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Tools for Metrology  - Recalibration Intervals and Drift Prediction
    The Predictor
(version 3-0,  1.8 MB zipped)

Calibration intervals of measurement standards are efficiently estimated using the Predictor Software tool. 

Calibration interval estimates are actually a compromise. Too frequent calibrations are financially unfeasible, while infrequent calibration may result in lose of accuracy. This program, based on past calibration results and their uncertainties, forecasts the calendar date at which the sum of the standard's parameter deviation plus its uncertainty will reach a specified limit. This date provides the longest interval in which the measurement standard will be kept within specifications despite its natural aging and instability. Using the “deviation plus its uncertainty” for a test of compliance with specifications is in accordance with ILAC G8 document.

In addition, the Predictor estimates changes in the measurements standard due to drifts since the standards last calibrration. Using estimated drifts and their uncertainties in an uncertainty budget is an improvement over using data from an old calibration.

Calibration labs use the Predictor to improve the uncertainty in their measuring standards and provide objective calibration interval service to their clients. Note that labs complying with ISO/IEC 17025 are required to have a recalibration program.

  Past Calibrations Database and Prediction Displayed as Graph

Reporting recalibration dates and intervals

Due-Date   Interval Parameter  Nominal-Value Unit1  Predicted-Dev.  Uncertainty Tolerance Unit2   k    d.f.

2001-4-19  532      100Hz       2.5          A       0.00048        0.00012     0.0003    A       3.14 3.38

2005-5-6   1697     DC          10           ohm    -7.7            0.99        1         ppm     2.4  7.53

1996-11-9  0        test        1            ohm     18             50          2.5       ppm     2    50   

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