Patent ID: 9581433
Date: 2017-02-28
CPC Classifications: G01B

Claim:
1. A method of measuring the thickness of a moving web, which has a first side and a second side, that comprises: a. supporting the moving web so that the moving web has a free standing portion where the moving web has an exposed outer surface on the first side and an inner surface on the second side; b. directing a laser beam at a selected angle of incidence onto a single spot on the exposed outer surface on the first side, wherein the laser beam comprises substantially monochromatic radiation having a wavelength in the 3-50 micron range; c. scanning the laser beam through a selected angle range as the laser beam is directed onto the single spot on the exposed outer surface; d. measuring the intensity of an interference pattern that forms from the superposition of radiation that is reflected from the first side, the exposed outer surface, and from the second side, the inner surface; and e. extracting the thickness of the moving web at the single spot by utilizing a relationship among the laser beam incident angle, wavelength, index of refraction of the web, and web thickness.