3.3.1 General

The collection of parameters listed above as amplitude spacing and hybrid were established mainly on an ad hoc basis with little regard to forming a coherent set. The amplitude distribution and material ratio, however, fit into the class called random processes. In its simplest form, the process functions are the amplitude distribution (or the materials ratio; which is its integral). The amplitude distribution has shape, position and scale and can be the basis for the amplitude parameters given above. Likewise, there is a similar function for the basis of the horizontal information. This can take two forms. One is the autocorrelation function. The other is the power spectral density.

3.3.2 Explanation

A profile is quite complicated. Any one point can be made up of random and/or deterministic information. It is very difficult to identify the components of manufacture simply from the chart - there are too many unknowns. Random process analysis is a way of reducing the unknown factors, thereby allowing the basic mechanisms of the surface generation to be revealed. How do the amplitude distribution (or MR( %)) and autocorrelation function (or power spectrum) remove irrelevant information? The answer is that both remove positional information from the profile. The amplitude distribution looks at what is left in terms of the heights of the profile and the autocorrelation looks at spacings (but not position).

Figure 3.27 (a) shows that two profiles on the same surface i.e. (i) and (ii)...