Abstract: A method and apparatus for measuring simultaneously the thickness and the composition of a coating on a metal substrate. A first beam of radiation that produces a primary beam of photons is directed substantially perpendicularly to the surface of the coating. A first detector is positioned substantially perpendicularly to the surface of the coating to receive a first fluoresced beam. The photons having a first energy level representing a higher concentration element of the coating are selected. A first electrical signal is provided that is a function of the intensity of the photons having the first energy level. A second beam of radiation producing a second primary beam of photons is directed at an acute angle to the surface of the coating. A second detector is positioned substantially perpendicularly to the surface of the coating to receive a second fluoresced beam. The photons having a second energy level representing a lower concentration element of the coating are selected.

Abstract: This invention applies to thickness gauges consisting of a radiation source producing a beam aimed at a detector. Whenever a material to be gauged obstructs the radiation beam, the intensity received by the detector (detector output) varies and said variation can be translated into a thickness measurement. Standards are used for calibration. This invention provides computer means and methods that provide better measurements by using a function relating the thickness to the detector output in a large range and independently of random inaccuracies of the standards.