Research On Temperature Characteristics Of High Temperature Eddy Current Sensor

Eddy current displacement measurement is the method that is non-contact and can achieve high precision signals at normal temperature.However,in the high temperature environment,on the one hand,eddy current sensor coil will be damaged due to high temperature expansion and high temperature oxidation,greatly reducing its service life;on the other hand,the conductivity of the coil and the measured object and the permeability of the measured metal will be changed with the temperature changing,so that the skin depth of coil and the measured metal will be changed.The series AC resistance and the inductance of coil,and the equivalent loss resistance and equivalent inductance of measured metal will be changed by the changing skin depth,thus affecting the parameters of coil,such as equivalent inductance(L),complex impedance(Z)and quality factor(Q).So that the eddy current sensor has obvious temperature drift,which makes the detection accuracy worse and the eddy current sensor even cannot work properly.In view of the problems existing in the eddy current displacement measurement,this paper has carried on the corresponding research:the working principle and equivalent circuit of eddy current displacement sensor are analyzed,and the analytical formulas of the inductance value(L)and the quality factor(Q)of the eddy current displacement sensor in the normal temperature environment are obtained.Furthermore,the temperature characteristics of the eddy current sensor are studied by analyzing the mechanism that L and Q of coil are influenced by temperature,and found that the relative changed amplitude of L was lower than that of Q in high temperature environment However,the equation of permeability of measured metal and temperature is unknown,so that it is impossible to obtain the analytical expression of L and Q of coil in the high temperature environment,and the displacement(X)and temperature(T)can not be obtained by analytical method.Therefore,the method of establishing the model with the experimental data is used to get X and T.In the experiment,L and Q of coil were collected under different different excitation frequencies(f)and different T.The correctness of the mechanism is verified by the experimental data.In order to obtain a more effective method for temperature compensation of eddy current displacement sensor,the support vector regression(SVR)is used for model identification in the paper,then accurate X and T are obtained using the parameters(L and Q)of coil and the mathematical model,which provides basic theory for the temperature compensation of the eddy current displacement sensor.