| Lubricating oil,which is widely used in mechanical equipment,has the functions of lubrication,cooling,rust prevention,oxidation resistance,sealing and buffering.During the operation of mechanical equipment,the lubricating oil contains various types of pollutants.Among them,the pollution of metal particles are most serious.Due to the high hardness of metal particles,it is easy to cause wear and operation failure of moving parts in mechanical equipment.Through monitoring the metal particles in the lubricating oil,the working state of the friction pair in the equipment can be obtained from the information of the material,quantity,size and shape,so as to predict and warn the fault.Therefore,the monitoring of metal particles in lubricating oil is an important and effective sensing technology.In this paper,an inductive metal particle online monitoring sensor is designed based on electromagnetic induction.According to the law of electromagnetic induction,the distribution characteristics of magnetic induction intensity in single solenoid coil and two parallel solenoid structures are analyzed.It is found that the magnetic field in the radial position of the coil is weaker but more uniform than that in the internal axial region.When the two solenoids are placed side by side,the axial magnetic field between the two coils can be more uniform by adjusting the distance between the two coils to 1.18 times of the radius of the coils.Through the electromagnetic simulation of Ansoft Maxwell,the static magnetic field distribution of two parallel double coils(with or without ferrite)is analyzed.It is found that the magnetic field in the central radial region is strengthened without affecting the uniformity of the magnetic field after adding ferrite into the coil.The structure design and theoretical model of the sensor detection section are determined.Through the transient simulation of the sensor,the effects of the type,size,velocity and path of metal particles in lubricating oil on the magnetic field in the detection area are studied.The results show that the sensor detection section designed in this paper can effectively distinguish ferromagnetic and antiferromagnetic metal particles.The frequency range caused by iron and copper particles of 50?m to 400?m is-0.55121% to-0.66513% and 0.021359% to 0.033597%,respectively.The velocity of metal particles has little effect on the detection effect.In different motion paths,when iron particles move along paths within 1mm in longitudinal direction and 2 mm in transverse direction from the center path,the influence on the magnetic induction intensity of the original magnetic field does not exceed 100 mT,so the influence of different motion paths on the original magnetic field can be neglected within the allowable range of errors.According to the principle of LC oscillation circuit,a detection circuit matching the sensor detection section is designed.The data acquisition and signal processing system of sensor is established by using Keysight frequency meter as data acquisition hardware when LabVIEW and MATLAB as data processing software.By means of sliding average filtering and wavelet packet analysis,the collected frequency signals are processed and the effective output signals containing particles information are obtained.The designed sensor is tested and its response to different sizes of ferromagnetic and antiferromagnetic metal particles in laboratory is analyzed.The test results show that the sensor can distinguish and detect metal particles with sizes ranging from 50?m to 400?m.The relative error of iron particles between experimental and simulation results is 1.81%~2.21% and that of the copper particles is 1.28%~4.76%.Therefore,the actual detection characteristic curve of the sensor for iron and copper particles is determined by the fitting curve of the experimental results.The new metal particle sensor proposed in this paper can effectively distinguish iron and copper particles,has high sensitivity and the advantages of wide flow channel and small sensor size.It has important theoretical and application value in practical engineering applications. |
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