MSA vs. Measurement Capability Analysis - What are the differences?

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#33
Welcome to the Cove, Errol! :bigwave:

Yes, they are basically the same. The whole exercise of MSA helps you quantify the two types of variation (position variation - bias, linearity and width variation-GRR) for measuring a particular characteristic.

Various indexes can be computed.

A. Based on a Bias/Repeatability Study

(Ref: My old notes based on the booklet "Capability of Measuring Instruments": Robert Bosch)
Take repeated measurements (25-50) on a production master, calculate average and Repeatability StDev.

The two indexes calculated are:
1. Cgm = (0.2 * Tolerance) / (6 * Rpt_Stdev)
2. Cgmk = Least of
( RefValue + (0.1 * Tolerance) - XBar) / (3 * Rpt_StDev)
-OR-
( XBar - (RefValue - (0.1 * Tolerance)) ) / (3 * Rpt_StDev)

Both should be >= 1.33; and bias (XBar-RefValue) not significant.

B. Based on GRR, typically two indexes are recommended:

1. Measurement Capability Index (MCI_I) based on Process Variation is defined as:
MCI_I = 100 (Sigma_GRR/Sigma_process)
Sigma_Process is calculated from ongoing SPC studies: RBar/d2

2. The other index, (MCI_II) is based on tolerance:
MCI_II = 100 (5.15 * Sigma_GRR/ Tolerance )
In place of 5.15 you can also use 6 to cover 99.73% spread.

Acceptance criteria for both these are:
<=20% :Good
>20 - <=30% :Marginal
>30% :Unacceptable
Thanks for the information can I get the excel sheet of this calculation
 
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