An optical sensor based on a reflective method to measure the roughness of a surface (Ra) compares the light reflected from the surface being measured with that of light reflected from a standard surface of known Ra. The range of Ra values that can be measured is 0.05-1.3 mu m. the sensor was tested in factory conditions to determine the surface roughness of a mill roll during grinding. The results corresponded with those from a profilometer within 10 percent. The measurement of surface roughness in factory conditions is usually performed using contact profilometers in which a stylus is drawn over the surface and a trace of the undulations recorded. However, vibrations frequently take place during the trace as a result of various nearby activities, this significantly decreasing the accuracy of measurement. For such conditions, optical reflectometers, which have a low sensitivity to vibrations, are very attractive for surface roughness measurements~[1]. However, this method requires a knowledge of the optical constants of the surface measured and the angular distribution of scattered light intensity ~[1,2], if absolute values are to be determined. To avoid this problem, an optical sensor calibrated against standard surfaces of known roughness has been developed and tested under factory conditions.
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