Simulation And Design Of Eddy Current Distance Measurement System

As a nondestructive testing component, Eddy Current Sensor (ECS) operates on the principle of eddy current effect. It has been widely used in many sections of engineering and science researches due to its advantages such as non-contacting, high measuring accuracy, fast response, simple structure, wide frequency response range and strong ability of oil contamination immunity. However, there still exist some shortcomings in ECS, such as small linear range and sensitive to the material properties, which hinder the further application of the sensor. So it is of great significance to study this to improve its performance.Eddy current distance measurement system consists of four parts: eddy current sensor, signal measuring circuit, data processing and result display part. Because of eddy current effect, the change of distance will affect the coil impedance which is then transformed into electric signal and calculated by the signal measuring circuit. As a result, the reliability and stability of the signal measuring circuit has an important impact on system performance.In this thesis, the author studies the characteristics of eddy current effect and the performance of ECS by means of finite element method and then puts forward a new type of signal measuring circuit. The main works are as follows:1. Based on the electromagnetic foundational theory, modeling theory and process of Finite Element Method, two 3D models of ECS are built by analyzing the working principle of ECS and optimizing the original model. In addition, the two models, single-coil structure and dual-coil structure, are also compared. Then, on the basis of two models, characteristics of eddy current and eddy effect are calculated and demonstrated. Furthermore, the relations between the performance of ECS and conduct material properties and the coil parameters are analyzed by way of finite element simulation.2. The traditional signal measuring circuit of ECS is composed of discrete components, so circuit parameters vary with environment remarkably. In order to enhance integration, stability and reliability of the circuit, the author designs a novel signal measuring circuit based on impedance converter integrated chip AD5933. Firstly, impedance analysis and orthogonal signal demodulation algorithm are introduced. And the internal functional modules of AD5933 with their working principle are introduced in detail. Secondly, the impedance measurement circuit based on AD5933 is designed and produced. The paper describes the overall profile of the hardware circuit, with an emphasis on design of voltage reference circuit and signal processing circuit. Finally, the new measurement circuit is verified by experiment.