Development Of Oil Quality Monitoring System Based On The Principle Of Benchmark-Level Calculable Capacitance

With the improvement of China’s industrialization level,the contradiction between the requirements for safe and green operation of machinery equipment,and the untimely detection as well as unclear replacement cycle of oil are becoming more and more prominent.A precise oil replacement cycle has become an important means to reduce the machinery malfunction rate and the intensity of oil consumption.At present,most of the oil quality detection is based on spectral analysis instruments,these have high detection accuracy but are limited by the laboratory environment,which leads to detection result lag.Supported by semiconductor technology and Calculable Capacitance theory.The research and development of new sensors have become an important direction to break through the high-precision real-time detection of oil quality.The purpose of this thesis was to apply the Benchmark-Level Calculable Capacitance to the detection of oil quality,taking automobile engine oil as the research object,facing the application scenario of high-precision real-time monitoring of automobile engine oil quality,the Calculable Capacitance permittivity calculation model with support structure was proposed.The specific research contents included the following aspects:（1）Building the Sensor Computing Model:For the purpose of accurate measurement of oil quality.Starting from the principle of Calculable Capacitance and real-time monitoring of oil quality.Based on a Calculable Capacitance model of an unsupported structure,a Calculable Capacitance permittivity calculation model with support structure was established,which provided a theoretical basis for the design of subsequent oil quality sensors.（2）Model Simulation Verification and Sensitivity Optimization:For the question of the feasibility of calculable capacitance permittivity calculation models with support structures.Validated by comparing the analysis of FEM software simulation results with theoretical calculations.For the sensitivity of the model,the structure and parameters of the model were optimized in terms of three aspects:the shielding layer,the protective electrodes,and the thickness of the support structure.（3）Oil Quality Monitoring System Terminal Design:Firstly,the design of an oil quality sensor based on the Calculable Capacitance model with a support structure for the high temperature and pressure environment in the engine.Then,according to the real-time measurement requirements,an oil quality monitoring system terminal based on embedded and One NET is designed.To further improve the Signal-to-Noise ratio of the system measurement signal,a noise reduction method combining Variational Mode Decomposition and mean filtering is used.（4）Oil Proportioning Experiments,System Performance Analysis:For the quantitative analysis of the performance of the oil quality monitoring system,automobile engine oil proportioning experiments were carried out in this thesis.At the same time,the noise reduction performance of Variational Modal Decomposition combined with the mean filter and the static performance of the oil quality monitoring system are analyzed.The results of the analysis indicated that:noise reduction by Variational Modal Decomposition combined with mean filtering improves the Signal-to-Noise ratio from10d B to 22.9d B,compared with only using mean filter noise reduction,the Signal-to-Noise ratio was improved by 29.3%.The Class A uncertainty of the oil quality monitoring system was 4.2×10^-4.The meter accuracy grade of the Oil Quality Monitoring System was 0.5,a sensitivity of 0.088p F,a nonlinearity error of 2.5%,and a repeatability error of4.71%.