An Approach To Reduce The Lift-off Effect On Pulsed Eddy Current Testing Technique Based On The Investigation On The Lift-off Effect

Pulsed Eddy Current(PEC) testing has been widely used in many fields, such as aerospace, nuclear energy, rail systems, oil transportation, etc. But when the lift-off(the distance between the probe coil and the surface of the tested object) increases, the mutual inductance of the test coil and the tested object will rapidly decrease, and the eddy current density in the tested object will change a lot along with the small changes of lift off, this is called as lift-off effect. When the pulsed eddy current testing system is used to detection of defects, many factors will cause the changes of lift-off, such as the tested object,s coating thickness, expansion/contraction, surface irregularities, and even a little moving of the operator.In order to eliminate the effects caused by lift-off on PEC testing, the precision of PEC in quantitative detection of defects must be improved. This paper will help the experiment testing system more accurate and complete on the basis of the or iginal experiment system. The influence of the lift-off on PEC is been investigated based on the PEC experiment testing system. In investigation, the way to excited, tested object,s material, defect form, structure parameter of drive wire and test components are taken into accounted. According to the conclusions of the investigation, present an approach to eliminate the effects caused by lift-off on PEC testing. Finally, this approach is performed by the hardware design and software design. The experiment result indicated that the proposed approach can reduce the lift-off. The research content of this paper is as follows:(1)In order to optimize the experiment platform, the writer develops the procedure to process data, the circuits of current excitation signal and signal amplification and filter.(2)The writer studied by using the finished experiment testing platform in the condition of different variables of forms of motivation, material of tested item, defect form, parameters of excitation coil structure and tested components, and finally presents in this paper that how the lift-off effect impacts on the defects of pulsed eddy current quantitative detection.(3)The writer puts forward the solutions to eliminate the impacts of lift-off effect on the defects of pulsed eddy current quantitative detection by combining the theoretical analysis and simulation result on the basis of the result above point(2).By combining the experiment research and the improved experiment testing system and using the new approach to eliminate the effects of lift-off effect, this paper verifies the feasibility of experiment testing system and the approach to eliminate the effects of lift-off effect in quantitative detection of defects.