1. Engineering 1181 College of Engineering Engineering Education Innovation Center Collecting Measured Data Classroom Lecture Slides

2. Engineering 1181 Assessment of Variation In order to assess variation of measurements, one must understand the following terms: –Accuracy –Resolution –Repeatability (Precision) –Systematic Variation –Random Variation

3. Engineering 1181 Accuracy Degree of closeness between a measured value and desired value

4. Engineering 1181 Resolution The smallest increment a tool/device is capable of measuring reliably

5. Engineering 1181 Repeatability The ability of an instrument to reproduce a measurement

6. Engineering 1181 Systematic Variation The variation of measured values that differ from the nominal value in a predictable pattern

7. Engineering 1181 Random Variation The unpredictable variation that occurs when an object is measured multiple times

8. Engineering 1181 Classroom Exercise You are in charge of designing a new vending machine mechanism that will dispense cans. A critical measurement you need to finish your design is the “size” of the can. As pairs, use one tool to measure something that represents the “size” of the can. Each table should have one measurement from each device

9. Engineering 1181 Measured Data What needs to be measured to determine “size”? Now measure the “correct” dimension Record Results

10. Engineering 1181 Discussions of Results What did you get? Why are the measurements different?

11. Engineering 1181 Sample Class Data

12. Engineering 1181 Accuracy

13. Engineering 1181 Resolution

14. Engineering 1181 Repeatability

15. Engineering 1181 Systematic Variation

16. Engineering 1181 Random Variation

17. Engineering 1181 Outliers Values that differ greatly from specified value

18. Engineering 1181 Propagation of Error

19. Engineering 1181 Example Base Case:I=1/12bh 3 b=3.421 in h=2.129 in I=1/12(3.421)(2.129) 3 = I 1 =2.751 in 4 Assume 9.5% error in b b=3.124 in I=1/12(3.124)(2.129) 3 I 2 =2.512 in 4 (difference of 0.239 in 4 ) Assume 9.5% error in h h=1.927 in I=1/12(3.421)(1.927) 3 I 3 =2.04 in 4 (difference of 0.711 in 4 )

20. Engineering 1181 Summary Variation occurs in measured data. This presentation has identified types of variation and possible sources of variation. Next class we will discuss how to interpret this variation using statistics