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Proceedings Paper

Calibration method for accurate optical measurement of thickness profile for the paper industry
Author(s): Jussi Graeffe
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Paper Abstract

Online measurement of paper thickness profile is essential in paper production. For decades paper thickness has been measured online with sensors that are contacting the web on both sides. In 2005 a new optical online paper thickness gauge was introduced which only contacts the web on the other side. The sensor is based on a laser triangulation sensor and a magnetic sensor, and it determines the paper thickness from the difference of the two measurements. For calibration of the two sensors, a robust concept has been developed which utilizes the measured object and takes place in the measuring environment so that the calibration is automatically adjusted to the current measuring circumstances. More importantly, with the presented method the non-linearity of the laser sensor is cancelled enabling the measurement of the thickness profile shape with an accuracy much better than that of the laser sensor. Profile accuracy of 0.5 μm (2σ) has become normal while the measuring range is often several hundreds of microns and the measuring distance to the paper web 1.0-1.5 mm with a laser sensor having linearity of ±2 μm.

Paper Details

Date Published: 17 June 2009
PDF: 9 pages
Proc. SPIE 7389, Optical Measurement Systems for Industrial Inspection VI, 738920 (17 June 2009); doi: 10.1117/12.827538
Show Author Affiliations
Jussi Graeffe, Metso Automation (Finland)

Published in SPIE Proceedings Vol. 7389:
Optical Measurement Systems for Industrial Inspection VI
Peter H. Lehmann, Editor(s)

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