Validating system

Posted by / 05-Mar-2018 19:37

Validating system

The measurement system’s variance contribution is assessed against the natural part-to-part variation of a process.The smaller that percentage, the better the measurement system can be judged.Therefore, these points are special-cause variants, and, as such, they offer practitioners a chance to conduct further investigation to learn something about the process – perhaps even improve its variability.In Figure 1, note, the grouping of five data points to the right; yellow dots track estimates of the percentage of total process variability contributed by the measurement system (read from the right-side axis).If the parts used in the assessment are not distributed evenly between the specification limits, the GRR assessment of the measurement system will have errors.Think of it this way: If there is little variation among tested parts because they are all near target (or more likely, “most near target with a few outliers”), the measurement system will be judged as worse than it actually is because the variation it is being assessed against has been narrowed artificially.3.These are calculated using standard deviations instead of variances.

Short term, it can vary within a multi-day manufacturing campaign and introduce product variation as process conditions shift or drift.Over the longer term, product variation might reflect targeting issues encountered from one production campaign to the next.Process control strategies address not only these targeting issues, but also short-term (σ, the lot-to-lot variation in a batch process, or shift-to-shift variation in a continuous production line, is due to variation in the sampling and measurement system itself.The third problem is that the typical GRR assessment is a once-only static measure.It does not address the stability of the measurement system over time.

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This strategy can be used as an alternative to gage R&R (GRR) studies.