Design Of Eddy Current Testing System For Metal Surface Defects Based On ZYNQ

In the process of manufacturing and using metal devices,due to the influence of the environment,there will be bubbles,corrosion,cracks and other defects on the surface.The existence of defects will affect the corrosion resistance,wear resistance and fatigue resistance of the devices.If not found in time,it will cause huge economic losses and safety accidents.Eddy current testing,as a method of metal surface defect detection,is widely used because it does not need couplant,and is easy to operate and automatic.According to the principle of eddy current testing,the eddy current nondestructive testing system based on zynq is designed,and the relevant experiments are carried out to verify the system.The main work is as follows:(1)The theoretical basis of eddy current testing is described,and the testing model is equivalent to the corresponding circuit.The influence of sensor probe parameters on the testing results is analyzed.The process of sensor scanning metal plate is simulated by COMSOL finite element software,and the influence of excitation frequency and lift off distance on the testing results is analyzed.According to the principle of eddy current testing,the excitation signal output circuit and the detection signal acquisition circuit are designed.(2)According to the principle of digital phase sensitive detection,the corresponding algorithm IP core is designed,the DMA communication is explained and the implementation method is given.The frequency conversion control module is designed,which can change the excitation signal frequency through the upper computer.This paper expounds the principle and structure of FIR low-pass filter,designs the FIR filter coefficient by using FDATool tool of MATLAB,and simulates the designed FIR filter by using system generator.After the simulation,the on-board test is carried out to observe the filtering effect.Finally,the initialization and coordination control flow of each module from PS(processing system)to pl(programmable logic)is designed,and the functions needed to realize UDP(User Datagram Protocol)communication are given.(3)The hardware interface of this system is designed with LabVIEW.Firstly,the excitation signal output circuit and detection signal acquisition circuit are tested to verify the function of the circuit.Then,the change of the detection results is observed from three aspects:changing the excitation signal frequency,changing the lift off distance and changing the defect depth.The system designed in this paper is a single channel eddy current testing system,which has only one excitation signal output channel and one detection signal acquisition channel.The frequency range of excitation signal is 1kHz ～ 1MHz,and the minimum defect depth detected by the sensor is 1.375 mm.