Conductivity Measurement of Nonferrous Plates using A Novel Sensor with Triangular Arrangements of Triple Coils

A novel eddy current sensor is proposed in this paper for conductivity measurement of nonmagnetic metals. It has one excitation coil and two antiserially pick up coils. The three coils have rectangular forms with the equilateral triangular arrangement. The induced voltage of antiserially connected pick up coils is zero when all coils are far enough from conductive objects. However, the induced voltage is nonzero when one pick up coil is close to the conductive object due to the induced eddy currents in the conductive objects and unequal flux linkage in the pick up coils. The real and imaginary components of the induced voltage and their ratio are functions of plate conductivity. The experiments and 3D finite element method analysis of the triple coils sensor are conducted for conductivity measurement of nonferrous plates to estimate their conductivities. The accuracy of the eddy current sensor was tested and analyzed, showing that its error can be as low as 0.2%. Conductivity measurement is also presented using measured impedance change of single rectangular coil parallel to conductive plates with minimum accuracy error 0.4% and the results of conductivity estimation are compared with triple coils sensor.