ON THE RELEVANCE OF NDC INDICATOR IN MEASUREMENT SYSTEMS ANALYSIS

A correct performance of measurement systems is a key element in the Quality effort of manufacturing organizations. At least as important as calibration processes, Measurement System Analysis is essential to ensure a solid baseline for decision making. Confirming this relevance, Measurement System Analysis is one of the quality core tools for automotive industry, as ensures the validity of the measurements obtained. In variables measurement, some indicators describe different aspects of the measurement system performance, and simultaneously serve as validation criteria for system acceptance. Probably the most important two indicators are the gage repeatability and reproducibility as a percentage of the total process variation (%GRR) and the number of distinct categories (ndc), for which threshold values apply (%GRR should be less than 10% and ndc should be greater than 5). In this paper we enhance the fact that these two indicators aren't independent, and the threshold values are incoherent, creating a possible conflict when deciding the acceptance of a measurement system.