Nowadays, before undergoing downstream processing into refrigerators, roofs or automo-biles, hot-dip coated sheet is already provided with a paint coating to give it the desired sur-face characteristics (corrosion resistance, colour, etc.). The paint coatings have to keep within a certain thickness over the width and length of the sheet. The coating thickness is measured by means of traversing systems located at a distance behind the coater and fur-nace, respectively.

Because of the great non-linearity of the coating system and the speed-dependent delay be-tween coating system and measuring system, an Internal Model Control Approach with adaptive gain shuttling has been selected and successfully installed and put into operation at a paint coating line. It has been possible, for example, to keep the paint coating thickness of 30 µm within a tolerance range of ± 0.3 µm.