1.
Dimensional
Metrology

2.
Table of Contents
• Introduction
• Basic Terminologies
• Inspection Process
• Measurement Process Validation

3.
Introduction
• In 1999 NASA sent a mission to MARS
• Climate Orbiter
• It completed its 99% of journey
• Fired steering rocket to control its final approach
• However, the thrust value had a
Martian Blunder

4.
Introduction
• 1776 war of independence
• Had to deliver 10000 muskets in two years
• With no factory
• Did it in 10 years
• Then took the order of 15000 muskets and delivered them
in two years
Eli Whitney Order of Muskets

5.
Introduction
The need

6.
“When you measure what you are speaking about and
express it in numbers, you know something about it, but
when you cannot express it in numbers your knowledge is of
a meagre and unsatisfactory kind...”
Lord Kelvin (1824~1907)
Introduction
The need

7.
As a result of its importance, measurement has a science of its
own, called metrology, from the Greek words metron (‘measure’)
and logos (‘study’)
Introduction
Metrology

8.
Introduction
Measurement Domain

9.
BASIC TERMINOLOGIES
Error & Uncertainty
Error is the difference between the measured value and the
true value of the thing being measured
Uncertainty is the parameter, associated with the result of
a measurement, that characterizes the dispersion of the
values that could reasonably be attributed to the
measurand.
Whereas,

10.
BASIC TERMINOLOGIES
Accuracy & Precision

11.
BASIC TERMINOLOGIES
Resolution
The resolution of an instrument is a quantitative expression of the
ability of an indicating device to distinguish meaningfully between
closely adjacent values of the quantity indicated.

12.
BASIC TERMINOLOGIES
Trueness
Trueness is a similar concept to accuracy, but while accuracy refers
to the closeness between an individual measurement and the true
value, trueness refers to the closeness of agreement between the
average value obtained from a set of test results and the true value.

13.
BASIC TERMINOLOGIES
Repeatability
Repeatability is the closeness of agreement between repeated
measurements of the same thing, carried out in
the same place, by the same person, on the same equipment, in the
same way, at similar times.

14.
BASIC TERMINOLOGIES
Reproducibility
Reproducibility is the closeness of agreement between
measurements of the same thing carried out in different
circumstances, e.g. by a different person, or a different method, or
at a different time

15.
BASIC TERMINOLOGIES
Confidence Level
Make a number of measurements of something – like the
concentration of carbon monoxide gas in your vicinity –
True value lies between, say, 9 parts per million (ppm) and 11 ppm
– probably (or 10±1 ppm).
You could not be sure that this was the case, but you could express
your confidence that it is. So you might decide that you are 90%
confident that the answer lies between those values.

16.
BASIC TERMINOLOGIES
Tolerance
A tolerance is the maximum acceptable difference between the
actual value of some quantity, and the value specified for it.

17.
BASIC TERMINOLOGIES
Validation
Validation is confirmation that some aspect of a measurement
process is fit for purpose.
Verification
Verification is making measurements to ensure conformance to
specifications.

18.
BASIC TERMINOLOGIES
Calibration
Comparison of an instrument against a more accurate one (or
against a reference signal or condition), to find and correct any
errors in its measurement results.

19.
BASIC TERMINOLOGIES
Accreditation
Accreditation is the independent, third-party evaluation of a
conformity assessment body (such as certification body, inspection
body or laboratory) against recognised standards, conveying
formal demonstration of its impartiality and competence to carry
out specific conformity assessment tasks (such as certification,
inspection and testing).

20.
BASIC TERMINOLOGIES
Certification
Certification is the provision by an independent body of written
assurance (a certificate) that the product, service or system in
question meets specific requirements.

21.
INSPECTION USES
• Document Changes in process performance
• To distinguish between good lots and bad lots
• Distinguish between good product and bad product
• Determine status of process control
• Evaluation of process capability / adjustment of process
• To rate accuracy of inspectors / inspection equipment

22.
INSPECTION PROCESS
What to
measure?
Instrument
Selection
Knowledge
of MSA
Rounding
Rules
Inspection
Stage
Errors in
inspection
Sampling
Regular
Review
Traceability of
Inspections

23.
INSPECTION PROCESS
What to measure?
• Measurement is made for a reason
• It needs to be defined and understood
• Only then can a right measurement be made

24.
INSPECTION PROCESS
What to measure?

25.
INSPECTION PROCESS
Instrument selection

26.
INSPECTION PROCESS
Knowledge of MSA
• Measurement System Validation
• Repeatability & Reproducibility (ISO5725-1,2: 2019)
• Uncertainty of the measurement (ISO 21748: 2017)
• Proficiency Testing
• Comparison with other results

27.
INSPECTION PROCESS
Knowledge of MSA (ISO14253)

28.
INSPECTION PROCESS
Knowledge of MSA (ISO14253)

29.
INSPECTION PROCESS
Rounding Rules (ASTM E29)

30.
INSPECTION PROCESS
Rounding Rules (ASTM E29)

31.
INSPECTION PROCESS
Sampling
Sr. # Characteristic
MIL-STD-
105 E
MIL-STD-1916 ISO 2859 ISO 3951
1. Basics Attributes Attribute / Variables Attributes Variables
2.
Acceptance
Criteria
# of Non
Conformin
g products
/ AQL
# of Non Conforming
Products or s-
characteristic /
verification levels
No. of Non
Conforming
Products /
AQL
S-
characteristi
c / AQL
3. Distribution Any Any Any Normal only
4. Sample Sizes
Standard
Tables
Follows 105 E Follows 105 E
Different
(usually
smaller)
5. Switching Standard Follows 105 E
Slightly
Different
Different

32.
INSPECTION PROCESS
Inspection stages
• Incoming
• Final
• Pre Process
• Post Process
• Verification Inspection

33.
INSPECTION PROCESS
Measurement Errors
Temperature Compensation

34.
INSPECTION PROCESS
Measurement Errors
Cosine Error

35.
INSPECTION PROCESS
Measurement Errors
Sine Error

36.
INSPECTION PROCESS
Measurement Errors
Abbe Error

37.
INSPECTION PROCESS
Measurement Errors
Elastic Compression

38.
INSPECTION PROCESS
Measurement Errors
Parallax Error

39.
INSPECTION PROCESS
Regular Review
• Check Instruments
• Check Measurement Procedures
• Inspection Audit

40.
INSPECTION PROCESS
Inspection Traceability
• Keeping Controlled Records

41.
Six Guiding Principles
Regular Review
• Check Instruments
• Check Measurement Procedures
Demonstratable Consistency
• Gauge R&R Studies
• Proficiency Testing
• Regularly Analyse factors that could effect measurements

42.
Six Guiding Principles
The Right Procedures
• Written Procedures of measurement
• Include risk assessment in the procedure

43.
Building Blocks of Measurement System Analysis
1. Measurement System Validation
a) Accuracy (ISO 5725-1: 2019)
b) Repeatability & Reproducibility (ISO 5725-2: 2019)
2. Uncertainty Assessment (ISO 21748:2017)
3. Comparison of results with other methods
4. Proficiency Testing