This document discusses measurement system analysis (MSA) and key terms related to evaluating measurement systems. It provides the following information: 1. An MSA seeks to identify sources of variation in a measurement process. Steps include determining the system to study, establishing test procedures, and choosing operators and sample parts. 2. Measurement systems should demonstrate stability, minimal variation compared to specifications, and minimal variation compared to the process being measured. 3. Key terms defined include reference value, resolution, precision, accuracy, repeatability, reproducibility, and measurement error. Repeatability and reproducibility are primary contributors to measurement error. 4. Sources of variation include stability, linearity, calibration, operators, and environmental factors.

1. MSA
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• AEW
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• MEASUREMENTSYSTEMANALYSIS
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• PROJECT GUIDEs
• Mr. ALOK SHARMA

2. • 1. Determine which measurement system
will be studied ACCORDING TO MSA PLAN AND THE STUDY OF GAGE R &
r.
• 2. Establish test procedure IN DIFFERENT DEPARTMENTS FOR GAGE R
& r.
• 3. Establish the number of sample parts, the number of repeated readings,
and the number of operators that will be used.
• 4. Choose operators and sample parts.

3. Measurement as a Process
• As in any process, regardless of the
nature of data collected or generated,
measurement systems must
demonstrate
–Stability through time, or control
–Minimal variation as a proportion of
specifications, or capability
–Minimal variation as a proportion of
process variation

4. MEASUREMENT
PROCESS Equipment
Standard
Procedure
Operator
Measurement
Ambient
Environmental
Characteristics
Product or
Process to be
Measured

5. Definition of Terms
A Measurement System Analysis (MSA) is a
specially designed experiment that seeks to
identify the components of variation in the
measurement.
• Reference Value
– The theoretically or agreed upon correct value of
the characteristic being measured, traceable to
some standard
• Resolution
– The smallest increment, or unit of measure,
available from a measurement process
– Generally at least 1/10th of the specification
range

6. • Precision
– The degree of agreement (or variability)
between individual measurements or test
results from measuring the same
specimen(s)
• Accuracy (Bias)
– The difference between the average of the
measurement error distribution and the
reference value of the specimen measured

7. Accuracy
Precision

8. Measurement Error
Reference Value
Accuracy
(Bias)
Distribution of repeated
measures on a single
specimen or part
Precision
- Repeatability
- Reproducibility

9. Possible Sources of Process Variation
Stability Linearity
Long-term
Process Variation
Short-term
Process Variation
Variation
w/i sample
Actual Process Variation
Repeatability Calibration
Variation due
to gage
Variation due
to operators
Measurement Variation
Observed Process Variation
SystemtMeasuremen
2
ocesslActua
2
ocessObserved
2
  PrPr
ityproducibil
2
ypeatabilit
2
SystemtMeasuremen
2
ReRe  
We will look at “repeatability” and “reproducibility” as primary contributors to
measurement error

10. Measurement System Terminology
Discrimination - Smallest detectable increment between two measured values.
Accuracy related terms
True value - Theoretically correct value.
Bias - Difference between the average value of all measurements of a sample and the
true value for that sample.
Precision related terms
Repeatability - Variability inherent in the measurement system under constant
conditions
Reproducibility - Variability among measurements made under different
conditions (e.g. different operators, measuring devices, etc.)
Stability - distribution of measurements that remains constant and predictable over time
for both the mean and standard deviation.
Linearity - A measure of any change in accuracy or precision over the range of
instrument capability.

11. MSA for Continuous Processes
11 .PPT
True
Value or
Standard
Bias
Observed
Average
Possible Causes of Bias
 Sensor not properly calibrated
 Improper use of sensor
 Unclear procedures
 Human limitations
Bias

12. MSA for Continuous Processes
12 .PPT
Repeatability
Possible Causes of Poor
Repeatability
Equipment
 Gage instrument needs
maintenance
 The gage needs to be more rigid
People
 Environmental conditions
(lighting, noise)
 Physical conditions (eyesight)
Repeatability

13. MSA for Continuous Processes
13 .PPT
Reproducibility
Mean of
the measurements
of Operator B
Mean of
the measurements
of Operator A
Possible Causes of Poor
Reproducibility
 Measurement procedure is not
clear
 Operator is not properly trained in
using and reading gage
 Operational Definitions not
established
Reproducibility

14. Precision to Tolerance Ratio
Addresses what percent of the tolerance is taken up by measurement error
Includes both repeatability and reproducibility
Operator x Unit x Trial experiment
Best case: 10% Acceptable: 30%
P T
Tolerance
MS
/
. *

515 
Measurement Capability Index - P/T
Usually expressed as
percent
Note: 5.15 standard deviations accounts for 99% of Measurement System (MS) variation.
The use of 5.15 is an industry standard.

15. AddresseswhatpercentoftheObservedProcessVariationistakenupby
measurementerror
%R&Risthebestestimateoftheeffectofmeasurementsystemsonthevalidityof
processimprovementstudies(DOE)
Includesbothrepeatabilityandreproducibility
Asatarget,lookfor%R&R<30%
100&%
Pr
xRR
VariationocessObserved
MS


 Usually expressed as
percent
Measurement Capability Index - % GR&R

17. Measurement Systems Capability
22
RpdRptE  
LSL USL
5.15E
(USL - LSL)
Measurement
Error Distribution
100
LSLUSL
5.15R&R% E 

 

18. THANK YOU