Metal Debris Detection Technology Study In Aero-engine Lubrication Oil

The main function of lubrication oil system is to ensure lubrication and heat dissipation of aero engine, and the other important function is to be used as the transmission medium of debris. Therefore, in the process of wearing which generates debris, lubrication oil contains rich and valuable wearing information about engine. Therefore, engine lubrication oil metal debris detection technology is used as an important mean of engine fault diagnosis and prediction. Traditional spectral analysis, iron spectrum analysis and other off-line metal debris detection technology costs mush and cannot detect in real time. Therefore, on-line detection technology has become an important searching direction. Therefore, it is necessary to study in depth the on-line metal debris detection technology, to develop an on-line detection sensor with high accuracy, stability and flexibility.Firstly, this paper analyzes the basic principle of inductive sensor detection and establishes the calculation model of magnetic field of current carrying coil and based on which establishes the calculation model of magnetic field of electrified solenoid. Finally, establish the calculation model of magnetic disturbance by metal particles with specified volume on electrified solenoid. Analyzes the equivalent circuit of three coils differential inductive sensor and establishes the calculation model of sensor output voltage which determines the mapping between metal debris size and sensor output voltage.The hardware circuit of the sensor detection system is designed, which includes two parts: sensor driver circuit and sensor detection circuit. Lower computer software is developed in Keil IDE, using programming language C. The main contents of the circuit design are as follows: firstly, the peripheral circuit is designed by AD9850 and based on operational amplifier OPA228 the voltage polarity inversion circuit is designed. Elliptic low pass filter circuit is designed to remove clutter signal component according to the characteristics of output signal of frequency synthesizer. Finally, based on operational amplifier OPA165 design voltage current conversion circuit to generate sinusoidal current for driving the sensor. The sensor detection circuit design includes: conditioning circuit, SCM control circuit and host computer communication circuit. Firstly, theoretical model of the sensor output is analyzedto design pre-amplifying circuit. Based on the theoretical model precision rectification circuit is designed to demodulate the amplitude of output signal, and particle size information is got. For removing signal noise low pass filter is designed. Finally, the core control circuit based on MCU C8051f060 is designed and host computer communication interface circuit. By Altium Designer software the entire system hardware circuit schematic and PCB is designed.Software design includes two parts: upper computer software and lower computer software. The lower computer software design includes hardware initialization, data acquisition and host computer communication interface modules etc. initialization module realizes the function of setting AD9850 registers, A/D conversion mode and sampling frequency. Data acquisition module is within the process of interrupt subroutine which happens at the time of completion of once A/D conversion. The conversion is triggered by overflow of timer. When conversion is complete, interrupt subroutine is entered, program read A/D conversion result register and send the data to host computer. Host computer communication interface module is programed based on read and write timing of FT245 RL. Upper computer software is developed by using LabVIEW, the main function includes: lower computer data reception, data splice, data smoothing and waveform display. Lower computer data reception is realized by using VISA API and then connect the high byte and low byte data to a complete 16 bits data. Process the data by using median filter and Butterworth low pass filter. Call waveform display control to display the data waveform.Finally, the system is tested by using metal particles with different sizes, and the system results are compared with the sensor software simulation results. The experimental results show that the theoretical model of the senor output is basically consistent with the real system testing results. This detection system minimum detected diameter of ferromagnetic particles is up to about 200μm. In this paper, the designed system has a certain ability of detecting metal debris and an advantage of small size, low cost and high accuracy. It has an important theoretical significance and provides a good reference value for the future research on on-line oil metal debris detection system technology.