Surface imperfection and wringing thickness in uncertainty estimation of end standards calibration

Empirical estimation of uncertainty in dimensional metrology is a vital part in calibration processes. Uncertainty estimation in gauge block measurement mainly depends on three major areas, thermal effects, dimension metrology system that includes measurement strategy, and end standard surface perfection grades. This paper focuses precisely to estimate the uncertainty due to the geometrical imperfection of measuring surfaces and wringing thickness U(Lg+Lw) in calibration of end standards grade 0. An optomechanical system equipped with Zygo interferometer and AFM techniques have been employed. A novel protocol of measurement covering the geometric form of end standard surfaces and wrung base platen was experimentally applied. Surface imperfection characteristics of commonly used 6.5 mm GB have been achieved by AFM in 2D and 3D to be applied in three sets of experiments. The results show that there are obvious mapping relations between geometrical imperfection and wringing thickness of the end standards calibration. Moreover, the predicted uncertainties are clearly estimated within an acceptable range from 0.132 to 0.202 µm respectively. Experimental and analytical results are also presented and discussed.