Different Elements of MSA

Different elements of MSA

Different Elements of MSA

 - The study of this 5 elements are very important in MSA and calibration. It is combination and interaction of part, operator and instrument.


 - Bias means difference between measured value and true value (Actual value / Metrological value)

 - The true value is also known as accepted, reference or master value. 

 - If the true value or actual value is unknown it can be calculated by averaging several measurements with the most accurate measuring equipment. 


Bias Study

 - Find the true value for the part.

 - Use layout inspection equipment.

 - Measure same part at least 10 times using gauge.

 - calculate average of all readings.

 - Bias = Measured Average - True Value

Possible Causes of Bias

 - Instrument is not calibrated

 - Improper instrument handling

 - Human limitations


 - Linearity means consistency of instrument over the different range of measurement.

 - e.g. If we measure one object (30 mm width) with Vernier it shows 30 mm and another object (130 mm width) with the same Vernier and it shows 130.1 mm. then it is not linear as 0.1 mm bias is observed.


Linearity Study

 - Select 8-10 parts that can be measured at different operating ranges of the measurement system.

 - Determine measured value of each part by using layout inspection.

 - Take 10-12 repeated readings of each part by one appraiser only.

 - Calculate part's bias and plot it against the measured value.

 - Linearity represented by the slope of the best fit line of these points.

Possible Causes of Linearity

 - Instrument is not calibrated

 - Problem with master sample

 - Temperature, Humidity, Cleanliness


 - Stability Means capacity of a measurement system to produce the same value over time when measuring the same sample by same person.

 - If for each time period, the average measured value are similar the measurement system has good stability.

 - If the average values are different then the system has not good stability.

 - Stability means the absence of "Special Cause Variation", present of "Common Cause Variation" (random variation).



 - Repeatability means variation when same operator measures the same part repeatedly with the same instrument in the same environment condition.


Possible Causes of Repeatability

 - Equipment should be more rigid or properly maintenance to be done.

 - Physical condition (Eyesight) and Environmental condition (Lighting, Noise)


 - Reproducibility means variation when different operator measures the same part with same instrument.

 - This is because of operator error.


Possible Causes of Reproducibility

 - Measurement procedure is not clear.

 - Proper training not given to operator for handling of instrument.

Also Visit What is MSA

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