On-line web inspection system

A flying spot scan automatic on-line inspection system for a running web for detecting defects in a sequence of areas of preselected size associated with said web by repetitively measuring a plurality of web features represented by a first set of electrical signals extracted in the course of scanning said web and analyzing said first set of feature electrical signals with regard to each said scanned area of preselected size, comprising:

• means for converting said first set of electrical signals into a second set of electrical signals representative of the magnitudes and distribution of said plurality of repetitively measured features over each said scanned area;
• means for calibrating each said second set of second electrical signals to obtain calibrated signals that correspond with the ranges of values specifying one or more sets of reference feature values;
• means for classifying each said set of calibrated signals according to its relationship with said one or more sets of stored reference feature values;
• and
• means based on the outcome of said classification for grading said classified calibrated signals for each said area in said inspected sequence of areas as to acceptability.