Steel belts in coils are tinned by being lead through a series of tanks containing electrolyte. Layer thickness, hardness and smoothness depend on a multitude of variables: the speed of the steel sheet, the composition of the electrolyte, the flux and roller pressure. The tin concentration of the electrolyte in the last tank is important for the quality of the surface. A concentration of tin which is too high causes deposits on the roller, leading to indentations on the surface of the steel sheet. Low concentration leads to voids and imperfections in the tin surface.
The concentration of tin can be measured online by a BERTHOLD measuring system LB 379.  Using the same method, other metals in acids or solutions can be measured.