Research On Ultrasensitive Metal Debris Inductive Detector

Inductive debris sensor plays an important role in the health monitoring of mechanical equipment.They which have the advantages of simple structure,low production cost and providing detailed wear particle informantion,have received extensive attention.However,compared with other principles of online debris monitoring sensors,inductive debris sensor has lower particle detection sensitivity.The stability and reliability of the sensor need to be improved in practical applications.In addition,there are still great problems in accurately determining the particle information by output signal of the sensor.These are obstacles that restrict the wide application of inductive debris sensor in the online monitoring of equipment.Although it has been studied at home and abroad for many years,it lacks systematic analysis and optimization of structural parameters affecting sensor performance.In this dissertation,by simply establishing the equivalent mathematical model of the sensor and electromagnetic field simulation,the operating characteristics and performance parameters of the inductive sensor are analyzed.For the improvement of the detection sensitivity,stability and noise suppression of the inductive debris sensor,we focused on the coil probe structure and signal processing circuit of the sensor.A new type of coil probe with one energizing coil and multi-sensing coil,an ultra-efficient automatic unbalanced voltage compensation circuit,and structure of mesh electrostatic shielding have respectively designed.The results show that the indications of the sensor performance have the world's leading level.The main work and conclusions of this dissertation include:1)An equivalent mathematical model of three-coil differential sensor structure is established,and a calculation formula for the output of the detection coil is obtained when a metallic particle passes.The influence of operating frequency,coil structure and particle properties on the output amplitude of the sensor was analyzed by finite element simulation software COMSOL.According to the analysis of relevant factors,the sensitivity coefficient S,is simply defined for comparing sensitivity performance of various inductive debris sensors.2)A new type of sensor coil probe,namely multiple sensing coils inside the excitation coil is proposed.The weak coupling transformer model is established to analyze the coil output signal.This structure helps to increase the degree of the coupling between the detection coil and the particles.So the particle detection sensitivity of the sensor can be improved.The probe structure of two semi-circular sensing coils was produced.A simple and effective signal processing method was used to build a complete platform to test its performance.3)The development of a complete and efficient signal post-processing analog circuit can improve the overall performance of the inductive debris sensor.Firstly,the basic signal processing circuit including low noise amplification,phase sensitive detection demodulation and post amplification is built.The output signal of the coil is effectively processed to extract the particle information.After careful analysis of the influence of the unbalanced voltage on the sensitivity and stability of the sensor in the initial state,the manual compensation circuit was introduced in detail.The test platform was built with the three-coil differential probe.The manual compensation circuit can easily compensate the unbalanced voltage to less than 1 mV.The experiment verifies the effectiveness of the compensation circuit for the sensor operation,enabling the sensor to successfully detect 134 ?m ferromagnetic particles and 230 ?m non-ferromagnetic particles in oil tube of 43 mm diameter.The sensitivity parameter S is 0.003.4)It is proposed that the noise of the excitation voltage is an important factor to influence high-resolution detection.The ultra-balanced condition is necessary to obtain high resolution.Also,in order to overcome the change of the unbalance voltage with temperature and time,the circuit achieving the automatic balance is designed on the basis of manual balance and integrates into the signal processing system.The performance test and analysis of the entire sensor system is conducted.Finally,the automatic compensation circuit can compensate the unbalanced voltage to the,uV level,enabling the sensor to detect 100 ?m ferromagnetic particles and 165 ?m non ferromagnetic particles in a 43 mm pipe.The sensitivity exceeds any inductive particle detector on the market.5)The effects of several external disturbances on the performance of the sensor are analyzed and the solutions are provided.The electrostatic interference generated by the dielectric impurity in the lubrication oil need to be shielded.A shielding layer is specially designed and a simple test platform is built.Experiments show that this structure can effectively shield the electric field interference caused by air bubbles and water droplets,and does not affect the detection performance of the original sensor.For the probe with a very thick aluminum shell,analysis of shielding the external electromagnetic field and a comparative experiment was carried out.The protective methods of mechanical vibration interference are put forward,which is of great significance for the reliable operation of high-resolution sensors.This dissertation can contribute to further studying the theory and design of inductive debris sensors in the future,and promoting the wide application of inductive debris sensors in related fields.