Electrical & Electronics

❑ Electronics is a subset of electrical where you influence and control the behaviour of electrons
in a circuit by another current, without mechanical parts (switches) or electro magnetism (coils,
oscillators)
❑ Electric term refers to a quantity which deals with higher voltages, transformers , generators etc.
where as electronic are those which uses low voltages like ICs of magnitude (0-15 V)

X1 Y1
Inputs
X2
Electronics Y2
Outputs

X3 Y3
 Introduction

Instrumentation :
• Instrumentation is the use of measuring instruments
to monitor and control a process.
• It is the art and science of measurement and control
of process variables within a production, laboratory,
or manufacturing area.
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 Key Definitions
Measurement: It is the act, or the result of quantitative comparison between a predetermined
std. and an unknown magnitude. Since two quantities are compared and the result are
expressed in numerical value.

Measurand: The physical quantity or the characteristic conditions which is the object of
measurement in an instrumentation system is termed as measurand or measurement variable or
process variable.
e.g. Fundamental Quantity: length, mass, time.
Derived Quantity : Speed, Velocity, Pressure etc.
Measurand (Qty. to be measured)

` Std. Unknown Quantity Result (Read out)

Process of Comparison

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 Significance of Measurement
• “When you can measure, what you are speaking and express it in numbers, you
know something about it, when you cannot express in it numbers, knowledge is
of meagre and unsatisfactory kind” – Lord Kelvin

• The measurement confirms the validity of a hypothesis and also add to it the
understanding. This eventually leads to new discoveries that require new and
sophisticated measuring techniques.

• Through measurement a product can be designed or a process be operated with

max. efficiency, minimum cost and with desired degree of reliability and
maintainability.
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 Contd..

Measured Value: Any value or any reading calculated from measurement system or
measuring instrument.

True value: Any value calculated from rated value known as True value or Actual Value.
e.g. Motor Actual Speed

True Value Measured Value

Measuring Instrument

Error : Any deviation of measured

value from true value
Measured Value-True Value

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 Methods of Measurement

Method of Measurement

Direct Method Indirect Method

The unknown quantity (measurand) In this method the comparison
is directly compared against a standard. is done with a standard through
The result is expressed as a numerical number the use of a calibration. These
and a unit. Direct methods are common methods are used in those cases
for the measurement of physical quantities where the desire parameter to
like length, mass and time be measured can’t be compared
directly. E.g. Acceleration,
power
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 Direct Methods are Classified as:

✓ Deflection methods
“Deflection method” includes the deflection of pointer on a scale due
to the quantity to be measured. Example: Wattmeter, ammeter
voltmeter

✓ Comparison methods
“Comparison method” include the comparison of the quantity under
measurement with a pre-defined standard quantity which gives
measurement. Example: potentiometer.

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Indirect Methods
• Indirect measurement is an approach to measure quantities using alternative
techniques.

• In indirect method of measurement, the physical parameters of the quantity

are measured by the direct method, and then the numerical value of the
quantity is determined by the mathematical relationship.

Example: The length, breadth and height of the substance is measured by the
direct method and then by the help of the given relation the weight of the
substance is calculated as.

• Weight = Length X Breadth X Height X Density

 Sensor vs transducer

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 Functional Elements of an Instruments
✓ Any instrument or measuring can be represented by block diagram, that
indicates necessary elements and its functions.
✓ The entire operation of the measuring system can be understand from the
bock diagram
Data storage element

Qty. to be
measured Primary Variable Variable Data Data
sensing conversion manipulation transmission presentation
element element element element element

Data conditioning element Observer

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 Example:

❑ Consider an example of an Analog meter (Ammeter) which

measures current.

Current Moving Magnets and other Force Mechanical Pointers and

Coil components Linkages scale

Primary Sensing Data conditioning Data Transmission Observer

BASIC SCHEMATIC OF AN AMMETER

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 Instruments and Measurement Systems
Measurement:
✓ An act or the result of comparison between the quantity (whose magnitude is
unknown) and a predefined standard
✓ As two quantities are compared result is numerical value
✓ Process by which physical parameters are converted into numbers

Measurement involve the use of instruments as a physical means of determining

quantities or variables.
✓ Mechanical/Electrical or Electronic Instruments
✓ Absolute/ Secondary Instruments
✓ Active/Passive Instruments
✓ Deflection/null/ o/p instruments
✓ Self contained /Remote Indicating Instruments
✓ Analog/ Digital Instruments

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Mechanical/Electrical or Electronic Instruments
Mechanical Instruments
• Reliable for static and stable conditions
• Slow response for dynamic and transient conditions
• Large mass and inertia
• Unable to measure 50Hz signal quantity
• Have noise problem
Electrical Instruments
• Fast as compare to mechanical methods
• Depends upon mechanical systems for movement
• Less time and frequency response
Electronic systems
• Very fast response

• Most of scientific and industrial meters

• Light in weight

• Meter systems are compact

• Can be used for dynamic and transient parameters

• Can give millisecond response time

 Absolute or Primary/Secondary
Instruments
Absolute Instruments
✓ It gives the magnitude of quantity under measurement in
terms of physical constants of the instrument e.g. Tangent
Galvanometer
✓ In this type of instruments no calibration
or comparison with other instruments is necessary.
✓ They are generally used in laboratories and
are seldom used in practice by electricians and engineers.

Secondary Instruments
✓ These instruments are so constructed that the quantity being measured can only be
determined by the output indicated by the instrument.
✓ These instruments are calibrated by comparison with an absolute instrument or another
secondary instrument, which has already been calibrated against an absolute instrument.
e.g. Ammeter, Voltmeter etc.

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 Classification of Secondary Instruments
(a) Classification based on the various effects of electric current (or voltage)
upon which their operation depend.
• Magnetic effect: Used in ammeters, voltmeters, watt-meters,
integrating meters etc.
• Heating/thermal effect: Used in ammeters and voltmeters.
• Electromagnetic field of attraction/repulsion: Wattmeter's
• Electrostatic effect: Used in voltmeters.
• Electromagnetic induction effect: Used in ac ammeters,
voltmeters, watt meters and integrating meters.

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 (b) Classification based on the Nature of their Operations
• Indicating instruments: Indicating instruments indicate, generally the
quantity to be measured by means of a pointer which moves on a
scale. Examples are ammeter, voltmeter, wattmeter etc.
• Recording instruments: These instruments record continuously the
variation of any electrical quantity with respect to time. In principle,
these are indicating instruments but so arranged that a permanent
continuous record of the indication is made on a chart or dial.
• Integrating instruments: These instruments record the consumption
of the total quantity of electricity, energy etc., during a particular
period of time. : Ampere-hour meter: kilowatt hour (kWh) meter,
kilovolt-ampere-hour (kVARh) meter.
 Classification of Secondary Instruments
(c) Classification based on the kind of Current that can be Measurand.
• Direct current (dc) instruments
• Alternating current (ac) instruments
(d) Classification based on the method used
• Direct measuring instruments: These instruments converts the energy of the
measured quantity directly into energy that actuates the instrument and the value of
the unknown quantity is measured or displayed or recorded directly Examples are
Ammeter, Voltmeter, Watt meter etc.
• Comparison instruments: These instruments measure the unknown quantity by
comparison with a standard. Examples are dc and ac bridges and potentiometers.
They are used when a higher accuracy of measurements is desired

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Analog/ Digital Instruments
• Secondary instruments works in two modes viz. analog or digital
• Signal which varies continuous w.r.t. time are analog signals
• The discrete value signals are known as digital

Analog signal
Deflection and Null instruments

• Deflection type provides a basis for • In a null type instrument a zero or null
determining the quantity under measurement indication leads to determination of
measures quantity.
• Measured quantity produces some physical
effects which deflects or produces a • The null condition is dependent upon some
mechanical movement other known conditions.
 Active/Passive Instruments

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