3.0 - Experimental Error Analysis
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3.0– Experimental Error Analysis Uncertainity cannot be avoided in engineering. It is very difficult to determine the values of parameters with an extreme degree of accuracy. All experimental data have some form of error, leading to a degree of uncertainty. Experimental errors may be separted in two causes: 1. Systematic errors – due to the instrument or its environment. • Constant throughout a set of readings. • May result from equipment which is incorrectly calibrated or how measurements are performed. • Cause average (mean) of measured values to depart from correct value. • Difficult to spot presence of systematic errors in an experiment. 2. Random errors – due to scatter in repeated readings. • An error that varies between successive measurements • Equally likely to be positive or negative • Presence obvious from distribution of values obtained • Can be minimised by performing multiple measurements of the same quantity or by measuring one quantity as function of second quantity and performing a straight line fit of the data • Sometimes referred to as reading errors Systematic errors are minimised by careful calibration. Random errors are then estimated using statistical analysis. Prof. Ing. Tonio Sant 2015/16 Department of Mechanical Engineering, University of Malta 2.1
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Transcript of 3.0 - Experimental Error Analysis
3.0– Experimental Error Analysis
Uncertainity cannot be avoided in engineering. It is very difficult to determine the values of parameters with an extreme degree of accuracy.
All experimental data have some form of error, leading to a degree of uncertainty. Experimental errors may be separted in two causes:
1. Systematic errors – due to the instrument or its environment.
• Constant throughout a set of readings.• May result from equipment which is incorrectly calibrated or how measurements
are performed.• Cause average (mean) of measured values to depart from correct value.• Difficult to spot presence of systematic errors in an experiment.
2. Random errors – due to scatter in repeated readings.
• An error that varies between successive measurements• Equally likely to be positive or negative• Presence obvious from distribution of values obtained• Can be minimised by performing multiple measurements of the same quantity or
by measuring one quantity as function of second quantity and performing a straight line fit of the data
• Sometimes referred to as reading errors
Systematic errors are minimised by careful calibration. Random errors are then estimated using statistical analysis.
Figue 3.1 – Random and systematic errors
Prof. Ing. Tonio Sant 2015/16 Department of Mechanical Engineering, University of Malta 2.1
True value
Random errors only
Random + systematic
Difference between accuracy and precision
A result is said to be accurate if it is relatively free from systematic error
A result is said to be precise if the random error is small
Statistical Analysis
Mean or average Standard Deviation Correlation and Regression
Prof. Ing. Tonio Sant 2015/16 Department of Mechanical Engineering, University of Malta 2.2
