measurment-uncertainty

# measurment-uncertainty - University of Florida Mechanical...

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Unformatted text preview: University of Florida Mechanical and Aerospace Engineering 1 Useful Tips for Presenting Data and Measurement Uncertainty Analysis Ben Smarslok University of Florida Mechanical and Aerospace Engineering 2 Outline • Why is presenting data properly important? • Explain important terminology and definitions – NIST vs. ISO vs. ASME/ASTM – Oberkampf definitions of model uncertainty (not included) • Experimental scenarios and corresponding methods – Uncertainty propagation – Crossed vs. nested factors (ANOVA vs. VCA) – p-values – Interlaboratory Studies (not included) University of Florida Mechanical and Aerospace Engineering 3 • Best guess by experimenter • Half the smallest division of measurement • Standard deviation: σ • Standard error: σ m = σ / √ n • Expanded uncertainty of ± 2 σ or ± 3 σ (95% or 99% confidence interval) • Standard uncertainty: u • Combined standard uncertainty: u c *(Courtesy of Duane Deardorff presentation from UNC) m = 75 ± 5 g What is the meaning of ± 5 ? University of Florida Mechanical and Aerospace Engineering 4 What does x ± u mean? • Engineers think in terms of ±2 σ (95%) • Physicists generally report ±1 σ (68% CI) • Chemists report ±2 σ or ±3 σ (95% or 99% CI) • Survey/poll margin of error is 95% CI • Accuracy tolerances are often 95% or 99% • NIST Calibration certificate is usually 99% • Conclusion : The interpretation of ± u is not consistent within a field, let alone between fields – It is very important to explain the statistical relevance of the uncertainty bounds!!! University of Florida Mechanical and Aerospace Engineering 5 Presenting Uncertainty Precisely • Choose a standard for presenting uncertainty (I prefer NIST), and reference the standard • Explain the source of the uncertainty – Type A – calculated by statistical methods (it is useful to explain the design of experiments and the number of samples involved) – Type B – determined by other means, such as estimate from experience or manufacturers specifications • Use terms carefully!...
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## This note was uploaded on 06/06/2011 for the course EAS 4240 taught by Professor Peterifju during the Spring '08 term at University of Florida.

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measurment-uncertainty - University of Florida Mechanical...

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