633994170-Unit-1-Metrology-Basics-elements-in-measurements-Line-and-end-Standards-ppt.ppt

Metrology

1. Metrology
The word metrology is derived from two Greek words
Metro=measurement
logy=science
Thus metrology is the science of measurement
Dimensional metrology is that branch of Metrology which
deals with measurement of “dimensions“ of a part or
workpiece (lengths, angles, etc.)

2. The length is most important parameter
in metrology.
Measurement play a vital role in every
filed of investigation.
Metrology is the science of
measurement.
Result which is given with the sufficient
correctness and accuracy for the
particular need or not.

3. •A metrologist is concerned with both measurement and
Inspection.
•A metrologist will design the equipment and devices for
measurement and inspection.
•The inspectors job is to use the equipment designed by
the metrologist as per the standard procedure
•Metrology is concerned with establishment,
reproduction, conservation and transfer of units of
measurements and standards.
•Also associated with the evaluation of its uncertainty.

4. Linear measurements
Non-precision Measuring Instruments
•Steel Rule
•Calipers
•Divider
•Telescopic Gauge
•Depth Gauge
Precision Measuring Instruments
•Vernier Calipers
•Micrometers
•Height Gauge &
•Slip Gauges

5. Standards of length, end and line standards,
Types of standards
Line standard
• Standard yard
• Standard metre
End standard
• End bar
• Slip gauges
Wavelength standard

6. When a length is measured between centres of two engraved lines, it is
called line standard
Imperial Standard yard

7. •An imperial standard yard, shown in fig, is a bronze
(82% Cu, 13% tin, 5% Zinc) bar of 1 inch square section
and 38 inches long.
•A round recess, 1 inch away from the two ends is cut at
both ends up to the central or ‘neutral plane’ of the bar.
•Further, a small round recess of (1/10) inch in diameter is
made below the center. Two gold plugs of (1/10) inch
diameter having engravings are inserted into these holes
so that the lines (engravings) are in neutral plane.

8. Yard is defined as the distance between the two central
transverse lines of the gold plug at 62
0
F.
The purpose of keeping the gold plugs in line with the
neutral axis is to ensure that the neutral axis remains
unaffected due to bending, and to protect the gold plugs
from accidental damage.

9. International Prototype meter(1875)
It is defined as the straight line distance, at 0
o
C, between the
engraved lines of pure platinum-iridium alloy (90% platinum &
10% iridium) of 1020 mm total length and having a ‘tresca’ cross
section as shown in fig. The graduations are on the upper surface
of the web which coincides with the neutral axis of the section.

10. Characteristics of Line Standards
1.Scales can be accurately engraved but it is difficult to
take the full advantage of this accuracy.
Ex: A steel rule can be read to about ± 0.2 mm of true dimension.
2. A scale is quick and easy to use over a wide range of
measurements.
3. The wear on the leading ends results in ‘under sizing’
5. Scales are subjected to parallax effect, which is a source of
both positive & negative reading errors.
6. Scales are not convenient for close tolerance length
measurements except in conjunction with microscopes.

11. End Standards
When the length being measured is expressed as the distance
between two parallel faces, then it is called ‘End standard’.
End standards can be made to a very high degree of
accuracy.
Ex: Slip gauges, Gap gauges, Ends of micrometer anvils, etc.

12. Characteristics of End Standards:
1. End standards are highly accurate and are well suited for
measurements of close tolerances as small as 0.0005 mm.
2. They are time consuming in use and prove only one dimension
at a time.
3. End standards are subjected to wear on their measuring faces.
4. End standards have a ‘built in’ datum, because their measuring
faces are flat & parallel and can be positively located on a datum
surface.
5. They are not subjected to the parallax effect since their use
depends on “feel”.
6. Groups of blocks may be “wrung” together to build up any
length. But faulty wringing leads to damage.
7. The accuracy of both end & line standards are affected by
temperature change

13. Wave length standard
Because of the problems of variation in length
of material length standards, the possibility of
using light as a basic unit to define primary
standard has been considered.
 The wavelength of a selected radiation of
light and is used as the basic unit of length.
 Since the wavelength is not a physical one, it
need not be preserved & can be easily
reproducible without considerable error.

14. 1907- Angstrom(A)- wavelength of
red cadmium in dry air at 15
0
C.

15. 1 metre = 1650763.73 wave length of the red
orange radiation of krypton isotope 86 gas.
I yard = 0.9144 metre
= 1509458.3 wave length.
Wavelength 
is the distance between identical
points (adjacent crests) in the adjacent cycles of
a waveform signal propagated in space or along
a wire. In wireless systems, this length is usually
specified in meters (m), centimeters (cm) or
millimeters (mm).

17. slip gauges
Slip gauges are rectangular blocks of steel
having cross section of 30 mm face length &
10 mm face width as shown in fig.

19. •Slip gauges are blocks of steel that have been hardened
and stabilized by heat treatment.
•They are ground and lapped to size to very high
standards of accuracy and surface finish. They are end
Standards.
•Two adjacent surfaces are highly finished (Ground &
lapped)
•They come in Standard series-to built any dimension up
to 0.001mm/0.0005mm
•Tool steel, chrome plated steel, stainless steel, tungsten
carbide and chrome carbide are used for making gauge.

20. Wringing of Slip Gauges
1.It is the joining process of 2 slip gauges.
2.By this method you get any dimension to be
measured/built-up.
3.Method of wringing shown in Fig.