Precision measurement of thickness and conductivity of circular and plane products with eddy current metrology

We report here the following topics of a quantitative nondestructive evaluation using eddy currents: cross-section measurements of long conductive products; measurement of the wall thickness and conductivity of conductive non-magnetic tubes; measurement of the thickness and conductivity of foils. On non-magnetic circular rods and tubes, and accuracy of the cross-section measurement was better than 0.3%. for hexagonal and square profiles, the accuracy was typically within 2%. Measurements performed on copper wires (empty set 0.9-1.5 mm) at 1 MHz implied errors on diameter determination typically lower than 4 mu m. Experiments on circular steel rods and wires (empty set 0.9-13 mm) in presence of the magnetic field H=40000 A/m have shown the accuracy of the diameter measurements better than 40 mu m. Experimental tests for brass and copper tubes (empty set 12-20 mm) with nominal wall thickness from 0.9 to 2.5 mm were carried out. Thickness was typically determined with a 2% accuracy simultaneously with a tube electrical conductivity. An uncertainty on conductivity measurements lower than 5% is obtained. An eddy current method based on the theoretical model of two-conductor line placed above a plane conductive medium is also developed. Copper and aluminium foils having thicknesses 15-200 mu m are studied experimentally in the frequency range 5-100 kHz. The uncertainty of the conductivity and thickness measurement better than 2% typically within 1% is obtained