A method of measuring the degree of alloying of galvanized steel sheet through the use of laser beams includes the steps of directing a laser beam on a standard sample and reflecting and splitting the beam and detecting the intensity of specular reflection I.sub.0 (.alpha.) at an angle of reflection (.alpha.) and the intensity of scattering I.sub.0 (.beta.) at an angle of reflection (.beta.) to thus obtain the degree of alloying (X.sub.0) of the standard sample by the formula: ##EQU1## The above steps are repeated to obtain values I.sub.1 (.alpha.) and I.sub.2 (.beta.) to obtain a comparative degree of alloying (X.sub.1) of the standard sample using the above equation form. The arrangement of the laser, mirror and first and second beam splitters are corrected based on a comparison of the X.sub.0 and X.sub.1 values. The above steps are then repeated by directing the laser onto a galvanized steel sheet to obtain the degree of alloying (X.sub.2) of the galvanized steel sheet.
To measure the characteristics of the surface coating of a moving metal strip, such as the alliation level of a coating including zinc and iron, the product is exposed to the radiation of a radiative source with a predetermined wavelength directed orthogonally to the surface of the product and the energy reflected by the surface is measured also in a direction orthogonal to the surface so as to overcome reflectivity variations due to the morphological characteristics of the surface and these operations are performed with the help of off-the-shelf optical fibres previously stripped at their free ends of their normal optical focusing accessories so that they can be brought as near to each other as possible and placed parallel to each other.
