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MSA – Measurement System Analysis

(Validating measurement systems )

  • Measurement Systems Analysis (MSA) is a tool for analyzing the variation present in each type of inspection, measurement, and test equipment.
  • It is the system to assess the quality of the measurement system.
  • It allows us to make sure that the variation in our measurement is minimal compared to the variation in our process.

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  • Total Variation = Process Variation + Measurement Variation

Inspection process

Component/Feature

to be measured

Equipment's &

Inspectors

Measured Value

Measurement variations cause inaccurate result

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Measuring system variation

Due to Inspector

Variation (Width Variation)

(PRECISION)

Due to equipment

Variation (Location Variation)

(ACCURACY)

Repeatability

Reproducibility

Accuracy

(Bias)

Linearity

Stability

(consistency)

Source of

process variation

  • Man
  • Machine
  • Material
  • Method
  • Tooling's
  • Parameters
  • Environment
  • Measuring system

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Instrument selection criteria

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Resolution: (Rule of 10 to 1)

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  • The discrimination (resolution) of the measuring instrument should divide the tolerance

of the characteristic to be measured into ten parts.

  • The gage or measuring instrument should be 10 times as accurate as the characteristic to be measured.

PARAMETER

REQ. SPEC

TOTAL TOL.

REQ.LEAST COUNT OF INSTRUMENT AS PER 1/10 RULE (MAX)

MIN

MAX

LENGTH (25± 0.10)

24.90

25.10

0.20

0.020

OD (10 `.025)

9.975

10.025

0.050

0.005

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ACCURACY VS PRECISION

Accuracy is closeness of the measurements

to a specific value, while precision is the

closeness of the measurements to each other.

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Accuracy: Difference between true value and observed average measurement of the same dimension.

Linearity: Difference in bias value over the normal operating range of measuring instrument.

10.0

-0.5

+0.5

9.8

10.0

-0.5

+0.5

10.1

9.8

100.0

-0.5

+0.5

0.3

99.5

100.1

0.6

Stability: This is the difference in average value, when measure the same size of the same part

With same gauge and inspector over an extended time period.

10.0

-0.5

+0.5

10.1

9.8

10.1

9.5

10.1

10.3

Time-1

Time-2

Time-3

0.3

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Calibration

Master�value

First Reading

Master�value

Second Reading

Master�value

Third Reading

10.00

10.00

10.00

50.000

50.00

50.00

150.000

150.00

150.00

9.99

9.98

49.99

49.98

150.00

149.90

Temperature & Humidity control

Temperature : 20° +/-1°

Relative Humidity : 50 +/-10%

Digital Caliper (0 - 150)mm

Allowable Error for V.Calliper : :0.030mm

(JIS B7507)

Actual Error : 0.010 to 0.020

Calibration status : Pass

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Repeatability : Repeatability is the variation between successive measurements of the same part, same characteristic, by the same person using the same gage. In other words, how much variation do we see in measurements taken by the same person, on the same part, using the same tool?

Actions: repair, replace, adjust

Repeatability

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Reproducibility

Reproducibility: Reproducibility is the difference in the average of the measurements made by different people using the same instrument when measuring the identical characteristic on the same part. In other words, how much variation do we see in measurements taken by different people on the same part, using the same tool?

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Actions: training