Techniques for measuring strip cleanliness directly in or at cold rolling, cleaning, annealing and galva-nising lines are being examined within the scope of a multinational ECSC research project .
The work at the BFI is concentrating on ellipsometry and the testing of its capability to measure low amounts of contamination left on strips in the form of oil residues and iron abrasion fines.

The measurement principle is based on polarised light changing its polarisation state (orientation and ellipticity) when reflected on a surface.
From these changes in polarisation it is possible to calculate the optical constants of a material and, by using suitable models, to determine the thickness and refractive index of surface layers.

Ellipsometry is very sensitive in comparison with other techniques, enabling the measurement of layer thicknesses down to the atomic level