustrate the characteristics of water in oil, three typical hybrid states, including dissolved, free, and emulsified states, were discussed focusing on the physical structures, hazards, and electric properties. Aiming at the on-line monitoring of molecular water in engine oil, a conductivity-based sensor was proposed. Two enamel wires, with partial naked surfaces, were winded around an insulated pole in parallel to serve as a probe. A higher cell constant was obtained with a high sensitivity. A multi-channel sensor with four probes was designed for on-line monitoring. The performance of the sensor was examined experimentally. As main result, the sensor has explicit effects on detecting free and emulsified water. The sensor also has a good linearity and repeatability when water content increasing from 0% to 3%, and has a high reliability under the disturbances of air and metal debris.