Presentation on Electrical Measurement and Instrumentation

Presented By Salma Akter BKH F

Presentation On Indicating Instruments

Overview  Introduction of Indicating Instruments  Essential requirements of Indicating Instrument  Types of Indicating Instrument  PMMC(Permanent magnet moving coil)  MI(Moving iron Instrument)  Types of MI instrument  Basic comparison between moving coil and moving iron instruments

Indicating instruments indicate the value of the electrical quantity to be measured generally by the deflection of the pointer which moves on the calibrated scale. Examples are ammeter, voltmeter, wattmeter etc. Introduction

Deflection Torque Controlling Torque Damping torque Essential requirements of Indicating Instrument Air friction damping Eddy current damping Spring Control method Gravity control method

PMMC(Permanent magnet moving coil) MI (Moving iron) Types of Indicating Instrument

PMMC(Permanent magnet moving coil) It is the basic measuring instrument which can be used for measuring current and voltages. They can be converted into either voltmeter and ammeter.

Parts of PMMC  Permanent Magnet  Controlled Springs  Aluminum Cylindrical Core  Pointer  Pivots  Scale  Rectangular Coil

 It Works on the principle of DC motor  When current passes through the coil, it produces flux of the core.  Principle of the operation is based on Flemings left hand rule, that means when a conductor is placed in a magnetic field it experiences a force because of which it moves away Working Principle Flemings left hand rule

APPLICATION  PMMC instruments can be used as dc ammeter. And its range can be increased by using a large number of turns in parallel with the instrument.  The range of this instrument, when used as a dc voltmeter, can be increased by using a high resistance in series with it.

Advantages  Uniform scale for the instrument  Power consumption is very low  A single instrument can be used for different current and voltage ranges  The toque-weight ratio is high gives higher accuracy. Disadvantages  This instrument can be used only on DC supply  The cost of the instrument is more than M.I. Instruments

MI(Moving iron) The instrument in which the moving iron is used for measuring the flow of current or voltage is known as the moving iron instrument. Types of MI instrument  Repulsion (or double iron) type  Attraction (or single-iron) type

Repulsion (or double iron) type  This instrument consists of two iron vanes, one is attached to the stationary coil and other one is attached to the movable spindle.  Both vanes are surrounded by the stationary coil, current to be measured is passing thorough this coil. Repulsion Type Moving Coil

Attraction (or single-iron) type The instrument in which the iron plate attracts from the weaker field towards the stronger field such type of instrument is known as the attraction type instrument. Parts of Attraction Type MI Instrument  Pointer  Moving Iron  Control Weight  Balance Weight  Coil Winding

Advantages  Cheap, robust and give reliable service.  Usable in both AC and DC circuits. Disadvantages  Have non-linear scale.  Cannot be calibrate with high degree of precision for dc on account of the affect of hysteresis in the iron vanes.  Deflection up to 240º only may be obtained with this instrument.  This instrument will always have to be put in the vertical position if it uses gravity control.

Basis for ComparisonMoving Iron InstrumentMoving Coil Instrument DefinitionIn moving iron instrument the soft iron is used for moving mechanism. In moving coil instrument the conductor coil is used for measuring the current and voltage. Working PrincipleMagnetismSimilar to working principle of DC Motor UsesBoth for AC and DC measurementDC Measurement AccuracyLessMore ScaleNon-uniformUniform DampingAir Friction DampingEddy Current Damping Power ConsumptionHighLow Controlling TorqueGravity or springSpring DeflectionProportional to CurrentSquare of current Hysteresis LossNot occursOccurs Can be used asAmmeter, Voltmeter and WattmeterVoltmeter, ammeter, galvanometer, ohmmeter Basic comparison of Moving Iron and Moving coil instruments

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