Eddy current measurement of the wall thickness and conductivity of circular non-magnetic conductive tubes

A method to determine the wall thickness and conductivity of non-magnetic tubes using eddy-current measurements is presented. The equivalent circuit impedance formulae for an infinitely long solenoid with a conductive tube inside are derived. Th is simplified theoretical model is appl led to calculate the tu be wall thickness using the measured resistance and inductance of a real long coil with a long tube inside. In order to take into account the coil's finite length, an apparent fill factor is introduced. The last parameter is determined experimentally and used as the fill factor in the theoretical model. We report experimental tests for brass and copper tubes of nominal diameters in the range 12-20 mm and nominal thickness from 0.9 to 2.5 mm. An uncertainty of the wall thickness measurements typically within 2% is obtained. Copyright (C) 1996 Elsevier Science Ltd.