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ME 322: Instrumentation Lecture 10

ME 322: Instrumentation Lecture 10. February 10, 2014 Professor Miles Greiner. Announcements/Reminders. HW 3 due now (use ME 322 ID number!) HW 4 due Friday , HW 5 Due Wednesday 2/19/14 Review 2/19, Midterm Friday 2/21/14 This week: Lab 4 Strain Gage Installation

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ME 322: Instrumentation Lecture 10

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  1. ME 322: InstrumentationLecture 10 February 10, 2014 Professor Miles Greiner

  2. Announcements/Reminders • HW 3 due now (use ME 322 ID number!) • HW 4 due Friday, HW 5 Due Wednesday 2/19/14 • Review 2/19, Midterm Friday 2/21/14 • This week: Lab 4 Strain Gage Installation • Everyone must wear safety glasses

  3. UNR General Undergraduate Research Award • Apply for up to $1,500 to perform 2014-5 academic-year-projects in close collaboration with a faculty mentor • Application Deadline: April 14th, 2014 • http://environment.unr.edu/undergraduateresearch/opportunities/gura.html • I am interested in working with students who do very well in this class • Opportunities in Heat Transfer applied to Geothermal Power Plants and Nuclear Packaging

  4. Last Lecture • Propagation of Uncertainty in calculations • R = fn(x1, x2, x3, …, xn), • Likely Uncertainty in Power Product calculations • is

  5. Lab 5 Measurement of Elastic Modulus of Steel or Aluminum Beams • Find slope a of micro-strain reading meR versus end mass m • , where and a = slope • Find uncertainty wE • Power Product? (Yes or no?) • Fill in blank • Need to find best-estimate and 95%-confidence-level uncertainties of all 5 inputs

  6. Strain Gage Factor Uncertainty • In L5PP, manufacturer states • S = 2.075 ± 0.5% (pS not given) • In Lab 5, the values of and wS may be different! • In L5PP and Lab 5, assumepS = 68% (1s) • So assume the 95%-confidence-level uncertainty is twice the manufacturer stated uncertainty • S = 2.075 ± 1% (95%) • So (95%)

  7. Distance between Gage to Mass Centers, L • Measure using a ruler • In L5PP, ruler’s smallest increment is 1/16 inch • Uncertainty is 1/32 inch (half smallest increment) • Lab 5 – depends on the ruler you are issued • may be different • Assume the confidence-level for this uncertainty is 99.7% (3s) • The uncertainty with a 68% (1s) confidence level • (1/3)(1/32) inch • The uncertainty with a 95% (2s) confidence level • (2/3)(1/32) = 1/48 inch

  8. Beam Thickness T and Width W • Each are measured multiple times using different instruments • Use sample mean for the best value, • Use sample standard deviations and for the 68%-confidence-level uncertainty • The 95%-confidence-level uncertainties are • = 2 • = 2

  9. Uncertainty of the Slope, a • Fit data to yFit = ax + b using least-squares method • Uncertainty in a and b increases with standard error of the estimate (scatter of date from line)

  10. Uncertainty of Slope and Intercept • = (68%) • = (68%) • Not in the textbook • wa= ?sa (95%)

  11. Lab 5 Sample Calculations • http://wolfweb.unr.edu/homepage/greiner/teaching/MECH322Instrumentation/Labs/Lab%2005%20Elastic%20Modulus/Lab%20Index.htm • Slope uncertainty calculation, sa • 95%-confidence-level uncertainties for each input • Relative contribution to the uncertainty in the result from the uncertainty in each input • Comparison of a result to reference value • Reference citation format

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