Experimental verification of the evaluation method of creep uncertainty from reversibility error prescribed in ISO 376:2011

ISO 376:2011 prescribes two ways of evaluating creep uncertainty in calibrations of force proving instruments: (a) one is to evaluate it from the relative creep error and (b) the other from the reversibility error. The reversibility error is a function of calibration forces, while the creep error is one single value and is not depend on the calibration forces, because the creep test is performed only once during the calibration procedure and the test result is applicable to all of the calibration forces. When the creep uncertainty is simply calculated from the reversibility error as a function of calibration forces, the creep uncertainty becomes zero at the maximum calibration force even though creep phenomenon surely appears at that force in practice. The authors proposed to revise uncertainty estimation method in ISO 376:2011 that the relative creep uncertainty calculated from the reversibility error should be uniform over the calibration range and be calculated from the maximum reversibility error expressed in terms of deflection. This report gives an experimental verification of the authors' proposition.