A decay time approach for linear measurement of electrical conductivity

Nitrogen contamination of weld material affects mechanical properties and results in small change of the electric conductivity. This small difference of resistivity needs to be measured since the material property is affected by the nitrogen contamination level. A major challenge in determining the contamination level is the accurate measurement of resistivity in the presence of lift-off variation, top oxide layer and surface irregularities. In this paper, a novel approach based on Decay Time (DT) using Pulsed Eddy Current (PEC) and a high sensitive magnetoresistive (MR) sensor is proposed to measure small changes in electrical conductivity of materials. The DT parameter defined herewith is linearly correlated with material conductivity allowing it to be used for estimating the conductivity from transient PEC measurements. Moreover, this method is less sensitive to lift-off variations. The operation principle of this method is demonstrated using finite element model (FEM) simulation and validated using a prototype probe comprising an excitation coil and MR sensor. Weld metal samples with varying levels of nitrogen contamination are tested using the prototype probe demonstrating the feasibility of the method. © 2018