MECH215-Chapter01-SolutionstoSampleProblems_2

MECH215-Chapter01-SolutionstoSampleProblems_2 - PROBLEM 1.5...

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PROBLEM 1.5 FIND: How does resolution affect accuracy? SOLUTION The resolution of a scale is defined by the least significant increment or division on the output display. Resolution affects a user's ability to resolve the output display of an instrument or measuring system. Consider a simple experiment to show the effects of resolution. Under some fixed condition, ask several competent, independent observers to record the indicated value from a measurement system. Collect the results – this becomes your dataset. Because the indicated value is the same for each observer, the scatter in your dataset will be close to the value of the resolution of the measurement system. Data scatter contributes to the random error. As such, the output resolution of a measurement system forms a lower limit as to the random error to be expected. The resolution would not contribute to systematic error. Systematic error is an offset. PROBLEM 1.6 FIND: How does hysteresis affect accuracy? SOLUTION Hysteresis error is the difference between the values indicated by a measurement system when the value measured is increasing in value as opposed to when it is decreasing in value; this despite the fact that the value being measured is actually the same for either case. A common cause of hysteresis in analog instruments is friction in the moving parts. This can cause the output indicator to 'stick'. In digital instruments, hysteresis can be caused by the discretization. If hysteresis error is ignored, the effect on any single measurement can be seen as a systematic error. On multiple measurements in any one direction, the effect can be to impose a 'trend' on the data set. The use of randomization methods can break up the trends incorrectly implied by
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This note was uploaded on 10/31/2009 for the course MECH 420 taught by Professor M.s during the Spring '09 term at American University of Beirut.

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MECH215-Chapter01-SolutionstoSampleProblems_2 - PROBLEM 1.5...

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