Research On Oil Wear Debris Multichannel Inductive Detection Method Based On Parallel Resonance Principle

The wear debris detection is vital to marine equipment wear status monitoring.Owing to the simple structure and the ability to differentiate ferrous and nonferrous wear debris,inductive sensor has been widely used for real-time online wear debris detection.When the particle passes through the sensing coil,the magnetic field will be disturbed,which further change the output signal of the sensor.The output signal contains much of wear debris information(namely,particle size,material,concentration,etc.)in lubricants.For certain structure of the inductive sensor,the sensitivity and throughput would limit each other.The sensor with narrow inner diameter has high sensitivity,but the throughput would be relative low,and vice versa.In this work,The wear debris detection system based on the parallel inductance-capacitance(LC)resonance principle with current inductive sensors was built;the sensitivity improvement method by optimizing the parallel capacitance was proposed;and the multichannel wear debris detection methods based on phase and time division multiplexing was designed.(1)The influence mechanism of the metallic particle magnetization effect and eddy current effect act on the coil impedance was demonstrated.And the sensing coil magnetic field numerical simulation model was established based on Maxwell equations.The particle influence that act on coil magnetic field under the excitation of alternating voltage was analyzed,and the particle diameter and radical position influence on the coil impedance was investigated.The results shown that,when the ferrous particle passes through the coil,magnetization effect and eddy current effect generated inside the particle,which leading to the coil inductance increase and tiny resistance increase.Finally,the impedance increased.When nonferrous particle passes through the sensing coil,only eddy current effect generated inside the particle,which leading to the inductance decrease and resistance increase,and finally the impedance decrease;the larger the particle diameter,the stronger the magnetization effect and eddy current effect,and the higher the impedance variation;with the particle position moving from the center to the edge of the inner hole,the induced impedance variation also enhanced.(2)The wear debris detection method based on the parallel resonance principle was investigated.Firstly,the parallel resonance detection circuit system for single sensing coil,and detect the output sine wave peaks by synchronized sampling method was designed.Secondly,the parallel capacitance influence on the particle induced impedance variation was theoretically analyzed and experimentally investigated.The relative impedance variations of ferrous and nonferrous particles have different growth trends,and two kinds of particles need different optimal parallel capacitances.To obtain both optimal detection sensitivity of two kinds of particles,we designed double-resonance circuit parallel detection system.Two sensing coils are separately connected with two optimal capacitances to obtain the optimal detection signals for two kinds of particles.Experimental results shown that two sensing coils were independent in particle detection and no crosstalk was found in the detection signal.The double-resonance system could detect iron and copper particles as small as 25 μm and 66 μm.(3)A multichannel wear debris detection method based on phase division multiplexing was promoted.The same frequency sine wave peaks from multiple parallel resonance circuits are integrated into one output signal.The peaks are arranged on different phases with equal distance which would be sampled to obtain the detection signal of each channel.The fourchannel detection system were designed to verify this method.Four sine wave peaks are combined into one output signal by phase shifting,peak cutting,signal synthesis.The output signal is recorded by synchronized sampling method.The experimental detection results of single particle shown that the signal detection procedure in four channels are independent from each other.Only one excitation signal and one sampling channel are required to simultaneously detect signals of four channels,which would promote the sensing throughput for four times.(4)A novel multichannel wear debris detection method based on time division multiplexing method was promoted.The peaks of multiple sine waves were cutted out and were combined into different periods of output signal.The peaks of output signal were sampled to obtain the detection signal of multiple sensing coils.Ten-channel wear debris detection system were designed to verify the proposed method.Ten special square waves were introduced into the system to separately lift the peaks of ten sine waves.Ten peaks were cut out and combined into one output signal.Comparing with the phase division multiplexing method,this multichannel detection method does not increase the peaks number in output signal,then there is no need to increase the sampling frequency.The pseudo-dynamic testing results shown that the particle detection procedure in ten channels are independent from each other,and no sensitivity loss in all channels.The dynamic testing results shown that the system is able to detect oil wear debris in ten channels.With the existing sensor structure,this thesis improved the oil wear debris detection sensitivity and throughput by mechnism analysis and circuit optimization,facilitated the application of inductive sensor in ship and ocean engineering area.