The Gauge R&R method analyzes how much of the variability in your measurement system is due to operator variation (reproducibility) and measurement variation (repeatability). Gauge R&R studies are available for many combinations of crossed and nested models, regardless of whether the model is balanced.
Tip: Alternatively, you can use the EMP method to assess your measurement system. See Measurement Systems Analysis.
Before performing a Gauge R&R study, you collect a random sample of parts over the entire range of part sizes from your process. Select several operators at random to measure each part several times. The variation is then attributed to the following sources:
• The process variation, from one part to another. This is the ultimate variation that you want to be studying if your measurements are reliable.
• The variability inherent in making multiple measurements, that is, repeatability. In Table 5.1, this is called the within variation.
• The variability due to having different operators measure parts—that is, reproducibility.
A Gauge R&R analysis then reports the variation in terms of repeatability and reproducibility.
|
Variances Sums |
Term and Abbreviation |
Alternate Term |
|---|---|---|
|
V(Within) |
Repeatability (EV) |
Equipment Variation |
|
V(Operator)+V(Operator*Part) |
Reproducibility (AV) |
Appraiser Variation |
|
V(Operator*Part) |
Interaction (IV) |
Interaction Variation |
|
V(Within)+V(Operator)+V(Operator*Part) |
Gauge R&R (RR) |
Measurement Variation |
|
V(Part) |
Part Variation (PV) |
Part Variation |
|
V(Within)+V(Operator)+ V(Operator*Part)+V(Part) |
Total Variation (TV) |
Total Variation |
A Shewhart control chart can identify processes that are going out of control over time. A variability chart can also help identify operators, instruments, or part sources that are systematically different in mean or variance.