Uncertainty-based determination of recalibration dates

Abstract

Traceability is of vital importance in metrology and is achieved by an unbroken chain of calibrations that relate the measurement result to a reference. Less clear is the temporal aspect of traceability, namely the determination of recalibration dates. Relevant standards require the conduction of recalibrations in a planned manner, and thus in general there is a calibration history consisting of a number of past calibrations for measurands that are part of the traceability chain. Nevertheless, commonly only the results of the last calibration of the standards of the traceability chain are considered when determining a measurement result. Furthermore, recalibration dates are often determined in a rather unscientific manner. Within this paper, a method is proposed to predict the current value of a measurand along with its uncertainty, taking into account all past calibrations. Based on the predetermined target measurement uncertainty of the measurand, it is possible to recognize the need for and thus to date recalibrations. The applicability of the method is investigated by examining the metrological compatibility of the predicted results with the results of subsequent calibrations of the calibration histories of a number of different standards. There is an explainable limitation of the applicability of the method to calibration histories that exhibit a correlation of time and the chosen calibration laboratory. However, the paper leads the way of future research to remedy the currently unsatisfying state regarding the handling of calibration histories and the determination of recalibration dates.