These slides describes the deifintion of measurement, Classification of instruments and methods of measurement. Read the full blog post here: https://bit.ly/32prjeT

1. Introduction
•Principles of Measurement
•Classification of instruments
•Methods of measurement

2. Principles of Measurement
What is Measurement?
• Measurement tell us about property of something.
• Measurement provide us with a means of describing
various phenomena in quantitative terms.
• Measurement is the process by which one can
convert physical parameter to meaningful numbers.
• Measurement are always made by using an
instrument (tool) of some kind. (Example: Ruler,
Thermometer, Stop watch, Weighing machines)
• Measurement gives a number to that property.

3. Principles of Measurement
What is Measurement?
Result of measurement contains two parts
i) Unit of measurement
ii) Number

4. Principles of Measurement
What is Measurement?
Measurement is the act or the result of a quantitative
comparison between the quantity (whose magnitude is
unknown) and a predefined standard.
Measurand: Physical parameter or variable to be
measure.
Standard: A quantity of the same kind chosen as a
unit or basis for comparison of quantitative value to
measure.

5. Principles of Measurement
BASIC REQUIREMENTS OF MEASUREMENT
• The standard used for comparison purposes must be
accurately defined & should be commonly accepted
• The standard must be of the same character as the
measurand
• The apparatus used & the method adopted must be
provable.

6. Principles of Measurement
MEASURING INSTRUMENT:
It may be defined as a device for determining the value or
magnitude of a quantity or variable.
Electronic instrument :
• An electronic instrument is the one which is based on
electronic or electrical principles for its measurement
function.
• The measurement of any electronic or electrical quantity or
variable is termed as an electronic measurement.

7. Principles of Measurement
Advantages of Electronic Measurement :
1. Most of the quantities can be converted by transducers
into the electrical or electronic signals.
2. An electrical or electronic signal can be amplified,
filtered, multiplexed, sampled and measured.
3. The measurement can easily be obtained in or converted
into digital form for automatic analysis and recording.
4. The measured signals can be transmitted over long
distances with the help of cables or radio links, without any
loss of information.
5. Electronic circuits can detect and amplify very weak
signals and can measure the events of very short duration as
well.

8. Principles of Measurement
FUNCTIONAL ELEMENTS OF AN INSTRUMENT
Most of the measurement systems contain three main functional elements. They are:
i) Primary sensing element
ii) Variable conversion element
iii) Data presentation element.

9. Principles of Measurement
FUNCTIONAL ELEMENTS OF AN INSTRUMENT
• Primary sensing element: which senses the quantity under
measurement
• Variable conversion element: which modifies suitably the output of
the primary sensing element
• Variable Manipulation Element: The signal gets manipulated here
preserving the original nature of it
• Data Transmission Element: The transmission of data from one
another is done by the data transmission element
• Data presentation element : The display or readout devices which
display the required information about the measurement.

10. Principles of Measurement
Just take an example of analogue meter used to
measure current (Ammeter), all necessary
elements are shown in block diagram.

11. Classification of Instruments
Instruments can classified into many
categories, one classification is given as under.
1. Active/Passive instruments
2. Null or deflection type
3. Monitoring or control type
4. Analogue or digital
5. Absolute or secondary

12. 1. Active/Passive
Passive Instruments: (Easy design, cheap)
• In which the output is produced completely
by the quantity that is measured.
• An example of a passive instrument is the
pressure measuring device. The pressure of
the fluid is translated into movement of a
pointer against a scale. The energy expended
in moving the pointer is derived entirely
from the change in pressure measured; there
are no other energy inputs to the system.

13. Active Instruments: (Difficult to design, costly)
In which the quantity being measured activates the
magnitude of some external power input source,
which in turn produces the measurement.
Example: Float-type petrol-tank level indicator
• Change in petrol level moves a potentiometer arm
• Output signal consists of a
proportion of the external voltage source.
• The energy in the output signal
comes from the external power source.
• The primary transducer float system is merely modulating
the value of the voltage from this external power source.

14. 2. Null/Deflection
Null type instruments:
In which a zero or null indication leads to the
determination of magnitude of the quantity being
measured.
Example: DC potentiometer, Wheatstone Bridge
Deflection type instrument:
In which the quantity being measured produces some
effect due to which pointer deflects.
Example: PMMC instrument.

15. 3. Monitoring /Control
Monitoring type instruments:
In which some indication or condition of
parameter value under study is obtained.
Example: All deflection type or digital instruments
Control type instruments:
These are used in automatic control systems in the
feedback path, to send a feedback signal from the
output of a process to its input.
Example: Automatic air- conditioning system.

16. 4. Analogue/digital
Analogue type instruments:
In which output varies in continuous fashion as quantity
being measured, having infinite values in a given range.
Example: Deflecting Instruments are good examples of
analogue instruments.
Digital Instruments:
In which output varies in discrete step and
thus give finite values in a given range.
Example: Digital Multi-meter

17. 5. Absolute/ Secondary
Absolute Instruments:
In which magnitude of quantity is measured in terms of
physical constants of the instrument.
Example: Tangent galvanometer
Secondary type instruments:
In which the reading shown by the instrument gives
directly the measurement of the quantity being
measured.
Example: Voltmeter, ammeter, wattmeter.

18. There are two methods of measurement.
1. Direct measurement
2. Indirect Measurement
Direct Measurement:
In direct measurement the quantity being measured
produce certain effect which gives the indication
on meter.
Example: Measurement of current by ammeter.

19. Direct methods are classified as
1. Deflection methods
2. Comparison methods
“Deflection
pointer on
measured.
method” includes the deflection of
a scale due to the quantity to be
Example: Wattmeter, ammeter voltmeter
“Comparison method” include the comparison of the
quantity under measurement with a pre-defined standard
quantity which gives measurement.
Example: potentiometer.

20. Indirect measurement:
In which the quantity to be measured is not measured directly,
but other parameter related to the quantity are measured.
Example 1:
For measurement of power (P) we measure voltage
(V) and current (I) then P = V*I
Example 2:
For measurement of resistance (R) we measure (V) and current
(I) then R=V/I