The residual moisture of foils (and tarps) can also be determined by ACO sensors. Especially in foils the residual moisture is a decisive factor. It can effect the quality of the foil itself but as well the quality of following steps of production like applying the coating. Based on the capacity method of measurement the sensor can also supervise the process of coating by detecting discrepancies caused by too much or too little material on the foil. Depending on the kind of treatment the sensor can be placed at various positions.