Measurement Principle
A non-contact optical inspection system utilizes axial dispersion of white light to map topography and measure the thickness of multi-layered substrates with sub-micron precision. This chromatic confocal technology separates light into discrete wavelengths, directing the spectrum toward the surface of paper or polymer sheets so that each specific colour achieves focus at a unique vertical depth. When a beam hits the target, only the wavelength that focuses exactly on the surface reflects back through a small aperture to reach the detector.
The system identifies which wavelength returns with maximum intensity, translating that spectral peak into a precise physical distance or material thickness calculation. Light sources remain constant, yet the device detects minute variations in surface height or layer separation by analyzing which frequency of the visible spectrum corresponds to the focused return signal. Sensors detect height changes across uneven paper coatings or thin barrier films without exerting mechanical force that would compress the material or distort the test result.
Conversion Integrity
Accurate sensing depends upon the stability of the light source and the calibration of the dispersive lens assembly within the optical head. Production lines apply chromatic confocal monitoring to track the thickness of high-barrier food packaging where even subtle deviations in coating distribution compromise oxygen transmission rates. Operators link these sensors to feedback loops that adjust doctor blades or slot die applicators instantly if the measurement drifts beyond defined tolerances.
Deviations from the target thickness trigger corrective actions in the substrate extrusion or coating process, preventing the generation of waste stock.
Sensor Limitation
Signal degradation occurs if the substrate surface absorbs too much light or scatters incident beams at angles that prevent return travel through the return pinhole. Rough textures or materials with high degrees of transparency sometimes create signal noise that masks the primary spectral peak. Ambient vibrations reduce the resolution of high-frequency measurements on moving webs.
Successful implementation requires a clean optical path free from dust or particulate interference. Reliability hinges on the optical properties of the substrate.
