2. ๏ผ Basic of Metrology,
๏ผ Need for Inspection,
๏ผ Accuracy and Precision,
๏ผ Objective of Metrology,
๏ผ Standards of Measurement.
Unit No:- 06 Metrology
2 hours 4% Weightage (Approx. 3 Marks)
3. ๏ผ Derived from two Greek words โMetroโ = Measurements &
โLogyโ = Science. Metrology is the science of measurement
๏ผ Metrology is the science concerned with the establishment,
reproduction, conversion & transfer of units.
๏ผ Dimensional metrology is that branch of Metrology which
deals with measurement of โdimensionsโ of a part or work
piece (lengths, angles, etc.)
๏ผ Dimensional measurements at the required level of accuracy
are the essential link between the designersโ intent and a
delivered product.
Metrology
4. Need for Inspection
๏ผ To Determine the true dimensions of a part.
๏ผ To convert physical parameters into meaningful numbers.
๏ผ To test if the elements that constitute the system function as per the
design.
๏ผ For evaluating the performance of a system.
๏ผ To ensure interchangeability with a view to promoting mass
production.
๏ผ To establish the validity of design and for finding new data and new
designs
๏ผ To ensure that the part conforms to established standard
๏ผ To meet interchangeability of manufacture
๏ผ To maintain customer relations
๏ผ To find shortcomings in manufacture
๏ผ Helps to purchase good quality of raw materials
๏ผ Helps co-ordination of different departments
๏ผ To take decision on defective parts
5. ๏ผ Accuracy is how close a measured value is to the actual (true) value.
๏ผ It is closeness with the true value of the quantity being measured.
๏ผ Precision is how close the measured values are to each other.
๏ผ It is a measure of the reproducibility of the measurement.
Accuracy v/s Precision
7. Accuracy v/s Precision
# Accuracy Precision
1
It is closeness with the true value of the
quantity being measured.
It is a measure of the reproducibility of
the measurement.
2
The accuracy of measurement means
conformity to truth.
The term precise means clearly or
sharply defined.
3 Accuracy can be improved. Precision cannot be improved.
4
Accuracy depends upon simple
techniques of analysis.
Precision depends upon many factors
and required many sophisticated
techniques of analysis.
5
Accuracy is necessary but not sufficient
condition for precision.
Precision is necessary but not a
sufficient condition for accuracy.
8. Elements of a Measuring System
S W I P E
1. Standards :- Physical quantity or property relative to which
quantitative comparison is made.
2. Workpiece:- Features of the workpiece to be measured.
3. Instrument:- Instruments needed for measurement.
4. Person:- The skill of the human operator.
5. Environment:- The conditions in which measurement is
done.
9. Objective of Metrology
๏ผ Complete evaluation of newly developed products.
๏ผ Determination of Process Capabilities.
๏ผ Determination of the measuring instrument capabilities and ensure that
they are quite sufficient for their respective measurements.
๏ผ Minimising the cost of inspection by effective and efficient use of available
facilities.
๏ผ Reducing the cost of rejects and rework through application of statistical
quality control techniques.
๏ผ To standardise the measuring methods.
๏ผ To maintain the accuracies of measurement.
๏ผ To prepare design for all gauges and special inspection fixtures.
10. Measurement Standards
๏ผ Standard is defined as โsomething that is set-up and
established by authority as a rule for the measure of
quantity, weight, extent, value or quality.โ
Role of Standards
๏ผ To support the system which makes measurements possible
throughout the world.
๏ผ Facilitates โinterchangeabilityโ of parts.
11. 1. Line Standard: When length is
measured as the distance
between centers of two
engraved lines
2. End Standard: When length is
measured as the distance
between to flat parallel faces
3. Wavelength Standard: When
length is measured as the
distance between wave length of
light.
Types of Measurement Standards
12. Metre and Yard
๏ Meter: The meter is defined as 1650763.73 wavelength of the
orange radiation in vacuum of krypton 86 isotope.
๏ Yard: The yard is defined as 0.9144 meter. This is equivalent to
1509458.35 wavelengths of the same radiation.
14. # Characteristics Line Standards End Standards
1 Principle Length is measured between
two Lines.
Length is expressed between
Two Parallel Flat Surfaces.
2 Measurement Simple and Quick. Time for measurement is
more.
3 Error Possibility of Parallax Error. Error due to improper
Wringing or Change in
Temperature.
4 Accuracy Upto ยฑ 0.2 mm unless provided
with magnifying glass.
ยฑ 0.001 mm.
5 Manufacture
and Cost
Comparatively simple to
manufacture and Cheaper.
Complex method or
manufacturing and Higher
Cost.
6 Effect of Use End of the scale is subjected to
wear.
Due to continuous use
measuring faces get worn out
special end pieces may be
needed.
Line Standards v/s End Standards
15. Metal Standards v/s Wavelength Standards
# Characteristics Metal Standards Wavelength Standards
1 Effect of
Environment
Influenced by variation of
environment conditions like
temperature, pressure,
humidity etc.
Not affected by environmental
conditions.
2 Replacement
after Damage
If damaged exact copies
cannot be made.
Can be easily reproduced.
3 Wear and Tear Affected by wear and tear. Not subjected to wear and
tear.
4 Availability of
Replicas
Exact replicas are not available
elsewhere.
Identical copies can be kept in
all standard laboratories.
5 Security
Requirement
Required to be preserved or
stored under strict surveillance
to prevent damage or
destruction.
No such security requirements.
16. Assignment No. 6
1) List the various elements of a measuring system.
2) Differentiate between Accuracy and Precision with neat
sketch.
3) Describe with sketch international prototype meter (material
length standards) stating material composition and
limitations.
4) Differentiate between line standard and end standards.
5) Differentiate between Metal standard and Wavelength
standards.
Submit Assignment No. 6
Before 27/01/2017 4:30 PM
