Fluke Digital Multimeter - Page 41

©Fluke Calibration 2011 Basics Of Measurement Uncertainty for DMM Calibration 41
Calculating u
2
• Step 2: Convert the specified
error to an error value that
covers ±one standard deviation
(or a ±1 sigma confidence
interval)
− If no other information is provided
by the manufacturer, assume a
rectangular distribution
±1σ = ±spec / (√3)
− If manufacturer specifies a different
distribution, such as a normal
distribution, then calculate as
appropriate.
For example with a normal
distribution at 99%
±1σ = ±spec / (2.58)
Normal Probability Distribution
1
2 3-123
Uniform or Rectangular
Probability Distribution
Probability of Occurrence
Value of Reading
Full width
Mean or
Average reading
-a
+a
±spec
limits
±spec limits