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Understanding the ramifications of important proposed changes to decision rules in three standards within ISO and ASME

Published

Author(s)

Craig M. Shakarji, Steven D. Phillips

Abstract

Decision rules define how measurement uncertainty is used (in conjunction with measured values and specification zones) to make acceptance or rejection decisions of products. Decision rule changes that are being proposed in key standards—some of which are quite likely to be implemented—can have important ramifications to the metrological world. Firstly, this paper seeks to highlight proposed changes to ISO 14253-1, which standardizes the default decision rule for the scope of ISO/TC 213, Dimensional and geometrical product specification and verification. Briefly, the change is a shift from a universally-applied guard band with a magnitude equal to 100 % of the expanded (k = 2) uncertainty to a more general guard band equal to the 95th percentile of the error distribution, which is equivalent (in most cases) to a guard band equal to 82.5 % of the (k = 2) expanded uncertainty. Secondly, this paper seeks to highlight a proposed addition to ASME B89.7.3.1, a standard dealing with decision rules. The proposal—presented at a recent B89.7 meeting—could lead to an additional definition of an extended 4:1 simple acceptance/rejection decision rule that allows for acceptance and rejection decisions in some cases when 4:1 is not met, yet the measured value is sufficiently far from the specification limit such that the risk probability is no greater than that implied by the conventional 4:1 rule. Finally, this paper seeks to highlight a proposal from a joint working group between ASME B89 and Y14.5, to be made at the design stage, that can influence decision rule requirements, based on a designer’s need to mitigate the risk of potential pass errors. The proposed design requirement would not explicitly state the decision rule but would limit the maximum probable error and hence constrain a metrologist’s choice of decision rules.
Proceedings Title
NCSLI 2015 Conference Proceedings - NCSL International
Conference Dates
July 19-23, 2015
Conference Location
Graprevine, TX
Conference Title
2015 NCSL International Workshop & Symposium

Keywords

ASME, decision rule, ISO, measurement uncertainty, metrology, standard

Citation

Shakarji, C. and Phillips, S. (2015), Understanding the ramifications of important proposed changes to decision rules in three standards within ISO and ASME, NCSLI 2015 Conference Proceedings - NCSL International, Graprevine, TX (Accessed April 18, 2024)
Created July 31, 2015, Updated February 19, 2017