Research On Data Acquisition System Of Capacitance Type Lubricating Oil Debris Online Monitoring

The abnormal friction and wear of the engine inside is a significant cause of aircraft operation fault, the debris it produced will carry a large amount of equipment wear information. The debris in the lubricating oil system will change its physical and chemical properties(including dielectric constant), the equipment running status information could be determined by monitoring lubricate oil system. Some of existing oil debris monitoring methods are inefficient or not sensitive enough, and some make high demands on experimental person. So a data acquisition system of oil debris based on AC bridge capacitance measurement circuit is proposed in this paper.This paper firstly introduces the work principle of the system, then lists some common small capacitance measurement circuit and analyses their advantages and disadvantages. AC bridge capacitance measurement circuit was selected as the design scheme of the system through analyses and comparison. Next, the principle of capacitance sensor was introduced in this paper, and the arc plate capacitance sensor was proposed. Then we use ANSYS software to model, simulate and analyses on the sensor and get the capacitance change of this sensor is fF level and it approximately change as sine wave with debris position. After we designed and made the hardware circuit of oil debris data acquisition system, it mainly includes signal generate module, AC bridge capacitance measurement module, differential amplifier module, phase sensitive demodulation module and low pass filter module. Then we analyses the possible interference problem of hardware circuit combined with related theory of anti interference, and give some solutions. The last work is to design process of system control and data acquisition, test and analyses the experimental performance of designed oil debris data acquisition system by building experimental platform and write the software program.The experimental results show that the amplitude and frequency of signal generate circuit are relatively stable, the output voltage of the system is well corresponded with size of debris. Later, we get the average accuracy of measurement approximately is 138.14uV/um by using MATLAB software to fit the experimental data. It shows that the relevance of debris characteristics, change of oil physicochemical properties and engine wear fault of exactly exist, the equipment running status information could be judged by monitoring lubricate oil system.