Microwave resonant device for water content on-line measurement of lubricating oil

An on-line measurement device of water content in lubricating oil based on microwave resonance technology is presented. By utilizing finite-element analysis and high-frequency structure simulator software HFSS, a semi-hermetic resonator (22 mm in diameter and 25 mm in length) for this device is designed, and the measurement results are simulated. In the experiment, the resonance frequency is chosen as the measurement parameter, in which the frequency band is 9.302 similar to 9.307 GHz. In the water content range of 0 to 500 ppm (by volume), the resonance frequency decreases linearly with increasing water content, which is consistent with the simulation. The sensitivity is 1 MHz per 100 ppm of water content, and the maximum error in water content is 33 ppm. With temperature compensation in the range of 15 degrees C to 25 degrees C, the measurement resolution of this device is better than 100 ppm.