· Mechanical sensors,

composed of a pivoting stylet fitted at one end with a diamond tip which rests on the surface to be analysed, and a system which measures the displacement of the arm. The measurement of the displacement most often uses an inductive principle : a ferrite core integral with the stylet is displaced in a two range winding coil, the conditioner of the sensor performing the excitation of the first coil by a 20 KHz sinisoidal signal and the synchronous detection of the signal induced on the second coil.

·Laser optic roughness sensors,

using the servo-control principle of compact disk heads. there are made up of an optical assembly which ensures the fixed focusing of a laser beam onto the surface and which projects the reflected beam onto four photodiodes, and by vertical diplacement system permitting the slaving of the focusing point.

· White light optic roughness sensors,

White light confocal optic sensors use the chromatic aberration of a lens. A white source is focused on the surface by an optical assembly which presents a strong chromatic aberration. The altitude of the surface is determined by a spectral analysis of the light reflected by this surface

· Triangulation optic sensors,

Their principle is founded on the measurement of the look angle of a laser beam projected onto the surface.