Output Characteristic Model And Analysis Of Magnetostrictive Displacement Sensor

As one of the ultra-precision displacement measuring instruments,magnetostrictive displacement sensor is broadly used in the fields of water conservancy and hydropower,aerospace,nuclear power plant,etc.due to its advantages of non-contact measurement,anti-interference,strong adaptability and long service life.In order to develop a magnetostrictive displacement sensor with large range and high accuracy,the output characteristics of magnetostrictive displacement sensor are studied in this paper.It is devoted to solving the problems existing in the theoretical model of sensor,such as the unclear relationship between magnetostriction of waveguide wire and output voltage,the absence of considering the attenuation characteristics of stress wave and the influence of torsional stress on output characteristics,and so on.Firstly,the working principle and complex magnetic field distribution of magnetostrictive displacement sensor are systematically analyzed,and the magnetic field distribution is simulated by finite element analysis method.The optimization scheme of sensor structure is proposed,the position of exciting current and detection device of sensor are adjusted,and the signal-to-noise ratio and measurement accuracy of sensor are improved.Secondly,by analyzing the propagation attenuation of stress wave in the waveguide wire,the functional relationship between the output voltage of the sensor and the propagation distance of the stress wave is established based on the relationship between the acoustic pressure intensity and the peak value of the acoustic wave,and based on the electromagnetic theory of Weidmann effect and magnetostrictive inverse effect,the output characteristic model of the sensor is deduced.The dependences of output voltage on propagation distance,magnetostrictive strain of waveguide wire,bias magnetic field and excitation magnetic field is quantitatively analyzed.In addition,the prototype of displacement sensor is fabricated and the output voltage test platform is built.Based on the principle of undamped stress wave reflection,a test method for sensor output characteristics is proposed.The Fe-Ga wire is tested with a diameter of 0.5mm and the stress wave attenuation coefficient of 0.1323Np·m^-1.It is measured that when the propagation distance increases from 0.312m to 4.266m,the output voltage of the sensor decreases from 172m V to 99.5m V when the bias magnetic field is 10k A/m and the excitation magnetic field is 4.25k A/m.The accuracy of the output model is verified experimentally.The research shows that,in order to improve the output voltage and test range of the sensor,the waveguide wire with large magnetostrictive strain should be selected,the bias magnetic field should be within the range of 9?12k A/m,and under the premise of ensuring the normal and stable work of the sensor,the closer the excitation magnetic field is to the bias magnetic field,the better.At last,the influence of torsional force on the Weidmann effect is analyzed from the perspective of magnetic domain.Combining the material mechanics,the nonlinear constitutive model of Fe-Ga alloy and the magnetostrictive inverse effect,the output characteristic model of magnetostrictive displacement sensor under the combined action of helical magnetic field and torsional stress is established and calculated accordingly.A test platform of output voltage under pre-applied torsional stress is built.The law of non-linear decrease of output voltage with the increase of torsional stress is determined theoretically and experimentally.The research shows that under the same magnetic field,the voltage drop caused by forward torsional stress is less than that caused by reverse torsional stress.Increasing bias magnetic field or exciting magnetic field can offset the influence of torsional stress on voltage to some extent.In this paper,the relationship between output voltage and propagation distance is clarified,the output characteristic model of the magnetostrictive displacement sensor under the spiral magnetic field and torsional stress is established.The linear relationship between output voltage and magnetostrictive difference(?_l-?_t)is determined for the first time.The research can provide theoretical basis and guidance for the design of displacement sensors with large range and high accuracy.