The paper presents the building up of a computer controlled measurement system based on National Instruments Data Acquisition card and National Instruments LabVIEW software package. The aim of this research is to detect surface cracks on steels by applying a Magnetic Flux Leakage (MFL) testing method. First, a finite element based procedure has been implemented to analyze the arrangement. One important question is the position of the sensors. Now, eddy currents have been neglected, but the nonlinear characteristics of specimen have been taken into account.