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NIST provides measurement services for roughness calibration specimens, other types of roughness specimens, and step height calibration specimens (see standards ASME B46.1-2002 and ISO 5436, Part 1-2000). Surface roughnesses up to 10 µm Ra and step heights up to 75 µm are measured by means of a computerized stylus instrument system. Using an interferometrically measured step or a calibration ball, the system is calibrated at each value of magnification employed during a measurement. Certain horizontal parameters are calibrated using a laser interferometer. A number of other statistical parameters and functions may also be calculated, including the rms roughness, average slope, average wavelength, skewness, amplitude density function, autocorrelation function, and power spectral density.
In measurements of roughness, surface profiles are taken according to American National Standard, ASME B46.1-2002, using a Gaussian filter with a 0.8 mm cutoff length and a traversing length of 4 mm. In step height measurements, straight lines are fitted by the method of least squares to the top and bottom of the profile of the step, and the step height is calculated from the vertical difference of the lines at the middle of the step transition. The uncertainty in the NIST calibration for step height or Ra depends on a number of factors, the most important being the step or Ra value itself. The expanded uncertainties (k=2) range approximately from 0.4 µm at a step height of 75 µm to 0.3 nm at a step height of about 8 nm. Comparable uncertainties are achieved for measurements of Ra.
See Standard Reference Materials to calibrate stylus instruments that measure surface roughness.
Stylus-laser surface calibration system, T. V. Vorburger, J. F. Song, C.H.W. Giauque, T. B. Renegar, E. P. Whitenton, and M. C. Croarkin, Precision Engineering 19, 157 (1996).
Methods of Characterizing Surface Topography, T. V. Vorburger, Tutorials in Optics, D. T. Moore, ed. (Optical Society of America, Washington, DC, 1992).
Standard Reference Specimens in Quality Control of Engineering Surfaces, J. F. Song and T. V. Vorburger, J. Res. Natl. Inst. Stand. Technol. 96(3) 271-288 (1991).
Surface Finish Metrology Tutorial, T. V. Vorburger and J. Raja, NISTIR 89-4088 (National Institute of Standards and Technology, Gaithersburg, MD, June 1990).
Surface Texture, J.F. Song and T. V. Vorburger, ASM Handbook 18, 334. 16010C.
A Simplified Realization for the Gaussian Filter in Surface Metrology, Y. B. Yuan, T. V. Vorburger, J. F. Song, and T. B. Renegar in Tenth International Colloquium on Surfaces, M. Dietzsch, H. Trumpold, eds., Aachen: Shaker Verlag GmbH, p.133 (2000).