Research On Detection System For The Metal Surface Defect Based On Eddy Current

Metal is widely used in various fields of national economy and people's life,but many are active metals which are easy to be oxidized and corroded when they are long-term exposure to air.This feature will result in the metal surface defects,such as cracks and potholes,which will cause great potential safety hazard.Eddy current testing,as a non-destructive testing method of metal surface defects,with its high efficiency and safety,are more and more widely used.The most famous eddy current testing technique is implemented by the equivalent impedance method based on the coil.Due to mutual inductance,the coil and the detection metal can be equivalent to an impedance circuit,so the metal surface defects can be judged by measuring the impedance of the equivalent circuit.The advantage of this method is easy to detect,and the disadvantage is not directly obtained eddy current information,so the detection error will be relatively large.Therefore,how to quickly and accurately detect the metal defects becomes an important research problem.Using the detection of metal surface defects in practical engineering applications as background,this paper presents a defect detection method based on the frequency response characteristics of the system,and designs a detection system that separates the transmitter from the receiver.The experimental platform of defect detection system was successfully built,and the feasibility of the proposed method was verified by experiments.The main work and innovations of the paper are as follows:1.Propose a method to judge the metal surface defect by calculating the system frequency response characteristics of a composite system which is composed of coil?metal and magnetic sensitive resistance.2.Design a detection system separating transmitter and receiver.In the detection system,the transmitter uses the symmetrical coil,which can inhibit the excitation signal interference of received signal;the receiver uses the sensitive magnetic resistor,which can improve the accuracy of eddy current magnetic signal.3.Analyze a variety of signal filter method.Signal energy received by magnetic resistor is weak and is easy to be polluted by noise,so directly using the received signal which not deal with the noise,will make the system frequency response great error and then lead to miscalculation of defects.4.Develop an experimental platform based on defect detection system.The paper designed experiments to test defects with different area and different depth respectively and analyzed the testing results.Through actually testing the system,the feasibility of the proposed detection method and the accuracy of the detection system are verified.