2. Introduction for Metrology and Measurement
• Metrology word is derived from two Greek words such as
“metro” and “logy”.
• Metro means ???? and logy means ????
• Metrology: is the scientific study of measurement.
• Classification of Metrology,
Industrial metrology
Medical metrology
3. Objectives of Metrology:
• To provide the required
minimum cost.
accuracy of measurement at
• To evaluate the newly developed products completely.
• To determine measuring instruments capabilities and ensure
that they are quite sufficient for their respective
measurements.
• To standardize the measuring methods.
4. Need and Importance of Metrology:
• It is essential for solving almost all technical problems in the
field of engineering.
• Quality control in production
• Reduce rejection rate
• Minimise the cost of production
• Develop the inspection procedure
• Calibrate the measuring instruments time to time.
5. Introduction to Measurements:
• Measurement is defined as the process of numerical
evaluation of a dimension or the process of comparison with
standard measuring instruments
• Important requirements of measurements,
Standard
Instruments
Process
• Process of measurement,
Measurand
Reference
Comparator
6. Need of Measurement:
• Establish standard
• Interchangeability
• Validate the design
• Physical parameter into meaningful number
• True dimension
• Evaluate the Performance
• Customer Satisfaction
7. Why measure things?
• Check quality?
• Check tolerances?
• Allow statistical process control (SPC)?
(Quality control)
14. The instrument which gives output that varies continuously as
quantity to be measured is known as analog instrument. The
instrument which gives output that varies in discrete steps and only
has finite number of values is known as digital instrument.
17. Advantages
•Mechanical comparators are not
expensive as compared to other types of
amplifying devices.
•These types of comparators don't need
any external electricity supply.
•It has extremely high magnification.
•Its optical lever is lightweight.
•These are easily understood due to a
linear scale.
19. Advantages of Electrical
Comparator:
•Vibrations are reduced due to
least weight of mechanical.
•It consists of less moving parts.
•By AC supply the friction errors
are reduced.
•For measuring units the
indicating instrument can be held
at remote locations.
20.
21. Advantages of pneumatic
comparator
It is very accurate and precise.
High magnification up to 30000:
1 is possible in a pneumatic
comparator. Since indicating
device and measuring head are
placed at different places, there
is no interference. They are self-
cleaning because a jet of air
helps in cleaning the workpiece
22. LIMITS
Limits establish the absolute extremes that a dimension or parameter must not exceed
No component can be manufactured precisely to a given dimension; it can only be made to lie between two limits,
upper (maximum) and lower (minimum).
TOLERANCE
Tolerance is a trade-off between the economical production and the accuracy required for proper functioning of the
product.
In fact, the tolerance limits specified for the components to be manufactured should be just sufficient to perform
their intended functions.
CLASSIFICATION OF TOLERANCE
Tolerance can be classified under the following categories:
1. Unilateral tolerance
2. Bilateral tolerance
3. Compound tolerance
4. Geometric tolerance
23. UNILATERAL TOLERANCE
When the tolerance distribution is only on one side of the basic size, it is known as unilateral tolerance. In
other words, tolerance limits lie wholly on one side of the basic size, either above or below it.
Unilateral tolerance is employed in the drilling process wherein dimensions of the hole are most likely to
deviate in one direction only, that is, the hole is always oversized rather than undersized.
24. Bilateral Tolerance
When the tolerance distribution lies on either side of the basic size, it is known as bilateral tolerance. In other
words, the dimension of the part is allowed to vary on both sides of the basic size but may not be necessarily
equally disposed about it.
The operator can take full advantage of the limit system, especially in positioning a hole. This system is generally
preferred in mass production where the machine is set for the basic size.
compound tolerance
When tolerance is determined by established tolerances on more than one dimension, it is known as compound
tolerance For example, tolerance for the dimension R is determined by the combined effects of tolerance on
40mm dimension, on 60º, and on 20mm dimension. The tolerance obtained for dimension R is known as
compound tolerance. In practice, compound tolerance should be avoided as far as possible. .
25. Geometric tolerance
It is defined as the total amount that the dimension of a manufactured part can vary. Geometric tolerance underlines
the importance of the shape of a feature as against its size. Geometric dimensioning and tolerancing is a method of
defining parts based on how they function, using standard symbols. This method is frequently used in industries.
Form tolerances
Form tolerances are a group of geometric tolerances applied to individual features. They limit the amount of error in the
shape of a feature and are independent tolerances. Form tolerances as such do not require locating dimensions. These
include straightness, circularity, flatness, and cylindricity.
Orientation tolerances
Orientation tolereances are a type of geometric tolerances used to limit the direction or orientation of a feature in
relation to other features. These are related tolerances. Perpendicularity, parallelism, and angularity fall into this
category.
Positional tolerances
Positional tolerances are a group of geometric tolerances that controls the extent of deviation of the location of a
feature from its true position. This is a three-dimensional geometric tolerance comprising position, symmetry, and
concentricity.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60. Accuracy and Precision:
Accuracy:
The ability of an instrument to respond to true value of a
measured variable under the reference condition.
It refers how closely the measured value agrees with the
true value.
The accuracy of measurement depends upon the following
factors,
1. Ability of the operator
2. Variation of temperature
3.method adopted for measurement
4.Deformation of the instrument
61. Accuracy and Precision: (contd.,)
Precision:
The degree of exactness for which an instrument is designed
to perform.
It refers to the repeatability or consistency of measurement
when the measurement are carried out under identical
condition at a short interval of time.
It can also be defined as the ability of the instrument to
reproduce a group of measurements of the same measured
quantity under the same condition.
63. Activity: 1
Who is more accurate when measuring a book that
has a true length of 17.0 cm?
A :
17.0 cm, 16.0 cm, 18.0 cm, 15.0 cm
B ::
15.5 cm, 15.0 cm, 15.2 cm, 15.3 cm
64. Who is more precise when measuring the same
17.0 cm book?
A:
17.0 cm, 16.0 cm, 18.0 cm, 15.0 cm
B ::
15.5 cm, 15.0 cm, 15.2 cm, 15.3 cm
Activity: 2
