tailieunhanh - The gauge block handbook Episode 9

Tham khảo tài liệu 'the gauge block handbook episode 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | L n1 f1 X1 2 where ni is any integer. If we look at a second color there will be another fringe fraction f2. It also will be consistent with any block length satisfying the formula L n2 f2 X2 2 where n2 is any integer. However we have gained something since the number of lengths which satisfy both relations is very much reduced and in fact are considerably further apart than Ầ 2. With more colors the number of possible matches are further reduced until a knowledge of the length of the block to the nearest centimeter or more is sufficient to determine the exact length. In theory of course knowing the exact fringe fractions for two colors is sufficient to know any length since the two wavelengths are not commensurate. In practice our knowledge of the fringe fractions is limited by the sensitivity and reproducibility of our equipment. In practice 1 20 of a fringe is a conservative estimate for the fringe fraction uncertainty. A complete analysis of the effects of the uncertainty and choice of wavelengths on multicolor interferometry is given by Tilford 49 . Before the general availability of computers the analysis of multicolor interferometry was a time consuming task 50 . There was a large effort made to produce calculation aids in the form of books of fringe fractions for each popular source wavelength correction tables for the index of refraction and even fringe fraction coincidence rules built somewhat like a slide rule. Since the advent of computers it is much easier to take the brute force approach since the calculations are quite simple for the computer. Figure shows a graphical output of the NIST multicolor interferometry program using a cadmium light source. The program calculates the actual wavelengths for each color using the environmental factors air temperature pressure and humidity . Then using the observed fringe fraction shows the possible lengths of the gauge block which are near the nominal length for each color. Note that the possible

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