| The information of metal particles in oil can reflect the actual health state of mechanical equipment,thus distinguishing and detecting metal particles in oil of marine machinery is helpful to timely judge the wear degree,rate,type and position of marine equipment,which plays an important role in improving the reliability of marine equipment and saving operation cost.For the differential detection of metal particles in oil,based on the National Natural Science Foundation of China,considering the non-uniformity of magnetic field distribution in the coil,a model for calculating coil impedance increment triggered by a metal particle at any position was established firstly,and the effects of metal particles at different positions on the detection sensitivity were analyzed;Then the coupling impedance model of magnetizing medium and coil was developed,which revealed the mechanism of sensitivity improvement for the detection chip by the geometric and electromagnetic parameters of magnetizing medium.Based on this,microfluidic detection chips using magnetizing medium were designed,which realizes the detection sensitivity improvement for ferromagnetic metal particles and nonferromagnetic metal particles;Finally,for the aliasing problem triggered by multiple metal particles,the impedance signal aliasing experiments of multiple metal particles with different sizes,different spacing and different magnetic properties were designed,so as to reveal the impedance signal aliasing law caused by different combinations of metal particles.The main research work and related results are as follows:(1)Considering the non-uniformity of magnetic field distribution in coil,the inductance and resistance change rules of the detection chip coil induced by ferromagnetic metal particles and non-ferromagnetic metal particles at any position were studied.Firstly,based on BiotSavart law,the single integral expression of magnetic induction intensity in coil was derived,and the axial and radial distribution characteristics of magnetic induction intensity in coil were analyzed.Then a model for calculating coil inductance and resistance increments triggered by a metal particle at any position was established,and experimental verification was carried out.The inductance increment triggered by ferromagnetic metal particles decreases slowly with the frequency.The coil resistance increment triggered by ferromagnetic metal particles and the inductance and resistance increments triggered by non-ferromagnetic metal particles increase quickly with the frequency.Finally,the experiment for the influence of metal particles at different positions on coil impedance signal of detection chip is designed,and the variation rules of coil inductance and resistance signals triggered by metal particles with different positions at different frequencies,different particle sizes and different speeds were analyzed,which confirmed that there will be a “double peak” in impedance signals triggered by metal particles passing along the radial direction of the coil.The larger the particles are,the more serious the “double peak” phenomenon is.The increase of particle velocity will aggravate the signal “double peak” phenomenon for ferromagnetic metal particles,while the increase of excitation frequency and the decrease of particle velocity will aggravate the signal “double peak”phenomenon for non-magnetic metal particles.(2)The coupling magnetic field model and the coupling impedance model of magnetizing medium and the coil were established,which revealed the mechanism of the geometrical and electromagnetic parameters of magnetizing medium on the sensitivity improvement of the detection chip.Firstly,the influence of the length,diameter,relative permeability and conductivity of magnetizing medium on the magnetic field distribution in the detection area was studied by building a three-dimensional model of the coupling magnetic field between magnetizing medium and the coil.When the electromagnetic parameters of magnetizing medium are fixed,the magnetic induction intensity in the detection area increases with the radius of magnetizing medium when the ratio of magnetizing medium to the coil radius is less than 0.2;the magnetic induction intensity in the detection area reaches the maximum value when the length ratio of magnetizing medium to the coil is 1.When the geometric parameters of magnetizing medium are fixed,the magnetic induction intensity in the detection area reaches the maximum value when the relative permeability of magnetizing medium is 300;the magnetic induction intensity in the detection area begins to decrease when the conductivity of magnetizing medium increased to 3.0×107 S/m.Secondly,starting with the current carrying ring containing magnetizing medium,the vector magnetic potential constraint equation and boundary conditions were constructed,then the vector magnetic potential expressions of the current carrying ring containing magnetizing medium in three fields were obtained through the separation of variables method.Combined with the superposition principle,the coupling impedance model of magnetizing medium and coil was obtained finally and verified by experiments.On this basis,the influence of the geometrical and electromagnetic parameters of magnetizing medium on the coil impedance increment was analyzed.The coil inductance increment first increases and then decreases slightly with the length of magnetizing medium,and the resistance increment increases with the length of magnetizing medium;The coil inductance and resistance increments both increase with the diameter of magnetizing medium,and increase firstly and then become stable with the relative permeability of magnetizing medium;With the increase of conductivity of magnetizing medium,the coil resistance increment increases first and then decreases slightly,and the coil inductance increment decreases.(3)According to the mechanism of improving the detection sensitivity to metal particles by using magnetizing medium,two microfluidic detection chips with the magnetic medium were designed to improve the detection sensitivity of ferromagnetic metal particles and nonferromagnetic metal particles.Firstly,taking ferrite as magnetizing medium,a planar coil detection chip with ferrite was designed.The addition of ferrite can effectively improve the magnetic field distribution in the detection area of the planar coil chip.The experimental results show that the planar coil detection chip with ferrite can eliminate the “double peak” problem of impedance signals triggered by the radial passage of metal particles,and can improve the impedance signal amplitude and signal-to-noise ratio of metal particles.Based on the joint observation of inductance and resistance signals,the planar coil detection chip with ferrite can detect ferromagnetic metal particles with diameter of 40μm onwards and non-ferromagnetic metal particles with diameter of 90μm onwards in the oil.Secondly,taking silicon steel sheet as magnetizing medium,a solenoid coil detection chip with two tip silicon steel sheets was designed.The two tip silicon steel sheets formed a conical flux aggregator,by which a highgradient magnetic field in the detection area was generated.The experimental results show that the solenoid coil detection chip with two tip silicon steel sheets can significantly improve the sensitivity of metal particle detection.Based on the joint observation of inductance and resistance signals,the solenoid coil detection chip with two tip silicon steel sheets can detect ferromagnetic metal particles with diameter of 30μm onwards and non-ferromagnetic metal particles with diameter of 60μm onwards in the oil.(4)For the signal aliasing problem of multiple particles caused by the sensitivity improvement,the experiments for signal aliasing of metal particles with different sizes,different spacing and different combinations of magnetic properties were designed,and the impedance signal aliasing rules of metal particles with different combinations were analyzed.For two metal particles with the same magnetic property pass through the detection chip simultaneously,the signals are aliased to generate an independent impedance pulse signal,and the inflection points are generated in the rising or falling edge of the aliasing signals.The size relationship between the two-particles can be judged based on the height of aliasing signals before and after the inflection points.The aliasing signal amplitude increases with the particle size,but decreases with the spacing between two-particles.For two metal particles with different magnetic properties,the amplitude of aliasing signals is suppressed when the spacing between two-particles is smaller;and the magnetic properties can be distinguished and the sizes can be well estimated by aliasing inductance signals when the spacing between two-particles is larger.The amplitude of aliasing resistance signals is between the single component particle signal amplitude and the sum of the component particle signal amplitude,and decreases with the increase of the spacing. |
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