Study Of Oil Monitoring Technology Based On Dielectric Constant Measurement

Abrasion is one of the main factors that affect machinery equipment's reliability and working life-span. Particles produced by abrasion are important information carriers which reflect the abrasion status inner a machine. Lubricating oil has the important function of lubrication, seal and rinse. When lubricating oil is circulating, the particles move within it. Monitoring the particles and other contamination in oil is an important means to status monitoring and fault diagnosis. By oil monitoring, latency faults can be predicted, rational time of maintain and oil changing can be determined, intermission time can be cut short, maintenance and using cost can also be reduced.Lubricating oil's dielectric constant has some relevant change when it is contaminated or wearing off. The capacitance variance of capacitive sensor can reflect that of the lubricating oil's dielectric constant. Therefore, fault information can be gained by monitoring dielectric constant variance using capacitive sensor. In this thesis, a method of oil monitoring based on dielectric content measurement is studied. The principle of the method is expatiated, furthermore, capacitive sensor is designed, methods of tiny capacitance testing are studied, and an applied scheme of testing capacitance is also designed.The main contents of this thesis are as follows:1. Relationship between the quantity of electric metal particles and dielectric constant variance of lubricating oil is analyzed based on the expatiation of capacitance detecting principle. Three typical capacitive sensors, which are sensitive to dielectric constant, are designed. And the characteristics of these sensors are proposed.2. Several detecting methods are studied, aiming at its tiny characteristic. A scheme for detecting capacitance variance precisely and expeditiously is given. At last, oil monitoring system and its communication ports are set up.3. Software of the monitoring system was designed for data collecting and monitoring, which includes USB port chip's firmware, apparatus'driver of exterior parts and applications for monitoring and analyzing.4. A simulative and experimental lubricating oil circulation system is set up for cutting periods of data collection and analysis shorter. Oil samples in different conditions are chosen to carry experiments and analysis through. Meanwhile, relationship between dielectric constant changes and fault information is studied.Experiments validation and data analysis indicate that dielectric constant's variance has correlation with ingredients of lubricating oil and machinery equipment's abrasion fault, and its trend goes in accord with that of lubricating oil wearing off and occurrence of abrasion fault. Dielectric constant variance can reflect oil conditions in wearing off and machinery equipment's malfunction information. Changes of lubricating oil's dielectric constant can be detected effectively and properly using the monitoring system in this thesis. It will afford some referenced evidence in lubricating oil replacing and fault diagnosis of machinery equipments after further quantitative experiments and studies.