Precision and Accuracy

Precision and Accuracy - ME 3260 Measurement Techniques...

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Bi Zhang, UConn 1 ME 3260 Measurement Techniques Definition of Terms Measurement Errors Instructor: Dr. B. Zhang •Te rms Contents • Accuracy & Repeatability • Errors – Random (non-repeatable) – Systematic (repeatable) Significant Figures • Significant Figures •Un i ts
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Bi Zhang, UConn 1 Measurement Terms • Range – The extent over which the machine functions within specifications • Resolution – Smallest discernable change that can be registered by machine • Repeatability – Scatter of results obtained when a machine tries to exactly reproduce a given operation • Accuracy – Worst case deviation of measured result from true value • Ex: Difference between commanded move and actual move More Measurement Terms Precision – Three definitions 1 Synonym for Repeatability 1. Synonym for Repeatability 2. Resolution / Range 3. Better accuracy or smaller precision than typically obtained Error – Amount an assumed value deviates from true value – Random Error vs. Systematic Error Traceability – Enables “legal metrology” in any machine shop or lab – Relates practical measurements to international standards –N I S T • Engineering Metrology Toolbox
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Bi Zhang, UConn 1 Accuracy, Resolution, & Repeatability • Accuracy is the ability to tell the truth. • Repeatability is the ability to tell the same story each time. • Resolution is the detail to which you tell a story. Alexander Slocum, MIT Precision, Accuracy and Bias Errors
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Bi Zhang, UConn 1 Precision and Accuracy • How well the goal is achieved Accuracy From “Multi-Scale System Design,” Culpepper Precision Accuracy • How well the goal is achieved From “Multi-Scale System Design,” Culpepper
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Bi Zhang, UConn 1 Repeatability • How well you perform a function multiple times From “Multi-Scale System Design, 2.76,” Culpepper
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Precision and Accuracy - ME 3260 Measurement Techniques...

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