MSA TRN

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o

MSA-R R

Training Program27/7/2013DATE-

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M.S.A. (R &R)

TRAINING

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What is MSA ?

MSA primarily deals with analyzing the effect of themeasurement system on the measured value

Emphasis is on the effect due to equipment and personnel

We test the system to determine numerical values of itsstatistical properties and compare them to acceptedstandards

Quality of the data is of great importance ( Bias & variance)

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MSA

Define the

Measurement System

Dis

crimination

Metrological

Calibration,

Traceability

& Uncertainty

Bias,Linearity,

Stability

Conducting

GRR

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MEASUREMENT SYSTEM DATA

Data collected for controlling a process contains variations from two

different and independent sources:

- Manufacturing Process Variation ( MPV)

- Measurement System Variation (MSV )

- Total Variation (TV)= MPV+MSV

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Measurement System Variation must be smallerthan the manufacturing process variation

MSV < MPV+

MSV MPV

TOTAL VARIATION ( TV )

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MEASUREMENT SYSTEM ERRORS

FIVE CATEGORIES:• BIAS

• LINEARITY

• STABILITY• REPEABILITY

• REPRODUCIBILITY

LOCATION ERRORS

WIDTH ERRORS

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Repeatability : Variation in measurements obtained with one

Measurement instrument when used several times by oneassessor While measuring identical characteristics on the same

part graph on R- Chart

Reproducibility : Variation in average of measurements made

by different assessors using same measuring instrument

when measuring identical characteristic on same part graph on

X - Chart

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MEASUREMENT SYSTEM ERRORSAverage and Range Method:

The method allows the measurement system’s variation to be

Decomposed into Repeatability and Reproducibility but not

Their Interaction.

GRR = EV2 + AV

2( Graphical & numerical Method )

ndc = 1.41 ( PV / GRR )

ndc > 5

Note : The sum of the percent consumed by each factorwill not be equal 100 %

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Repeatability > Reproducibility

- Instrument needs maintenance

- Improve clamping or location of gaging

- Excessive within – part variation

Reproducibility > Repeatability

- Appraisers need better gage use training

- need better operational definition

- need fixture to provide consistency in gage use

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CASE STUDY :

A V.C of L.C 0.02 mm is used for the measurement

Of O.D having a tolerance of +/- 1.5 mm. The VC is used forThe Process capability studies and the results of R&R

Study carried out indicated the following results:

1) EV = 0.20188

2) AV = 0.229633) PV= 1.10456

Calculate the GRR,ndc and TV.Also suggest the usage of VC

based on R&R results.

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Uncertainty of Measurement

Used internationally to describe the quality of ameasurement value.

The width of the statistical band in which the

true value would lie is termed as Uncertainty inmeasurement.

The first measurement system uncertainty is

generated by the process of calibration


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Uncertainty of Measurement

•The reference material itself

•The calibration process

•The environment and personnel performing

calibration actually contribute to themeasurement uncertainty

Thus the need for accredited labs

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HIERARCHY OF TRACEABILITY

ProductBIS-BS-IS 1mm up to 1 m

Working

Inspection

Reference

Quantum

International

VC,Mic,HG,

Plug

Grade 1 & 2

Slip Gauge

Grade 00 & 0

Slip Gauge

Monochromatic Wavelength of

Hg-198 & Cd- 114 Lamps

Meter (m)

SI unit of LengthIBWM

National Lab

0.1 to 5 parts in 108

NPL

Interferometer

0.04 to 0.1 m

Comparator

0.1 to 0.2 m

Length Standards

1 m to 0.1 m

Measurement System Evaluation

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Measurement System EvaluationBias

Bias is the difference between

the observed average of the

measurements and the reference

value.The referenc e 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.

Bias

Reference

Value

Observed

Average

MSE/970311/RK17

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1. Three (or two) operators are involved: A, B, and C.

2. Ten parts are used. They are numbered in a way which wi

interfere with the measurement.

3. Ensure the measuring equipment is calibrated before the

commences.

4. Operator A measures the 10 parts. The results are recor

an observer.

5. Step 4 is repeated by operator B and C. The measuremen

performed in the same order.

6. The cycle of measuring the 10 parts is repeated twice (i.e.

repeats per part per operator).

repeatability & ReproducibilitProcedure

repeatability & Reproducibility

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1. repeatability (Equipment Variation, EV):

2. Reproducibility (Appraiser Variation, AV):

q = number of parts

n = number of repeats

3. repeatability & Reproducibility (r&R ):

repeatability & ReproducibilityCalculation

MSE/970311/RK32


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Factors K 1 and K 2

Repeats

2 3 4 5

K1 4.566 3.042 2.501 2.214

Operators

2 3 4 5

K2 3.652 2.703 2.302 2.077

MSE/970311/RK33


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repeatability & ReproducibilityBased upon the Tolerance

repeatability = (EV / Tolerance) x 100%

Reproducibility = (AV / Tolerance) x 100%

r & R = (r&R / Tolerance) x 100%

MSE/970311/RK34


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repeatability & Reproducibility Acceptance Criteria

%r&R < 20% Measurement System is acceptable

20% < %r&R < 30%Measurement System is may be acceptable : - improve for critical applications - decrease sorting limits for critical parameters

%r&R > 30%

Measurement System needs improv ement

- process control:

measurement masks process variation no realistic Cp/Cpk - inspection: decrease sorting limits

The basis of the calculation of %r&R, i.e. Tolerance orProcess Capabil i ty must be stated.

MSE/970311/RK36

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Documents

MSA TRN