Estimating the Hot Rod and Wire Displacement in an Eddy-Current Sensor for Cross-Sectional Area Measurement

The cross-sectional area measurement of hot rolled steel rod and wire is an essential part of the process automation in rolling mills to improve the product quality and to reduce scrap metal and costs. A contactless and nondestructive measuring method is using an encircling pass-through coil as an eddy-current sensor. This rather simple method allows measuring the cross-sectional area of a hot rod based on the almost linear relationship between the coil impedance and the cross-sectional area of a rod inside of it. The radial displacement of the rod inside the coil, causes a deviation in the measured cross-sectional area. This paper shows the proof of concept to estimate the rod displacement passively using two embedded differential coils in a specialized 3D printed coil carrier.