Rapid-scanning infrared sensor

A system for measuring optically-sensitive properties relating to the composition of travelling webs of sheet material during manufacture, comprising:

• (a) first track means mounted to extend generally parallel to one face of a travelling web in the cross direction;
• (b) a stationary light source means arranged to direct collimated light, having ranges of wavelengths, parallel to the first track means;
• (c) first parabolic reflector means mounted to travel along the first track means and to focus the collimated light as rays directed directly from the first parabolic reflector means. onto the adjacent face of the web;
• (d) second track means mounted to extend generally parallel to the first track means adjacent the opposite face of the web;
• (e) second parabolic reflector means mounted to travel along the second track means to immediately collect rays that are transmitted through the web from the first parabolic reflector means;
• and
• (f) stationarily-mounted light detector means to detect rays collected by the second parabolic reflector means at least at two selected ranges of wavelengths to provide measurement of optical absorption properties relating to the composition of the travelling web at selected locations.