Electrical And Electronics
Instruments
N Krishna Prakash
04-03-09
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UNIT - 2
ELECTRICAL AND ELECTRONICS INSTRUMENTS
Principle and types of analog voltmeters
Principle and types of digital voltmeters
Principle and types of Multimeter
Single and three phase wattmeter
Single and three phase energy meters.
Magnetic measurements
Determination of B-H curve
Measurements of iron loss
Instrument transformers
Instruments for measurement of frequency and phase
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2
Analog Instruments

An analog device is one in which the
output or display is a continuous
function of time and bears a constant
relation to its input.
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Classification
Classified based upon the quantity they
measure (ammeter, voltmeter)
 Classified according to the current that can be
measured by them.(DC,AC)
 Classified according to the effects used for
working.
 Classified as Indicating, Recording,
Integrating.
 Classified on the basis of method used for
comparing the unknown quantity. (Direct /
Comparison
measurement
)
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
Principle of operation
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Magnetic Effect.
Thermal Effect.
Electrostatic Effect
Induction Effect.
Hall Effect.
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Magnetic Effect
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Force Between Current carrying
Magnet
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Force Between Two Current
Carrying Coils
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Hall Effects
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Operating Forces
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Deflecting Force.
Controlling Force.
Damping Force.
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Supporting the moving
element
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Suspension
Taut Suspension
Pivot and jewel bearings.
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Control Systems
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Gravity Control.
Spring Control.
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Analog Ammeters

Ammeters are connected in series in
the circuit whose current is to be
measured. The power loss in an
ammeter is I2Ra.Therefore ammeters
should have a low electrical
resistance so that they cause a small
voltage drop and consequently
absorb small power.
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Analog Voltmeters

Voltmeters are connected in parallel
in the circuit whose voltage is to be
measured. The power loss in an
ammeter is V2/RV.Therefore
voltmeters should have a high
electrical resistance so that they
cause a small voltage drop and
consequently absorb small power.
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Types of Instruments
Permanent magnet moving coil
(PMMC).
 Moving Iron
 Electro-dynamometer type.
 Hot wire type.
 Thermocouple type.
 Induction type.
 Electrostatic type.
 04-03-09
Rectifier type.
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
PMMC
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Moving Iron Instruments
Attraction Type
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Repulsion Type Moving Iron
Instruments
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Electrodynamometer Type
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Wattmeter
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Power Measurement in 3 phase 3
wire system
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Two wattmeter method
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Energy meters
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Single Phase Energy Meter
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Poly Phase Energy Meter
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THANK YOU
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