In contrast to a purely dimensional measurement, measuring surface roughness is a complex task. Traditionally a diamond stylus is dragged across the surface and a trace profile is created. Generally, profile height-dependent characteristic values like Ra, Rz or Rk are determined. Although this is a widespread technology, its usefulness is limited when measuring finely machined surfaces with Rz-values < 1 µm. Moreover, functional behavior characteristics like friction, gloss or adhesive properties are difficult to measure with this technique.
Scattered light technology offers numerous advantages, especially for the measurement of these types of surfaces. Instead of a trace profile, the surface information is gained by measuring the deflected micro angles. With this technique, a rougher surface will result in a more widely scattered light curve. This measurement method is recommended in VDA2009 for production methods in the automotive industry.