Measurement system of ultra-low moisture content in oil based on the microwave transmission method

As an important index of industrial oil, moisture content affects the performance of oil. With the increase of requirement to the oil quality, the measurement of ultra-low moisture content is gradually concerned. To achieve nondestructive measurement of the moisture content in oil, this paper analyzes the principle of dielectric loss of oil-water mixture and proposes a measurement system based on the microwave transmission method. The hardware of the system, horn antenna, and experimental device were designed and built. The system uses a subtracter circuit together with a high-performance microwave chip and high-precision analog-to-digital converter to detect 1dB microwave attenuation. The results showed that the system can measure the moisture content of 0.01%-0.8% in quenching oil and the single detection absolute error is less than +/- 0.05%, and the average detection absolute error of 10 detections is less than +/- 0.02%. This study is useful for nondestructive detection of the moisture content in oil and provides a reference for related product development.