Working principle of GUM Workbench

Jens Bo Toftegaard

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Working principle of GUM Workbench

This is an introduction to what GUM Workbench essentially does.

Introduction

The 'GUM Workbench' program is used to analyse the uncertainty of physical measurements and calibrations. The analysis and computations follow the rules of the 'ISO guide to the expression of uncertainty in measurement' and the requirement document EA-4/02 of the 'European cooperation for Accreditation of Laboratories'.

Computation examples of the EA-4/02 can be analysed with the help of the program. They are included with the software package as example models.

GUM Workbench supports a systematical procedure in building an uncertainty analysis as required by the EAL document. Starting with the mathematical equation which models the physical relationship of quantities in the respective measurement, the data needed for the analysis, like the standard uncertainty or the distribution of values, is interactively requested. The analysis process is controlled by appropriate classification of the input values according to the available information.

The result of the analysis is a clear table of the uncertainty budget. This table holds all used measurands with their symbols and values, the assigned standard uncertainty and actual degrees of freedom, the sensitivity coefficient calculated from the model equation and their contribution to the standard uncertainty of the result of the measurement. In the end the complete result of the examination is presented as a value with an attached expanded uncertainty and automatically or manually selected coverage factor. All values are rounded to an appropriate number of decimal places.

For documentation purposes the result of the uncertainty analysis together with all input data can be printed as a report. All input texts are part of the printout and used for a clear and structured documentation. Before the actual printing process is initiated, you can check the result in a preview window.

The analysis together with all the input (the model equation, the values and all the texts) can be saved in a file with a selectable name. That way the examination is available at any time for a later check.

Each saved analysis can be used as a starting point for new uncertainty analyses utilising the same model but using new or changed data. Therefore the program is suited especially for the examination of the influence of the various values and their accompanying uncertainties on the result.

How to make an uncertainty analysis.

Using GUM Workbench, uncertainty analysis is reduced to the following simple steps:

  1. To start a new analysis select New from the menu File.
  2. Click the button "Model". Provide a title and a general description for the measurement procedure in the data fields offered by the screen display.
  3. The Model Equation field holds the model equation for the measurement to be analysed. The program will then analyse the model equation and will as a first step produce a list of the input quantities.
  4. The type of each input quantity and other necessary details are now to be entered in easy-to-use screens facilitating the proces with pull-down menus.
  5. 5.Input of observation data is done in the screen Observation.
  6. 6.Correlation coefficients between input values can be edited in a Correlation Matrix.
  7. 7.The program then produces a detailed result that is shown in screen called Uncertainty Budget.
  8. 8.The final result is given with a automatically or manually chosen coverage factor.
  9. 9.The Report-Generator prints a structured report which follows the rules given by the EA and ISO-guides.
  10. 10.To save an uncertainty analysis select Save from the File menu.