It is often stated that the arithmetic mean surface roughness, Sa is used to describe the deviation of a surface from an ideal level (reference surface?). It is however not quite clear to me how this ideal level is determined. For instance, i have a depth profile Z(x,y) of a rough surface. How do i go about computing Sa from this profile?
If you are using NT-MDT based NOVA-px system, then there is option for calculating the roughness, where it provide all parameters. From help file you can get details of each parameter.
Thank you Thomas for your response. Actually, i already have the Sa values from an analysis software, however, i want to really understand how the Sa values were computed by the software.
My sample is a sphere (say Z3d(x,y)), hence, I flattened the surface by fitting a 2nd degree polynomial (say Zfit(x,y)) and then subtracting that from Z3d(x,y) to obtain my depth profile Z2d(x,y).
The Sa formula requires that i subtract the height of the mean plane (i.e., the reference plane) from Z2d(x,y). Thus, if i understand you correctly, you're saying that Zfit(x,y) is the mean plane?
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