A new eddy current displacement measuring instrument independent of sample electromagnetic properties

Eddy current sensors, as one of nondestructive testing and evaluation instruments, have been widely used in displacement measurement as well as defect characterization. However, in eddy current displacement measurement, the test not only depends on the displacement between the coil and samples, but also relates to the electrical and magnetic properties (such as electrical conductivity and magnetic permeability) of samples. So, the eddy current sensor is limited to test one sample after one calibration. In order to make eddy current sensors compatible with more samples after one calibration without testing error, this paper designed a new eddy current displacement instrument extended from the previous theoretical analysis and experiment study investigating the relationship of the coil resistance and inductance. A series of experiments indicate that the designed new eddy current displacement instrument can eliminate the influence of the samples' electromagnetic properties effectively.

► A new eddy current displacement measuring instrument (NECDMI) is proposed and designed.
► The coil impedance vector-projection (CIVP) approach is used in NECDMI.
► The coil impedance is seprated as resistance and indutance by the measuring circuit system.
► The experiments on the designed NECDMI validates the feasibility of CIVP.
► The NECDMI can eliminate the influence of sample electromagnetic properties effectively.