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Products Software UncertaintyAnalyzer 3.0 Software Comparison Combining Uncertainties

 

Combining Uncertainties

 

When combining uncertainties we must account for any correlations between measurement process errors and, for multivariate analyses, any cross-correlations between component errors. For multivariate analyses, it is also important that the uncertainties are multiplied by the appropriate sensitivity coefficients.  Finally, we must also estimate the effective degrees of freedom associated with the combined uncertainty.

  

A in the cell indicates that the particular capability or feature is available.  Alternatively, a blank cell indicates that the capability or feature is not available.  Comments and footnotes are included to clarify significant differences between software applications or to provide necessary details.

 

Features

and

Capabilities

Uncertainty Calculator 3.2

Uncertainty

Sidekick

1.0

 

Assistant

2.3

Uncertainty

Sidekick

Pro 1.0

Uncertainty

Toolbox

2.8

Uncertainty

Analyzer

3.0

GUM

Workbench

1.3

Correlations

Between

Measurement

Process

Errors

Limited to

One Pair

of

Error

Sources

Limited to

Two Pairs

of

Error

Sources

Cross-

correlations

Between

Component

Errors

 

 

Limited to

Two Pairs

of

Error

Sources

Correlation

Coefficients

Table

 

 

Automatic

Computation

of

Sensitivity

Coefficients1

 

 

See

Footnote2

User

Defined

Sensitivity

Coefficient

Equations

           

Entry and

Display of

Analysis

Information

Scratchpad/

Remarks

Screen

Notes

Screens

Comment/

Description

Fields

Notes

Screens

Comment/

Description

Fields

Notes & Analysis

Description

Screens

Comment/

Description

Fields

Effective

Degrees of

Freedom3

 

Computation

of Confidence

Limits or

Expanded

Uncertainty4

 

1  In a multivariate analysis, the sensitivity coefficient of a variable is the partial derivative of the equation that defines a quantity of interest with respect to that variable.  The product of the sensitivity coefficient and the variable's standard uncertainty reflects the contribution of the uncertianty in the variable's error tot he overall uncertainty in the computed quantity.

2  A Sensitivity Coefficient Worksheet can be used to compute partial derivatives for up to 10 variables.  The computed sensitivity coefficients must then be copied and pasted into the appropriate cells on the Uncertainty Budget Worksheet.

3  Computed using Welch-Satterthwaite formula given in Annex G of the GUM.

4  Computed by multiplying the combined uncertainty by 1) user specified coverage factor or 2) coverage factor computed from effective degrees of freedom and user specified confidence level.

 

 

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Page Updated February 12, 2015