| Magnetostrictive displacement sensor has the advantages of high measurement precision,high range,easy installation,safety and high reliability,so it plays an important role in many fields,such as measurement of displacement of hydraulic system,liquid level monitoring of giant tank,detection of position in industrial production.There are some problems in magnetostrictive displacement sensor,such as interference of reflected wave and blind distance in measurement,which may lead to the decrease of accuracy in measurement,and even make the sensor failure.In view of the above problems,based on the influence factor of output characteristics of sensor,this thesis discusses the effective method of restraining the interference of reflected wave,by analyzing the influence of waveguide wire,fixed device and damping device on the output voltage of the sensor.And then,the detection coil is optimized to reduce the length of blind distance when the sensor is measuring,by analyzing the influence of the detection coil and permanent magnet on the impulse response signal and the blind distance in measurement.In this thesis,a fast measurement method of the elastic parameters of the Fe-Ga waveguide wire is proposed,which provides guidance for the selection and preparation of the waveguide wire.Based on the reflection effect of the fixed device on the stress wave,the cause of the interference of reflected wave is analyzed.Based on the propagation process of stress wave in the sensor,the expression of the voltage of reflected wave is derived and verified by experiments.The influence of stress wave attenuation coefficient of waveguide wire and reflection coefficient of stress wave of fixed device on the interference of reflected wave is studied,which provides the basis for the adjustment of the fixed device and the reasonable selection of the waveguide wire.Based on the function of the damping device,an experimental system is designed to study the parameters of the damping device.The influence of the Shore hardness,length and diameter of the damping device on the voltage of characteristic wave is analyzed by experiment.The optimized damping device can effectively reduce the voltage of reflected wave and suppress the interference of reflected wave.Based on the theory of magnetic-mechanical coupling,the relationship between the radial pressure and the output voltage of the sensor is analyzed,and a new method is proposed to suppress the interference of reflected wave by applying radial pressure on the waveguide wire.The influence of the value of radial pressure and the acting length of radial pressure on the voltage of characteristic wave is studied by experiment,and the optimal range of radial pressure is obtained.This method can not only suppress the interference of reflected wave,but also improve the effective range of the sensor.The failure reason of the sensor in blind distance caused by the impulse response signal is analyzed.Based on the circuit theory,the transient response expression of the equivalent circuit of the detection coil is derived.The relationship between the impulse response signal and the parameters of the detection coil is analyzed.The influence of the detection coil of the sensor on the impulse response signal and blind distance in measurement is analyzed by finite element analysis.The optimized structure of the detection coil can reduce the blind distance in measurement and improve the effective range of the sensor.In this thesis,the theory and solution about interference of reflected wave and blind distance in measurement can provide theoretical and methodological basis to improve the accuracy and the effective range of the sensor.The research results can provide guidance for the development of high-performance magnetostrictive displacement sensor. |
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