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1. METROLOGY (MEE 322)
COURSE LECTURER:
Prof. JS Ajiboye

2. COURSE CONTENT
S/N TOPIC/FOCUS
1. General Introductory Class
2. Theory and practice of high precision
3. Mechanical measurements under strict control conditions
4. Super micro-metry,
5. Comparator Profilometry
TEST 1
6. Collimators application in machine installations, etc.
7. Tolerances and quality.
8. Fits: Clearance, transition and interference fits
TEST 2

3. Recommended Books
1. Metrology and Measurement by Anand K Bewoor and Vinay A
Kulkarni, McGraw Hill Education(India) Ltd 2013 seventh reprint,
2. Engineering Metrology and Measurements by N V Raghavendra and
L Krishnamurthy, Oxford University Press 2013
3. Precision Engineering by V C Venkatesh and Sudin Izman, McGraw
Hill Education(India) Ltd 2007,

4. INTRODUCTION TO METROLOGY
i. Measurement in our everyday life
ii. Definitions of Metrology
iii. Types of Metrology
iv. Need for Inspection
v. Principal Aspects of Measurement
vi. Methods of Measurements
vii. Factors affecting Accuracy of Measuring Instruments
viii. Errors in Measurement
ix. Metric Units in Industry

5. Measurement in Our Everyday Life
•Greek word of Metrology –
Metro(Measurement) + Logy(Science)
•Metrology is the Science of measurement
•Measurement is defined as the set of
operations having the objective of determining
the value of a quantity

6. Definitions of Metrology
a. Metrology is the science of measurement
b. Metrology is the field of knowledge concerned with measurements and
includes both theoretical and practical problems with reference to
measurement, whatever their level of accuracy and in whatever fields
of science and technology they occur
c. Metrology is the process of making extremely precise measurements of
the relative positions and orientations of different optical and
mechanical components
d. Metrology is the science concerned with the establishment,
reproduction, conversion, and transfer of units of measurement and
their standards

7. Types of Metrology
a) Scientific Metrology(standards)
b) Industrial Metrology
c) Legal Metrology
d) Fundamental Metrology

8. Need for Inspection
1. To ensure that the part, material, or component conforms
to the established standard.
2. To meet the interchangeability of manufacture.
3. To maintain customer relations by ensuring that no faulty
product reaches the customers.
4. It also helps to purchase good quality raw materials, tools,
and equipment which governs the quality of the finished
products.

9. 5. Provide the means of finding out shortcomings in
manufacturing. The results of the inspection are not only
recorded but forwarded to the manufacturing department for
taking necessary steps, so as to produce acceptable parts and
reduce scrap.
6. It also helps to coordinate the functions of quality control,
production, purchasing, and other departments of the
organization.
7. To take a decision on the defective parts i.e., to judge the
possibility of making some of these parts acceptable after
minor repairs.
Need for Inspection

10. Objectives of Metrology
1. Thorough evaluation of newly developed products, to ensure that
the components designed are within the process and measuring
instrument capabilities available in the plant.
2. To determine the process capabilities and ensure that these are
better than the relevant component tolerance.
3. To determine the measuring instrument capabilities and ensure
that these are adequate for their respective measurements.
4. Maintenance of the accuracies of measurement. This is achieved
by periodical calibration of the metrological instruments used in the
plant.

11. Objectives of Metrology
5. To minimize the cost of inspection by effective and efficient use of
available facilities and to reduce the cost of rejects and rework
through the application of Statistical Quality Control
Techniques.
6. Standardization of measuring methods. This is achieved by laying
down inspection methods for any product right at the time when
production technology is prepared.
7. Arbitration and solution of problems arising on the shop floor
regarding methods of
measurement.

12. Measuring system element
A measuring system is made of five basic elements. These
are:
1. Standard
2. Workpiece
3. Instrument
4. Person
5. Environment.
The most basic element of measurement is a standard
without which no measurement is possible.

13. Methods of Measurement
The methods of
measurement can be
classified as:
1. Direct method
2. Indirect method
3. Absolute/Fundamental
method
4. Comparative method
5. Transposition method
6. Coincidence method
7. Deflection method
8. Complementary method
9. Contact method
10. Contactless method etc.

14. Methods of Measurement
•Direct Method
- In this method the value of a quantity is obtained directly by comparing the
unknown with the standard.
- It involves, no mathematical calculations to arrive
at the results, for example, measurement of length by a graduated scale.
- The method is not very accurate because it depends on human insensitiveness
in making judgement.

15. • Indirect Method:
- In this method several parameters (to which the quantity to be
measured is linked with) are measured directly and then the value is
determined by mathematical relationship.
- For example, measurement of density by measuring mass and
geometrical dimensions.
Methods of Measurement

16. Precision
The terms precision and accuracy are used in connection with the performance of the
instrument. Precision is the repeatability of the measuring process.
It indicates to what extent the identically performed measurements agree with
each other. If the instrument is not precise it will give different (widely varying) results for
the same dimension when measured again and again. The set of observations will scatter
about the mean. The scatter of these measurements is designated as 0, the standard
deviation. It is used as an index of precision. The less the scattering more precise is the
instrument. Thus, lower, the value of 0, the more precise is the instrument
Precision and Accuracy

17. Accuracy
 Accuracy is the degree to which the measured value of the quality
characteristic agrees with the true value. The difference between the
true value and the measured value is known as the error of
measurement.
It is practically difficult to measure exactly the true value and
therefore a set of observations is made whose mean value is taken as
the true value of the quality measured.
Precision and Accuracy

18. Distinction between Precision and Accuracy
Accuracy is very often confused with precision though much different. The
distinction between precision and accuracy will become clear in the following
example. Several measurements are made on a component by different types
of instruments (A, B, and C respectively) and the results are plotted.
In any set of measurements, the individual measurements are scattered about
the mean, and the precision signifies how well the various measurements
performed by the same instrument on the same quality characteristic agree
with each other.

19. The difference between the mean of a set of
readings on the same quality characteristic and the
true value is called error. The fewer the error more
accurate the instrument. Figure 1(a) shows that
instrument A is precise since the results of several
measurements are close to the average value.
However, there is a large difference (error) between
the true value and the average value hence it is not
accurate.
For Fig 1(b), readings taken by the instruments are
scattered much from the average value and hence it
is not precise but accurate as there is a small
difference between the average value and true
value. Fig. 1 (c) shows that the instrument is
accurate as well as precise.
Distinction between Precision and Accuracy

20. Factors Affecting Accuracy of Measurements
i. Standards of Calibration for Setting Accuracy
ii. Workpiece Control During Measurement
iii. Inherent Characteristics of Measuring Instrument
iv. Human Factor
v. Environmental Conditions

21. Errors in Measurement
It is never possible to measure the true value of a dimension, there is
always some error.
The error in measurement is the difference between the measured
value and the true value of the measured dimension.
Error in measurement = Measured value - True value. The error in
measurement may be expressed or evaluated either as an absolute
error or as a relative error.

22. The accuracy of measurement, and hence the error depends upon so
many factors, such as:
- Calibration standard
- Work piece
- Instrument
- Person
- Environment etc. as already described.
Errors in Measurement

23. No matter, how modern is the measuring instrument, how skillful is the
operator, and how accurate the measurement process, there would
always be some errors.
It is therefore attempted to minimize the error.
To minimize the error, usually, a number of observations are made and
their average is taken as the value of that measurement.
Errors in Measurement

24. If these observations are made under identical conditions i.e., same observer,
same instrument, and similar working conditions except for time, then, it is
called a Single Sample Test’.
If however, repeated measurements of a given property using alternate test
conditions, such as different observers and/or different instruments are
made, the procedure is called a `Multi-Sample Test’.
The multi-sample test avoids many controllable errors e.g., personal
error, instrument zero error, etc. The multi-sample test is costlier than the
single-sample test and hence the latter is in wide use.
In practice, good numbers of observations are made under single-sample
tests, and statistical techniques are applied to get results that could be
approximate to those obtainable from the multi-sample test.
Errors in Measurement

25. During measurement several types of error may arise, these are
1. Static errors which includes
- Reading errors
- Characteristic errors
- Environmental errors.
2. Instrument loading errors.
3. Dynamic errors.
Errors in Measurement

26. Static errors
These errors result from the physical nature of the various components
of the measuring system. The three components are listed above.
i. Reading errors
ii. Reading errors apply exclusively to the read-out device. These do
not have any direct relationship with other types of errors within
the measuring system. Reading errors include: Parallax error,
Interpolation error.
Errors in Measurement

27. ii. Characteristic Errors
It is defined as the deviation of the output of the measuring
system from the theoretically predicted performance or from
nominal performance specifications. Linearity errors,
repeatability, hysteresis, and resolution errors are part of
characteristic errors if the theoretical output is a straight line.
Calibration error is also included in characteristic error.
Errors in Measurement

28. iii. Loading Errors
Loading errors result from the change in measurand itself when
it is being measured, (i.e. after the measuring system or instrument is
connected for measurement). Instrument loading error is the
difference between the value of the measurand before and after the
measuring system is connected/contacted for measurement.
For example, soft or delicate components are subjected to deformation
during measurement due to the contact pressure of the instrument
and causing a loading error.
Errors in Measurement

29. Iv Environmental Errors
These errors result from the effect of surrounding such as temperature,
pressure, humidity, etc. on the measuring system.
External influences like magnetic or electric fields, nuclear radiations,
vibrations or shocks, etc. also lead to environmental errors.
V Dynamic Errors
A dynamic error is an error caused by time variations in the measurand. It
results from the inability of the system to respond faithfully to a time-
varying measurement. It is caused by Inertia, damping, friction, or other
physical constraints in the sensing or readout, or display System.
Errors in Measurement

30. For statistical study and the study of the accumulation of errors,
these errors can be broadly
classified into two categories
1. Systematic or controllable errors, and
2. Random errors.
Errors in Measurement

31. Comparison between Systematic Errors and
Random Errors
Systematic or controllable error Random error
These errors are repetitive in nature and are of constant
and similar form
These are non-consistent. The sources giving rise to such
errors are random.
These errors result from improper conditions or
procedures that are consistent in action.
Such errors are inherent in the measuring system or
measuring instruments.
Except for personal errors, all other systematic errors can
be controlled in magnitude and sense.
Specific causes, magnitudes and sense of these errors
cannot be determined from the knowledge of measuring
system or condition.
If properly analyzed these can be determined and
reduced or eliminated.
These errors cannot be eliminated, but the results
obtained can be corrected.
These include calibration errors, variation in contact
pressure, variation in atmospheric conditions, parallax
errors, misalignment errors etc.
These include errors caused due to variation in position
of setting standard and work-piece, errors due to
displacement of lever joints of instruments, errors
resulting from backlash, friction etc.

32. General Care of Metrological Equipment
The equipment (apparatus) used for precision measurements is
designed to fine limits of accuracy and is easily liable to be
damaged by even-slight mishandling and such damage may not
be noticeable. A great deal of careful handling is, therefore,
required.
As far as possible, the highly finished surfaces should not be
touched by hand because the natural acids on the skin are likely
to corrode the finished surface and also the temperature of the
body may upset the dimensions of the precision instruments.

33. In order to overcome this many standard metrology laboratories
recommend washing of hands thoroughly and coating them with a
thin film; of pure petroleum jelly before handling the instruments.
Further very precise equipment like slip gauges is allowed to be
handled only by using a piece of chamois leather or tongs made from
a strip of "Perspex".
This mixture spreads much more easily and is applied with cloth or
with fingers. Brushing is not recommended as it is liable to ti air
which, with the moisture, it contains, may cause rusting.
General Care of Metrological Equipment

34. General Care of Metrological Equipment
When the equipment is not in use, it should be protected from
atmospheric corrosion. For this purpose the highly finished surfaces
are first wiped with a solvent to remove any finger mark and then
coated with mixture of heated petroleum jelly and petrol.
As the standard temperature for measurement is 20°C, for very
precise measurement the instruments and work pieces should be
allowed to attain this temperature before use and the handling
should be as little as possible.

35. Metric Units in Industry
• SI Base Units
Length, Mass, Time, Electric Current, Thermodynamic
Temperature, Amount of Substance, Luminous Intensity
• SI Derived Units
Plane angle, Solid Angle, Angular Velocity, Angular Acceleration, Frequency,
Speed and Velocity, Acceleration, Force, Pressure and stress, Energy, Work and
Heat, Power, Power Flux Density, Linear Momentum, electric Charge, Celcius
Temperature