Abb Schweiz Ag

Martin Haldin

Jarl Sobel

Sten Linder

Anders Eidenvall

Aleksander Dzieciol

A method of non-contact measurement of a thickness (d) of an object of an electrically conductive material by means of a Pulsed Eddy Current, PEC, system including a transmitter coil and a receiver coil. The method includes, after having turned off a current in the transmitter coil, at the receiver coil, measuring a voltage induced by the decaying magnetic field at a first time point, a second time point, and a third time point. The method also includes calculating a total magnetic flux which is generated by the eddy currents in the object at the first time point and picked up by the receiver coil, by comparing the measured flux at the first time point with a predetermined total flux picked up by the receiver coil when no object is present. The method also includes normalizing measured magnetic flux resulting from the eddy currents and picked up by the receiver coil, using the calculated total magnetic flux as a normalization factor such that the normalized eddy current flux is independent of a distance between the object and the transmitter and receiver coils. The method also including, based on the measurements at the first, second and third time points, determining the thickness and the resistivity of the object.

Thickness measurement using a pulsed eddy current system

A method for determining a present thickness of a work item while being processed in a rolling mill, the method including: acquiring a data signal reflecting a time dependence of an eddy current decay in the work item caused by an applied pulsed magnetic field, determining a thickness parameter value based on the acquired signal, the thickness parameter value being determined from samples in the data signal, the thickness parameter value being dependent on a ratio between a thickness of the work item and a resistivity of the work item, computing a ratio between a reference thickness value of the work item and the thickness parameter value to thereby provide an instantaneous resistivity value, determining a mean resistivity value based on the instantaneous resistivity value, and providing an output signal based on the mean resistivity of the work item and the thickness parameter value, the output signal being indicative of the determined present thickness of the work item.

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Västerås, Sweden

Martin Haldin