![]() ![]() The ANOVA then allows the individual sources of variation in the measurement data to be identified the part-to-part variation, the repeatability of the measurements, the variation due to different operators and the variation due to part by operator interaction. In one common crossed study, 10 parts might each be measured two times by two different operators. Several methods of determining the sample size and degree of replication are used. The "10×2×2" (ten parts, two operators, two repetitions) is an acceptable sampling for some studies, although it has very few degrees of freedom for the operator component. There is not a universal criterion of minimum sample requirements for the GRR matrix, it being a matter for the Quality Engineer to assess risks depending on how critical the measurement is and how costly they are. Įxamples of gauge R&R studies can be found in part 1 of Czitrom & Spagon. Īnova gauge R&R is an important tool within the Six Sigma methodology, and it is also a requirement for a production part approval process (PPAP) documentation package. A P/T ratio greater than 0.3 suggests that unacceptable parts will be measured as acceptable (or vice versa) by the measurement system, making the system inappropriate for the process for which it is being used. Generally, a P/T ratio less than 0.1 indicates that the measurement system can reliably determine whether any given part meets the tolerance specification. If the P/T ratio is larger, it means the measurement system is "eating up" a large fraction of the tolerance, in that the parts that do not have sufficient tolerance may be measured as acceptable by the measurement system. If the P/T ratio is low, the impact on product quality of variation due to the measurement system is small. It is common to examine the P/T ratio which is the ratio of the precision of a measurement system to the (total) tolerance of the manufacturing process of which it is a part. Gauge R&R addresses only the precision of a measurement system. ![]() It is important to understand the difference between accuracy and precision to understand the purpose of Gauge R&R.
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