VERIFICATION OF THICKNESS MODULATIONS IN OR ON SHEET-TYPE PRODUCTS

摘要

The invention relates to a method for verifying thickness modulations, in particular, watermarks, in or on sheet-type products. To reduce the influence of environmental disturbances and to reduce the adjustment costs during the production and maintenance of appropriate measurement systems, the sheet-type product is subjected to sound, in particular to ultrasound. The sound, which is transmitted through the sheet-type product and/or is reflected by the sheet-type product is measured at several points on said product. At least one value that is characteristic of the transmitted and/or reflected sound is produced for each of the points and the thickness modulations are verified by comparing the values with predetermined reference values.