Displacement Detection System Through Eddy Current Measurement With GMR Sensor

The eddy current displacement sensor is a kind of non-contact sensor.Its working principle is based on the eddy current effect and can convert the non-electrical parameter displacement into electrical signal.It has the advantages of strong anti-interference ability,high sensitivity,high reliability,strong stability and simple structure,and is widely used in many application.However,how to improve the sensitivity and stability of the eddy current displacement sensor,enlarge the measurement range of the displacement and the optimization of the size of the detection coil are still waiting to be solved.In order to find a solution to the problem,this dissertation makes a corresponding research on the design of eddy current displacement detection system from the following aspects: First,equivalent transformer model can be divided into excitation coil model,eddy current model and mutual inductance model to solve the system equivalent impedance.The mathematical modeling is used to analyze the functional relationship between equivalent impedance and the measured displacement and to provide the basis for optimizing the coil parameters.The analysis of the results is compared with the results on the study to verify the rationality of the model;Second,the amplitude modulation used in the circuit design is consists of a constant frequency AC signal as the excitation signal and the GMR sensor.The micro-controller controls the external circuit to deal with the GMR sensor output voltage signal and circuit design is also simple,which can effectively overcome the external interference on the output voltage signal and improve measurement accuracy.The software mainly completes the program of the initialization of the micro-controller and the AD9850 chip,the excitation signal frequency writing and key's adjustment and elimination,making the completion of the program to compile and run,and the output voltage signal uses digital filtering algorithm to reduce the measurement;Third,after calibrating the experimentally measured data,it can establish the functional relationship between the output voltage and the displacement of the GMR sensor by the method of least squares curve fitting.We can obtain the result of hysteresis error and repeat-ability error of the eddy current displacement sensor and nonlinear erroranalysis.Finally,the total accuracy of the eddy current displacement detection system can be calculated,which provides a basis for judging the performance of the improved eddy current displacement sensor and the accuracy of the eddy current displacement sensor.The experimental results show that the displacement detection system based on GMR sensor designed in this paper can realize the function of displacement measurement,high precision and good stability and reliability.The device can not only realize the function of displacement measurement,but also meet the industrial technical requirements of simple measurement circuit,low cost and high anti-interference ability.On the one hand,it improves the working efficiency of the measurement system and on the other hand,it lays the foundation for the further improvement of the research of the non-contact eddy current sensor.