In electromechanicalsystems, energy isstored in magnetic andelectric fields.
These instrument are appropriately called as universal instruments.
Sr NAME OF PURPOSE No. EQUIPMENT1 Ammeter Measures current2 Voltmeter Measures p.d. between 2 points in circuit3 Wattmeter Measures the power4 Multimeter Measures V,I,R,C etc5 LCR Meter Measures L,C & R6 Oscilloscope Displays waveform of a signal7 Ohm-meter Measures R8 Signal Generator Generates signal for testing purpose9 Network Analyzer Measures Network parameter10 Q-meter Measures Q-factor of the RF circuits (Ratio of reactance to resistance)11 Etc…………………………………….. ………………
AMMETERAn ammeter is a measuringinstrument used to measurethe electric current in a circuit.UNIT= Amperes (A)Instruments used to measure smallercurrents, in the milliampere ormicroampere range, are designatedas milliammeters or microammeters.
WORKING PRINCIPLE OF AMMETER An ammeter consists of acoil with very low resistance. when electric current flows through the coil, the coil induces a magnetic field which turns the needle.
As the currentthrough the coil increases,the plunger isdrawn furtherinto the coiland the pointerdeflects tothe right.
Wire carrying current to be measured. Spring providing restoring force
Basic Function of Moving AmmetersWith both moving coil and moving iron ammeters, an electric current is used to create magnetic energy, which in turn causes a moving part within the ammeter to shift in response. Theamount of the shift moves a needle on the display, which in turn measures the amount of the current.
USE IT ????? HOW TO USE AMMETER? HOW TO USE VOLTMETER? HOW TO USE WATTMETER?HOW TO USE MULTIMETER? Calculation of R, L, C etc.. HOW TO USE LCR METER?HOW TO USE OSCILLOSCOPE?
Moving Coil AmmetersIn a moving coil ammeter, the magnetstimulates a coil that has the oppositepolarity, causing it to be repelled from the magnet. Moving coil ammeters have a linear display.
Moving Iron AmmetersIn a moving iron ammeter, twopieces of iron are housed inside of a coil that becomesmagnetized and repels the two pieces of iron from one another. The result is anonlinear, arced measurement.
Digital Display Ammeters A digital display has no moving parts,and instead measures the proportional drop across a reader located inside ofthe ammeter. Digital ammeters are far more accurate than their moving counterparts.
Indicating:- Indicates magnitude of quantity being measured. E.g.- Ordinary voltmeter, ammeter, wattmeter etcRecording:- Recording over a specified period. E.g.- Recording voltages in a sub-station during the day.
Integrating:- Totalize events over aspecified period of time. E.g.-Ampere Hour Meter (Energy).
There are two types of moving coilinstruments.1. permanent magnet moving coiltype which can only be used for directcurrent, voltage measurements.2.The dynamometer typewhich can be used on either direct oralternating current, voltagemeasurements.
Permanent Magnet Moving Coil (PMMC)The permanent magnet moving coil instruments aremost accurate type for direct current measurements.The action of these instruments is based on themotoring principle. When a current carrying coil isplaced in the magnetic field produced by permanentmagnet, the coil experiences a force and moves. As thecoil is moving and the magnet is permanent, theinstrument is called permanent magnet moving coilinstrument. This basic principle is called D’Arsonvalprinciple. The amount of force experienced by the coilis proportional to the current passing through the coil.
In PMMC meter or (D’Arsonval) meter or galvanometer all are the same instrument.
Mathematical Representation of PMMC Mechanism:- F=N⋅B⋅I⋅L where , N: turns of wire on the coil I: current in the movable coil B: flux density in the air gap L: vertical length of the coil
DYNAMOMETERThis instrument is suitable for themeasurement of direct and alternatingcurrent, voltage and power.The deflecting torque in dynamometeris relies by the interaction of magneticfield produced by a pair of fixed aircored coils and a third air cored coilcapable of angular movement andsuspended within the fixed coil.
For small current measurement (5mAto 100mA), fixed and moving coils areconnected in series. While larger current measurement(up to 20A) , the moving coil is shuntedby a small resistance.
VOLTMETER A voltmeter is an instrument used for measuring electrical potential difference betweentwo points in an electric circuit.
Working Principle of VoltmeterThe moving coil galvanometer is atype of voltmeter working on thisprinciple.The voltmeter measures voltage bypassing current through a resistance.It is designed in such a way so as tooffer minimum disturbance to thecircuit. This is made possible by using asensitive ammeter in series with a highresistance.
Technically specified, all types of voltmeters are Ammeters becausethey measure current rather than thevoltage. A voltmeter measures voltage only when current is transmitted in a circuit through a resistance. Due tothis reason, voltmeters are sometimes referred to as high resistance Ammeters too.
Uses of Voltmeters Voltage Sensing Voltage Measurement Electrical Testing Educational Laboratory Electronics Industry
Types of Voltmeters1.Digital Voltmeters2.Analog Voltmeters3.Electrostatic Voltmeters (measure voltages without any charge transfer)4.Oscilloscope Voltmeter(react fast enough to follow rapid voltage changes)5. Microvoltmeters6. Electronic voltage meter or vacuum tube voltmeter (VTVM)
OscilloscopeAllows the amplitude of electricalsignals, whether they arevoltage, current; power, etc., to bedisplayed primarily as a function oftime.Depends on the movement of anelectron beam.Beam to impinge on a phosphorsurface
TransducersNon-electrical quantity isconverted into an electrical signal by adevice called electrical transducer.Non-electrical = electrical, mechanical,chemical, optical (radiant), or thermal.
Types of Transducers 1. Primary & Secondary 2.Active & Passive 3.Analog & Digital
Primary Transducer Converts energy from one form to electrical form (photovoltaic cell) Secondary transducer Coverts any form to non electrical orsignal form.(displacement transducer)
Active (self generating) transducers:- without any source of electrical excitation. (thermocouples, tacho generator) passive transducers: in connection with electrical power source. (a potentiometer, thermistor)
Analog transducer converts input signal into output signal, which is a continuous function of time. Digital transducer converts inputsignal into output signal in a discrete forms.
Displacement Transducerconvert the applied force into adisplacement. Measured by following Electrical Principle:1) Capacitive 2) Inductive3) Differential transformer4) Photoelectrical 5) Potentiometer6) Ionization 7) Oscillation8) Piezoelectric 9) Velocity
LVDT(Linear Variable Differential Transformer)It is produces an electrical signal that is linearly proportional to mechanical displacement.
emf opposes each other.Left when more flux links and so on
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