Study On Measurement Of Electrical Conductivity Of Metals Based On Eddy-current Method

As one of the most important physical property of metal materials, conductivity can be used to select material, determine the hardness and the heat treatment condition of the metal materials. Based on the principle of electromagnetic induction, eddy current method has the advantages of high speed and low cost, is widely used to detect the electrical conductivity of the metal material. Combining the theory of eddy current measurement, this thesis built a finite element model, conducted simulation and experimental study of conductivity measurement, developed a suit of conductivity experiment system as the core of FPGA.The main research work includes:(1) Finite element algorithm theory of eddy current field and boundary conditions is researched, then the theory model of measurement of electrical conductivity is established with the application of Ansys Maxwell software. The results showed that the phase of the amount of the impedance correspond to electrical conductivity, can be used for electrical conductivity measurements; the changes of lift-off has an impact on phase signal, and measures need to be taken to suppress it.(2) This Thesis designed and developed an experimental system as the core of FPGA. The hardware circuit section includes vortex excitation signal generation and amplification, the eddy current sensor and the signal picking up, analog signal data acquisition, FPGA internal logic function design, PCI interface circuit design and power supply module. The software section includes PCI driver development, DLL design of hardware and software interface, matlab interface design.(3) The algorithm of electrical conductivity measurements based on linear fitting and BP neural network is developed. Experimental results show that the conductivity measurement accuracy of neural network method is higher than linear fitting method. And the accuracy of measurement slightly higher after add lift-off suppression algorithm. The accuracy of the conductivity experimental system developed at around 3%.