This document discusses different methods and elements of metrology. It describes direct and indirect methods of measurement such as using scales, vernier callipers, and sine bars. It also discusses standards used for measurement, including line standards like standard yards and metres, end standards like end bars and slip gauges, and wavelength standards using laser sources. Environmental factors that influence measurement are also mentioned, along with the importance of measuring in a standard environment.

1. Unit-I Basics of
Metrology
ME6504 Metrology and Measurements

2. Methods of Measurement
• Direct method
Scales, vernier callipers, micrometers, bevel protractors,
• Indirect method
• angle measurement using sine bar.
• Fundamental or absolute method
• The quantity under consideration is directly measured and
is then linked with the definition of that quantity.
• Comparative method
• The quantity is compared with the master gauge and only
the deviations from the master gauge are recorded after
comparison.
• Eg. Dial indicators

3. Elements of Metrology
• Standard
• The most basic element of measurement is standard without
which no measurement is possible.
• Standard is a physical representation of unit of measurement.
• Different standards have been developed for various units
including fundamental units as well as derived units.
• The measurement should be performed under standard
environment
• Temperature, dirt, humidity and vibration are the four
environmental factors that influence measurement.
• Vernier scale division of vernier caliper always changes when
the measurement process is carried for ‘n’ number of times for
the same dimension. The environment is indirectly related to
temperature, humidity, conditioning etc.,

4. Standards
Types of standards
• Line standard
• Standard yard
• Standard metre
• End standard
• End bar
• Slip gauges
• Wavelength standard

5. Line standard
 The measurement of distance may be made between
two parallel lines or two surfaces.
 When a length is measured between as the distance
between centres of two engraved lines, it is called line
standard
Standard yard

6. • Yard is made of a one inch square cross section
bronze bar and is 38 inches long
• The bar has a round recess (gold plug) of 0.5 inches
diameter and 0.5 inches deep. The gold plug is 1
inch away from both the ends
• The highly polished top surfaces of these plugs
contain three transversely and two longitudinally
engraved lines lying on the neutral axis
• The yard is the distance between two central
transverse lines on the plugs when the temperature
of the bar is constant at 62OF
• To protect the gold plug from accidental damage, it
is kept at the neutral axis as the neutral axis
remains unaffected even if the bar bends

7. Standard metre
• The metre is the distance between the centre portions
of two lines engraved on the polished surface of bar
made up of platinum (90%) and iridium (10%) having a
unique cross section
• The web section gives maximum rigidity and economy
in the use of costly material
• The upper surface of the
web is inoxidizable and
needs a good finish for
quality measurement
• the bar is kept at 0OC and
under normal
atmospheric pressure.

8. Prepared by, S.David Blessley AP/MECH,
Kamaraj College of Engineering & Technology
End standard
The need of an end standard arises as the use of line standards and
their copies was difficult at various places in workshops
These are usually in the form of end bars and slip gauges
• End bar
• End bars made of steel having cylindrical section of 22.2 mm diameter
with the faces lapped and hardened at the ends are available in
various lengths.
• Flat and parallel faced end bars are firmly used as the most practical
end standard used for measurement.
• These are used for measurement of larger sizes
• Slip gauges
• Slip gauges are rectangular blocks of hardened and stabilized high
grade cast steel
• The length of a slip gauge is strictly the dimension which it measures
• The blocks after being manufactured are hardened to resist wear and
are allowed to stabilize to release internal stresses
• A combination of slip gauges enables the measurements to be made in
the range of 0.0025mm to 100mm but in combinations with end bars,
the measurement range upto 1200mm is possible.

9. Prepared by, S.David Blessley AP/MECH,
Kamaraj College of Engineering & Technology
Wavelength standards
• Line and end standards are physical standards and
are made up of materials that can change their size
with temperature and other environmental
conditions
• In search for such suitable unit of length, wave
length source is established
• Laser is used as primary level wavelength standard
• According to this standard, a metre is defined as
equal to 1650763.73 wavelength of the red orange
radiation of krypton isotope gas
1 metre
1 yard
=1650763.73 wavelengths
=0.9144m
=0.9144x1650763.73
=1509458.3 wavelength.