3D Spatial Parameters: SAL - Michigan Metrology

Sal (Auto-Correlation Length) and Str (Texture Aspect Ratio)

Sal, the Auto-Correlation Length, is a measure of the distance over the surface such that the new location will have minimal correlation with the original location. The direction over the surface chosen to find Sal is the direction which yields the
lowest Sal value. Str, the Texture Aspect Ratio, is a measure of the spatial isotropy or directionality of the surface texture.
For a surface with a dominant lay, the Str parameter will tend towards 0.00, whereas a spatially isotropic texture will result in
a Str of 1.00.

Sal = Length of fastest decay of ACF in any direction	Str =	Length of fastest decay of ACF in any direction Length of slowest decay ACF in any direction

Highly Directional Surface with Str of 0.11 and Sal of 37mm	Highly isotropic surface with Str of 0.88 with an Sal of 21mm

Application

Str is useful in determining the presence of lay in any direction. For applications where a surface is produced by multiple processes,
Str may be used to detect the presence of underlying surface modifications. Str may find application in detecting subtle directionality on an otherwise isotropic texture. Sal is a quantitative measure as to the distance along the surface by which one would find a texture that is statistically different from the original location. Sal is useful in establishing the distance between multiple measurements made on the surface to adequately determine the general texture specification of the surface. Sal may find application related to the interaction of electromagnetic radiation with the surface and also tribological characteristics such as friction and wear.