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Video Link - What is Measurement System Analysis?

What is Measurement System Analysis?

Q: What is Measurement System Analysis (MSA)? A: It’s a set of techniques that allow us to answer the question: IF I USE THIS GAGE TO MEASURE, HOW MUCH CAN I TRUST THE MEASUREMENTS I GET? MSA is based on Measurement Error

Understanding Measurement Error Take a single item, and measure it multiple times using the same gage/same technique/same appraiser

Understanding Measurement Error Record the measurements and draw a histogram

Understanding Measurement Error The histogram represents a sample from a normal distribution with a Mean, and a Standard Deviation (derived from spread)

Understanding Measurement Error Consider the position of the mean – This is how we determine the bias of the system Imagine we had measured a reference size – a standard – of a known dimension. We could compare the mean of our results to the actual size of the standard. The difference is Bias

Bias Reference Value = 0.500 – This is a known size Mean of multiple measurements = 0.525 The gage is, on average, measuring about 0.025 too big. It has a positive bias of 0.025

Bias The gage is, on average, measuring about 0.025 too small. It has a negative bias of 0.025

Bias The gage is, on average, measuring the same size as the standard. It has a zero bias

Bias But, we have only dealt with Bias at one size at one point in time A Gage is used over a range of sizes And over a period of time Bias may change depending on these factors: Linearity Change in Bias over the operating range of the gage Stability Change in Bias over time

Bias Linearity – Change in Bias over operating range

Bias Stability – Change in Bias over time

Bias Stability & Linearity For standard Gages - How does the calibration system deal with Bias?

Variation Repeatability & Reproducibility Bias is based on the location of the mean of the distribution What about the spread of sizes? For a perfect gage this spread would be as small as possible We need to determine if we can live with the spread (variation) of measurement error from the gage We know that when one person uses the gage we get variation – This is the variation inherent in the Gage – REPEATABILITY If we have more than one person using the gage, this may introduce more variation - REPRODUCIBILITY

Variation Repeatability & Reproducibility

Variation Gage R&R One way to determine the amount of variation in the Measurement System is through a Gage R&R Study Take say, 10 parts, 3 appraisers, and measure each part 3 times ( or 15 parts x 4 appraisers x 5 replicates – whatever you want) Analyze the results using statistical methods e.g. Analysis of Variance (ANOVA) to determine how much variation comes from Gage R&R Repeatability Reproducibility

Variation Gage R&R Screenshot from Free Online Gage R&R ANOVA Calculator at www.GageRandR.com

Variation Gage R&R

Variation Gage R&R When we’ve calculated the magnitude of the Repeatability Reproducibility Both together – Gage R&R We can compare them to: A Tolerance A Process Capability The amount of Total variation in the Gage R&R Study Anything else that helps answer the question: How much can I trust my data if I use this Gage ?

Visit: www.GageRandR.com For more info about: Measurement System Analysis Gage R&R Free Online Gage R&R Calculator (ANOVA) Interactive Process and Gage Simulation Other helpful stuff dave@gagerandr.com