An optical system for the online measurement of roughness parameters in a strip processing line was first used at ThyssenKrupp Stahl AG in the mid-90s. The system used at the time was developed by the Munich-based company Sick and made available for tests by the company Opdix, Based on the generally positive laboratory results, a decision was made to install the measuring equipment on the top and bottom sides of the strip in hot dip galvanizing line No. 7 in Bochum. To assess the optical measurement method, the roughness parameters determined by the line operators using a mechanical stylus instrument were compared with the results (average over strip length) of the optical measurements. Initially, the results obtained in production use were virtually the same as those of the laboratory tests. Over time, the coefficient of determination of the comparts deteriorated increasingly. Fig, 1 illustrates this trend schematically, it shows the progression over time of the coefficient of determination of comparisons between stylus measurements by the line operators and optical measurements.
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