The parameters are differentiated by their prefix where P is for the primary or the raw profile, R is for the roughness profile, and W is for the waviness profile.  The ISO 4287-1997 defines some parameters within a sampling length and others within an evaluation length.  ISO 4288 indicates that parameters defined over the sampling length should be calculated based on only one sampling length if the user wants to calculate parameter estimate. On the other hand, if the user wants to calculate an average parameter estimate, the average parameter estimated is calculated by taking an average of the parameter estimates from all available sampling lengths.

• Pp, Rp, Wp: Maximum Profile Peak Height.  ASME defines Pp, Rp, and Wp as a distance between the highest point of the profile and the mean line in the evaluation length L (see figure 1). ISO 4287-1997 defines Pp, Rp, and Wp as a highest peak profile depth within a sampling length l.  

• Pv, Rv, Wv: Maximum Profile Valley Depth. ASME defines Pv, Pv, and Wv as a distance between the lowest point of the profile and the mean line in an evaluation length (see figure 1).  ISO 4287-1997 defines Pv, Rv, and Wv as a lowest valley profile depth within a sampling length l.

• Pt, Rt, Wt: Total Height of Profile, which is a total of maximum profile peak height with maximum profile valley depth.

• Pz, Rz, Wz: Maximum height of profile within a sampling length (ISO 4287-1997) or average maximum height of the profile within the evaluation length (ASME B46)

• Pa, Wa, Ra: arithmetic mean deviation of the assessed profile
Analytical Form:

Digital Form:



• Pq, Wq, Rq: Root mean square deviation of the assessed profile
Analytical Form:

Digital Form:



• Psk, Wsk, Rsk: : Skewness of the assessed profile
Analytical Form:

Digital Form:



• Pku, Wku, Rku: Kurtosis of the assessed profile
Analytical Form:

Digital Form:

• Pc, Wc, Rc: mean height of profile elements

Digital Form:

Spacing and height discrimination are required. If they are not specified, then height discrimination will be 10% of Rz and spacing discrimination is 1 % of the sampling length. For a roughness and waviness profile, the sampling length is equal to a cutoff.




Figure 1 Mean height of profile elements parameter is calculated according to the ASME B46 Standard. For the ISO 4287 standard, the evaluation length would be replaced by the sampling length.

References:

ISO 4287, Geometrical Product Specifications (GPS) -- Surface texture: Profile method -- Terms, definitions and surface texture parameters, 1997

ISO 4288, Geometrical Product Specifications (GPS) -- Surface texture: Profile method -- Rules and procedures for the assessment of surface texture

Surface Texture (Surface Roughness, Waviness, and Lay), an American National Standard, ASME B46.1-2002, New York, NY