Measurement Systems Analysis Introduce Measurement Systems Assess Measurement Systems Performance Understand Measurement System Variation Measurement Systems Analysis

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

Measurement Systems Analysis Assessing Measurement Systems Observed Process Variation Actual Process Variation Production Gauge Variation  2 T =  2 p +  2 m How good is our measurement system?

Measurement Systems Analysis Location variation –Bias –Stability Width variation –Linearity –Repeatability, Reproducibility Assessing Measurement Systems

Measurement Systems Analysis 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. Reference Value Observed Average Value Bias

Measurement Systems Analysis 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 Reference Value Time

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

Measurement Systems Analysis 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 Repeatability

Measurement Systems Analysis 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 Reproducibility

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