Calculating Interval Uncertainties for Calibration Standards That Drift with Time

Abstract

Calibrated values of many devices exhibit predictable drift over time. To provide an uncertainty statement valid over the entire calibration interval, one must account for drift. In this article, a method of accounting for drift is proposed based on guidance in the Guide to Expression of Uncertainty in Measurement. An additional uncertainty term is computed using a linear regression of historical measurement data, which is included along with the time-of-test uncertainty. This method is evaluated by analyzing its average out-of-tolerance (OOT) rate using a Monte Carlo simulation, which results in the desired 5 % average OOT rate when the total uncertainty is expanded to a 95 % confidence interval.

Acknowledgements

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. LA-UR-19-22614. SAND2020-3749 J. The authors would like to thank Hy Tran, Eric Forrest, Raegan Johnson, Eddie O’Brien, and Ricky Sandoval, all of Sandia National Laboratories, for their valuable input.