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# 04 - ENGR 201 Evaluation Presentation of Experimental Data...

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4/18/2011 ENGR201 Lecture 4 Spring 2011 1 ENGR 201 Evaluation & Presentation of Experimental Data Lecture 4: Uncertainty Analysis Part 1 T. Chmielewski, Electrical & Computer Engineering D. Miller, Mechanical Engineering & Mechanics Drexel University 19 April 2011 4/18/2011 ENGR201 Lecture 4 Spring 2011 2 Announcements 1 On-line Midterm will be given in Week 5 Coverage reading and notes from lecture 1, 2, and 3 Homework problems for lectures 1, 2, and 3 Quizzes for lecture 1, 2, & 3 (including this week’s quiz) Test will be TBD hour duration containing multiple choice, true-false, vocabulary match and computational problems It is suggested that you have prepared a formula sheet and have a calculator or spread sheet program available There is NO MAKEUP Check Bb Vista later this week for additional details and for those with special arrangements

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4/18/2011 ENGR201 Lecture 4 Spring 2011 3 Announcements 2 • Quiz this week on Finite Statistics – Open Thursday 5:00 PM through Friday 5:00 PM – Coverage Lecture 3 reading, lecture notes and problem set 4/18/2011 ENGR201 Lecture 4 Spring 2011 4 Homework and Readings for Week 4 • Reading from text: – Section 5.1, 5.2, 5.3, 5.4 and 5.5 – make sure to pay attention to examples • Problems from text: – 5.6, 5.8, 5.10
4/18/2011 ENGR201 Lecture 4 Spring 2011 5 Measurement Process of assigning a value to a physical quantity Error Difference between our assigned value and the true value Uncertainty Estimate of the probable error in our measurement Errors are a property of the measurement Errors come from instruments, finite statistics, procedures Uncertainty is a property of the result Using uncertainty analysis we will identify, quantify, and combine error estimates to estimate the error in our final result Definition Review 4/18/2011 ENGR201 Lecture 4 Spring 2011 6 Purpose Estimating the ± what? as we design a measurement system Method Introduce uncertainty analysis Why? Develop a methodical approach Make critical evaluations of potential elements of the apparatus Spend your money on components that will really make a difference in reducing the uncertainty This Lecture

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4/18/2011 ENGR201 Lecture 4 Spring 2011 7 Repeated Measurements Width of the distribution is a measure of the random error Shifts the center of the distribution from the true value Result of the i-th measurement 4/18/2011 ENGR201 Lecture 4 Spring 2011 8 Total Error • Here’s what you will report as a result of your measurements • We are going to work on how to estimate u x when the experiment (measurement system) is being designed Uncertainty analysis is the method to quantify the u x term %) ( ' P u x x x ± =
4/18/2011 ENGR201 Lecture 4 Spring 2011 9 Assumptions for Uncertainty Analysis Test objectives are known & process is clearly defined Known corrections to systematic error have been applied (Set the bathroom scale to zero before getting on) Systematic errors are independent (uncorrelated) of each other Data are obtained under fixed operating conditions As the engineers, you have some “ experience ” with

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04 - ENGR 201 Evaluation Presentation of Experimental Data...

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