Metrology Viva Questions

Viva Questions: Metrology Lab
1. What is metrology?
Metrology is the science of measurement. Metrology includes all theoretical and practical
aspects of measurement. Metrology is the process of making extremely precise
measurements of the relative positions and orientations of different optical and mechanical
components. Metrology is concerned with the establishment, reproduction, conservation
and transfer of units of measurement & their standards.
2. What are the objectives of metrology?

To provide accuracy at minimum cost.
Thorough evaluation of newly developed products, and to ensure that components are within
the specified dimensions.
To determine the process capabilities.
To assess the measuring instrument capabilities and ensure that they are adequate for their
specific measurements.
To reduce the cost of inspection & rejections and rework.
To standardize measuring methods.
To maintain the accuracy of measurements through periodical calibration of the instruments.
To prepare designs for gauges and special inspection fixtures
3. What is calibration?
Calibration is the comparing of an unknown measurement device against equal or better known
standard under specified conditions. Every measuring system must be provable. The procedure
adopted to prove the ability of a measuring system to measure reliably is called calibration.
4. Give the importance of calibration.

Assurance of accurate of measurements
Ability to trace measurements to international standards
International acceptance of test/calibration reports
Consumer protection (legal metrology)
Correct diagnosis of illness (medical reports)
Meeting the requirements of ISO 9000 & 17025
5. List the various linear measuring instruments.

a) Scale
b) Vernier Calipers
c) Height Gauge
d) Micrometer etc.
6. Define an error.
Error may be defined as the difference between the best measured or indicated value and the true
or actual value. No measurement can be made without errors at all times i.e. 100% accurate
measurements cannot be made at all the times. Classified in different ways, they
are: Systematic error, Random errors and illegitimate errors.
7. Define Standard with an example.
Something that is set up & established by an authority as a rule of the measure of the quantity,
weight, extent, value or quality Ex: A meter is a standard established by an international
organization for the measure of length.
8. Define measurements. Mention different methods of measurements.

Measurement is a process or an act of comparing a quantitatively an unknown magnitude
with a predefined standard. For Example, consider the measurement of a length of a bar.
We made use of a scale/ steel rule (i.e. a standard). It is a collection of quantitative data. A
measurement is a process of comparing a quantity with a standard unit. Since this
comparison cannot be perfect, measurements inherently include error. There are two
methods of measurement: 1) direct comparison with primary or secondary standard & 2)
indirect comparison through the use of calibrated system.
9. What is Precision?
Precision of an instrument indicates its ability to reproduce a certain reading with a given
accuracy. It is the degree of agreement between repeated results.
10. Define Linearity.

A measuring system is said to be a linear if the output is linearly proportional to the input.
11. Define Repeatability.

Repeatability is defined as the ability of a measuring system to reproduce output readings
when the same input is applied to it consecutively under the same conditions & in the same
directions.
12. Define Accuracy.

Accuracy of an instrument indicates the deviation of the reading from a known input.
13. Define least count.

It is the smallest difference between two indications that can be detected on the instrument scale.
14. Define measure.

It means, to determine the dimension, quantity or capacity of something.
15. Define result.

It is obtained by making all known corrections to the indicated value.
16. What are slip gauges?

Slip gauges a very accurately ground block of hardened steel used to measure a gap with close
accuracy: used mainly in tool-making and inspection.
17. What is Tolerance?

It is the difference between the upper limit and the lower limit of a dimension. It is
impossible to make anything to an exact size, therefore it is essential to allow a definite
tolerance. It is also the maximum permissible variation on every specified dimension.
18. What are Limits?
The maximum and minimum permissible sizes within which the actual size of a Component lies
are called Limits.
19. Define fits.

The relationship existing between two parts, shaft and hole, which are to be assembled, with
respect to the difference in their sizes is called fit.
20. What is Range?

Range represents the highest possible value that can be measured by an instrument or Range is
the difference between the largest & the smallest results of measurement.
21. What is comparator?

Comparator is a precision instrument used for comparing dimensions of a part under test with the
working standards. It is an indirect type of instrument and used for linear measurement. If the
dimension is less or greater than the standard, then the difference will be shown on the dial. It
gives only the difference between actual and standard dimension of the work piece.
22. Name the different types of comparator?

Mechanical Comparator, Pneumatic Comparator, Optical Comparator, Electrical Comparator,
Electronic Comparator and Combined Comparator (ex: mechanical optical comparator).
23. What are advantages and disadvantages of mechanical comparator?

Advantages of Mechanical Comparator:
1. They do not require any external source of energy.
2. These are cheaper and portable.
3. These are of robust construction and compact design.
4. The simple linear scales are easy to read.
5. These are unaffected by variations due to external source of energy such air, electricity
etc.
Disadvantages:
1. Range is limited as the pointer moves over a fixed scale.

2. Pointer scale system used can cause parallax error.
3. There are number of moving parts which create problems due to friction, and ultimately
the accuracy is less.
4. The instrument may become sensitive to vibration due to high inertia.
24. What is a sine bar?

Sine bar is a high precision & most accurate angle measuring instrument. It is used for
measurement of an angle of a given job or for setting an angle. They are hardened and
precision ground tools for accurate angle setting. It can be used in conjunction with set of
angle gauges and dial gauge for measurement of angles and tapers from horizontal surface.
25. What is a sine center?
These are used in situations where it is difficult to mount the component on the sine bar. It
is basically used for conical work pieces. It is the extension of sine bars where two ends are
provided on which centers can be Clamped. These are useful for testing of conical work
centered at each end, up to 60.

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Viva Questions: Metrology Lab

2. What are the objectives of metrology?

4. Give the importance of calibration.

5. List the various linear measuring instruments.

8. Define measurements. Mention different methods of measurements.

10. Define Linearity.

11. Define Repeatability.

12. Define Accuracy.

13. Define least count.

14. Define measure.

15. Define result.

16. What are slip gauges?

17. What is Tolerance?

19. Define fits.

20. What is Range?

21. What is comparator?

22. Name the different types of comparator?

23. What are advantages and disadvantages of mechanical comparator?

1. Range is limited as the pointer moves over a fixed scale.

24. What is a sine bar?

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