Method and apparatus for the on-line measurement of transmission or reflection on moving objects in the range of detectable electromagnetic radiation

An apparatus for photometrically determining optical properties of a test specimen, comprising in combination;

• light source means for producing a light beam having a range of detectable frequencies;
• means for periodically interrupting said light beam prior to impingement thereof on said test specimen;
• means for directing said light beam to said test specimen;
• filter means for filtering said light beam, upon impingement thereof on said test specimen, to obtain essentially a single wavelength beam of light;
• focusing means for focusing said single wavelength beam, said single wavelength beam having an intensity determined in part by optical characteristics of said test specimen;
• detector means for sensing said intensity of the focused single wavelength beam and for generating an electrical analog signal proportional to said intensity;
• analog-to-digital conversion means operatively connected to said detector means for converting said analog signal to a digital signal;
• sampling means operatively connected to said analog-to-digital conversion means for sampling said digital signal at a sampling frequency during a period of continuous impingement of said light beam on said test specimen to obtain a plurality of sample intensity values and for further sampling said digital signal at said sampling frequency during a period of continuous interruption of said light beam substantially contiguous in time with said period of continuous impingement of said light beam to obtain a plurality of additional sample intensity values, said period of continuous interruption being at least as long as said period of continuous impingement, said sampling frequency being selected so that first and last sample intensity values of a predetermined number of consecutive ones of said sample intensity values are separated in time from one another by at most half of said period and so that first and last sample intensity values of said predetermined number of consecutive ones of said additional sample intensity values are separated in time from one another by less than half of said period of continuous interruption;
• and
• computation means operatively connected to said sampling means for automatically calculating a first average intensity value from said consecutive ones of said sample intensity values, for automatically calculating a second average intensity value from said consecutive ones of said additional sample intensity values, for automatically calculating from said first average intensity value and said second average intensity value a background corrected light intensity value associated with said test specimen, and for automatically calculating a quotient of said background corrected light intensity value and a predetermined background corrected reference light intensity value associated with said light beam at the wavelength of said single wavelength beam.