Method for thickness measurements of a work item in a rolling mill

A control unit configured to generate an output signal indicative of a present thickness of a work item while being processed in a rolling mill, the control unit being configured to:

• acquire a data signal reflecting a time dependence of an eddy current decay in the work item caused by an applied pulsed magnetic field,
• determine a thickness parameter value based on the signal, wherein the thickness parameter value is 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,
• compute a ratio between a reference thickness value of the work item and the thickness parameter value to thereby provide an instantaneous resistivity value,
• determine a mean resistivity value based on the instantaneous resistivity value, and
• provide the output signal being based on the mean resistivity of the work item and the thickness parameter value, the output signal being indicative of the present thickness of the work item.

A rolling mill comprising:

• a control unit, configured to:
• acquire a data signal reflecting a time dependence of an eddy current decay in a work item caused by an applied pulsed magnetic field, determine a thickness parameter value based on the signal,
• wherein the thickness parameter value is 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,
• compute a ratio between a reference thickness value of the work item and the thickness parameter value to thereby provide an instantaneous resistivity value,
• determine a mean resistivity value based on the instantaneous resistivity value,
• provide an output signal being based on the mean resistivity of the work item and the thickness parameter value, the output signal being indicative of a present thickness of the work item, and
• a set of work rolls configured to process the work item between work rolls to a predetermined work item thickness, and
• a rolling mill stand supporting the work rolls, the rolling mill stand being controllable based on the output signal as a feed-forward signal to alter a distance between the work rolls to thereby alter the thickness of the work item being processed in the rolling mill.