Patent ID: 8444821

Claim:
A measuring method for a moving web in a paper or board machine, including focusing optical radiation on the moving web, the method comprising: producing, by LEDs, pulses of at least two different optical bands within a predetermined time window which is shorter than 2 μs for determining a smallest distinguishable detail of the moving web to have a size of 10 μm, focusing radiation pulses of the at least two different optical bands on a region in a web surface as pulses so that illumination areas of the pulses overlap at least partly on a plane of the moving web, at most one optical radiation band is focused on the moving web from a normal direction, a spatial intensity distribution of at least one optical band differs from a uniform distribution and intensity distributions of the at least two different optical bands differ from one another in a predetermined manner; forming pulse-based images of said web region on said bands of at least two different optical radiations; and determining a surface topography of the moving web based on at least two images formed on the bands of different optical radiations.