Machinery's Handbook, 31st Edition
Surface Texture 811 Roughness topography is the modified topography obtained by filtering out the longer wavelengths of waviness and form error. Sampling length is the nominal spacing within which a surface characteristic is deter mined. The range of sampling lengths is a key specification of a measuring instrument. Spacing is the distance between specified points on the profile measured parallel to the nominal profile. Spatial (x) resolution is the smallest wavelength that can be resolved to 50 percent of the actual amplitude. This also is a key specification of a measuring instrument. System height resolution is the minimum height that can be distinguished from back ground noise of the measurement instrument. Background noise values can be determined by measuring approximate rms roughness of a sample surface where actual roughness is significantly less than the background noise of the measuring instrument. It is a key instrumentation specification. Topography is the three-dimensional representation of geometric surface irregularities. Topography, measured is the three-dimensional representation of geometric surface irregularities obtained by measurement. Topography, modified is the three-dimensional representation of geometric surface irregularities obtained by measurement but filtered to minimize certain surface characteristics and accentuate others. Valley is the point of maximum depth on that portion of a profile that lies below the mean line and between two intersections of the profile with the mean line. Waviness, evaluation length (L), is the length within which waviness parameters are determined. Waviness, long-wavelength cutoff (lcw) is the spatial wavelength above which the undulations of waviness profile are removed to identify form parameters. A digital Gaussian filter can be used to separate form error from waviness, but its use must be specified. Waviness profile is obtained by filtering out the shorter roughness wavelengths charac teristic of roughness and the longer wavelengths associated with the part form parameters. Waviness sampling length is a concept no longer used. See waviness long-wavelength cutoff and waviness evaluation length. Waviness short-wavelength cutoff (lsw) is the spatial wavelength below which rough ness parameters are removed by electrical or digital filters. Waviness topography is the modified topography obtained by filtering out the shorter wavelengths of roughness and the longer wavelengths associated with form error. Waviness spacing is the average spacing between adjacent peaks of the measured profile within the waviness sampling length. Sampling Lengths.— Sampling length is the normal interval for a single value of a surface parameter. Generally it is the longest spatial wavelength to be included in the profile measure - ment. Range of sampling lengths is an important specification for a measuring instrument.
Sampling Length
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Traverse Length Evaluation Length, L Fig. 3. Traverse Length
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