Patent ID: 7365854

Claim:
A device for inspecting a moving workpiece having a polychromatic region, comprising: a solid-state light source adapted to emit light in a range of wavelengths, said light source positioned relative to the moving workpiece to illuminate the polychromatic region with the light; a first photodetector positioned relative to the moving workpiece to intercept a first portion of the light reflected by the polychromatic region, said first photodetector adapted to detect an intensity of the first portion of the light within a first wavelength band defined within the range of wavelengths and to generate a first output signal proportional to the intensity of the first portion of the light within the first wavelength band; a second photodetector positioned relative to the moving workpiece to intercept a second portion of the light reflected by the polychromatic region, said second photodetector adapted to detect an intensity of the second portion of the light within a second wavelength band defined within the range of wavelengths and to generate a second output signal proportional to the intensity of the second portion of the light within the second wavelength band; and a computer electrically coupled with said first and second photodetectors, said computer configured to determine a ratio of the first and second output signals and to compare said ratio with a reference so as to ascertain a variation in said ratio relative to the reference.