Measurement Uncertainty & Error Analysis Flashcards
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What does 'measurement uncertainty' represent in calibration?
Answer: A parameter characterizing the dispersion of values that could reasonably be attributed to the measurand
Measurement uncertainty is a parameter that characterizes the range of values within which the true value is estimated to lie, reflecting the doubt about the measurement result.
Type A evaluation of measurement uncertainty is based on:
Answer: Statistical analysis of repeated measurement observations
Type A uncertainty evaluation uses statistical methods applied to a series of repeated measurements to estimate the standard deviation and standard uncertainty.
Type B evaluation of measurement uncertainty is characterized by:
Answer: Information from sources other than repeated observations, such as certificates and specifications
Type B uncertainty evaluation uses information such as calibration certificates, manufacturer specifications, reference data, and expert judgment rather than statistical analysis of repeated measurements.
The combined standard uncertainty (uc) is calculated from individual uncertainty components by:
Answer: Taking the square root of the sum of the squares of individual standard uncertainties
Combined standard uncertainty is obtained by the root sum of squares (RSS) method, which combines individual uncertainty components assuming they are uncorrelated.
A coverage factor of k=2 applied to the combined standard uncertainty typically corresponds to a confidence level of approximately:
Answer: 95%
For a normal distribution, a coverage factor k=2 yields an expanded uncertainty that encompasses approximately 95% of the distribution of values.
Which international document provides the primary guidance on expressing measurement uncertainty?
Answer: JCGM 100:2008 (GUM — Guide to the Expression of Uncertainty in Measurement)
The GUM (JCGM 100:2008) is the internationally recognized guide that establishes general rules for evaluating and expressing measurement uncertainty.
What is the key difference between accuracy and precision in measurement?
Answer: Accuracy describes closeness to the true value; precision describes the spread of repeated measurements
Accuracy indicates how close a measurement is to the accepted true value, while precision describes the reproducibility or spread of repeated measurements regardless of how close they are to the true value.