Measurement Systems Analysis Introduce Measurement Systems Assess Measurement

Process Control A Typical Process People Methods Material Equipment Environment Input PROCESS Product Process

Assessing Measurement Systems How good is our measurement system? • • Observed Process Variation

Assessing Measurement Systems • Location variation – Bias – Stability • Width variation –

Determining and Assessing Bias • Bias is the difference between the observed average of

Determining and Assessing Stability • Stability (or drift) is the total variation in the

Determining and Assessing Linearity • Linearity is the difference in the bias values through

Determining Repeatability • Repeatability is the variation in measurements obtained • By one appraiser

Determining Reproducibility • Reproducibility is the variation in the average of the measurements made

Preparing For A Measurement System Study • Variable Gauge Study (Average and Range Method)

Determining and Assessing Repeatability and Reproducibility • If repeatability is large compared to reproducibility,

Acceptability Criteria • R&R Indices – 10% – 10% - 30% – 30% •

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Measurement Systems Analysis • Introduce Measurement Systems • Assess Measurement Systems Performance • Understand Measurement System Variation Measurement Systems Analysis www. qualimations. com

Process Control A Typical Process People Methods Material Equipment Environment Input PROCESS Product Process / System Output Identifying Improvement Opportunities Accurate Measurement using Measurement System Analysis Measurement Systems Analysis www. qualimations. com

Assessing Measurement Systems How good is our measurement system? • • Observed Process Variation 2 T = 2 p + 2 m • Production Gauge Variation Actual Process Variation Measurement Systems Analysis www. qualimations. com

Assessing Measurement Systems • Location variation – Bias – Stability • Width variation – Linearity – Repeatability, Reproducibility Measurement Systems Analysis www. qualimations. com

Determining and Assessing Bias • Bias is the difference between the observed average of measurement and the reference value. • The reference value, also known as the accepted reference value or master value, is a value that serves as an agreed-upon reference for the measured values. A reference value can be determined by averaging several measurements with a higher level of measuring equipment. Measurement Systems Analysis Observed Average Value Bias Reference Value www. qualimations. com

Determining and Assessing Stability • Stability (or drift) is the total variation in the measurements obtained with a measurement system • on the same master or part when measuring a single characteristic • over an extended time period Time Reference Value Measurement Systems Analysis www. qualimations. com

Determining and Assessing Linearity • Linearity is the difference in the bias values through the expected operating range of the gauge. Reference Value Observed Average Value Smaller Bias Reference Value Observed Average Value Larger Bias 50 mm Measurement Systems Analysis 200 mm www. qualimations. com

Determining Repeatability • Repeatability is the variation in measurements obtained • By one appraiser • with one measurement instrument • when used several times • while measuring the identical characteristic • on the same part Measurement Systems Analysis Repeatability www. qualimations. com

Determining Reproducibility • Reproducibility is the variation in the average of the measurements made • by different appraisers • using the same measuring instrument • when measuring the identical characteristic • on the same part Measurement Systems Analysis Reproducibility www. qualimations. com

Preparing For A Measurement System Study • Variable Gauge Study (Average and Range Method) The average and range method of gauge study breaks the gauge error into repeatability and reproducibility. Optimum conditions: • 3 operators; • 3 trials; • 10 parts. Study of the results can provide information concerning the causes of the measurement error. • If reproducibility is large compared to repeatability then; • The operator is not properly trained in how to use and read the gauge; • Graduations on the gauge are not clear. Measurement Systems Analysis www. qualimations. com

Determining and Assessing Repeatability and Reproducibility • If repeatability is large compared to reproducibility, the reasons may be: – – • The instrument needs maintenance; The gauge should be redesigned to be more rigid; The clamping or location for gauging needs to be improved; There is excessive part variation. If reproducibility is large compared to repeatability, then possible causes could be: – The appraiser needs to be better trained in how to use and read the gauge instrument; – Calibrations on the gauge dial are not clear; – A fixture of some sort may be needed to help the appraiser use the gauge more consistently. Measurement Systems Analysis www. qualimations. com

Acceptability Criteria • R&R Indices – 10% – 10% - 30% – 30% • Acceptable Measurement System May be acceptable based upon application, cost of measurement device, cost of repair, Not acceptable. Measurement system needs improvement. Number of Distinct Categories Index – 1 Unacceptable. One part cannot be distinguished form another. – 2 -4 Generally unacceptable – 5 Recommended Measurement Systems Analysis www. qualimations. com