An approach to ERO problem in displacement eddy current sensor

Abstract Eddy current (EC) sensors are widely applied in displacement (proximity) measurement as well as nondestructive testing and evaluation for defect detection or material characterisation. For displacement measurement, one of the research aims is to overcome measurement uncertainties due to material variation and inhomogeneity. This problem is called as electrical runout (ERO) problem. In this paper, an approach to ERO problem is presented based on the coaxial ellipse distribution (CED) pattern of the EC sensor. In the CED pattern, the real and the imaginary parts of the magnetic flux density in the z-component (B z ), with the variation of the sample conductivity under the different lift-offs, are located on an ellipse curve. Furthermore, the CED pattern is verified by the different sensor specifications, such as excitation frequency and probe coil geometry. According to the CED pattern, the ERO problem in EC sensors can be overcome well when the sample is magnetised to saturation. Keywords: eddy current sensorsERO problemcoaxial ellipse distributionsample conductivitymagnetic flux density Acknowledgements The authors would like to thank the National Nature and Science Committee for the research under the Grant No. 51005039 and the State Key Laboratory for Manufacturing System Engineering (Xi'An Jiaotong University) under the Grant No. sklms2011005 for their financial support. The authors also thank Associate Professor Yong Li of the Xi'an Jiaotong University for helpful discussions.