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Software tools for the calculation of measurement uncertainties in force measurement

15.08.2016

Record-breaking heights for buildings and wind turbines, record-breaking lengths for bridges: an increasing number of requirements are being made on the resilience of construction materials. This is also a challenge for materials testing, where sometimes forces in the two-digit meganewton range occur. The installations generating such forces must be traceable and calibrated. In PTB’s Solid Mechanics Department, methods for the better traceability of force measurement have thus been developed and examined, especially in the meganewton range. This work took place within the scope of the European Metrology Research Programme EMRP under the title "SI Broader Scope II" (Project SIB63), and the results are now available online.

Within the scope of this research project, methods of traceability in the extended measuring range (among other things: by means of build-up systems and extrapolations) were developed, but so were procedures for the calculation of corrections for various influence quantities and the associated measurement uncertainties. Thereby, the influence quantities were subdivided into the following:

-    geometrical (in build-up systems, eccentricity)
-    mechanical (torque and bending moments, lateral forces, multi-component loading)
-    time-related (creep, storage, drift)
-    electrical (excitation voltage) and
-    environmental influences (temperature, relative humidity and ambient pressure).


It turned out that most of the effects can be described by means of very similar models. Procedures are derived from these models according to which the influences are to be taken into account metrologically. If the effect is known and reproducible, a better result can usually be calculated. In addition, it is possible to attribute a measurement uncertainty to the new result. This uncertainty can be determined by standard procedures.
To allow the user to apply these results by putting in only little effort relating to familiarization and training, tools were developed within the scope of the project which make it possible to carry out calculations online or offline. To this end, the project partners have developed suitable input masks (see Figure 1) into which all the values which are required for the calculation must be entered in the white fields. The calculation is triggered via the "Evaluation" button. The results appear in the shaded fields and comprise – besides the corrected values – their measurement uncertainties, the components contributing to the total measurement uncertainties as variances in descending order, as well as an explanation. By means of the "Reset" button, the results are removed, whereby the output data will be retained. It is easy to modify a numerical value and to carry out the calculation once again.

Figure 1: Example of the calculation of a corrected measurement value (result) with attributed measurement uncertainty,
individual contributions (variance) and explanation

For calculations which are to be carried out without access to the browser and to the internet, an Excel file can be downloaded that basically fulfils the same purpose and has a comparable scope of functions.
 
Bibliography:

[1] Website of the EMRP SIB63 project: Opens external link in new windowhttp://www.ptb.de/emrp/forcemetrology.html
 
Contact person:

Dirk Röske, Department 1.2, WG 1.21, e-mail: Opens window for sending emaildirk.roeske(at)ptb.de

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