Distributions for Uncertainty Estimation using the ISO Guide to the Expression of Uncertainty in Measurement.

Type Normal Triangular Rectangular U-shaped Step
Graphical Representation dnorm.gif (1503 bytes) dtri.gif (1465 bytes) drect.gif (1522 bytes) dusha.gif (1641 bytes) dstep.gif (1428 bytes)
Equivalent Standard Deviation

enorm.gif (931 bytes)

etri.gif (1239 bytes)

erect.gif (1231 bytes)

Images/eusha.gif (1212 bytes)

estep.gif (1239 bytes)

Use When type A-evaluations can be shown to follow this distribution. When 'hard' limits can be estimated easier than sigma,e.g.:
  • Noise
  • Vibration
When only the variation limits are known, e.g.:
  • Calibration Certificates
  • Manufacturer's Specifications
For cyclic influences, e.g.:
  • Temperature Variation
When resolution is limited, e.g.:
  • Digital Readout
  • Verniers
  • Scale read by Operator

hn.gif (1361 bytes)

HN Metrology Consulting
10219 Coral Reef Way, Indianapolis, IN 46256
Phone: (317) 849 9577
Fax: (866) 792 2286
E-mail hsnielsen@HN-Metrology.com

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