Research on capacitive sensor for online oil monitoring

Wearing information of machinery equipments is often contained in lubricating oil. In the process of wearing off, the dielectric constant of the oil would change accordingly. In the paper, a new type of capacitive sensor for online oil monitoring is designed to measure the variation of dielectric constant of the lubricating oil, including the principle of dielectric constant monitoring using capacitive sensor, the structure of the sensor and high precision capacitance detecting system. Experimental apparatus for online oil monitoring is presented. The temperature characteristic curve of the designed sensor is obtained which shows a good linearity, and it is ideal for temperature compensation of the sensor in service use. Experiments are carried out on five lubricating oil samples containing different ferrous powder quantity. The results show that designed capacitive sensor can properly distinguished these five oil samples, which can be further used for proper oil-replacing period determination and fault prediction.