B1.1M03 Presentation V1.0 Dated 02.02.09

MODULE 3 : ELECTRICAL

FUNDAMENTALS

PART 66 CATEGORY B1.1

Slide No 2B1.1M03 Presentation V1.0 dated 02.02.09

ELECTRON THEORY (EASA Ref : 3.1)


EASA Ref:3.1

ATOMIC STRUCTURE

- smallest part of an element (solar system)

element, molecules and compound

- nucleus consists of PROTONS and NEUTRONS

- electrons – around the orbit of an atom

- Charge of proton – positive

Charge of electron – negative

Charge of neutron – neutral

- Proton and Neutron makes up app. 98% of the mass


EASA Ref :3.1


EASA Ref :3.1


EASA Ref :3.1


IONISATION

FACTORS AFFECTING IONISATION:

HEAT

LIGHT

ELECTRIC FIELDS

MAGNETIC FIELDS

CHEMICAL ACTION

PRESSURE

CAN BE:

POSITIVE ION (LOSS OF ELECTRON) or

NEGATIVE ION (GAIN OF ELECTRON)

MOVEMENT OF ELECTRON IS CURRENT FLOW

EASA Ref :3.1


EASA Ref :3.1


EASA Ref :3.1


MOLECULAR STRUCTURE OF CONDUCTOR, INSULATOR AND SEMICONDUCTOR

A MATERIAL WHICH ALLOW ELECTRONS TO FLOW IS KNOWN AS CONDUCTOR. EX: GOLD, COPPER, SILVER and ALUMINUM

A MATERIAL WHICH PREVENTS ELECTRON FLOW IS KNOWN AS INSULATOR. EX: DRY AIR, MICA, EBOLITE, PORCELIN and RUBBER

A MATERIAL WHICH RESTRICTS ELECTRON FLOW IS KNOWN AS SEMICONDUCTOR. EX: SILICON, GERMANIUM and TELLURIUM

EASA Ref :3.1


STATIC ELECTRICITY AND CONDUCTION ( EASA Ref : 3.2 )


STATIC ELECTRICITY AND DISTRIBUION OF ELECTROSTATIC CHARGES

FRICTION:

RUBBING OF 2 DIFFERENT MATERIALS, WHEREBY ONE MATERIAL LOSSES ELECTRONS AND THE OTHER GAINS ELECTRONS

MATERIAL WITH LESS ELECTRONS IS CALLED POSITIVELY CHARGED

MATERIAL WITH GAINED ELECTRONS IS CALLED NEGATIVELY CHARGED

EASA Ref : 3.2


MATERIALS THAT ACQUIRE A CHARGE OF STATIC ELECTRICITY:

GLASS,AMBER,

HARD RUBBER,WAXES,

NYLON,RAYON,

SILK, FLANNEL.

EX: HARD RUBBER RUBBED AGAINST FUR.

ROD – NEGATIVE CHARGE

FUR – POSITIVE CHARGE

EASA Ref : 3.2


ELECTROSTATIC LAW OF ATRACTION AND REPULSION:

(COULOMB’S LAW)

LIKE CHARGES REPELS and

UNLIKE CHARGES ATTRACTS

COULOMB’S LAW – UNITS OF CHARGE:

QUANTITY (UNIT OF CHARGE) OF ELECTRICITY = COULOMB

SYMBOL FOR COULOMB = Q

1 COULOMB = 6,290,000,000,000,000,000 ELECTRONS = 6.29 x1018 ELECTRONS

EASA Ref : 3.2


CONDUCTION OF ELECTRICITY

IN SOLIDS – ELECTRONS

IN LIQUIDS – POSITIVE IONS OR NEGATIVE IONS

IN GASES – ELECTRONS AND IONS

IN A VACUUM – ELECTRONS AND IONS

EASA Ref : 3.2


ELECTRICAL TERMINOLOGY, UNIT and AFFECTIVE FACTORS:

DIFFERENCE IN POSITIVE AND NEGATIVE CHARGE = POTENTIAL

DIFFERENCE (PD)

UNIT OF PD - VOLTS

120 VOLTS WITH 0 VOLTS = A PD of 120 VOLTS

- 120 VOLTS WITH 0 VOLTS = A PD of 120 VOLTS

+ 120 VOLTS WITH - 120 VOLTS = A PD of 240 VOLTS

THIS PD CAN FORCE ELECTRONS TO FLOW FROM NEGATIVE CHARGE TO POSITIVE CHARGE DUE TO ELECTRICAL PRESSURE

ELECTRICAL TERMINOLOGY (EASA Ref : 3.3 )


EASA Ref : 3.3


EASA Ref : 3.3


CONVERSION OF ENERGY:

- CHEMICAL ENERGY CONVERTED TO ELECTRICAL ENERGY

- ELECTRICAL ENERGY CONVERTED TO LIGHT ENERGY

- LIGHT ENERGY CONVERTED TO HEAT ENERGY

EASA Ref : 3.3


EASA Ref : 3.3


EMF CAN BE MEASURED WHEN NO CURRENT FLOWS

PD CAN BE DETERMINED

Reason:

voltage will be dropped across the internal resistor of the battery

EMF = PD + INTERNAL VOLTAGE DROP

NO CURRENT FLOWS , EMF =PD

UNIT FOR EMF AND PD IS VOLTS

EASA Ref : 3.3


EASA Ref : 3.3


VOLTAGE:

ELECTRICAL POTENTIAL = JOULES PER COULOMB (VOLTS)

CURRENT:

1 AMPERE = 1 COULOMB PER SECOND

(Q = AMPERE X TIME) , Q=I/t

UNIT FOR CURRENT = AMPERE (Amp)

SYMBOL FOR CURRENT = I

EASA Ref : 3.3


EASA Ref : 3.3

PREFIXES:

0.1 Amp = 100 milliamp



0.000001 Amp = 1 microamps

3 TYPES OF CURRENT:

- DIRECT CURRENT (DC)

- PULSATING CURRENT (PULSATING DC )

- ALTERNATING CURRENT (AC)


DC - CURRENT FLOWS CONTINUOUSLY IN ONE DIRECTION

PULSATING DC - CURRENT FLOWS IN ONE DIRECTION BUT VARIES IN AMPLITUDE BUT DOES NOT GO BELOW ZERO

AC - CURRENT FLOWS IN ONE DIRECTION , THEN IN THE OTHER DIRECTION AND CHANGES FROM POSITIVE TO NEGATIVE AND THEN POSITIVE AGAIN AND SO FORTH

EASA Ref : 3.3


FREQUENCY:

1 HERTZ = 1 CYCLE PER SECOND

UNIT FOR FREQUENCY = HERTZ (Hz)

EASA Ref : 3.3


EASA Ref : 3.3


EASA Ref : 3.3


RESISTANCE:

THE PROPERTY OF A MATERIAL WHICH OPPOSSES ELECTRON FLOW.

DIFFERENT MATERIAL HAVE DIFFERENT VALUE OF RESISTANCE

SILVER = VERY LOW RESISTANCE

RUBBER = VERY HIGH RESISTANCE

SYMBOL = R

UNIT = OHMS (Ω)

EASA Ref : 3.3


Prefixes:

1 MICRO OHM = 0.000001 OHM = 1µΩ

1 milliohm = 0.001 OHM = 1 mΩ

1000 ohms = 1 kilo ohm = 1 k Ω

1000000 ohm = 1 M Ω

Note: resistor are used to control current flow

EASA Ref : 3.3


3 FACTORS AFFECTING RESISTANCE:

- LENGTH

- CROSS-SECTION

- MATERIAL ρ (rho)

Rho = the resistance of 1 meter of the material and the cross-section of 1 millimeter square

EASA Ref : 3.3


CONDUCTANCE:

- OPPOSITE TO RESISTANCE – THE EASE OF CURRENT FLOW

- IT IS THE RECIPROCAL OF RESISTANCE

- UNIT FOR CONDUCTANCE = SIEMENS (S)

G = 1 / R or R = 1 / G

G= V / I

EASA Ref : 3.3


ELECTRIC CHARGES:

ELECTRIC CHARGES GIVES A MATERIAL ITS ELECTROMAGNETIC PROPERTIES

PROTON - POSITIVE CHARGE

ELECTRON - NEGATIVE CHARGE

NEUTRON - ZERO CHARGE / NEUTRAL

EASA Ref : 3.3


2 TYPES OF CURRENT FLOW:

ELECTRON FLOW - ELECTRONS FLOW FROM NEGATIVE TO POSITIVE

CONVENTIONAL CURRENT FLOW - HOLES TRAVEL FROM POSITIVE TO

NEGATIVE

EASA Ref : 3.3


EASA Ref : 3.3


EASA Ref : 3.3


WHEN A BATTERY IS CONNECTED TO A LOAD ELECTRONS FLOW FROM NEGATIVE TO POSITIVE AT THE TERMINALS.

CURRENT (ELECTRONS) FLOWS FROM THE POSITIVE ROD TO THE NEGATIVE

ROD INSIDE THE BATTERY THROUGH THE ELECTROLYTE.

EASA Ref : 3.3


EASA Ref : 3.3


6 BASIC MEANS OF GENERATING ELECTRICITY

- FRICTION

- PRESSURE

- HEAT

- LIGHT

- MAGNETISM

- CHEMICAL ACTION

GENERATON OF ELECTRICITY ( EASA Ref : 3.4 )


EASA Ref : 3.4


FRICTION:

WHEN 2 DIFFERENT MATERIALS ARE RUBBED TOGETHER ELECTRONS TEND TOTRANSFER FROM ONE MATERIAL TO ANOTHER

ONE BECOMES POSITIVE AND THE OTHER WILL BE NEGATIVE

EASA Ref : 3.4


EASA Ref : 3.4


MAGNETISM

WHEN A MAGNET IS MOVED INTO A COIL AND REMOVED, A VOLTAGE IS PRODUCED KNOWN AS INDUCED VOLTAGE.

THE PROCESS IS KNOWN AS INDUCTION

THE VALUE OF VOLTAGE INDUCED DEPANDS ON THE SPEED OF MOVEMENT AND NUMBER OF COILS

FREE ELECTRONS ARE FORCED TO MOVE WITHIN THE WIRE

EASA Ref : 3.4


EASA Ref : 3.4


EASA Ref : 3.4


HEAT:

WHEN HEAT IS APPLIED TO A JUNCTION OF 2 DIFFERENT MATERIAL, ELECTRONS ARE FORCED TO MOVE.

2 JUNCTIONS, COLD AND HOT JUNCTION

THE EFFECT IS KNOWN AS THERMO-ELECTRIC EFFECT

USED IN ENGINES, EXHAUST GASES, OVENS and FURNACES

EASA Ref : 3.4


EASA Ref : 3.4


PRESSURE:

WHEN QUARTZ PLATE IS COMPRESSED, A VOLTAGE IS PRODUCED

WHEN A VOLTAGE IS APPLIED, COMPRESSION OF THE QUARTZ IS

PRODUCED

THIS EFFECT IS KNOWN AS PIEZOELECTRIC EFFECT

USED FOR TRANSMISSION AND RECEPTION OF ULTRASONIC VIBRATION

IN WATER (SONAR, ECHO SOUNDER )

EASA Ref : 3.4


EASA Ref : 3.4


LIGHT

WHEN LIGHT STRIKES A PHOTO-VOLTAC MATERIAL, A VOLTAGE IS PRODUCED

THIS EFFECT IS KNOWN AS PHOTO-ELECTRIC EFFECT

USED IN PHOTO-DIODES, PHOTO-TRANSISTORS, SOLAR CELLS AND SILICON CELLS ALSO SMOKE DETECTOR.

EASA Ref : 3.4


EASA Ref : 3.4


CHEMICAL EFFECT

WHEN 2 DISSIMILAR METALS ARE PLACED SIDE BY SIDE, ELECTRONS TEND TO FLOW.

ELECTRONS FROM THE NEGATIVE POLARITY WILL MOVE TOWARDS THE POSITIVE POLARITY.

WHEN 2 PLATES OF DISSIMILAR METALS ARE PLACED IN AN ELECTROLYTE, OPPOSITE ELECTRIC CHARGES WILL BE ESTABLISHED ON THE PLATES, RESULTING AN ELECTRICAL VOLTAGE(PD)

EASA Ref : 3.4


EASA Ref : 3.4


DC SOURCES OF ELECTRICITY:

WHEN 2 DISSIMILAR METALS ARE PLACED IN A CHEMICAL (ELECTROLYTE), AN ELECTRIC CELL IS FORMED KNOWN AS SIMPLE CELL

WHEN MORE THAN 2 CELLS JOINT TOGETHER, IT IS KNOWN AS A BATTERY

WHEN CERTAIN SUBSTANCES ARE DISSOLVED IN WATER +ION OR -ION IS PRODUCED.

THIS EFFECT IS KNOWN AS ELECTROLYTIC DISSOCIATION AND THIS SUBSTANCE IS KNOWN AS ELECTROLYTE

THEY CAN BE ACID OR ALKALINE

DC SOURCES OF ELECTRICITY ( EASA Ref : 3.5 )


THE RELATIONSHIP BETWEEN DISSIMILAR METALS IS KNOWN AS ELECTRO-

CHEMICAL SERIES.

EX: A NICKEL CADMIUM BATTERY

NICKEL = -0.22V

CADMIUM = - 0.40V

PD OF THE CELL = - 0.22 – (- 0.40) = 0.18V

EASA Ref : 3.5


EASA Ref : 3.5


ENERGY CONVERSION:

CHEMICAL ENERGY IS CONVERTED TO ELECTRICAL ENERGY

AS ZINC DISSOLVES, THE +IONS MOVE TOWARDS THE COPPER ELECTRODE (ZINC BECOMES EVEN MORE NEGATIVE WITH RESPECT TO THE ELECTROLYTE

1.1 V IS PRESENT AT THE TERMINALS (ANODE AND CATHODE )

2 CONDITIONS WHEN ELECTRICITY CAN BE EXHAUSTED

a) ZINC FULLY DISSOLVED or

b) ELECTROLYTE EXHAUSTED (THE IONS USED UP)

EASA Ref : 3.5


HYDROGEN BUBBLES FORM WHEN ELECTRIC CURRENT IS GENERATED

BUBBLES FORM BARRIER AT THE ANODE CAUSING A REDUCTION IN CURRENT

FLOW

THIS EFFECT IS KNOWN AS POLARIZATION

FORMATION OF HYDROGEN BUBBLES AT THE ANODE OF THE CELL

EASA Ref : 3.5


EASA Ref : 3.5


EASA Ref : 3.5


CLASSES OF CELLS

PRIMARY CELL = NOT RECHARGEABLE = CAN BE USED ONLY ONCE

SECONDARY CELL = RECHARGEABLE = CAN BE REUSED MANY TIMES

EASA Ref : 3.5


CELLS CAN BE CONNECTED IN 2 WAYS

SERIES = EX: 3 CELLS OF 1.2V = 3.6V, HIGHER OUTPUT VOLTAGE

AND CAPACITY OUTPUT (AH )THE SAME

PARALLEL = EX: 3 CELLS OF 1.2V = 1.2V ,OVERALL VOLTAGE THE

SAME BUT CAPACITY OUTPUT ( AH ) INCREASED

EASA Ref : 3.5


EASA Ref : 3.5


EASA Ref : 3.5


EASA Ref : 3.5


EASA Ref : 3.5


INTERNAL RESISTANCE OF BATTERY

Ri = 0.5Ω Rex = 5.5 Ω EMF = 12 V

RT = 0.5 + 5.5 = 6Ω

IT = EMF/RT = 12/6 = 2Amp

Uri = IT X Ri = 2 X 0.5 = 1V

PD = 12 – 1 V = 11V

EASA Ref : 3.5


EASA Ref : 3.5


EASA Ref : 3.5


AIRCRAFT BATTERIES

A device composed of two or more cells that convert chemical

energy into electrical energy.

has 2 terminals:

- negative terminal with excess of electrons

- positive terminal with lack of electrons

-output is steady DC voltage

-purpose on aircraft:

- stand-by power

- auxiliary power start up

EASA Ref : 3.5


EASA Ref : 3.5

Dry cell also known as leclanche cell

-produced by a French, Georges leclanche in 1839-1889

-commonly used but can be used only once (primary cell)


EASA Ref : 3.5


EASA Ref : 3.5

Secondary cell also called storage batteries

-can be recharged

-do not produce electrical energy but can be recharged by storing in

chemical form

-after a certain number of charges and discharges the battery should be

replaced

e.g. - lead acid battery

nickel cadmium battery etc


EASA Ref : 3.5

Lead Acid


EASA Ref : 3.5

LEAD ACD BATTERIES

- positive plate is made of lead peroxide (PbO2)

- negative plate is made of pure spongy lead (Pb)

- the electrolyte is made up of sulphuric acid (30%) and distilledwater (70%)

- the 2 plates are separated by plates known as separators

- purpose of the porous separators is to prevent short circuit

- offer minimum resistance to current flow due to the material of the

separators (porous )


EASA Ref : 3.5


EASA Ref : 3.5

Lead acid battery construction

-consists of a group of lead acid cells connected in series.

-the positive plates are connected together to a plate strap, the negative

plates are also connected together to a different plate strap

-they are both insulated from each other


EASA Ref : 3.5

Lead acid


EASA Ref : 3.5

the 3 elements are placed inside a hard rubber of plastic composite

container

the container are sealed to prevent leakage or spillage and loss of

electrolyte

ventilation caps are located at the top to let the gasses due to chemical

action.


EASA Ref : 3.5

Construction


EASA Ref : 3.5

Specific Gravity Test Procedure

- wear goggles to protect eyes

- ventilation caps to be removed

- squeeze the hydrometer rubber bulb hard and insert it into the cell hole closest to the positive terminal. (to be repeated at all cell holes)

- release the bulb slowly without removing the tube out of the electrolyte

- the float movement should not be restricted

- observe the reading at eye level.


EASA Ref : 3.5

Specific gravity


EASA Ref : 3.5

Lead Acid Battery Inspection and Service

-inspect for cracks on supporting structure

-inspect for corrosion and evidence of leakage by opening the covers

-refill electrolyte if the level is below the level

-check for defect by carrying out load test or hydrometer test

-check that the terminals are not corroded

-check that the cables are in good condition (not cracked or broken)

-check that the ventilation of the aircraft and battery box is good


EASA Ref : 3.5

Lead acid


ALKALINE BATTERIES

- positive plate, nickel hydroxide , NI(OH)2

- negative plate, metallic cadmium (Cd)

- electrolyte, potassium hydroxide (KOH)

- plates are made by sintering process

- active material impregnated into the plate by chemical deposition

EASA Ref : 3.5


Alkaline Battery

EASA Ref : 3.5


Nickel cadmium battery

EASA Ref : 3.5


Connections of

cells

EASA Ref : 3.5


Different capacity batteries

EASA Ref : 3.5


Inspection of Alkaline Battery

-inspections are based on:- flying hours- annual inspection- periodic inspection (normally 28 days)

-what is to be inspected:- the case- proper airflow of the vent system- the cells (clean if required)- the cell connector for corrosion, cracks and overheating- the cell caps are clean and not clogged- for correct electrolyte level

EASA Ref : 3.5


CHARGING OF BATTERY

2 methods (constant voltage or constant current)

constant voltage charging

- voltage is held constant always.

- current diminishes as the battery is charged

- the electron flow resistance is reduced as the charge increases

- as the battery voltage increases, the charger current reduces

- on the aircraft, batteries are normally constant voltage charged.

- if more than one battery is to be charged at one time, they must be

connected in parallel

EASA Ref : 3.5


Constant Current Charging

current is held constant but voltage varies

equipment monitors the current constant while the voltage decreases

if more than one battery is to be charged, it should be in series

over charging is to be prevented

EASA Ref : 3.5


THERMOCOUPLES

-a sensor for the measure of temperature

-consists of 2 dissimilar metals (also in the form of alloy wires)

-voltage is formed either heated or cooled and correlated back to

temperature

-a voltage produced by heating is known as Peltier Seeback Effect

(thermoelectric effect )

EASA Ref : 3.5


Operation of Thermocouples

voltage depends on:

-types of material used

-temperature difference between hot and cold junctions

Connected in a closed loop parallel circuit:

-when heated the resistance changes at a known rate

-voltage is proportional to the temperature

EASA Ref : 3.5


Measuring and Reference junctions

-measuring junction is the hot junction exposed to temperature

-reference junction is the cold junction where the temperature is held constant

EASA Ref : 3.5


Thermocouple

EASA Ref : 3.5


Types of Thermocouple

surface contact type

- measures temperatures of solid components

- cylinder head temperature-indicating systems of air cooled engines

immersion type

- measures gases and liquid temperatures (engine oil)

- gas temperature-indicating system of turbine engines

EASA Ref : 3.5


Thermocouples

EASA Ref : 3.5


– Copper – Constantan (T curve) Thermocouples

-copper wire is positive and constantan is negative wire

-used in mildly oxidizing and reducing temp. of up to 400º C

-suitable at moist and low temp. areas

-due to the low temp. the homogeneity of the component wire can be

maintained.

-errors are very low

EASA Ref : 3.5


Chromel-Alumel (K Curve)

-chromel : 90% nickel, 10% chromium

-alumel : 95% nickel, 2% maganese, 2% aluminium and 1% silicon

-positive is the chromel wire and the negative is the alumel wire

-used in clean oxidizing atmosphere

-operating temp. for the largest wire size is 1260ºC

-smaller wires operate at lower temp.

EASA Ref : 3.5


– Voltages produced by Thermocouples

C – tungstan rhenium = 15 µV / ºC

E – chromel constantan = 68 µV / º C

J – iron constantan = 52 µV / º C

K – chromel alumel = 41 µV / º C

R – platinum radium (13% platinum) = 10 µV / ºC

S – platinum rhodium (10% platinum) = 10 µV / ºC

T – copper constantan = 42 µ V / ºC

N – nicrosi (nickel, chromium and silicon) = 40 V /ºC

EASA Ref : 3.5


Temperature versus Voltage

EASA Ref : 3.5


EASA Ref : 3.5


PHOTOCELLS

-also known as Solar Cell or Photovoltaic cell

-converts ultra violet and infra red light directly into voltage

uses of photocells (known as electric eye)

-light activated counters

-automatic door opener

-intrusion alarms

EASA Ref : 3.5


Construction of photocell

-P-type Silicon the metal rib is the positive electrode ,

metal backing is the negative electrode (N type Silicon)

-each solar cell can produce about 1 watt of power and 0.5 volts

EASA Ref : 3.5


Operation of photocell

-P-type and N-type semiconductor are sandwiched together

-produces low power

-reacts to light in a short time period

- accurately controlling a great number of operations

Used in:

-video camera

-automatic manufacturing process controls

-door openers

-burglar alarms

-smoke detector

EASA Ref : 3.5


DIRECT CURRENT ELECTRICAL CIRCUITS

A DC circuit is necessary for DC electricity to exist

Types of DC circuits:

- series

- parallel

- combination of series and parallel

DC CIRCUITS ( EASA Ref : 3.6 )


Simple circuits:

If a load is connected to a battery, current flows from the pos. term. to the neg.

terminal.

the load, if it is a bulb, it should light up until the battery is discharged or the bulb has blown.

keeping in mind that electron flow from cathode to anode whereas conventional flow holes travel from anode to cathode

EASA Ref : 3.6


EASA Ref : 3.6


Sources of DC power supply:

- battery

- DC generator

- rectifier output

3 components associated with a circuit:

- voltage => unit volts

- current => unit amperes or amps

- resistance => ohms

EASA Ref : 3.6


Conductors:

wires are normally made of copper but it can also be aluminum or any other low resistance elements

tungsten is also a conductor but has a very high resistance to current therefore it heats and lights up

EASA Ref : 3.6


Series circuit

EASA Ref : 3.6


SERIES DC CIRCUIT

when 2 or more components are connected one after the other in a line, it is said that they are in series

the current that flows in this circuit is the same in all components but the voltage is divided among them

components cannot be controlled individually

disadvantage is that if one component fails, than all will not function

EASA Ref : 3.6


schematic

EASA Ref : 3.6


SCHEMATIC

The circuit elements in fig. 51 are connected end to end

The current flows through each element is the same, but volt drops different.

A component (ex. Bulb) will be represented as a resistor and drawn as a rectangular block or zig-zag

line.

EASA Ref : 3.6


parallel

EASA Ref : 3.6


PARALLEL DC CIRCUIT

2 or more components are connected side by side with each other.

if any one fails than the others will still be operational

all components can be controlled individually

EASA Ref : 3.6


EASA Ref : 3.6


EASA Ref : 3.6


When the series circuits and the parallel circuits are connected together,

they are said to be a combination.

EASA Ref : 3.6


OHM’S LAW

the current passing thru’ a conductor from one terminal to another is directly proportional to the PD across the 2 terminals and inversely proportional to the resistance of the conductor between the 2 points

it is true only for lower current and voltage

at high current and voltages the law does not apply (due to heat)

Formula:

I = V/R

EASA Ref : 3.6


sometimes the potential difference is also known as the voltage drop, abbreviated as E or U instead of V

when 1 amp of current flows thru’ an ohm resistor with 1 volt is known as one volt per ampere.

EASA Ref : 3.6


Figure 54 :Ohm’s Law

EASA Ref : 3.6


Using the equation

when 2 variables are known, the 3rd variable can be calculated.

voltage = current x resistance

current = voltage / resistance

resistance = voltage / current

EASA Ref : 3.6


Figure 55 : Solving Circle

EASA Ref : 3.6


– To find resistance:

R = V / I

= 6V / 2A

= 3 Ω

EASA Ref : 3.6


I = E / R

= 1.5V / 10Ω

= 0.15 Amp

= 150mA

EASA Ref : 3.6


ANALOGY:

E = I X R (constant)

(constant) E = I X R

(constant)

E = I X R

EASA Ref : 3.6


EASA Ref : 3.6


KIRCHHOFF’S LAW

KIRCHHOFF’S LAW IS DIVIDED INTO 2

- CURRENT LAW

- VOLTAGE LAW

KIRCHHOFF’S CURRENT LAW = KIRCHHOFF’S JUNCTION LAW = KIRCHHOFF’S FIRST LAW

STATES:

THE ALGEBRAIC SUM OF CURRENT INTO ANY JUNCTION IS ZERO

(This also means that the sum of current flowing into a junction equals the sum of current flowing out of the junction)

EASA Ref : 3.6


i1

i6

i2

i3

i4i5

SUM:

i1 + i2 +i4 + i5 = i3 + i6 => 5A + 5A + 5A + 4 A = 8A + 11A => 19A = 19A

ALGEBRAIC:

i1 + i2 - i3 + i4 + i5 - i6 = 0 => 5A + 5A -8A + 5A + 4A - 11A =0 => 0 = 0

i1=5amp, i2=5amp, i3=8amp, i4=5amp, i5=4amp, i6=11amp

OUT FLOWING

IN FLOWING

EASA Ref : 3.6


– KIRCHHOFF’S CURRENT LAW

EASA Ref : 3.6


KIRCHHOFF’S VOLTAGE LAW

STATES:

THE ALGEBRAIC SUM OF THE VOLTAGE (POTENTIAL DIFFERENCES) IN ANY LOOP MUST EQUAL ZERO

VR1 + VR2 + VR3 = 18 V => 6V + 6V + 6V = 18V => 18V = 18V => 0 = 0

R1

R2

R3

18V

6V 6V 6V

2K 2K 2K

3 mA

_ +++ _ _

EASA Ref : 3.6


EASA Ref : 3.6


EASA Ref : 3.6


EASA Ref : 3.6


SIGNIFICANCE OF THE INTERNAL RESISTANCE OF A SUPPLY

NEW BATTERIES WITHOUT INTERNAL RESISTANCE WILL PRODUCE AN EMF THAT IS EQUAL TO THE PD.

WHEN THE RESISTANCE OF THE ELECTOLYTE INCREASES THE PD WILL DECREASE

AS THE INTERNAL RESISTANCE INCREASES EVEN MORE, THE VOLTAGE DROP WITHIN THE BATTERY INCREASES EVEN MORE.

EASA Ref : 3.6


EX:

NEW BATTERY VOLTAGE = 12V AND THE INTERNAL RESISTANCE = 1Ω. THE LOAD TAKES UP 0.5 Amp. WHAT IS THE INTERNAL VOLTAGE DROP?

INT. VOLT DROP = 0.5 Amp X 1 Ω = 0.5 V AND THEREFORE, THE TERMINAL VOLTAGE = 12V – 0.5 V = 11.5V

FORMULA:

V = E – (I X r)

BULB

E = 12 VOLTS

r = 1 Ω

I =0.5 Amp

EASA Ref : 3.6


EASA Ref : 3.6


RESISTORS and RESISTANCE

COMES IN MANY

- SHAPES

- SIZES

- VALUES

- WATTAGES

RESISTANCE / RESISTORS ( EASA Ref : 3.7 )


SYMBOLS

EASA Ref : 3.7


SI UNIT for RESISTANCE – Ohm

1 OHM = 1 VOLT OF PRESSURE THAT CAN PUSH 1 AMP OF CURRENT THRU’ A RESISTOR IN A SECOND

181 AMP OF CURRENT = 6.24150629 X 10 ELECTRONS PER SEC

MULTIPLES:Ex:

1K Ω = 1000 Ω

1M Ω = 1000000 Ω = 1 X 10 6 Ω170K Ω =170000 Ω1M5 = 1500000 Ω

SI => Systeme international d’unites or International system of unitBody responsible => bureau international des poits et mesures (BIPM)

EASA Ref : 3.7


EASA Ref : 3.7


IF A RESISTOR HAS A NUMBER SUCH AS 10, 15 or 110 , IT MEANS THAT IT IS

10 Ω 15 Ω 110 Ω or 10R 15R AND 110R

R CAN ALSO BE REPRESENTED BY THE LETTER E. i.e: 10R 15R AND 110R. IT CAN BE REPRENENTED BY 10E 15E AND 110E

1.1 = 1E1 or 1R1 2.5 = 2E5 or 2R5 9.7 = 9E7 or 9R7

EASA Ref : 3.7


IDEAL RESISTOR DOES NOT CHANGE IN RESISTANCE IN THE CIRCUIT IN ANY CIRCUMTANCES.

RESISTANCE VALUES ARE AFFECTED BY THE APPLIED VOLTAGE, CURRENT, TEMPERATURE AND OTHER ENVIRONMENTAL FACTORS

EVERY RESISTOR OPERATES WITHIN THE TOLERENCE IT IS MEANT TO.

IF IT EXCEEDS THE WATTAGE TOLERENCE IT WILL BE DAMAGED

WATTAGE FOR CARBON FILM OR METAL FILM RESISTORS ARE 1/8, 1/4 OR 1/2 WATT

METAL FILM AND CARBON FILM RESISTORS ARE MORE STABLE WITH TEMPERATUE CHANGE THAN CARBON RESISTORS

LARGER ONES ARE HIGHER POWERED ex: WIRE WOUND AND CERAMIC RESISTORS

EASA Ref : 3.7


VARIABLES AFFECTING ELECTRICAL RESISTANCE

LENGTHRESISTANCE INCREASES WITH LENGTH

CROSS-SECTIONAL AREA OF THE WIRERESISTANCE DECREASES WITH INCREASE IN AREA

THE RHO OF THE MATERIALDIFFERENT MATERIALS HAVE DIFFERENT RESISTANCE (CONDUCTIVE ABILITY) RESISTIVITY: DEPENDS ON THE MATERIALS ELECTRICAL STRUCTURE AND ITSTEMPERATURE

TEMPERATUREMOST MATERIALS USED AS CONDUCTORS INCREASE IN RESISTANCE VALUE AS TEMPERATURE INCREASES. BUT THERE ARE MATERIALS THAT THEIR RESISTANCE DECREASE AS TEMPERATURE INCREASES

EASA Ref : 3.7


RESISTIVITY

EASA Ref : 3.7


LOWER RESISTIVITY =>HIGHER CONDUCTIVITY => HIGHER ELECTRON FLOW

HIGHER RESISTIVITY => LOWER CONDUCTIVITY => LESS ELECTRON FLOW

TEMPERATURE:

EFFECTS RESISTANCE THE MOST

MOST CONDUCTORS INCREASE IN RESISTANCE WITH INCREASE IN

TEMPERATURE

CARBON DECREASES,

CONSTANTAN AND MANGANIN CHANGES VERY LITTLE WITH

TEMPERATURE.

EASA Ref : 3.7


TEMPERATURE COEFFICIENT:

with the increase of the temp. by 1 degree from 0 degree causes one ohm to be increases in a conductor is known as temperature coefficient.

when the resistance increases with the increase in temperature it is known as positive temperature coefficient. Ex: silver, aluminum and copper

when the resistance decreases with the increase of temperature is known as negative temperature coefficient ex: insulators, semiconductors and thermistors

manganin and constantan changes very little over their working temperature

EASA Ref : 3.7


SPECIFIC RESISTANCE (RESISTIVITY)

THE RESISTANCE OFFERED BY A UNIT VOLUME. i.e *CIRCULAR-MIL-FOOT or

CENTIMETER CUBE, THAT RESIST CURRENT FLOW IS KNOWN AS SPECIFIC RESISTANCE

RESISTIVITY IS THE RECIPROCAL OF CONDUCTIVITY

FORMULA:

R = ρ L / A

(ρ – specific resistance in ohms per circular mil foot, L – length in feet and A –

circular area in circular mils)

* Circular mils => 1 thousandth of an inch

EASA Ref : 3.7


SELECTION OF WIRE

- IF THE PROPER WIRE IS NOT SELECTED, THERE CAN BE A SEVERE DAMAGETO AIRCRAFT OR OTHER EQUIPMENT

EX: IF THE SUPPLY IS 28VDC AND THE LOAD REQUIRES A MIN. OF 26VDC WITH 5 AMP, WHAT IS THE MAXIMUM RESISTANCE THE WIRE CAN HAVE (2 WAYS)?

R = E / I = 2V/5A = 0.4Ω

IF THE LENGTH OF THE WIRE IS 20FT LONG AND THE RHO FOR STEEL IS 100 Ohm – cmil / ft , what is the area?

A = ρ X L = 100 Ω-cm/ft X 2O = 5000cmilR 0.4

EASA Ref : 3.7


EASA Ref : 3.7


Ex 1: IN AN ALUMINUM WIRED CIRCUIT, AL 000 SWG IS USED. THE Rho OF THIS MATERIAL IS 0.920 Ω – cmil/ft AND WITH AN AREA OF 168872 cmil. THE LENGTH OF THE WIRE IS 20 ft. WHAT IS THE RESISTANCE OF THIS WIRE?

R = ρ L = 0.920Ω-cmil/ft X 20ft = 108.958 µΩ

A 168872 cmil

Ex 2: IN AN ALUMINUM WIRED CIRCUIT, AL 6 SWG IS USED. THE RESISTANCE IS 641 µΩ, AREA IS 28280 cmil AND THE LENGTH IS 30 ft. WHAT IS THE Rho OF THIS MATERIAL.

ρ = R X A = 641 µΩ X 28280cmil = 0.60425 Ω-cmil/ft

L 30ft

EASA Ref : 3.7


EASA Ref : 3.7


Figure 68

EASA Ref : 3.7


BUSBAR (ALUMINUM)

3CM

4CM125CM

AREA = WIDTH X HEIGHT A = 4CM X 3CM = 12 CM²

SPECIFIC RESISTANCE:

R = p L / A

2.65 µΩ-cm x 125cm / 12cm²

R = 27.604 µΩ

EASA Ref : 3.7


RESISTOR COLOUR CODE

4 COLOUR BANDS

- 3 BAND FOR OHMS => 1st AND 2nd BANDS FOR VALUE

THE 3rd BAND AS MULTIPLIER ( NUMBER OF ZEROES )

- 4th BAND FOR TOLERANCE 5%, 2% AND 1%

EASA Ref : 3.7


EASA Ref : 3.7


4 CODED RESISTORS

- 1001 = 100 + 0 = 1000 Ω = 1K Ω

1002 = 100 + 00 = 10000 Ω = 10K Ω

- 1003 = 100 + 000 = 100000 Ω = 100K Ω

- 4992 = 499 + 00 = 49900 Ω = 49.9K Ω

EASA Ref : 3.7


EASA Ref : 3.7


5 BAND RESISTORS

FOR MILITARY USE

- 1st, 2nd AND 3rd BANDS DETERMINE THE FIRST 3 DIGITS

- 4th BAND IS THE MULTIPLIER

- 5th BAND IS THE TOLERANCE

EASA Ref : 3.7


TOLERANCE FOR 5 CODED RESISTORS (BS 18520)

B = 0.1 %

C = 0.25 %

D = 0.5 %

F = 1 %

G = 2 %

J = 5 %

K = 10 %

M = 20 %

EASA Ref : 3.7


CYLINDRICAL SMD RESISTOR

- 1st, 2nd AND 3rd DIGITS ARE THE VALUE

- 4th BAND IS THE MULTIPLIER

- 5th BAND IS THE TOLERANCE

- 6th TEMPERATURE COEFFICIENT

EASA Ref : 3.7


SURFACE MOUNTED DEVICE

- THE SPACE AVAILABLE ON THE DEVICE IS LIMITED

- 3 DIGIT CODE HAS A 5% TOLERANCE

- 4 DIGIT CODE HAS A 1% TOLERANCE

- CERTAIN CIRCUITS TOLERANCES IS NOT IMPORTANT

- CERTAIN CIRCUITS TOLERANCE IS IMPORTANT

563

EASA Ref : 3.7


WATTAGE RATINGS

WHEN CURRENT FLOWS THROUGH A RESISTOR, IT HEATS UP.

IF THE TEMPERATURE EXCEEDS A CERTAIN CRITICAL VALUE

THE RESISTOR WILL BE DAMAGED

WATTAGE RATINGS OF A RESISTOR

THE POWER THE RESISTOR CAN DISSIPATE OVER A LONG PERIOD

OF TIME

THEY ARE PRINTED ONLY ON LARGE RESISTORS

EASA Ref : 3.7


EASA Ref : 3.7


WATTAGE RATING

-1/16W, 1/8W, 1/2W, 1/4W RESISTORS ARE USED FOR ELECTRONICS

-1W, 2W, 5W, 10W etc ARE USED FOR HEAVY DUTY CIRCUITS LIKE THE

POWER SUPPLY.

-IF REQUIRED A SMALL WATTAGE RESISTOR CAN BE REPLACE WITH A

LARGER WATTAGE RESISTOR FOR THE SAME VALUE.

EASA Ref : 3.7


WATTAGE CALCULATION:

1. P = V x I 2. P = V² / R 3. P = I ² x R

IF THE VOLATGE ACROSS A 250R RESISTOR IS 6 VOLTS, BATTERY POWER IS 15V, WHAT IS THE POWER DESSIPATED BY THIS RESISTOR?

P = V² / R = 6² / 250 = 36 / 250 = 0.144 Watts = 144mW

(RESISTOR REQUIRED IS ¼ Watt RESISTOR)

NORMALLY POWER DESSIPATION IS CALCULATED WITH THE BATTERY POWER

P = V² / R = 15² / R = 225 / 250 = 0.9Watts = 900mW

(RESISTOR REQUIRED IS 1 Watt RESISTOR)

EASA Ref : 3.7


RESISTORS CIRCUIT PATTERNS

RESISTORS ARE FOUND IN ALL ELECTRONIC CIRCUITS IN THE FORM OF:

-SERIES

-PARALLEL

-SERIES PARALLEL COMBINATION

EASA Ref : 3.7


SERIES CONFIGURATION

-CURRENT IS CONSTANT BUT THE VOLTAGE IS VARIABLE ACROSS EACH

RESISTOR

-THE RESISTORS ARE FITTED ONE AFTER THE OTHER

- ELECTRONS FLOW ONLY IN ONE DIRECTION

-THE TOTAL RESISTANCE IS THE SUM OF ALL THE RESISTORS

R1 + R2 + R3 + …………….Rn

EASA Ref : 3.7


EASA Ref : 3.7


SERIES CONFIGURATIONV1=5V

V2=8V

V3=7V

I=1A

R1 = V1/I = 5V/1A = 5 Ohms R2 = V2/I = 8V/1A = 8Ohms R3 = V3/I = 7V/1A = 7 Ohms

RT = 30 Ohms R4 = 30 – 5 – 8 – 7 = 10 Ohms THEREFORE V4 = I x R4 = 1 x 10 = 10V

THE TOTAL VOLTAGE IS = 5 + 8 + 7 + 10 = 30Volts

EASA Ref : 3.7


PARALLEL CONFIGURATION

-BRANCHED OUT FROM A SINGLE NODE AND RECOMBINE IN ANOTHER POINT

-CURRENT DIVIDES BETWEEN THE BRANCHES WHEREAS THE VOLTAGE IS THE SAME FOR ALL BRANCHES

1 = 1 + 1 + 1 +…………. 1

Req R1 R2 R3 Rn

-symbol for parallel is //

EASA Ref : 3.7


FORMULA

-SINCE R1 // R2, Req = R1 x R2

R1 + R2

-IN A PARALLEL CCT THE TOTAL RESISTANCE IS LESS THAN THE SMALLESTRESISTOR.

EASA Ref : 3.7


PARALLEL CONFIGURATION

EASA Ref : 3.7


EMF = 12 V.

SINCE VOLTAGE IS THE SAME IN ALL BRANCHES OF A PARALLEL CCT, R1, R2 AND R3 GETS 12V EACH

V1 = V2 = V3 = 12V Ohms LAW STATES THAT I = V/R

THEREFORE I1 = 12/2 =6A I2 = 12/3 = 4A I3 = 12/6 = 2A

KIRCHHOFF’S LAW STATES: CURRENT INTO A JUNCTION IS EQUAL TO THE CURRENT OUT OF THE JUNCTION.

IT =I1+I2+I3 = 6+4+2 = 12A

EASA Ref : 3.7


COMBINATION CONFIGURATION (SERIES PARALLEL)

FORMULA:

Req = (R1 // R2) + R3

= R1xR2 +R3

R1+R2

EASA Ref : 3.7


COMBINATION

RAB = R1 + R2 (SERIES)

RTOTAL= RAB x R3 (PARALLEL)

RAB + R3

EASA Ref : 3.7


1/RAB = 1/R1 + 1/R2 1/RCD = 1/R4 + 1/R5 RTOTAL =RAB +R3 + RCD

EASA Ref : 3.7


COMBINATION

1/RAB = 1/R1 + 1/R2= 1/10 + 1/4.0= 0.35

Therefore RAB=1/0.35= 2.857 Ohms

1/RCD = 1/R4 +1/R5= 1/8 +1/1

1.125Therefore RCD = 1/1.125

= 0.889 Ohms

EASA Ref : 3.7


RTOTAL = RAB + R3 + RCD

= 2.857 + 3 + 0.889

= 6.7 Ohms

EASA Ref : 3.7


EXAMPLE 2RAB = R1 +R2

= 1 + 2 = 3 Ohms

REF = R4 + R5

= 4 + 5

= 9 Ohms

EASA Ref : 3.7


1/RTot = 1/RAB + 1/R3 + 1/REF

1/RTot = 1/3 + 1/3 + 1/9

RTot = 1.286 Ohms

EASA Ref : 3.7


FIXED RESISTORS

-USED TO REDUCE CURRENT FLOW IN SOME PARTS OF A CIRCUIT

-THE CURRENT AND VOLTAGE IS CONSTANT AT THE OUTPUT IF THE INPUT

IS KEPT CONSTANT

-COMES IN DIFFERENT VALUES

- USED IN MOST ELECTRONIC EQUIPMENT AND ELECTRICAL DEVICES

INPUT OUTPUT

EASA Ref : 3.7


TOLERANCES AND LIMITATIONS

RESISTANCE IS PROPORTIONAL TO LENGTH AND Rho OF THE MATERIAL AND

INVERSE TO THE X-SECTIONAL AREA

-OHM’S LAW APPLIES

-3 FACTOR WHEN SELECTING A RESISTOR:

-TOLERANCE

-POWER RATING

-STABILITY

CONDUCTING MATERIAL

RESISTING MATERIAL

CONDUCTING MATERIAL

EASA Ref : 3.7


TOLERANCE

- SPECIFIES THE MAXIMUM AND MINIMUM VALUE OF RESISTANCE

- A RESISTOR VALUE IS 1K Ohm AND HAS A TOLERANCE OF 20%. THEREFORE THE ACTUAL VALUE OF THE RESISTOR WILL BE WITHIN THE RANGE OF:

20% OF 1000 = 200 Ohms THEREFORE THE VALUE IS WITHIN 800 Ohms AND 1200Ohms

TOLERANCE

EASA Ref : 3.7


POWER RATING

- INDICATES THE MAXIMUM POWER THE RESISTOR CAN HANDLE AT ROOM TEMPERATURE

- SHOULD NOT EXCEED THE RATING OR ELSE IT WILL BE DAMAGED FOREVER

- RATING CAN BE OF MANY VALUES Ex: ¼ W, ½ W, 1 W, 2W etc

- BIGGER THE RESISTOR, THE LARGER IS THE RATING

POWER RATING

2 WATTS 1/4 WATT

EASA Ref : 3.7


STABILITY

-THE ABILITY TO MAINTAIN THE RESISTANCE OF THE CIRCUIT

-CHANGES VERY LITTLE WITH CHANGE OF TEMPERATURE

-IMPORTANT IN ELECTRONIC PRECISION CIRCUITS

EASA Ref : 3.7


CONSTRUCTION METHODS

LOW POWER RESISTORS

CARBON FILM RESISTOR IS MADE OF GRAPHITE CUT INTO BLOCKS OR WRAPPED OR GRAFTED INTO REQUIRED SHAPE

X-SECT. DETERMINES THE POWER RATING

TYPES OF CARBON FILM RESISTORS

STANDARD FILM – BARREL OR CIRCULAR TYPE WITH PINS ON THE OPPOSITE SIDESCHIP TYPE – COMES UP TO 6 LAYERSNETWORK TYPE – CAN HAVE 12 RESISTORS IN 1 COMPACT SPACE.

MAX VALUE 10 M Ohms. TOLERANCE +- 5%. RATINGS 0.125 W TO 1 WATT WITH GOOD STABILITY

EASA Ref : 3.7


EASA Ref : 3.7


HIGH POWER RESISTORS

- POWER RATING OF 5 TO 50 WATTS

-USED IN POWER SUPPLIES AND AMPLIFIERS

GETS VERY HOT

USES RESISTANT WIRE WRAPPED WITH CERAMIC MATERIAL

SYMBOL IN CIRCUIT IS THE SAME AS OTHER CONVENTIONAL RESISTORS

LOW TOLERANCE AND HIGH STABILITY

MADE OF MAGANIN, NICHROME OR CONSTANTAN WIRE WOUND ON AFORMER AND A PROTECTIVE COATING

VALUES - 1 Ohm TO 25K Ohms, POWER RATING O- 10 TO 20 WATTS

EASA Ref : 3.7


EASA Ref : 3.7


VARIABLE RESISTORS

RHEOSTATS

-2 TERMINALS ( 1 MOVEABLE TERMINAL AND THE OTHER ONE CONNECTED TO THE TRACK END

-MOVABLE TERMINAL PROVIDES THE VARIED RESISTANCE BY TURNING A SPINDLE

-USED TO VARY CURRENT IN A CIRCUIT. Ex : VARY THE BRIGHTNESS OF ALAMP OR TO VARY THE CHARGING OF A CAPACITOR

-2 TERMINALS FOR RIGIDITY OF WHICH 1 IS FOR INPUT. WIPER IS THE OUTPUT

-USED WITH HIGH POWERED DEVICE > ½ WATT

EASA Ref : 3.7


POTENTIOMETER

-HAS 3 TERMINALS ( 2 FIXED AND 1 SLIDING TERMINAL )

-USED TO VARY VOLTAGES. Ex: VARY THE VOLUME OF AN AMPLIFIER, TO

SET AS A PRESET TO A SENSOR

-VOLTAGE CAN BE TAPPED ACROSS THE 2 FIXED TERMINALS

-OUTPUT VOLTAGE CAN BE VARIED WITH THE WIPPER ROTATION FROM 0

UP TO THE SUPPLY VOLTAGE

EASA Ref : 3.7


EASA Ref : 3.7


PRESETS

-VARIABLE RESISTORS BUT IN A MINIATURE FORM

-MOUNTED ON THE CIRCUIT BOARD DIRECTLY

-USED IN ALARM TONE SETTING, SENSITIVITY OF LIGHT SENSITIVE CIRCUITS ETC

-DOES NOT HAVE SPINDLES BUT VALUE ADJUSTED WITH A SMALLSCREWDRIVER

-CHEAP AND VERY ACCURATE

-CAN BE 1 TURN TYPE OR MULTI TURN (10X) TYPE FOR FINE ADJ.

EASA Ref : 3.7


Figure 87

EASA Ref : 3.7


POTENTIOMETER CONSTRUCTION

-2 TYPES:

COATED TYPE

-STRIP (ARC) OF INSULATING MATERIAL WITH A SLIDER MOVING OVER THE STRIP WHICH INCREASES AND DECREASES THE RESISTANCE AS IT MOVES OVER IT. RESISTANCE IS EITHER LINEAR, LOGARITHMIC (COMMONLY USED), INVERSE-LOGARITHMIC etc. USED FOR BALANCE, TONE AND VOL CONTROLS

COILED TYPE

-CONDUCTIVE WIRE WOUND OVER AN INSULATOR. BY MOVING THE SLIDER THE OUTPUT IS VARIED ACCORDINGLY. USED IN ACCURATE AND CONSTANCY CIRCUITS FUNCTIONS. USED FOR HIGH CURRENT APPLICATION WITH HIGHER POWER DISSIPATION

EASA Ref : 3.7


RESISTANCE VALUE,TOLERANCE AND WATTAGE

- RANGES FROM E6 SERIES = 1,2.2 AND 4.7. NORMALLY USED IN ELECTRONICS (1K, 2K, 5K, 10K, 1M, 10M, 50M etc)

- TOLERANCES RANGE FROM 30%, 20%, 10%, AND 5% (COILED POTS)

- COMES IN DIFFERENT SHAPES AND SIZES AND WATTAGE FROM ¼ WATTS (COATED POTS FOR VOLUME CONTROL) TO 10s OF WATTS (REGULATING HIGH

CURRENT )

EASA Ref : 3.7


EASA Ref : 3.7


POTENTIOMETERS

SYMBOL

RULER POTENTIOMETER

STEREO POTENTIOMETER

COILED POT

(20W RHEOSTAT) REGULATES

CURRENT

MONO POTENTIOMETER

EASA Ref : 3.7


TRIMMER POTENTIOMETERS (TRIMMERS)

-GIVES VERY ACCURATE VOLTAGE AND CURRENT VALUES

-ADJUSTABLE BY ADJ. SCREWS THAT HAS A SLIDING CONTACT

-WATTAGE RANGE 0.1 TO 0.5 WATTS

-NORMALLY USED FOR FINE ADJ. WITH MANY TURNS OF THE SCREW

EASA Ref : 3.7


EASA Ref : 3.7


OPERATION AND USE OF POTENTIOMETER (POTS) AND RHEOSTAT

-HAS 3 TERMINALS USED FOR VOLTAGE REGULATORS AND ELECTRONIC CIRCUITS (VOLUME CONTROL) AND VOLTAGE DIVIDERS OR VARIABLE RESISTOR (USES 2 TERMINALS)

-POTENTIOMETER CONVERTED TO VARIABLE RESISTORS ARE ALSO KNOWN AS RHEOSTAT (ONLY 2 TERMINALS ARE USED)

EASA Ref : 3.7


EASA Ref : 3.7


CONVERSION OF A POT TO RHEOSTAT

-ONLY 2 TERMINAL ARE USED OF WHICH ONE IS THE WIPER

-THE RESISTANCE CHANGES WITH THE POSITION OF THE WIPER

-IF END TERMINALS ARE USED, IT BEHAVES AS A FIXED RESISTOR

EASA Ref : 3.7


EASA Ref : 3.7


EASA Ref : 3.7


MOTOR CONTROLS

-IF A BULB IS CONNECTED TO THE 2 TERMINALS (ONE WIPER) IN SERIES AND THE RESISTANCE IS VARIED, THE BULB WILL CHANGE IN BRIGHTNESS.

-IF A MOTOR IS CONNECTED TO THE 2 TERMINALS IN SERIES, AND THE RESISTANCE IS VARIED, THE SPEED OF THE MOTOR WILL VARY BUT WITH POWER WASTAGE AT THE RHEOSTAT

-NORMALLY WHEN THE POT IS USED AS A RHEOSTAT THE UNUSED TERMINAL IS CONNECTED TO THE WIPER TO PREVENT COMPLETE OPEN CIRCUIT

EASA Ref : 3.7


MOTOR SPEED CONTROLLER

EASA Ref : 3.7


SPEED CONTROL

EASA Ref : 3.7


WIPER TERMINAL DISCONNECTED

EASA Ref : 3.7


THERMISTORS

-RESISTOR THAT SENSES TEMPERATURE

-MADE OF SINTERED SEMICONDUCTOR MATERIAL

-2 TYPES OF THERMISTORS

- POSITIVE COEFFICIENT (PTC) – RESISTANCE INCREASES WITH TEMPERATURE. USED IN TV DEMAGNETIZING COIL AND POLYSWITCH AS SELF REPAIR FUSE.

- NEGATIVE COEFFICIENT (NTC) – RESISTANCE DECREASES AS TEMPERATURE INCREASE. USED IN TEMPERATURE DETECTORS AND MEASURING INSTRUMENTS

EASA Ref : 3.7


-NTC, MADE OF OXIDES OF NICKEL, MANGANESE, COPPER, COBOLT AND OTHER SIMILAR MATERIAL.

-COMES IN THE FORM OF BEADS, RODS OR DISC

-USED IN AIRCRAFT AS TEMP SENSORS. Ex; IN HEATING, AIRCONDITIONING AND BATTERY SYSTEMS

-PTC, MADE OF BARIUM TITANATE TO PREVENT OVER CURRENT IN CIRCUIT DUE TO TEMP RISE

EASA Ref : 3.7


BENEFITS OF TERMISTORS

-ACCURATE BUT WORKS WITH A TEMP RANGE OF 0 TO 100 DEGREES C

-STABLE THEREFORE IS NOT EFFECTED BY AGING.

EASA Ref : 3.7


VOLTAGE DEPENDENT RESISTORS (VARISTOR)

-THE RESISTANCE IS INVERSLY PROPOTIONAL TO VOLTAGE

-MADE OF SILICON CARBIDE

-USED IN :

- VOLTAGE STABILIZATION CIRCUITS

- TRANSIENT VOLTAGE SUPPRESSION

- SWITCH CONTACT PROTECTION

-CONNECTED ACROSS THE PROTECTED DEVICE DUE TO SURGE CURRENT

EASA Ref : 3.7


METAL OXIDE VARISTOR (MOV)

-CONTAINS CERAMIC MASS OF ZINC OXIDE GRAINS IN A MATRIX OF OTHER METAL OXIDES. i.e. BISMUTH, MANGANESE AND COBALT.

-IT IS SANDWICHED BET. 2 METAL PLATES (ELECTRODES) LIKE THE DIODEJUNCTION

- CURRENT FLOWS ONLY IN ONE DIRECTION

-USED FOR SHORT CIRCUIT PROTECTION

EASA Ref : 3.7


WHEATSTONE BRIDGE CONSTRUCTION

-CONSISTS OF 4 RESISTORS. i.e. 2 VOLTAGE DIVIDERS

-BOTH DIVIDERS HAVE THE SAME VOLTAGE SUPPLY

-A GAGE IS CONNECTED BETWEEN THE 2 DIVIDERS TO DETECT THE CURRENT WITH A GALVANOMETER

-BALANCED CONDITION = VOLTAGE AT BOTH DIVIDERS ARE EQUAL. THEREFORE NO CURRENT FLOWS THRU’ THE METER.

-UNBALANCED CONDITION= VOLTAGE IS NOT THE SAME IN BOTH DIVIDERS. THEREFORE CURRENT FLOWS THRU’ THE METER.

EASA Ref : 3.7


FIGURE 97 : WHEATSTONE BRIDGE

EASA Ref : 3.7


v

I

B

D

C

A

27K

27K 2.7K

I3I4

I2I1

WHEATSTONE BRIDGE OPERATION

RXR3

R2R1

EASA Ref : 3.7


APPLICATION OF WHEATSTONE BRIDGE

-TO MEASURE THE INTERNAL RESISTANCE ACCORDANCE TO PRESSURE OR TEMPERATURE STRAIN

-LOCATING BREAKS IN POWER LINES

-ACTING AS TEMP. CONTROL DEVICE

-MEAUREMENT OF ACFT WEIGHT AND C of G POSITION

-MEASURING ELECTRICAL VALUES IN INSTRUMENTS

EASA Ref : 3.7


POWER AND ENERGY

-VOLTAGE DROPS ACROSS A RESISTOR BUT DOES NOT PASS THRU’

-CURRENT PASSES THROUGH A CIRCUIT BUT NOT ACROSS

-ENERGY IS THE CAPABILITY OF DOING WORK = ELECTRICAL ENERGY IS USED TO BE CONVERTED TO LIGHT OR HEAT ENERGY. ANOTHER IS THE MOVEMENT OF ELECTRIC MOTORS TO DO SOMETHING

-TYPES MECHANICAL ENERGY

-POTENTIAL ENERGY-KINETIC ENERGY

POWER ( EASA Ref : 3.8 )


POTENTIAL ENERGY

A BODY HAS BY VIRTUE OF ITS POSITION, POTENTIAL ENERGY

EASA Ref : 3.8


EASA Ref : 3.8


KINETIC ENERGY

-IF THE BOX IS KNOCKED OF THE TABLE, THE BOX HAS KINETIC ENERGY WHILE MOVING THRU’ SPACE.

-POTENTIAL AND KINETIC ENERGY ARE CAPABLE OF DOING WORK

ELECTRICAL ENERGY – JOULE(WATT/SEC )

- POWER IS = V X I BUT WORK IS DONE OVER A PERIOD OF TIME. THEREFORE, ENERGY = VOLTAGE X AMPERE X TIME

W = U X I X t

-CAN BE EXPRESSED IN Watt – Seconds (Ws) OR Watt – Hours (Wh)

EASA Ref : 3.8


KINETIC ENERGY

EASA Ref : 3.8


POWER

-RATE OF ENERGY BEING USED OR WORK DONE WITH RESPECT TO TIME

-POWER IS = ENERGY / TIME

-SINCE ENERGY IS V X I X t, POWER = (V X I X t) / t

-THEREFORE POWER IS = V X I, P = I²R, P = V² / R

EASA Ref : 3.8


– POWER TRANSFER

EASA Ref : 3.8


MAXIMUM POWER TRANSFER

- WHEN THE Ri = RLOAD , MAX POWER IS TRANSFERRED

- THIS CONDITION IS KNOWN AS RESISTANCE MATCHING

- P = V X I , I X R X I, I²R

EASA Ref : 3.8


CAPACITORS AND CAPACITANCE

OPERATION AND FUNCTION

-A DEVICE THAT STORES ELECTRICAL ENERGY IN THE FORM OF ELECTRIC FIELD BETWEEN 2 CONDUCTING BODIES

USES OF CAPACITORS

-DC BLOCKER

-STORES MEMORY IN COMPUTER CHIPS

-STORE CHARGE FOR CAMERA FLASH

-TUNED CIRCUIT IN RADIOS

CAPACITANCE / CAPACITORS ( EASA Ref : 3.9 )


DESCRIPTION OF A CAPACITOR

CONSISTS OF :

-2 PLATES (1 NEG. AND 1 POS.)

-1 DIELECTRIC

WHEN POWERED:

-THE NEG. PLATE GAINS ELECTRONS

-THE POS. PLATE LOSES ELECTRONS

- ONCE THE PLATES ARE AT THE SOURCE VOLTAGE, THE CHARGING

STOPS

EASA Ref : 3.9


COMES IN:- DIFF. SIZES

-DIFF. ARRANGEMENT OF PLATES-DIFF. TYPES OF DIELECTRIC

DIELECTRICS MADE OF:-PAPER-CERAMIC-AIR-MICA-ELECTROLYTIC MATERIALS

TYPES:-FIXED-ADJUSTABLE

EASA Ref : 3.9


CAPACITORS:

EASA Ref : 3.9


EASA Ref : 3.9


VARIABLE CAPACITOR

VARIABLE CAPACITOR

EASA Ref : 3.9


CAPACITOR

EASA Ref : 3.9


- AS THE CHARGE ON THE PLATES INCREASE, THE ELECTRIC FIELD ALSO INCREASES

-THE ELECTRIC FIELDS CREATES A POTENTIAL DIFFERENCE BET. THE PLATES

V = E x d

or

E = V / d

or

d = E / V

EASA Ref : 3.9


PARALLEL PLATES

EASA Ref : 3.9


• SYMBOLS

EASA Ref : 3.9


ANALOGY

Q = V x C

EASA Ref : 3.9


DIELECTRIC MATERIALS

-THE DIELECTRIC IS AN INSULATOR, IT PREVENTS DC CURRENT FROM FLOWING BET. THE PLATES

-IT STORES ELECTROSTATIC CHARGES

-DIELECTRIC’S ABILITY TO SUPPORT ELECTROSTATIC FORCES IS DIRECTLY PROPORTIONAL TO THE DIELECTRIC CONSTANT

EASA Ref : 3.9


EASA Ref : 3.9


CAPACITANCE

-ELECTRONS ARE REMOVED FROM 1 PLATE AND DEPOSITEDON THE OTHER.

-AS THIS GOES ON, THE CHARGE INCREASES

-THIS CHARGE IS STORED IN THE DIELECTRIC IN THE FORM OF ELECTRIC FIELDS

-THEREFORE THE PLATES POSSESES A CERTAIN CAPACITANCE

-CAPACITANCE IS THE CHARGE CAUSED BY A UNIT OF POTENTIAL (V) ON A CONDUCTOR (PLATE)

-UNIT FOR CAPACITANCE IS THE FARADS (F)

EASA Ref : 3.9


DEFINATION:

-1 FARAD IS THE CONDUCTANCE OF A CONDUCTOR (PLATE) WITH A POTENTIAL DIFFERENCE OF 1 VOLT WHEN IT CARRIES A CHARGE OF 1 COULOMB (6.28 x 10¹⁸ ELECTRONS).

-1 FARAD CAPACITOR STORES 1 COULOMB OF CHARGE WHEN A POTENTIAL OF 1 VOLT IS APPLIED ACROSS THE TERMINALS OF THE CAPACITOR

CAPACITANCE (C) = CHARGE (Q) / VOLTAGE (V)

CHARGE = CAPACITANCE x VOLTAGE

VOLTAGE = CHARGE / CAPACITANCE

(Q = QTY OF STORED ELECTRICAL CHARGE IN COULOMB; C = CAPACITANCE IN FARADS AND V = POTENTIAL DIFFERENCE IN VOLTS)

EASA Ref : 3.9


FARADS (F)

-1 FARAD IS TOO LARGE

-THEREFORE SMALLER VALUE ARE USED:

µ (MICRO) MEANS 1 MILLIONTH OF A FARAD

n (NANO) MEANS 1 THOUSAND MILLIONTH => 1000nF = 1 µf

P (PICO) MEANS 1 MILLION MILLIONTH => 1000 pF = 1 nF

EASA Ref : 3.9


PERMITTIVITY OF SPACE (ABSOLUTE)

ε0 = 8.854 x 10¯¹² F/m

PERMITTIVITY OF DIELECTRIC MATERIAL εr or kε = DIELECTRIC CONSTANT

C = Q/V

OR

C = ε A/d = k ε0 A/d

EASA Ref : 3.9


STORED ENERGY

-WHEN OPPOSITE CHARGES ACCUMULATE ON THE PLATES, THERE WILL BE ELECTRIC FIELDS FORMED. THEREFORE A VOLTAGE IS DEVELOPED

ENERGY STORED = ½ CV² ( JOULES )

-THE CAP. CAN BREAKDOWN IF THE MAX. WORKING VOLTAGE IS EXCEEDED AND THIS IS LIMITED BY THE ELECTRIC FIELD OF THE DIELECTRIC (JOULES OF ENERGY PER CUBIC METER)

Ex: WHAT IS THE ENERGY STORED BY A CAP. OF 20µ F, IF THE VOLTAGE IS 24V.

E = ½ CV ² = ½ x 20µF x 24V²

= 5.7mJ

EASA Ref : 3.9


FACTORS AFFECTING CAPACITANCE

DEPANDS ON 3 FACTORS:

-AREA OF THE PLATES

-DISTANCE BETWEEN THE PLATES

-DIELECTRIC CONSTANT OF THE MATERIAL

C = kε ε0 Ad

EASA Ref : 3.9


AREA

- THE LARGER THE AREA , THE LARGER IS THE CHARGE AND CAPACITANCE

DISTANCE

- THE CLOSER THE PLATES THE STRONGER IS THE ELECTROSTATIC LINES OFFORCE, THEREFORE THE CHARGE STORAGE IS GREATER

DIELECTRIC CONSTANT

- DIELECTRIC IS AN INSULATOR. DIFF. MATERIALS HAVE DIFF. CONSTANT VALUES

- HIGHER THE CONSTANT, HIGHER IS THE INSULATION

EASA Ref : 3.9


EASA Ref : 3.9


DIELECTRIC CONSTANT

EASA Ref : 3.9


ABSOLUTE CONSTANT

-ABSOLUTE CONSTANT = ε0 = 8.854 x 10¯¹² F/m

IF A CAPACITOR HAS AIR AS DIELECTRIC, THE AREA OF THE PLATE IS 2 Sq m AND A DISTANCE OF 1 cm, WHAT IS THE CAPACITANCE?

C = ε0 KA

d

= 8.854 x 10¯¹² F/m (1 x 2)

0.01m

= 1771 pF

EASA Ref : 3.9


C = ε0 KA/d

EASA Ref : 3.9


………… PicoFarads

C = ε0 KA/d

EASA Ref : 3.9


Bakelite 4.8 1 cm

……..picoFarads

0.1 sq m

C = ε0 KA/d

EASA Ref : 3.9


Mica 5.4

…….picoFarads

0.1 cm0.085 sq m

C = ε0 KA/d

EASA Ref : 3.9


THE CAPACITANCE IS DIRECTLY PROPORTIONAL TO THE DIELECTRIC AND THE AREA BUT INVERSELY PROPORTIONAL TO THE DISTANCE

C = ε0 KAd

EASA Ref : 3.9


VOLTAGE RATING

-SELECTION OF CAPACITOR DEPANDS ON:

DESIRED CAPACITANCE IN THE CIRCUITHOW MUCH VOLTAGE THE CAPACITOR CAN HANDLE (WORKING VOLTAGE) IN THE CIRCUIT

-IF THE VOLTAGE RATING IS SMALLER THAN THE REQUIRED VALUE THEN THE CAPACITOR WILL BE DAMAGED AND ARCING WILL TAKE PLACE WITHIN THE CAPACITOR

-IF THIS HAPPENS THAN IT CAN DAMAGE OTHER COMPONENTS

-THICKER THE DIELECTRIC, LOWER IS THE CAPACITANCE

-FREQUENCY INCREASES, THE LOSSES AND HEATING EFFECT INCREASES

WORKING VOLTAGECAPACITANCE

EASA Ref : 3.9


VOLTAGE RATING

-20 VRMS = 28.28V PEAK. THEREFORE A 50 V CAPACITOR WILL BE MOST APPROPRIATE (30V CAP. WILL ALSO DO)

-50 % OF THE RMS VALUE IS VERY SAFE

WORKING VOLTAGECAPACITANCE

ONAS KONAS KONAS KONAS KO

EASA Ref : 3.9


CAPACITOR LOSSES

2 TYPES OF DIELECTRIC LOSSES

HYSTERESIS LOSSES

DUE TO THE RAPID CHANGE IN ELECTRON CHANGE -OVER IN THECIRCUIT. LOSSES DEPANDS ON THE TYPE OF DIELECTRIC

LEAKAGE LOSSES

ALTHOUGH THE DIELECTRIC IS AN INSULATOR, CURRENT CAN STILL PASS THROUGH BUT IN A VERY SMALL AMOUNT. IF THE LEAKAGE IS TOO HIGH, THAN OVER HEATING TAKES PLACE AND IT CANNOT RETAIN THE CHARGE

EASA Ref : 3.9


TYPE, CONSTRUCTION AND FUNCTION

2 TYPE OF CAPACITORS

POLARIZED > ELECTROLYTICUNPOLARIZED > NON ELECTROLYTIC

POLARIZED CAPS HAS HIGHER POWER HANDLING CAPABILITY

MUST BE CONNECTED ACCORDING TO THE POLARITY, OTHER WISE CAN CAUSE BODILY INJURIES

THEY HAVE VERY LARGE VALUES (> 1 MICRO F). VALUE AND WORKING VOLTAGE IS PRINTED ON THE BODY

NOT DAMAGED DUE TO HEAT WHILE SOLDERING

EASA Ref : 3.9


EASA Ref : 3.9


ELECTROLYTIC CAPACITORS

-FIXED CAPACITIVE VALUE

-RANGE FROM 1 TO SEVERAL 1000 MICRO FARADS

-USED IN RECTIFIERS AS SMOOTHING CIRCUIT

-2 DESIGNS OF E – CAPS => AXIAL AND RADIAL (SMALLER)

-WORKING VOLTAGE CAN BE AS LOW AS 6 VOLTS

-CHOOSE THE CAP ACCORDING TO THE POWER SUPPLY

++

+

+

5000 µf 25 v +

KONAS KONAS

1000 µF 50V

KONAS KONAS

EASA Ref : 3.9


E – CAPS

EASA Ref : 3.9


TANTALUM BEAD CAPACITOR

- SPECIAL TYPE OF ELECTROLYTIC CAPACITOR

- HANDLES LOW VOLTAGES ONLY

- SMALL IN SIZE BUT LARGE CAPACITANCE AND EXPENSIVE

- BEAD CAPS ARE PRINTED WITH CAPACITY, VOLTAGE AND POLARITY IN FULL

- OLD TYPE USES COLOUR CODES (BODY, TIP AND SPOT)

EASA Ref : 3.9


CAP CODING

4 and 7 X 1000000

47,000,000 pF = 47µF

with a WV of 35V

EASA Ref : 3.9


COLOUR CODES

SPOT => GREY MEANS X BY 0.01 AND WHITE MEANS X BY 0.1

VALUES OF LESS THAN 10 MICRO F CAN BE READ

THIRD COLOUR STRIPE INDICATES VOLTAGE RATING

YELLOW MEANS 6.3 V

BLACK MEANS 10 V

GREEN MEANS 16 V

BLUE MEANS 20 V

GREY MEANS 25 V

WHITE MEANS 30 V and

PINK MEANS 35 V

EASA Ref : 3.9


BODY 1ST DIGIT

SPOT NUMBER OF ZEROS

TIP 2ND DIGIT

READING IN MICRO FARADS

VOLTAGE RATING

EASA Ref : 3.9


EXAMPLE:

- BLUE, GREY, BLACK AND YELLOW MEANS 68 MICRO F WITH A WORKING VOLTAGE OF 6.3 V

- BROWN, GREEN, WHITE AND PINK MEANS 1.5 MICRO F WITH WORKING VOLTAGE OF 35 V

- YELLOW, VIOLET, GREY AND GREEN MEANS 0.47 MICRO F WITH 10 WORKING VOLTS

EASA Ref : 3.9


UNPOLARISED CAPACITOR

- CAN BE CONNECTED IN EITHER WAY

- ITS ROBUST

- CAN STANDS HEAT DURING SOLDERING EXCEPT FOR THE POLYSTYRENE TYPE

- FROM 50 WORKING VOLTS TO 250 WORKING VOLTS

- 47 MEANS 47 MICRO F = 47000 NANO F

0.1 MEANS 0.1 MICRO F = 100 NANO F

- 4.7 n F CAN ALSO BE STATED AS 4n7

EASA Ref : 3.9


EASA Ref : 3.9


POLYSTYRENE CAPACITOR

- VALUES ARE NORMALLY IN PICOFARADS ( pF)

- CAN BE DAMAGED DUE TO HEAT

- ONLY CERTAIN VALUES ARE POSSIBLE

(E 3 SERIES) 10,22,47 => 100,220,470 =>1000,2200,4700 => 10000,22000,47000

(E 6 SERIES) 10,15,22,33,47,68 => 100,150,220,330,470,680 => 1000,1500,2200, 3300,4700,6800 => 10000,15000,33000,47000,68000

EASA Ref : 3.9


-

READ IN PICOFARADS

EASA Ref : 3.9


MICA SHEET

TIN FOIL PLATES

MICA CAPACITOR

- CAN BE MADE BY DEPOSITS OF SILVER FILM ON MICA OR INTERLEAVED SHEETS OF METAL FOIL (TIN,AL etc)

- POSSESES:

- HIGH STABILITY

- LOW TOLERANCE ( +_ 1% )

- HIGH WORKING VOLTAGE

- LOW LEAKAGE CURRENT

- RANGE => 0.01µF TO 10 nF

EASA Ref : 3.9


CERAMIC CAPACITOR:

- MANY SHAPES WITH CERAMIC DIELECTRIC OR BARIUM TITANATE DIELECTRIC

- DISC

- ROD

- PLATE

- SMALL IN CAPACITANCE (1pF TO 1 MICRO F)

- LARGE WORKING VOLTAGE (TO A FEW THOUSAND VOLTS)

- BARIUM TITANATE HAS V. HIGH CAPACITANCE ( DUE TO V. HIGH

DIELECTRIC CONSTANT) BUT SMALL IN SIZE

- HAS POOR STABILITY AND TOLERANCE

EASA Ref : 3.9


VARIABLE CAPACITOR (TUNING CAPACITOR)

- CAPACITANCE CAN BE CHANGED IN VALUE, MECHANICALLY

- USED IN THE RF AND OSCILLATOR STAGE OF THE RADIO

- HAS A STATOR (IMMOBILE) AND A ROTOR (MOBILE) CONNECTED WITH A

COMMON AXIS

- SMALL IN VALUE, IN THE RANGE OF 100pF AND 500pF (0.0001 µF TO

0.00005 micro F )

- HIGHER THE MESH, HIGHER IS THE CAPACITANCE

- CAPACITORS CONTAINED IN PLASTIC CONTAINERS HAVE VALUES OF 12 pF

TO 218pF

EASA Ref : 3.9


DUAL CAPACITORS

SINGLE CAPACITANCE

GANGED

QUADRUPLE CAPACITANCE

2 VARIACS AND 2 TRIMMERS

EASA Ref : 3.9


PRESET (TRIMMER) CAPACITORS

- MINIATURE CAP. WITH VERY SMALL CAPACITANCE = 2 TO 100 pF

- USED FOR FREQUENCY FINE TUNING IN TRANSCIEVERS AND OSCILLATORS

- CCT BOARD MOUNTED

- ADJUSTED WITH NON-MAGNETIC SCREWDRIVER

- SPECIFIED BY THE MINIMUM AND MAXIMUM VALUES

EASA Ref : 3.9


PRESET (TRIMMERS) CAPACITORS

EASA Ref : 3.9


COLOUR CODING (CERAMIC)

(JOINT ARMY-NAVY AND RADIO MANUFACTURERS CODE)

- CAPACITORS ARE MARKED WITH NUMBERS FOR:- VALUE- WORKING VOLTAGE- TOLERANCE- TEMPERATURE COEFFICIENT

- SMALL CAPS ARE MARKED WITH COLOURS LIKE THE RESISTOR CODING- 1ST 2 COLOURS REPRESENT THE 1ST 2 DIGITS - 3RD COLOUR REPRESENTD THE MULTIPLIER- 4TH COLOUR REPRESENTS TOLERENCE- 5TH COLOUR REPRESENT WORKING VOLTAGE- DISC CERAMIC AND TUBULAR CAPS DOES NOT HAVE

WORKING VOLTAGE- USED IN LOW OR NODC VOLTAGE- IF 5 COLOUR RING, THEN 1ST RING IS THE TEMP COEFF. AND THE OTHER 4

ARE AS THE NUMBERING SYSTEM

EASA Ref : 3.9


10 nF

EASA Ref : 3.9


MICA OR MOULDED PAPER CAPACITORS

- COMES WITH 3 DOTS OR 6 DOTS

- 3 DOT REPRESENTS

- 1ST, 2ND DOTS FOR 1ST 2 DIGITS

- 3RD DOT FOR MULTIPLIER

6 DOTS REPRESENTS

- 1ST (OR TYPE), 2ND, AND 3RD DOTS FOR FIRST 3 DIGITS

- 4TH DOT FOR MULTIPLIER

- 5TH DOT FOR TOLERENCE

- 6TH DOT FOR VOLTAGE RATING

- ALWAYS SELECT A CAP OF A VALUE ABOVE THE SUPPLY

VOLTAGE

EASA Ref : 3.9


FIRST DOT

BLACK OR WHITE FOR MICA

SILVER OR BODY COLOUR FOR PAPER

IN PICOFARADS

EASA Ref : 3.9


EASA Ref : 3.9


EASA Ref : 3.9


WHAT IS THE VALUE?

MICA CAP WITH 1.2 nF +- 6%

EASA Ref : 3.9


EASA Ref : 3.9


EASA Ref : 3.9


CAPS NUMBER CODING

- 1ST AND 2ND NUMBER IS THE DIGITS

- 3RD NUMBER IS THE NUMBER OF ZEROS

- LETTER STANDS FOR TOLERENCE

- READINGS IN PICOFARADS

- WORKING VOLTAGE, 25 VOLTS

103M

25V

10000 p F (0.01µ F), 20%, 25V

EASA Ref : 3.9


WHAT IS THE VALUE OF EACH CAPACITOR

683J

26 mF OR 260,000 pF 630 pF 9600 pF

68000 pF

EASA Ref : 3.9


CAPS IN SERIES

- BY CONNECTING IN SERIES THE PLATES ARE SEPERATED, THEREFORE CAPACITANCE IS REDUCED

- THE CAPACITANCE IS FELT ACROSS THE LEFT PLATE OF C1 AND RIGHT PLATE OF C2

- THE FORMULA FOR SERIES CAPACITANCE IS THE SAME AS FOR RESISTANCE IN PARALLEL

SERIES CAPACITANCE

- 1/CT = (1/C1) + (1/C2) + (1/C3) ………….OR

CT = C1XC2

C1+C2

1000 µF 50V

KO

NA

S K

ON

AS

1000 µF 50V

KO

NA

S K

ON

AS

NEUTRAL

C1 C2

EASA Ref : 3.9


EASA Ref : 3.9


AS FOR RESISTANCE, THE CAPACITANCE SHOULD BE CONVERTED TO FARADS FIRST

THE TOTAL CAPACITANCE SHOULD BE BELOW THE SMALLEST CAPACITANCE

CALCULATE THE TOTAL CAPACITANCE

1. C1 = 0.47 µF , C2 = 0.68p F, AND C3 = 50n F

2. C1 = 10µF, C2 = 0.47µF

EASA Ref : 3.9


CAPS IN PARALLEL

- CONNECTING CAPACITORS IN PARALLEL ADDS UP THE TOTAL AREA OF THE CAPACITORS,THEREFORE THE AREA IS BIGGER.

- TOTAL CAPACITANCE OF THE CAPACITORS IS:CT = C1 + C2 + C3 ………………

- ALL CAPS SHOULD BE CONVERTED TO THE SAME UNIT

CALCULATE THE TOTAL CAPACITANCE

1. C1 = 68µF, C2 = 0.01nF AND C3 = 47pF 2. C1 = 0.25µF, C2 = 0.03µF, C3 = 2µF

1000 µF 50V

KO

NA

S K

ON

AS

1000 µF 50V

KO

NA

S K

ON

AS

EASA Ref : 3.9


EASA Ref : 3.9


- WHEN PARALLELED THE TOTAL CHARGE INCREASES

ENERGY STORED = 0.5 X C X V ²

WHEN MORE THAN 2 CAPS ARE CONNECTED IN SERIES THE OVERALL WORKING VOLTAGE WILL ADD UP

EASA Ref : 3.9


5000 µf 25 v +

KONAS KONAS

5000 µf 25 v +

KONAS KONAS

5000 µf 25 v +

KONAS KONAS

5000 µf 25 v +

KONAS KONAS

5000 µf 25 v +

KONAS KONAS

5000 µf 25 v +

KONAS KONAS

5000 µf 25 v +

KONAS KONAS

5000 µf 25 v +

KONAS KONAS

5000 µf 25 v +

KONAS KONAS

25V

75V 1.667m F

3 X 3 MATRIX OF CAPACITORS

5 mF

75V 1.667m F

75V 1.667m F

EASA Ref : 3.9


CHARGING OF THE CAPACITOR

OFF CHARGE

NO POWER CONNECTED TO CAP

BOTH PLATES ARE NEUTRAL

NO ELECTRIC FIELDS BETWEEN THE PLATES

EASA Ref : 3.9


ON CHARGE

- POWER IS CONNECTED ACROSS THE PLATES

- CAP WILL CHARGE UP AT 5 TIMES CONSTANT

- ELECTRONS ARE REMOVED FROM THE POSITIVE PLATE AND FED TO THE

NEGATIVE PLATE.

- THE BUILD UP OF CURRENT OPPOSES THE SOURCE VOLTAGE

- THE CAP CONT. TO CHARGE UNTIL SOURCE VOLTAGE AND CURRENT

STOPS FLOWING

EASA Ref : 3.9


DISCHARGING OF THE CAPACITOR

- CHARGE ON THE 2 PLATES SHOULD BE NEUTRALIZES

- THE ELECTROSTATIC FIELD WILL VANISH

- THE SOURCE ENERGY IS RECOVERED FROM THE

CAPACITOR WHEN DISCHARGED

- CAPACITORS DO NOT CONSUME POWER, IT ONLY STORES ENERGY

EASA Ref : 3.9


RESISTOR / CAPACITOR TIME CONSTANT

FORMULA:

1TC = R x C

EASA Ref : 3.9


CHARACTERISTIC CURVE OF THE CHARGE

EASA Ref : 3.9


CHARGING

THE CURRENT WILL BE MAX AND THE VOLTAGE WILL BE MIN AS SOON AS THE VOLTAGE IS APPLIED TO THE CAP (INITIALLY)

THE VOLTAGE WILL BE MAX AND THE CURRENT WILL BE MIN WHEN THE CAP IS FULLY CHARGED

EASA Ref : 3.9


CHARACTERISTIC CURVE OF VOLTAGE AND CURRENT

CHARGING

EASA Ref : 3.9


DISCHARGING

THE VOLTAGE WILL BE MAX. AND THE CURRENT WILL ALSO BE MAX. AS SOON AS THE LOAD IS APPLIED (INITIALLY)

THE VOLTAGE WILL BE MIN. AND THE CURRENT WILL ALSO BE MIN. WHEN THE CAP. HAS FULLY DISCHARGED

EASA Ref : 3.9


CHARACTERISTIC CURVE OF VOLTAGE AND CURRENT

DISCHARGING

EASA Ref : 3.9


TESTING OF CAPACITORS

- MULTIMETER (EITHER ANALOGUE OR DIGITAL) SHOULD BE AT VERY HIGH RANGE

NON-POLARIZED

EASA Ref : 3.9


MAGNETISM

- CAN PRODUCE ELECTRICITY OR ELECTRICITY CAN PRODUCE MAGNETISM

- CONVERTING A METAL INTO A MAGNET IS THE PROCESS OF CONVERTION OF ELECTRICAL ENERGY INTO MECHANICAL ENERGY. Ex; GENERATOR

- MOVING A MAGNET THROUGH A COIL CAUSES AN ELECTRIC CURRENT TO FLOW. THIS PROCESS IS THE CONVERTION OF MECHANICAL ENERGY TO ELECTRICAL ENERGY.

Ex; MOTOR

MAGNETISM ( EASA Ref : 3.10 )


PROPERTIES OF MAGNETISM

NATURE OF MAGNETISM

- IT IS AN ELECTRIC CHARGE IN MOTION (ELECTRONS)

- ELECTRONS ARE MAGNETS SPINNING ON ITS AXIS

- SOME SPIN CLOCKWISE AND EQUAL AMOUNT IN

ANTICLOCKWISE

- THEY ARE MAGNETICALLY NEUTRAL, THEREFORE NO MAGNETIC CHARACTERISTICS

EASA Ref : 3.10


SUSPENDED MAGNET (PERMANENT MAGNET)

- EARTH IS A MAGNET ITSELF

- WHEN SUSPENDED THE MAGNET LIES IN THE NORTH-SOUTH DIRECTION

- MAGNETIC FIELDS (INVISIBLE) ARE ALSO KNOWN AS LINES OF FORCE

EASA Ref : 3.10


Magnet in earth magnetic field Magnetic field and poles of the earth

EASA Ref : 3.10


SHAPES OF MAGNETS

MADE OF STEEL

- COMPASS NEEDLES

- BARS

- RODS

- HORSE SHOES

- RINGS (CIRCULAR)

EASA Ref : 3.10


Shapes of magnets

EASA Ref : 3.10


MAGNETIC POLES

- MAGNETS HAVE 2 ENDS, 1 NORTH SEEKING POLE AND 1 SOUTH SEEKING POLE

- WHEN SUSPENDED THE END THAT POINTS TO THE NORTH POLE OF THE EARTH IS NORTH POLE. THE ONE THAT POINTS SOUTH IS SOUTH POLE

EASA Ref : 3.10


MAGNETISM BY INDUCTION

- ANOTHR NAME FOR NATURAL MAGNET -LODESTONE

- THEY CAN PICK UP IRON AND STEEL

- WHEN A SOFT IRON IS PLACED NEXT TO A MAGENT IT GETS INDUCED AND SLIGHTLY MAGNETIZED

- IF THE MAGNET IS STROKED A NUMBER OF TIMES, IT WILL BE EVEN MOREINDUCED AND MORE MAGNETIZED

EASA Ref : 3.10


MAGNETIC SHIELDING

- ALSO CALLED MAGNETIC SCREENING

- SOFT IRON IS USED AS MAGNETIC SCREEN FOR SHIELDING THE EFFECT

OF CONCENTRATING THE FLUX TO PREVENT STRAY MAGNETIC FIELDS

CAUSING INACCURATE OPERATION.

EASA Ref : 3.10


SCREENING OF COMPONENTS

- SINCE MAGNETIC FLUX CAN BE CONCENTRATED INTO IRON, THE CENTER PART OF THE IRON RING HAS NO MAGNETIC FLUX OUTSIDE THE IRON

CORE

- THE ABILITY OF THE SOFT IRON TO CONCENTRATE THE MAGNETIC FLUX IS KNOWN AS PERMEABILITY.

- SOFT IRON – HIGH PERMEABILITY AND AIR - LOW PERMEABILITY

EASA Ref : 3.10


TYPES OF MAGNETIC MATERIALS

- FERROMAGNETIC MATERIALS – CAN ATTRACT OTHER KIND OF METALS LIKE IRON, NICKEL AND COBOLT

- PARAMAGNETIC MATERIALS – CANNOT ATTRCT OTHER KINDS OF METAL, PAPER OR WOOD

- DIAMANGNETIC MATERIAL – REPELS ITSELF FROM MAGNETS (NOT IN USE)

- IF AN IRON IS MAGETIZED BY A LOADSTONE, THAT IRON IS KNOWN AS ARTIFICIAL MAGNET. THEY LOSE THEIR MAGNETISM EASILY (SOFT IRON)

- SOME IRONS CAN RETAIN THEIR MAGNETISM FOR A LONG PERIOD OF TIME.THEY ARE KNOWN AS PERMANENT MAGNET

EASA Ref : 3.10


TYPES OF MAGNETIC MATERIALS

EASA Ref : 3.10


RELAY

- CONSISTS OF A TEMPERORY MAGNET, COIL, ARMATURE AND CONTACTS

- CAN BE NORMALLY OPEN OR NORMALLY CLOSED TYPE

EASA Ref : 3.10


CONSTRUCTION OF RELAY

EASA Ref : 3.10


CIRCUIT SYMBOL AND CONTACTS OF A RELAY

EASA Ref : 3.10


OPERATION

- CURRENT FED TO THE COIL

- SORF IRON BECOMES MAGNET

- ATTRACTS THE ARMATURE

- CONTACTS EITHER CLOSES OR OPENS

- CURRENT DISRUPTED IRON LOSSES MAGNETISM

- ARMATURE RELEASED DUE TO SRINGY ACTION

- CONTACTS EITHER OPENS OR CLOSES

EASA Ref : 3.10


EASA Ref : 3.10


USES OF RELAY

REMOTE SWITCHING

- HIGH VOLTAGE DROP CAN BE EXPERIENCED IN LONG WIRES

- A RELAY CAN BE USED TO CONTROL EQUIPMENT AT A DISTANCE

- SINCE RELAY TAKES ONLY A SMALL CURRENT

- POWER LOSS AT THE EQUIPMENT WILL BE LESS

EASA Ref : 3.10


REMOTE SWITCHING USING A RELAY

EASA Ref : 3.10


HEAVY WORKING CURRENT SWITCHING

- EQUIPMENT CAN BE SWITCHED ON AND OFF WITH SMALL CURRENT

- CAN BE HEAVY DUTY RELAY OR LIGHT DUTY RELAY.

- USED IN

- PROTECTIVE CIRCUITS

- INDICATING SYSTEMS

- POWER CONTROL SYSTEMS

- TELEGRAPHIC CONTROL SYSTEMS

EASA Ref : 3.10


HEAVY WORKING CURRENT SWITCHING

EASA Ref : 3.10


MAGNETIC FIELDS ON CURRENT CARRYING CONDUCTORS

- CURRENT FLOWS, A MAGNETIC FIELD IS PRODUCED

2 METHODS TO DETERMINE THE FIELD DIRECTION

- RIGHT HAND RULE

- WIRE GRASPED WITH RIGHT HAND

- THUMB POINTS TO THE DIRECTION OF CURRENT

- FINGERS POINT TO THE DIRECTION OF THE MAGNETIC FIELDS

EASA Ref : 3.10


MAGNETIC FIELD AROUND A CONDUCTOR

EASA Ref : 3.10


RIGHT HAND RULE

EASA Ref : 3.10


CORKSCREW RULE

- WHEN THE CORKSCREW IS SCREWED INTO THE PAPER, THE CURRENT WILL FLOW INTO THE PAPER

- THE DIRECTION THE CORKSCREW IS TURNED , IS THE DIRECTION OF THE MAGNETIC FIELDS (CLOCKWISE)

- WHEN THE CORKSCREW IS REMOVED, THE CURRENT WILL FLOW OUT OF THE PAPER

- THE DIRECTION OF THE CORKSCREW IS THE DIRECTION OF THE MAGNETIC FIELDS (ANTI-CLOCKWISE)

EASA Ref : 3.10


COCKSCREW RULE

EASA Ref : 3.10


MAGNETOMOTIVE FORCE (MMF)

- THE FORCE THAT TENDS TO PRODUCE A MAGNETIC FIELD

- UNIT FOR MMF IS THE GILBERT, SYMBOL IS F

- 1 GILBERT IS EQUAL TO THE MAGNETIC FORCE THAT IS REQ. TO ESTABLISH AFLUX DENSITY OF 1 MAXWELL IN A FLUX PATH OR MAGNETIC CCT. HAVING A RELUCTANCE OF 1 UNIT

MAGNETIC CIRCUIT

EASA Ref : 3.10


FIELD STRENGTH

- MAGNETIC FIELDS ARE CONTINOUS, THEY CAN PASS THRU’ THE CORE AND ALSO THE AIR GAP

- SYMBOL FOR MAGNETIC FIELD STRENGTH IS H (UNIT IS TESLA)

- SYMBOL FOR MAGNETIC FLUX DENSITY IS B (LIKE THE VOLTAGE) (UNIT IS WEBER)

H = AMPERES x TURNS = IN/L Tesla

LENGTH (MAGNETIC CCT)

EASA Ref : 3.10


OUTSIDE –THE MAGNETIC LINES OF FORCE TRAVEL FROM NORTH SEEKING POLE TO THE SOUTH SEEKING POLE

INSIDE – THE MAGNETIC LINES OF FORCE TRAVELS FROM SOUTH TO NORTH

EASA Ref : 3.10


FLUX DENSITY (SYMBOL B)

MAGNETIC FLUX

- THE ENTIRE GROUP OF MAGNETIC FIELD LINES, WHICH CAN BE CONSIDERED TO FLOW OUTWARD FROM THE NORTH POLE OF A MAGNET, IS CALLED MAGNETIC FLUX

- SYMBOL IS Φ (phi)

- A STRONG FIELD HAS MORE LINES OF FORCE AND MORE FLUX THAN A WEAK MAGNETIC FIELD

EASA Ref : 3.10


PERMEABILITY

- THE ABILITY OF A MATERIAL TO BECOME A MAGNET IS THE PERMEABILITY. DIFFERENT MATERIAL HAVE DIFFERENT PERMEABILITY.

- WHEN AN IRON BECOMES A MAGNET IT PRODUCES MAGNETIC FIELDS OF ITS OWN, HENCE INCREASING THE FLUX DENSITY

- THE MULTIPLYING FACTOR OF A MATERIAL IS µ (mu) =B/H

- RANGES FROM 1 (AIR) TO A FEW THOUSANDS

EASA Ref : 3.10


EFFECT OF IRON IN MAGNETIC FIELD

EASA Ref : 3.10


HYSTERESIS LOOP

- WHEN A SOFT IRON IS SUBJECTED TO CURRENT AROUND IT, IT BECOMES A MAGNET

- IF THE MAGNETIC FIELDS ARE INCREASED EVEN MORE INTO SATURATION, TME IRON IS FULLY MAGNETIZED

- NOW IF THE CURRENT IS REMOVED, THE IRON STILL HOLDS SOME RESIDUAL MAGNETISM. THIS EFFECT IS KNOWN AS HYSTERESIS

- IT CAN BE SAID THAT THE LAG OF FLUX DENSITY (B) BEHIND THE MAGNETIC FIELD STRENGTH (H) IS HYSTERESIS

EASA Ref : 3.10


B-H CURVE

ONCE AT SATURATION AND THE MAGNETISM IS REMOVED THE ‘B’ DOES NOT DROP TO ZERO, INSTEAD IT HOLDS VALUE OF ‘B’ . THIS VALUE OF ‘B’ IS KNOWN AS REMNANT OR RESIDUAL MAGNETISM. KEEP IN MIND, ONLY IF IT REACHES SATURATION.

- REMNANT OR RESIDUAL MAGNETISM WILL REDUCE TO ZERO QUITE FAST UNDER NORMAL CONDITION.

IF THE INCREASE OF THE ‘H’ STRENGTH IS NOT TO SATURATION AND REMOVED, IT IS KNOWN AS REMNANT FLUX DENSITY

EASA Ref : 3.10


B-H CURVE

Remanence or Residual Magnetism

INITIAL BEFORE MAGNETISMAFTER INCREASING TO

MAX. MAGNETISM (SATURATION)

EASA Ref : 3.10


RETENTIVITY

- WHEN THE MAGNETISM IS HELD FOR A LONG PERIOD OF TIME, IT IS KNOWN AS RETENTIVITY

- RESIDUAL / REMNANT IS NOT THE SAME AS RETENTIVITY.

- IN NORMAL CONDITIONS THE REMNANT CAN DECREASE TO ZERO BUT THE RETENTIVE MAGNETISM MAY LAST A VERY LONG TIME DEPANDING ON THE TYPE OF MATERIAL USED

EASA Ref : 3.10


COERCIVE FORCE

- TO REMOVE THE REMNANT MAGNETISM, A NEGATIVE MAGNETISING FORCE IS REQUIRED

- THE AMOUNT OF NEGATIVE FORCE REQUIRED IS KNOWN AS COERCIVE

FORCE

- IF THE FIRST TIME IT REACHED SATURATION, THAN THIS VALUE IS KNOWN AS COERCIVITY OF THE MATERIAL.

EASA Ref : 3.10


COERCIVE FORCE

EASA Ref : 3.10


MAGNETIC ATTRACTION

- WHEN 2 UNLIKE POLES ARE PLACED CLOSE TOGETHER, THEY ATTRACT EACH OTHER.

- MAGNETIC FIELDS COMBINE

EASA Ref : 3.10


MAGNETIC POLES

EASA Ref : 3.10


MAGNETIC REPULSION

- WHEN 2 LIKE POLES ARE PLACED CLOSE TOGETHER, THEY REPEL

- MAGNETIC FIELDS REPEL EACH OTHER

EASA Ref : 3.10


REPULSION

EASA Ref : 3.10


SATURATION POINTS

- A CERTAIN AMOUNT OF FORCE IS REQUIRED TO REMOVE THE RESIDUAL MAGNETISM.

- IF THE FORCE IS TOO HIGH, THAN THE IRON WILL BE SATURATED IN THE OPPOSITE DIRECTION (NEGATIVE SATURATION)

- TO REMOVE THE MAGNETISM OF A PERMANANT MAGNET, A LARGE FORCE IS REQUIRED

- HARD IRON REQUIRES A LARGE FORCE TO ENERGIZE AND DEENERGIZE

EASA Ref : 3.10


NEGATIVE SATURATION

EASA Ref : 3.10


EDDY CURRENT

- IN A TRANSFORMER, WHEN THE MAGNETIC FIELD EXPENDS AND COLLAPSES, THE CORE IS INDUCED WITH VOLTAGE.

- THIS VOLTAGE IN TURN ESTABLISHES A CURRENT. THIS CURRENT IS KNOWN AS EDDY CURRENT THAT FLOWS IN A CIRCULAR PATH.

EASA Ref : 3.10


CARE AND STORAGE OF MAGNETS

- TO PREVENT THE LOSS OF MAGNETIC ENERGY OF A PERMANENT MAGNET A KEEPER IS REQUIRED

- A KEEPER CAN BE A SOFT IRON OR EVEN ANOTHER MAGNET

- WITH THE KEEPER, THE MAGNETIC CIRCUIT IS COMPLETE. THEREFORE THERE IS NO STRAYING OF THE MAGNETIC FIELDS

EASA Ref : 3.10


MAGNET WITH KEEPERS

EASA Ref : 3.10


DIRECTION OF CURRENT FLOW IN A WIRE

- WHEN CURRENT FLOWS THROUGH A WIRE, ELECTRONS (HOLES) SHOULD FLOW FROM POSITIVE TO NEGATIVE (CONVENTIONAL)

- ARROW SYMBOLIZES THE TAIL AS POSITIVE AND THE HEAD AS NEGATIVE

EASA Ref : 3.10


DIRECTION OF CURRENT FLOW

EASA Ref : 3.10


MAGNETIC FIELDS IN A COIL

- A PIECE OF STRAIGHT WIRE CARRYING CURRENT HAS MAGNETIC FIELDS AROUND IT , BUT VERY SMALL FOR PRACTICAL USE

- IF THE SAME WIRE IS TWISTED INTO A LOOP, THE MAGNETIC FIELDS WILL BE CONCENTRATED INTO A SMALL AREA

- ONCE CONCENTRATED, IT WILL HAVE 3 PROPERTIES

- BRINGS THE FLUX LINES TOGETHER

- CREATES NORTH AND SOUTH POLES

- CONCENTRATES THE FLUX LINES IN THE CENTRE

EASA Ref : 3.10


MAGNETIC FIELDS IN A COIL

EASA Ref : 3.10


RIGHT HAND GRASP RULE

- USING THE RIGHT HAND AND GRASPING THE COIL IN THE DIRECTION OF CURRENT FLOW, THE THUMB POINTS TO THE NORTH

- THE FLUX DENSITY DEPANDS ON:

- VALUE OF THE CURRENT IN THE COIL- NUMBER OF TURNS IN THE COIL- THE TYPE OF CORE MATERIAL

- IF A CORE IS USED, THE MAGNETIC FORCE STRENGTH IS INCREASED

- IF THE NUMBER OF TURNS INCREASE, THE MAGNETIC FORCE STRONGER TOO. (STRONGER ELECROMAGNETS)

- THE LEVEL OF CURRENT CAN ALSO VARY THE STRENGTH OF THEMAGNETIC FORCE

EASA Ref : 3.10


RIGHT HAND GRASP RULE

EASA Ref : 3.10


MAGNETIC CHARACTERISTICS

RELUCTANCE (S)

(IT IS THE SAME AS RESISTANCE IN AN ELECTRICAL CIRCUIT)

- IT IS THE OPPOSITE TO MAGNETIC FLUX

- IT IS RECIPROCAL OF THE PERMEABILITY

FORMULA :

PERMEABILITY = 1/ RELUCTANCE

S = 1 / µ OR µ = 1/S

Ex:

IF THE RELUCTANCE IS 0.0002, WHAT IS THE PERMEABILITY OF THIS MATERIAL.

µ = 1 / 0.0002

= 5000

EASA Ref : 3.10


MAGNETIC MATERIALS

- 2 TYPES OF USEFUL MAGNETIC MATERIALS

- FERROMAGNETIC MATERIAL

MATERIAL THAT CAN BECOME MAGNET ( NICKLE, COBALT, IRON etc). THEY HAVE THE ABILITY OF CONCECNTRATING AND MULTIPLING THE FLUX

- NON-FERROMAGNETIC MATERIALS

MATERIAL THAT CANNOT BECOME MAGNET ( ALLUMINUM WATER AIR etc). IT CANNOT CONCENTRATE THE MAGNETIC FLUX AND DOES NOT HAVE THE ABILITY OF MULTIPLING THE FLUX.

- AIR HAS A µ OF 1

EASA Ref : 3.10


MAGNETIC FIELD STRENGTH/ FLUX DENSITY CURVE ( B-H CURVE )

EASA Ref : 3.10


STRAIGHT LINE GRAPH BECAUSE AIR HAS A PERMEABILITY OF 1

EASA Ref : 3.10


B-H CURVE OF FERROMAGNETIC MATERIAL

Large increase of H causes a small increase of B

Small increase of H causes a large increase of B

Large increase of H causes a small increase of B

EASA Ref : 3.10


CLASSIFICATION OF FERROMAGNETIC MATERIALS

2 TYPES OF MAGNETIC MATERIALS:

HARD MAGNETIC MATERIAL-- MAKES A GOOD PERMANENT MAGNET, HIGH RETENTIVITY- LARGER HYSTERESIS LOSSES- ALNICO MAKES A GOOD PERMANENT MAGNET- ALNICO CONSISTS OF ALU, COBALT, NICKEL AND IRON

SOFT MAGNETIC MATERIAL -

- LOW RETENTIVITY, LOW HYSTERESIS LOSSES AND HIGH PERMEABILITY

- SUITABLE WITH AC DEVICES ex; ELECTRIC MOTOR,GENERATOR AND TRANSFORMER

- STEEL ALLOYS (PERMALLOY OR STALLOY) FOR AC USE- SORT IRON FOR DC USE,HAS HIGH PERMEABILITY BUT

RELATIVELY HIGH HYSTERESIS LOSS

EASA Ref : 3.10


HYSTERESIS LOOP

EASA Ref : 3.10


HYSTERERIS LOOP

EASA Ref : 3.10


INDUCTANCE AND INDUCTOR

- BY THE MOVEMENT OF A CONDUCTOR IN A MAGNETIC FIELD, ELECTRICAL ENERGY CAN BE PRODUCED

- BY MOVEMENT OF A MAGNET INTO A COIL, ELECTRICAL ENERGY CAN BE PRODUCED TOO.

Ex; GENERATOR AND TRANSFORMER

INDUCTANCE / INDUCTOR ( EASA Ref : 3.11)


INDUCING A VOLTAGE

- WHEN A CONDUCTOR IS MOVED INTO A MAGNETIC FIELD AT 90° THE

ELECTRONS ARE FORCED TOWARDS THE RIGHT OF THE CONDUCTOR,

- WHILE LACK OF ELECTRONS AT THE LEFT. A PD IS DEVELOPED.

- WHEN THE CONDUCTOR IS MOVED OUT OF THE MAGNETIC FIELDS, THE ELECTRONS MOVE IN THE OPPOSITE DIRECTION AND THE PD

DISAPPEARS WHENTHE CONDUCTOR IS OUT OF THE FIELDS

- IF THE CONDUCTOR STOPS IN THE FIELDS, THERE WILL BE NO PD

- THEREFORE PD IS CREATED ONLY WHEN THE CONDUCTOR IS MOVED

- MECHANICAL FORCE IS CONVERTED TO ELECTROMOTIVE FORCE BY ELECTROMAGNETIC INDUCTION

EASA Ref : 3.11


EASA Ref : 3.11


EFFECT OF MAGNETIC FIELD STRENGTH ON THE INDUCED VOLTAGE

- WHEN THE CONDUCTOR MOVEMENT AND THE MAGNETIC FLUX ARE IN THE SAME DIRECTION, THERE WILL BE NO EMF INDUCED IN THE OTHER CIRCUIT

EASA Ref : 3.11


MAGNETIC FIELD STRENGTH

EASA Ref : 3.11


EFFECT OF RATE OF CHANGE OF FLUX ON INDUCED VOLTAGE

- MOVING THE COIL AT 45 DEG. WILL INCREASE THE INDUCTION AND WHEN MOVED TO 90 DEG., THE INDUCTION WILL BE INCREASED TO MAXIMUM.

- TURNING A FURTHER 90 DEG. WILL PRODUCE ZERO INDUCTION

EASA Ref : 3.11


EASA Ref : 3.11


FACTORS AFFECTING THE RATE OF CHANGE OF FLUX

- SPEED OF CONDUCTOR MOVEMENT THRU’ THE FIELDS- THE STRENGTH OF THE MAGNETIC FIELDS- THE ANGLE BETWEEN THE CONDUCTOR AND FIELD- THE LENGTH (# OF TURNS) OF THE CONDUCTOR IN THE FIELD

FARADAY’S LAW:

WHEN A CONDUCTOR CUTS OR IS CUT BY THE MAGNETIC FLUX, THERE WILL BE INDUCED EMF PRODUCED. THIS IS PROPORTIONAL TO THE RATE OF MOVEMENT THRU’ THE FIELDS

FORMULA:

EMF = B x I x V

EASA Ref : 3.11


LENZ’S LAW

- WHEN A CURRENT IS SET UP IN AN INDUCED EMF CLOSED CIRCUIT, THE CONDUCTOR WILL PRODUCE ITS OWN MAGNETIC FIELDS

- THE MAGNETIC FIELDS IN FRONT OF THE CONDUCTOR’S MOTION IS STRENGTHENED

- BEHIND THE CONDUCTOR’S MOTION IS WEAKENED

EASA Ref : 3.11


EASA Ref : 3.11


FIELDS OF PARALLEL CONDUCTORS CARRYING CURRENT

- CURRENT CARRYING CONDUCTOR’S MAGNETIC FIELDS WILL ATTRACT EACH OTHER IF THEY ARE IN THE SAME DIRECTION

- CURRENT CARRYING CONDUCTOR’S MAGNETIC FIELDS WILL REPEL EACH OTHER IF THEY ARE IN THE OPPOSITE DIRECTION

- THE DIRECTION OF THE MAGNETIC FIELDS ARE IN ACCORDANCE WITH THE RIGHT HAND AND CORKSCREW RULE

EASA Ref : 3.11


FIELDS OF PARALLEL CONDUCTORS

EASA Ref : 3.11


FORCE ON A CURRENT CARRYING CONDUCTOR IN A MAGNETIC FIELD

- A CONDUCTOR CARRYING CURRENT IS PUT INTO THE MAGNETIC FIELDS, INTERACTION BETWEEN THE 2 FIELDS TAKE PLACE

- THE CONDUCTOR HAS ITS OWN FIELDS, THEREFORE ON 1 SIDE IT AIDS THE MAGNETIC FIELDS AND ON THE OTHER SIDE IT OPPOSES

- THE AIDED SIDE HAS A GREATER FORCE COMPARED TO THE OPPOSED SIDE. THEREFORE THE CONDUCTOR IS FORCED TOWARDS THE WEAKER SIDE

- ELECTRICAL ENERGY IS CONVERTED TO MECHANICAL ENERGY

EASA Ref : 3.11


EASA Ref : 3.11


THE CORKSCREW RULE IS USED TO DETERMINE THE FELD DIRECTION OF THE

CONDUCTOR

ANOTHER WAY TO DETERMINING THE DIRECTION OF FORCE IS BY THE LEFT HAND RULE

MAGNETIC FLUX IS FROM NORTH TO SOUTH

THE DIRECTION OF CURRENT FLOW IN THE CONDUCTOR (DIRECTION OF THEFINGERS)

WHEREBY THE THUMB DETERMINE THE DIRECTION OF FORCE

EASA Ref : 3.11


LEFT HAND MOTOR RULE

EASA Ref : 3.11


MAGNITUDE OF THE FORCE

THE MAGNITUDE IS PROPORTIONAL TO 3 FACTORS:

THE FLUX DENSITY OF THE MAGNET’S POLES

THE FLUX DENSITY OF THE CONDUCTOR (PROPORTIONAL TO THE CURRENT)

LENGTH OF THE CONDUCTOR

THEREFORE FORCE IS EQUAL TO (FORMULA):

FORCE = FLUX DENSITY (B) x CURRENT (I) x LENGTH (l)

= B. I. l NEWTONS

EASA Ref : 3.11


LENZ’S LAW

AN ELECTROMAGNETIC FIELD INTERACTING WITH A

CONDUCTOR WILL GENERATE ELECTRICAL CURRENT THAT

INDUCES A COUNTER MAGNETIC FIELD THAT OPPOSES THE

MAGNETIC FIELD GENERATING THE CURRENT

( THE INDUCED CURRENT ALWAYS OPPOSES THE MOTION ORCHANGE PRODUCING IT )

EASA Ref : 3.11


LENZ’S LAW

EASA Ref : 3.11


DETERMINATION OF THE INDUCED CURRENT FLOW WITH LENZ’S LAW

- FIRST THE DIRECTION OF THE CONDUCTOR MOVEMENT SHOULD BE KNOWN

- THE DIRECTION OF THE FIELD IN THE CONDUCTOR SHOULD ALSO BE KNOWN

- USING THE RIGHT HAND OR THE CORKSCREW RULE IN REVERSE TO DETERMINE THE INDUCED CURRENT

EASA Ref : 3.11


BACK EMF

- WHEN A CURRENT CARRYING CONDUCTOR MOVES THROUGH THE MAGNET’S MAGNETIC FIELDS, THE CONDUCTOR’S FIELD WILL CHANGE (RATE OF CHANGE OF FLUX).

- THIS CHANGE WILL INDUCE AN EMF (BACK EMF) WHICH WILL OPPOSE THE APPLIED EMF AND IN TURN, THE CURRENT OF THE CONDUCTOR.

- THIS CAUSES THE CONDUCTOR TO MOVE

BACK EMF IS ALSO KNOWN AS –EMF or COUNTER EMF

FORMULA:

-EMF = B x I x V

EASA Ref : 3.11


MAGNETIC LINE OF FLUX AROUND A LOOP

- IF CURRENT IS CHANGED IN A LOOP, THE FLUX ALSO CHANGES IN STRENGTH

- THE CHANGE CAUSES AN EMF (BACK) THAT OPPOSES THE EMF

- IF THE VOLTAGE AND CURRENT INCREASES THE OPPOSITION ALSO INCREASES AND VICE VERSA

- IF THE CURRENT INCREASES IN AN INDUCTOR, THE ENERGY IS STORED IN THE FIELDS AND WHEN THE CURRENT DECREASES, THE FIELD GIVES UP THE ENERGY.

- ENERGY STORED IN THE MAGNETIC FIELDS DEPEND ON THE INDUCTANCE AND COIL CURRENT

EASA Ref : 3.11


INDUCTANCE

THE OPPOSITION TO A CHANGE OF CURRENT OR FLUX-

- ANY IRCUIT WHICH HAS AN EMF INDUCED INTO IT BY A CHANGE OFCURRENT THROUGH THAT CCT POSSESS SELF INDUCTANCE.

- A COIL IS AN INDUCTOR

- SYMBOL FOR INDUCTANCE IS ‘L’ AND THE UNIT FOR INDUCTANCE IS HENRYS (H)

IF 1 AMPERE FLOWS IN A CIRCUIT FOR 1 SECOND PRODUCES 1 VOLT –EMF THE CCT IS SAID TO HAVE AN INDUCTANCE OF 1 HENRY.

FORMULA: - EMF(V )INDUCTANCE = RATE OF CHANGE OF CURRENT (A)

RATE OF CHANGE OF TIME (S)

EASA Ref : 3.11


INDUCTANCE OF A CORED COIL

- WHEN CURRENT FLOWS IN A COIL INCREASES , THE INDUCTANCE

INCREASES BUT WHEN THE COIL IS INSERTED WITH A CORE, THE

INDUCTANCE INCREASES UNTIL SATURATION.

- FURTHER INCREASE IN THE CURRENT WILL DRASTICALLY REDUCE THE INDUCTANCE

- NON-MAGNETIC MATERIALS SUCH AS AIR, COPPER AND ALUMINUM DOES NOT MULTIPLY FLUX, THEREFORE THE CORE DOES NOT SATURATE. IT IS INDEPENDENT OF CURRENT

EASA Ref : 3.11


EASA Ref : 3.11


- WHEN CURRENT FLOWS IN A COIL, A BACK EMF WILL BE PRODUCED

- THIS BACK EMF IS PROPORTIONAL TO THE AMOUNT OF MAGNETIC FORCE (RATE OF CHANGE) THAT CUTS THE COIL

THE INDUCTANCE ‘CUTTING’ DEPENDS ON:

- NUMBER OF TURNS (GREATER THE NUMBER OF TURNS, GREATER ISTHE CUTTING AND THEREFORE BACK EMF)

- CROSS-SECTIONAL AREA OF THE CORE (THE GREATER THE A, THE GREATER IS THE FLUX THAT CUTS THE CONDUCTOR)

- PERMEABILITY (GREATER IS THE MU, THE GREATER IS THE FLUX CUTTING CONDUCTOR AND THEREFORE GREATER –EMF

- LENGTH OF THE CORE (SHORTER THE CORE, LESS IS THE FLUX)

EASA Ref : 3.11


FORMULA

L = N2 A µ Henrys H

l

EASA Ref : 3.11


FORMULA: L = N² x A x µ Henrys H

l

Ex : 1

IF AN INDUCTOR HAS AIR AS ITS CORE AND THE NUMBER OF TURNS IT HAS IS 100 WITH A X-SECTIONAL AREA OF 0.2 x WHAT IS THE INDUCTANCE OF THIS INDUCTOR (µ ,³־10 OF AIR = 1.26 X 10 6־ )

N² x A x µ

L =

l

100² X ( 0.2 x 10 ³־) x (1.26 X 106־ )L =

0.2

= 12.6 X 10 6־ or 12.6 µ H

EASA Ref : 3.11


CALCULATION:

Ex: 2

IF N = 100 TURNS, A = 3µ METERS, l = 0.5 METERS, AND THE FERRITE CORE HAS

mu=1000. FIND THE INDUCTANCE.

N² x A x µ

L =

l

(100)² X (3 X 106־) X (1.26 X 106־ ) X 1000

=

0.5

= 756 mH or 0.756 µH

EASA Ref : 3.11


Inductor symbol

EASA Ref : 3.11


TIME CONSTANT

- as discussed earlier, the current that flows in an inductor is opposed by the

induced current

- as the current is increased, the opposed current also increases

- therefore this causes the current to delay in the circuit

EASA Ref : 3.11


RISE TIME

- WHEN POWER IS APPLIED TO AN INDUCTIVE CIRCUIT, THE CURRENT INCREASES AT A HIGH SPEED IN 1 TIME CONSTANT. IT IS 63.2%

- AS THE CURRENT INCREASES THE BACK EMF WILL BE REDUCED FROM MAXIMUM.

INITIALLY WHEN POWER IS APPLIED:

- TIME IS 0- RATE OF CURRENT CHANGE IS MAXIMUM- BACK EMF AND THE APPLIED VOLTAGE ARE ALMOST EQUAL THAT IS

MAXIMUM- THE VOLTAGE DROP (I X R) ACROSS R IS MINIMUM

FORMULA: t = L (Henrys)

R (OHMS)

EASA Ref : 3.11


5 TIME CONSTANT

- THE VOLTAGE IS MAX. WHEN THE APPLIED CURRENT WAS MIN.

- IN 1 TC THE EMF HAS DROPPED FROM 100% TO 63.2%, THEREFORE THE BACK EMF IS 36.8%

- IT TAKES 5 TC TO INCREASE THE CURRENT TO MAX. WHERE THE VOLTAGE DROPS TO ALMOST ZERO.

L

FORMULA: 5TC = 5 X

R

EASA Ref : 3.11


AT 5 TC

- BACK EMF OF THE INDUCTOR IS MINIMUM

- RATE OF CURRENT CHANGE IS MINIMUM

- CURRENT FLOW IS MAXIMUM

- APPLIED VOLTAGE DROP ACROSS THE R IS MAXIMUM

EASA Ref : 3.11


Time constant

EASA Ref : 3.11


DECAY TIME

- WHEN POWER IS REMOVED FROM THE CIRCUIT, THE CURRENT WILL DROP FROM MAX. TO 36.8 % OF THE MAX VALUE. THAT IS CURRENT FLOWS FROMTHE COLLAPSING MAGNETIC FIELDS

- THE BACK EMF IS MAX AND IT TRIES TO KEEP THE CURRENT FLOW- IT TAKES 1 TC TO DROP 63.2%. THEREFORE THE VOLTAGE DROP ACROSS THE

R IS 36.8%

- THE BACK EMF IS ALSO 36.8%- AT 5 TC THE CURRENT IS ALMOST ZERO AND ALL THE ENERGY IS DISCHARGED

THRU’ THE RESISTOR

- SMALLER RESISTOR VALUE MAKES THE DECAY TIME LONGER

- BACK EMF (MANY TIMES HIGHER THAN THE APP. VOLTAGE) CAN BE DANGEROUS AND CAN CAUSE DAMAGE TO EQUIPMENT AND PERSONAL

EASA Ref : 3.11


Example

INDUCTANCE = 10 H AND RESISTANCE IS 1K. WHAT IS THE 5 TC OF THIS CIRCUIT

L

Formula: 5TC = 5

R

5 x 10/1000

= 5 x 0.01

= 0.05 seconds

EASA Ref : 3.11


Example 2

IF THE INDUCTOR IS 10 H AND THE RESISTANCE IS 10 OHMS, WHAT IS THE TIME REQUIRED TO RISE THE CURRENT TO MAXIMUM.

L

Formula: 5TC = 5 x

R

= 5 x 10 / 10

= 5 x 1

= 5 seconds

EASA Ref : 3.11


Decay time

EASA Ref : 3.11


INDUCTANCE IN SERIES

- WHEN 2 OR MORE INDUCTORS ARE CONNECTED IN SERIES, THE TOTAL VOLTAGE IS THE SUM OF THE VOLTAGE ACROSS EACH INDUCTOR

UT = U1 + U2 + U3 +………………..Un

- WHEN 2 OR MORE INDUCTORS ARE CONNECTED IN SERIES THEY SHOULD BE ADDED UP JUST LIKE RESISTORS IN SERIES

LT = L1 + L2 + L3 +………………Ln

- TO CALCULATE, FIRST OF ALL THE VALUES OF THE INDUCTORS SHOULD BE CONVERTED TO THE SAME DENOMINATION

10 µH + 100 mH = 10 µH + 100000 µH = 100010 µH

Or

0.01mH + 100 mH = 100.01mH

EASA Ref : 3.11


MUTUAL INDUCTION

WHEN TWO INDUCTORS ARE PLACED CLOSE TO ONE ANOTHER,THE FLUX GENERATED WHEN A CHANGING CURRENT FLOWS INTHE FIRST INDUCTOR WILL CUT THROUGH THE OTHER INDUCTOR.

THE CHANGING FLUX WILL INDUCE A CURRENT IN THE SECOND INDUCTOR.

THIS EFFECT IS KNOWN AS MUTUAL INDUCTANCE

EASA Ref : 3.11


THE EFFECT OF THE RATE OF CHANGE OF PRIMARY CURRENT AND MUTUAL INDUCTANCE ON INDUCED VOLTAGE

INDUCED VOLTAGE = MUTUAL INDUCTANCE X RATE OF CHANGE PRIMARY CURRENT

= M didt

EASA Ref : 3.11


FACTORS AFFECTING MUTUAL INDUCTANCE

1. NUMBER OF TURNS OF COIL

2. PHYSICAL SIZE OF COIL

3. PERMEABILITY OF COIL

4. POSITION OF COIL WITH RESPECT TO EACH OTHER

EASA Ref : 3.11


PRINCIPLES USES OF INDUCTORS

1. TUNED CIRCUITS

2. FILTERS

3. TRANSFORMERS

4. CHOKES

EASA Ref : 3.11


DC MOTOR / GENERATOR THEORY ( EASA Ref : 3.12)

FORCE ON CONDUCTOR N A MAGNETIC FIELD


EASA Ref : 3.12

BASIC MOTOR THEORY

WHEN THE CURRENT CARRYING CONDUCTOR IS PLACED WITHIN THE MAGNETIC FIELD,THE TWO FIELDS CANNOT EXIST INDEPENDENTLY

A CURRENT CARRYING CONDUCTOR HAS A MAGNETIC FIELD SURROUNDING IT.

THE FIELD IS CLOCKWISE- CURRENT IN –COCKSCREW RULE

THE MAGNETIC FIELD BETWEEN THE TWO POLES OF A BAR MAGNET MOVES

FROM NORTH TO SOUTH

THE RESULT WILL BE,STRONG FIELDS ON THE LEFT WHILE FIELDS ON THE

RIGHT BECOMES WEAK( OPPOSE EACH OTHER ).

THEREFORE, THE CONDUCTOR WILL BE FORCED TO MOVE TOTHE RIGHT HAND SIDE. –FLEMING’S LEFT HAND RULE


EASA Ref : 3.12


THE PRINCIPLE OF ELECTRIC MOTOR

THE FORCE ON THE CONDUCTOR , F = B I l NEWTONS

F = FORCE ON CONDUCTOR, IN NEWTONS (N )

B = FLUX DENSITY OF MAGNETIC FIELD, IN TESLA

I = CURRENT FLOW IN CONDUCTOR, IN AMPERES

l = LENGTH OF CONDUCTOR , IN METERS

FLUX DDENSITY ,B =θ/A

F = θ I l

A

EASA Ref : 3.12


A PRACTICAL DC MOTOR

The construction of a dc motor is identical to that of a dc generator.

It consists of :

a) Armature assembly ( shaft, iron core, armature winding

and commutator)

b) Field assembly ( pole pieces , yoke, fields windings)

c) Brushes assembly ( brushes, brush holders, brush

rockers and brush spring )

d) Bearings

EASA Ref : 3.12


POWER

POWER IS PROPORTIONAL TO THE TORQUE AND THE SPEED

STRONG TORQUE AT LOW SPEED, LOW TORQUE AT HIGH SPEED

TORQUE

TORQUE IS PROPORTIONAL TO Φ X Ia

OUTPUT TORQUE (SHAFT TORQUE ) =ARMATURE TORQUE – LOST TORQUE

LOST TORQUE WILL VARY WITH SPEED

EASA Ref : 3.12


BACK EMF

BACK EMF IS THE INDUCED EMF OPPOSES THE APPLIED VOLTAGE (LENZ’S LAW )

BACK EMF PUSHING ONE WAY AND APPLIED VOLTAGE THE OTHER WAY, SO THE

DIFFERENCE BETWEEN THESE TWO ACTUALLY DRIVES CURRENT THROUGH THE

ARMATURE CCT KNOWN AS EFFECTIVE VOLTAGE OR ARMATURE VOLTAGE

EFFECTIVE VOLTAGE = APPLIED VOLTAGE – BACK EMF

EX. A 28 VOLTS DC MOTOR HAS A 1 OHM ARMATURE RESISTANCE AND ARMATURE

CURRENT OF 2 AMPS FLOWING. FIND THE BACK EMF

BACK EMF = APPLIED VOLTAGE – EFFECTIVE VOLTAGE

= 28 – 2X 1 = 26 VOLTS

EASA Ref : 3.12


SPEED CONTROL OF A DC MOTOR

SPEED CONTROL MAY BE OBTAINED BY CONTROLLING THE FIELD CURRENT

OR ARMATURE CURRENT

BY INSERTING VARIABLE RESISTORS IN THE FIELD CCTS OR ARMATURE CCTS

EASA Ref : 3.12


TO REVERSE THE DIRECTION OF ROTATION OF A MOTOR

IS TO REVERSE THE DIRECTION OF CURRENT FLOW THROUGH THE ARMATURE

OR THE FIELDS

IF THE CURRENT FLOW THROUGH THE ARMATURE AND THE FIELD ARE BOTH

REVERSED THE MOTOR CONTINUES IN THE SAME DIRECTION

ON AIRCRAFT IT IS NORMAL TO REVERSE THE DIRECTION OF CURRENT THROUGH

THE ARMATURE BY MEANS OF REVERSING RELAYS

USE TWO FIELDS BOTH WOUND ON THE SAME POLE PIECES BUT WITH ONE

GIVING OPPOSITE POLARITY TO THE OTHER

EASA Ref : 3.12


TYPES OF DC MOTORS

1. SERIES MOTOR

The field is connected in series with the armature, so the torque is proportional

to the square of the armature current

Large starting torque,

High torque at low speed – starting an a/c engine

The motor must be connected to a load permanently as the off load speed will be

very high

On engine starter motors a small shunt winding is incorporated to limit this off load

speed as the starter is disconnected from the engine.

EASA Ref : 3.12


SERIES MOTOR CHARACTERISTICS

EASA Ref : 3.12


2. SHUNT MOTOR

The field is connected in parallel with the armature and of fairly high resistance.

Considered to be a constant speed machine

It is a self regulating machine,( when a new load is placed on the motor’ the motor

automatically adjusts its own effective voltage)

Starting torque is small- slow build up of the field strength and restricted armature

current

Should be started on light load or no load conditions.

Used in inverter drives, windscreen wipers and fuel pumps

EASA Ref : 3.12


SHUNT MOTOR CHARACTERISTICS

EASA Ref : 3.12


3.COMPOUND WOUND MOTOR

Has two windings wound on the same pole pieces .They are wound to assist one another (cumulative ) or to oppose one another (differential )

a)Cumulative Compound

i )Predominantly shunt field winding, the series winding enables a fairly high starting torque and a constant torque machine

Used on fuel pumps and heavy duty actuators

ii) Shunt limited type – high torque at low speed. When the motor is disconnected

from the load ,the minor shunt limits the off load speed.

EASA Ref : 3.12


b) Differential Compound

The shunt and series field windings are wound to oppose one another.

Fairly constant speed/load characteristic which is fairly constant but increases speed

as the load becomes too great

Low starting torque, but if overloaded, the series field winding will cancel the

shunt field winding.

There will be no torque the motor will stop even though taking excessive current.

Has a problem on starting.

EASA Ref : 3.12


COMPOUND MOTOR CHARACTERISTICS

EASA Ref : 3.12


BASIC GENERATOR THEORY

When a conductor cuts a magnetic field, an emf is induced in the conductor

(Faraday’s Law )

A single coil which can be rotated between a magnetic field, the ends of the coil are

connected to slip rings, brushes spring on the slip rings make the connection to the

external circuit (load

The loop is rotated through 360 degrees and an alternating emf is generated.

The magnitude of the emf generated depends on :

- B = Flux Density in Tesla

- l = length of conductor in meters

v = velocity (speed ) of conductor in meters/sec

e= B l v

EASA Ref : 3.12


FLEMING’S RIGHT HAND RULE

TO FIND THE DIRECTION OF THE INDUCED EMF (HENCE THE CURRENT ) OF A

CONDUCTOR ROTATED IN A MAGNETIC FIELD

FIRST FINGER – DIRECTION OF MAGNETIC FIELD

SECOND FINGER – DIRECTION OF CURRENT FLOW (CONVENTIONAL)

THUMB - DIRECTION OF CONDUCTOR MOVEMENT

EASA Ref : 3.12


FLEMING’S RIGHT HAND RULE

EASA Ref : 3.12


CONSTRUCTION AND PURPOSE OF COMPONENTS IN DC GENERATOR

1. ARMATURE ASSEMBLY

a) Shaft

b) Iron Core - provides low reluctance path, core laminated –to reduce

eddy currents

c) Armature Windings ( output windings) –wound in longitudinal slots in the

core and wedged.

Wave windings – high voltage and low current output

Lap windings - high current and low voltage output.

d) Commutator – consists of a number of copper segments on the shaft

they are insulated from one another by strips of mica

rectify ac to dc

EASA Ref : 3.12


2. FIELD ASSEMBLY

a) Yoke – cylindrical frame of the machine.-part of the magnetic cct.Made of cast or rolled steel.

b) Pole Pieces – forms the core of the magnet coils. Bolted inside the yoke.laminated- reduces eddy currents

c) Field Windings – pre-formed coils mounted on the pole pieces.

provide the North and South polarity alternately

3. BRUSHES GEAR ASSEMBLY

a) Brush - made of material of low contact resistance, low specific resistance, low coefficient of friction, and good lubricating properties-graphite carbon.

b) Brush Holders - metal boxes for brush to fit in. Brush holders is secured tobrush rockers.

c) Brush Spring - maintain good contact with commutator

4. BEARINGS -supported the armature. Ball or roller

EASA Ref : 3.12


TYPICAL DC GENERATOR

EASA Ref : 3.12


CLASSIFICATION OF DC GENERATORS

1. PERMANENT MAGNET

2. SEPARATELY EXCITED

3. SELF EXCITED

SELF EXCITED DC GENERATORS

THE FIELD IS EXCITED BY CURRENT OBTAINED FROM THE ARMATURE OF

THE MACHINE ITSELF. THESE GENERATORS HAS A SMALL AMOUNT OF

RESIDUAL MAGNETISM IN THE POLE PIECES DUE TO PREVIOUS MAGNETISATIONS

A) SERIES WOUND

FIELD COILS ARE WOUND IN SERIES WITH THE ARMATURE. FEW TURNS OF

HEAVY WIRE OR COPPER STRIP OF LARGE CROSS SECTION AREA OF VERY LOW RESISTANCE.

HAVE POOR VOLTAGE REGULATION –NOT NORMALLY USED ON A/C

EASA Ref : 3.12


SERIES WOUND GENERATOR

EASA Ref : 3.12


B ) SHUNT WOUND

FIELD WINDINGS CONNECTED IN PARALLEL TO THE ARMATRE AND ALSO TO

THE EXTERNAL CCT.CONTAINS MANY TURNS OF SMALL WIRE OF HIGH

RESISTANCE.

SHUNTGENERATOR SHOULD BE ALLOWED TO BULD UP TO THEIR CORRECT

VOLTAGE BEFORE THE LOAD IS APPLIED.

IF THE LOAD IS INCREASED ABOVE THE FULL CONDITION THEN ,THE VOLTAGE

DROPS TO ZERO.

HAS A FALLING VOLTS/LOAD CHARACTERISTICS DUE TO IR DROP IN THE

ARMATURE WINDINGS

USED ON A/C AS ITS DC POWER SOURCE

EASA Ref : 3.12


SHUNT WOUND GENERATOR

EASA Ref : 3.12


C) COMPOUND WOUND

COMBINATION OF A SERIES WINDING AND A SHUNT WINDING.

IF THE SERIES FIELD ASSISTS THE SHUNT FIELD, THE GEN IS SAID TO BECUMULATIVE COMPOUND

a) FLAT COMPOUND – THE ‘NO-LOAD’ AND ‘FULL LOAD’ VOLTAGES ARE OFTHE SAME VALUE.

b) UNDER COMPOUND – THE ‘FULL LOAD’ VOLTAGE IS LESS THAN THE‘NO LOAD’ .

c) OVER COMPOUND – THE’FULL LOAD’ VOLTAGE IS HIGHER THAN THE‘NO LOAD’ VALUE

IF THE SERIES FIELD OPPOSES THE SHUNT FIELD, THE GEN IS SAID TO BEDIFFERENTIAL COMPOUND

USED WHERE VOLTAGE REGULATION IS OF PRIMARY IMPORTANCE

EASA Ref : 3.12


COMPOUND WOUND GENERATOR

EASA Ref : 3.12


REGULATION OF GENERATOR VOLTAGE

EASA Ref : 3.12


VIBRATING TYPE VOLTAGE REGULATOR

EASA Ref : 3.12


STARTER GENERATOR

CONSTRUCTION

CONSISTS OF SELF EXCITED COMPOUND WOUND GENERATOR WITH

COMPENSATING AND INTERPOLE WINDINGS AND INTEGRAL FAN COOLING.

IT IS COOLED BY RAM AIR

SPEED SENSOR –SIGNAL FOR STARTER CUTOFF

START AS COMPOUND MOTOR

SERIES MOTOR FOR TORQUE

SHUNT GENERATOR – CONNECTED TO BUS BAR

EASA Ref : 3.12


LOOP IN A MAGNETIC FIELD

AC THEORY ( EASA Ref : 3.13 )


EASA Ref : 3.13

EMF GENERATION


EASA Ref : 3.13

Flux Cut by a Loop in a Magnetic Field


EASA Ref : 3.13

Lines Cut against Loop Position


EASA Ref : 3.13

EMF against Loop Position


EASA Ref : 3.13

Peak Value of a Sinusoidal Wave


EASA Ref : 3.13

Peak to Peak Value of a Sinusoidal Wave


ROOT MEAN SQUARE VALUE

AN ALTERNATING CURRENT THAT WILL GENERATE THE SAME AMOUNT OF HEATAS DIRECT CURRENT THAT HAS A VALUE OF ONE AMPERE IS CONSIDERED TO HAVE AN EFFECTIVE VALUE OR RMS VALUE OF ONE AMPERE.

RMS VALUE = PEAK VALUE√2

AVERAGE VALUE =0.637 PEAK VALUE

INSTANTANEOUS EMF (U) =EMF max x Sinθ

EASA Ref : 3.13


Period of a Sinusoidal Wave

EASA Ref : 3.13


Frequency of a Sinusoidal Wave

EASA Ref : 3.13


Period and Frequency

EASA Ref : 3.13


Frequency Band

EASA Ref : 3.13


ANGULAR VELOCITY

ANGULAR VELOCITY (ω ) = 2 π f rad /sec

360 Degrees = π radians

RADIAN

EASA Ref : 3.13


Sine Waves in Phase

EASA Ref : 3.13


Sine Waves Out of Phase

EASA Ref : 3.13


Typical Waveforms

EASA Ref : 3.13


PRT and Mark to Space Ratio

EASA Ref : 3.13


Generation of Three Phase Alternating Current

EASA Ref : 3.13


RESISTIVE ( R ), CAPACITANCE ( C ), AND INDUCTANCE ( L )(EASA Ref : 3.14 )

RESISTORS,CAPACITORS AND INDUCTORS ARE IMPORTANT COMPONENTS IN

ELECTRICAL AND ELECTRONIC ENGINEERINGS.

IF A RESISTOR IS CONNECTED TO A SINUSOIDAL VOLTAGE, THE CURRENT AND

VOLTAGE ARE ALWAYS IN PHASE.

WITH A CAPACITOR,THE VOLTAGE LAGS THE CURRENT BY 90 DEGREES

WHEREAS WITH A COIL, THE VOLTAGE LEADS THE CURRENT BY 90 DEGREES

ALL THE ABOVE CAN BE REPRESENTED IN GRAPHS AND IN PHASOR DIAGRAMS.


EASA Ref : 3.14

RC Series Connection


EASA Ref : 3.14


EASA Ref : 3.14


EASA Ref : 3.14


EASA Ref : 3.14

Power Triangles for RC and RL Series Circuit


EASA Ref : 3.14

Mathematical Relationship for Power inRC/RL Series Circuits


EASA Ref : 3.14

Resistor/ Capacitor in Parallel


EASA Ref : 3.14

Resistor/Coil in Parallel


EASA Ref : 3.14

Mathematical Relationship for Currentin RC/RL Parallel Circuits


EASA Ref : 3.14

Mathematical Relationship for Admittance,

Conductance and Susceptances


EASA Ref : 3.14

RC/RL Frequency dependent Current Divider


EASA Ref : 3.14

Power Triangles for RC and RL Parallel Circuits


EASA Ref : 3.14

Mathematical Relationship for Power in RC/RLParallel Circuits


EASA Ref : 3.14


EASA Ref : 3.14


EASA Ref : 3.14


EASA Ref : 3.14


EASA Ref : 3.14


EASA Ref : 3.14


EASA Ref : 3.14


EASA Ref : 3.14


EASA Ref : 3.14


TRANSFORMER ( EASA Ref : 3.15 )

TRANSFORMER PRINCIPLES

A TRANSFORMER IS AN ELECTRICAL DEVICE FOR TRANSFERRING ELECTRICAL

ENERGY FROM ONE CIRCUIT TO ANOTHER CIRCUIT BY MUTUAL INDUCTANCE.

(ELECTROMAGNETIC INDUCTION ).

THE ELECTRICAL ENERGY IS TRANSFERRED WITHOUT A CHANGE IN FREQUENCY.

A TRANSFOERMER WILL NOT OPERATE WITH A STEADY CURRENT IN THE

PRIMARY. (DC )

WHEN AC IS USED,THE VOLTAGE AND CURRENT LEVELS CAN BE INCREASED OR

DECREASED.(STEP-UP OR STEP –DOWN).


EASA Ref : 3.15

Transformer Principles


EASA Ref : 3.15

BASIC CONSTRUCTION OF A TRANSFORMER

1. CORE - SUPPORTS THE WINDINGS AND PROVIDES A PATH FOR MAGNETIC FLUX-AIR –CORE – USED WHEN HIGH FREQUENCY ABOVE 20 KHz-IRON –CORE – FREQUENCY BELOW 20KH

-STEEL- CORE- LAMINATED FOR EFFICIENT POWER TRANSFERSHAPE OF CORE- HOLLOW SQUARE THROUGH THE CENTER

- SHELL –CONSISTS OF E AND I SHAPED SECTIONS OF METAL

2. WINDINGS – WRAPPED AROUND THE A CORE- PRIMARY – RECEIVES ENERGY FROM THE AC SOURCE - SECONDARY- RECEIVES ENERGY FROM THE PRIMARY WINDING AND DELIVERS TO THE LOAD

3. ENCLOSURE- PROTECTION FROM DIRT , MOISTURE, AND MECHANICALDAMAGE.


EASA Ref : 3.15

(a) Hollow –core construction (b) Windings wrapped around laminations(c ) Shell-type core construction


EASA Ref : 3.15

BASIC OPERATION OF A TRANSFORMER

WHEN AN ALTERNATING VOLTAGE IS APPLIED TO THE PRIMARY WINDING,IT

PRODUCES AN ALTERNATING CURRENT , WHICH SETS UP ALTERNATINGMAGNETIC FLUX (EXPANDING AND CONTRACTING ) THROUGH THE CORE.

THE MAGNETIC FLUX INDUCES AN EMF INTO THE SECONDARY WINDING.

( MUTUAL INDUCTANCE ).

THE VOLTAGE MAY BE STEPPED UP OR DOWN DEPENDING ON THE DESIGN

OF THE PRIMARY AND THE SECONDARY WINDINGS.


EASA Ref : 3.15

Mutual Inductance


EASA Ref : 3.15

Schematic symbols for transformer


EASA Ref : 3.15

TRANSFORMER LOSSES

1. COPPER LOSSES ( I2R LOSS )

- PRODUCED BY CURRENTS FLOW IN THE TRANSFORMER WINDINGS.

( RESISTANCE OF THE WINDINGS)

2. CORE LOSSES –IRON LOSSES

A) HYSTERESIS LOSS – THE BUILD UP AND COLLAPSE OF THE

MAGNETIC FLUX IN THE CORE.

B) EDDY CURRENT LOSSES – CIRCULATING CURRENTS PRODUCED

IN THE CORE BY THE CHANGING MAGNETIC FLUX.

3. STRAY LOSSES – POWER IS LOST IN AN INDUCTOR.(VARIOUS KINDS )


EASA Ref : 3.15

METHODS OF OVERCOMING LOSSES

COPPER LOSSES

MINIMISED BY USING LARGE DIAMETER CONDUCTORS FOR THE WINDINGS

HYSTERESIS LOSSES

THE CORES ARE FORMED INTO SQUARE OR RECTANGULAR BLOCK TO PROVIDE

A COMPLETE CLOSED PATH FOR THE MAGNETIC FLUX.

USED OF SOFT MAGNETIC MATERIALS- ADD 3% OF SILICON TO IRON

EDDY CURRENT LOSSES

THE IRON CORE IS LAMINATED AND INSULATING THE SEPARATE

LAMINATIONS FROM EACH OTHER.


EASA Ref : 3.15

PRIMARY AND SECONDARY VOLTAGE, PRIMARY AND SECONDARYCURRENT,TURNS RATIO, POWER AND EFFICIENCY

RELATION OF THE PRIMARY AND THE SECONDARY VOLTAGEU SU S = = N SN SU P N PU P N P

RELATION BETWEEN THE PRIMARY AND THE SECONDARY CURRENTI P = N SI S N P

TURNS RATIO = N S N P

POWER, P =U S. I S = U P . I P EFFICIENCY , η = P SP P


EASA Ref : 3.15

TRANSFORMER ACTION UNDER LOAD AND NO LOAD CONDITIONS

TRANSFORMER ON NO LOAD CONDITION

When the supply voltage is applied to the primary, an induced emf (back emf )

is produced in the primary which opposes the supply voltage. Very small

excitation current ( I e ) will flow in the primary winding to overcome losses

and to magnetise the core

The primary and secondary voltages are in anti-phase.

The off load primary current (I o ) lags the primary voltage with a large angle.

( poor power factor for a transformer on no load )


EASA Ref : 3.15

TRANSFORMER ON LOAD CONDITION

When a load is applied to the secondary, a secondary current will flow .

This current opposes the primary flux so reduce the total flux in the core.

The primary back emf is reduced and increase in effective emf in the

primary so increase in primary current.

The secondary current is 180 degrees out of phase to the primary current.

The total primary current is the phasor sum of off load primary current and

excitation current (I o ) .


EASA Ref : 3.15

POLARITY MARKINGS

PHASING DOTS

The dots at the ends of the winding are called the phasing dots.

The positioning of the dots is used to indicate the similar instantaneous

polarities.

When an instantaneous positive voltage is applied to the primary terminals

( dot) there will be an instantaneous positive voltage produced at the

secondary terminals (dot).


EASA Ref : 3.15

AUTOTRANSFORMER

IS ONE IN WHICH PART OF THE WINDING IS COMMON TO BOTH THEPRIMARY AND SECONDARY CIRCUITS.SUITABLE FOR APPLICATIONS THAT REQUIRE A VOLTAGETRANSFORMATION.OF NEAR UNITY, AND TO REDUCE THE APPLIED VOLTAGE TO AN AC MOTOR DURING STARTING.

ADVANTAGE – REQUIRE LESS COPPER WIRE, SO LESS I2R LOSSDISADVANTAGE – NOT SAFE FOR INTERCONNECTING HIGH-VOLTAGE ANDLOW –VOLTAGE CIRCUITS, BECAUSE OF THE COMMON WINDING.

A VARIABLE AUTOTRANSFORMER- PROVIDES AN ADJUSTABLE AC VOLTAGE.


EASA Ref : 3.15


EASA Ref : 3.15

EFFICIENCY

THE EFFICIENCY OF A TRANSFORMER IS

η = OUTPUT POWER

INPUT POWER

= OUTPUT POWER

OUTPUT POWER + LOSSES( COPPER + IRON )

REGULATION

= NO LOAD VOLTAGE – FULL LOAD VOLTAGE

FULL LOAD VOLTAGE


EASA Ref : 3.15

LINE AND PHASE VOLTAGES

STAR CONNECTIONS

LINE VOLTAGE = 3 PHASE VOLTAGE

UL = 3 UP

DELTA CONNECTIONS

LINE VOLTAGE = PHASE VOLTAGE

UL = UP


EASA Ref : 3.15

LINE AND PHASE CURRENTS

STAR CONNECTIONS

LINE CURRENT = PHASE CURRENT

IL = IP

DELTA CONNECTIONS

LINE CURRENT = √3 PHASE CURRENT

IL = √3 IP


EASA Ref : 3.15

CALCULATION OF POWER IN A PHASE SYSTEM

STAR CONNECTIONS

POWER = 3 UP IP COS θ WATTSALSO = 3 UP IL COSθ ,UP = UL/√ 3 COS θ , IL =IP

=√3 UL IL COS WATTS

DELTA CONNECTIONS

POWER = 3 UP IP COSθ WATTSALSO = 3 UL IP COSθ ‘ UP =UL, IP =IL/√3

= √3 UL IL COSθ WATTS


A FILTER IS ANY CIRCUIT THAT WILL REMOVE SOME PARTS OF A SIGNAL OR POWER SOURCE, WHILE ALLOWING OTHER PARTS TO CARRY ON WITHOUTHINDRANCE.EQUALIZERS, CROSSOVER NETWORKS, TWEETER, AND POWER CONDITIONING.

LOW PASS FILTER

PASSES LOW FREQUENCIES BUT BLOCKS FREQUENCIES HIGHER THAN THE CUTOFF FREQUENCY

1. INDUCTIVE LOW PASS ( LR FILTER )USE IN AC DC POWER SUPPLIES.

2. CAPACITIVE LOW PASS ( RC FILTER )USED IN AUDIO FREQUENCIES

3. T TYPETWO INDUCTORS AND A CAPACITOR

4. Π TYPEAN INDUCTOR AND TWO CAPACITORS

.

FILTERS ( EASA Ref : 3.16 )


EASA Ref : 3.16

Main characteristic of low pass filter


EASA Ref : 3.16

HIGH PASS FILTER

OFFER EASY PASSAGE OF HIGH FREQUENCY SIGNAL AND BLOCK LOW FREQUENCY SIGNAL

1. CAPACITIVE HIGH PASS ( CR FILTER )HIGH IMPEDANCE IN SERIES BLOCK LOW FREQUENCY SIGNALS

2. INDUCTIVE HIGH PASS (RL FILTER )LOW IMPEDANCE INPARALLE SHORT OUT LOW FREQUENCY SIGNAL

3. T TYPE2 SERIES CAPACITORS AND AN INDUCTOR

4. Π TYPEA CAPACITOR AND PARALLEL CAPACITORS


EASA Ref : 3.16

High pass frequency response curve


EASA Ref : 3.16

BAND PASS FILTER

BLOCKS FREQUENCIES THAT ARE TOO HIGH AND FREQUENCIES THAT ARE TOO LOW

SIGNAL INPUT -------LOW PASS--------HIGH PASS------------SIGNAL OUTPUT

1. CAPACITIVE BAND PASSLOW PASS –RC , HIGH PASS –CR

2. INDUCTIVE BAND PASSHIGH PASS – RL , LOW PASS – LR

3. MADE UP OF INDUCTORS AND CAPACITORSCR –HIGH PASS , RC – LOW PASS


EASA Ref : 3.16

Band pass frequency response


EASA Ref : 3.16

BAND STOP FILTER

STOPS TRANSMISSION OF FREQUNCIES BETWEEN f co1 AND F co 2ALSO KNOWN AS A NOTCH , BAND REJCT OR BAND ELIMINATION FILTER.SERIES ELEMENT – PARALLEL RESONANT CCTS ( 2 TUNED CCTS )SHUNT ELEMENT – A SERIES RESONANT CCT

AT LOW FR THE SERIES RESONANT CCT IMPEDANCE ( Z ) IS HIGH,PARALLEL CCT IMPEDANCE IS LOW. FREQUENCY PASSED.

AT RESONANT, THE PARALLEL CCT Z IS HIGH , SERIES RESONANT Z IS LOW.THEREFORE FREQUENCIES ARE BLOCKED IN THESE RANGE

AT HIGH FR, THE PARALLEL CCT Z LOW, SERIES ONE INCREASED,SO FREQUENCIES PASSED AGAIN.

.


EASA Ref : 3.16

Characteristics of band stop filter


EASA Ref : 3.16

APPLICATIONS OF FILTERS IN AIRCRAFT

HF COMMUNICATION TRANSCEIVER

VOR RECEIVERS

MARKER BEACON RECEIVER

ILS RECEIVER

ENGINE VIBRATION MONITORING SYSTEMS

AUTOMATIC FLIGHT CONTROL SYSTEMS

FLIGHT DIRECTOR SYSTEMS

VOICE RECORDER


ROTATION OF A LOOP IN A MAGNETIC FIELD AND WAVE FORM PRODUCED

WHEN LOOP OF COIL ROTATED IN A MAGNETIC FIELD, THE COIL CUTS THROUGH A MAGNETIC FIELD,GENERATING AN EMF.THE EMF PRODUCED ARE CONNECTED TO SLIP RINGS WHICH CAUSE CURRENTTO FLOW ALTERNATELY FIRST IN ONE DIRECTION AND THEN IN THE OTHERDIRECTION IN ONE COMPLETE REVOLUTION.THESE IS THE BASIC AC GENERATOR PRINCIPLE

THE WAVEFORM PRODUCED IS A SINOSOIDAL ( ALTERNATING )

AC GENERATORS ( EASA Ref : 3.17 )


EASA Ref : 3.17

Rotation of a loop in a magnetic field and waveform produced


EASA Ref : 3.17

CONSTRUCTION OF REVOLVING (ROTATING ) ARMATURE TYPE GENERATOR

STATOR - STATIONARY PART OF THE GENERATOR – FIELD WINDINGSDC EXCITATION ON POLE PIECE TO CREATE NORTH AND SOUTHPOLES AROUND THE STATOR.

ROTOR - ROTATING PART OF THE GENERATOR – ARMATURE WINDINGSIN SLOTS

SLIP RINGS - OUTPUT


EASA Ref : 3.17

OPERATION OF REVOLVING ARMATURE TYPE GENERATOR

THE ROTOR CUTS THE MAGNETIC FIELD AND PRODUCES AN AC EMF IN THE

STATOR.

THE GENERATED EMF IS BROUGHT TO THE LOAD BY SLIP RINGS

LOW POWER RATING

SELDOM USED ON A/C


EASA Ref : 3.17

Rotating armature alternator


EASA Ref : 3.17

CONSTRUCTION OF REVOLVING (ROTATING ) FIELD TYPE GENERATOR

STATOR – ARMATURE WINDINGS –OUTPUTROTOR - FIELD WINDINGS- FED VIA SLIP RINGS AND BRUSHES WITD DC

OPERATION OF REVOLVING FIELD TYPE

THE FIELD IS ROTATED AND CUTS THE STATIONARY WINDINGS.AN AC IS PRODUCED IN THE STATOR WINDINGS –OUTPUT

IT IS PREFFERED THAN REVOLVING ARMATURE TYPE BECAUSE:THE OUTPUT CAN BE CONNECTED DIRECTLY TO THE LOADPROBLEM OF HIGH VOLTAGE ARCING AT THE SLIP RINGS ARE ELIMINATED


EASA Ref : 3.17

Rotating field alternator


EASA Ref : 3.17

SINGLE PHASE ALTERNATOR

A GENERATOR THAT PRODUCES A SINGLE CONTINUOSLY ALTERNATING

VOLTAGE.

THE STATOR WINDINGS ARE CONNECTED IN SERIES.

THE INDIVIDUAL VOLTAGE THEREFORE ADD ,TO PRODUCE A SINGLE PHASE

AC VOLTAGE


EASA Ref : 3.17

TWPO PHASE ALERNATOR

IF ANOTHER SET OF SINGLE PHASE WINDINGS AT 90° TO ONE ANOTHER IS ADDED TO THE SINGLE PHASE, A TWO PHASE OUTPUT IS PRODUCED90° OUT OF PHASE WITH EACH OTHER.

THREE PHASE ALTERNATOR

THREE PAIRS OF COILS ARE USED.EACH PAIR OF COILS IS SPACED AT 120° TO ONE ANOTHERSO 3 PHASES ARE PRODUCED WHERE THE OUTPUTS ARE 120° OUT OF PHASE


EASA Ref : 3.17

Single phase alternator Two phase alternator


EASA Ref : 3.17

3 Phase rotating field generator


EASA Ref : 3.17

THREE PHASE STAR CONNECTION

LINE CURRENT = PHASE CURRENT

I L = I P

LINE VOLTAGE = √ 3 PHASE VOLTAGE

U L = √ 3 U P

ADVANTAGE

2 VOLTAGES – 200 V AC AND 115 V AC

USES –IN A/C POWER SUPPLIES


EASA Ref : 3.17

THREE PHASE DELTA CONNECTIONS

LINE CURRENT = √3 PHASE CURRENTIL = √3 IP

LINE VOLTAGE = PHASE VOLTAGEU L = U P

ADVANTAGE

2 VALUE OF CURRENTS – HIGHER CURRENT OUTPUT


EASA Ref : 3.17

PERMANENT MAGNET GENERATOR

ALSO CALLED BRUSHLESS GENERATORCONSISTS OF PMG, MAIN EXCITER GENERATOR AND MAIN GENERATOR

OPERATION OF BRUSHLESS GENERATOR

WHEN GENERATOR SHAFT ROTATES, PMG WILL ROTATE, ITS FIELD CUTS THE STATOR FIELD WINDING, INDUCES AC INTO IT.THE OUTPUT FED TO THE V/R IN THE GCU.THE AC RECTIFIED AND GOES TO MAIN EXCITER STATOR FIELD.THE EXCITER FIELD INDUCES VOLTAGE INTO THE EXCITER INPUT WINDING.THE OUTPUT IS RECTIFIED BY 6 SILICON DIODESSENT TO OUTPUT FIELD WINDINGVOLTAGE IS INDUCED IN THE MAIN OUTOUT WINDING


EASA Ref : 3.17

Brushless Generator


CONSTRUCTION OF THREE PHASE SYNCHRONOUS MOTOR

CONSISTS OF

1. STATOR FIELD WNDING

2. ROTOR- PERMANENT MAGNET OR ELECTROMAGNET

SALIENT POLE – WINDING RECEIVED DC

THROUGH SLIP RINGS

AC MOTORS ( EASA Ref : 3.18 )


EASA Ref : 3.18

Synchronous motor


EASA Ref : 3.18

OPERATION OF AC SYNCHRONOUS MOTOR

WHEN 3 PHASE AC POWER IS APPLIED TO THE STATOR,

ROTATING MAGNETIC FIELD IS SET UP AROUND THE ROTOR

THE ROTOR IS ENERGISED WITH DC ( ACTS AS A BAR OF MAGNET )

ATTRACTED BY THE ROTATING STATOR FIELD

THIS ATTRACTION WILL EXERT A TORQUE ON THE ROTOR

CAUSE THE ROTOR TO ROTATE WITH THE FIELD.


EASA Ref : 3.18

Action of synchronous motor


EASA Ref : 3.18

CHARACTERISTICS OF AC SYNCHRONOUS MOTOR

1. NOT SELF STARTNG

2. CONSTANT SPEED

DEPENDS ON THE FREQUENCY OF THE POWER SUPPLY

F = NP/60 HZ

3. USE AS MOTR IN ENGINE SPEED INDICATORS

4. DIRECTION OF ROTATION CAN BE ACHIEVED BY CHANGING ANY

TWO OF THE 3 PHASE INPUTS


EASA Ref : 3.18

CONSTRUCTION OF 3 PHASE INDUCTION MOTOR

1. STATOR FIELD WINDING

2. ROTOR – NOT CONNECTED TO EXTERNAL SOURCE VOLTAGE

- SQUIRREL CAGE ROTOR

- WOUND ROTOR


EASA Ref : 3.18

Types of ac induction motor rotors


EASA Ref : 3.18

OPERATION OF INDUCTION MOTOR

CURRENT IS INDUCED IN THE ROTOR BY THE ACTION OF THE ROTATING MAGNETIC FIELD CUTTING THE ROTOR CONDUCTORS.ROTOR CURRENT GENERATE A MAGNETIC FIELD INTEACTS WITH THE STATOR.TORQUE EXERTED ON THE ROTOR AND CAUSE IT TO ROTATE

AS THE STATOR FIELD IS ROTATING, THE ROTOR FOLLOW A LITTLE BEHIND.IF THERE IS NO RELATIVE MOTION, NO CURRENT AND NO ROTOR MOVEMENT.

THE DIFFERENCE BETWEEN THE ROTOR SPEED AND ROTATING MAGNETICFIELD SPEED ( SYNCHRONOUS SPEED ) IS THE SLIP SPEED.

SLIP SPEED = Ns – Nr ( SYN SPEED – ROTOR SPEED )SLIP = Ns – Nr x100

Ns


EASA Ref : 3.18

Production of motor torque


EASA Ref : 3.18

CHARACTERISTICS OF INDUCTION MOTOR

1. SELF STARTING

2. CONSTANT SPEED

USE AS HYDRAULIC PUMPS, FUEL PUMPS AND FLAP MOTOR

TO REVERSE THE DIRECTION OF ROTATION, CHABGE OVER ANY 2

CONNECTIONS OF THE 3 PHASE INPUTS

.


EASA Ref : 3.18

Speed/Torque characteristic of induction motor


EASA Ref : 3.18

Induction motor characteristics torque and current vs speed


EASA Ref : 3.18

CONSTRUCTION OF SINGLE PHASE INDUCTION MOTOR (SPLIT PHASE )

CAPACITOR STARTSTATOR - MAIN WINDING AND START WINDING-PARALLEL, 90 DEGREESPHASE DIFFERENCE CAPACITOR –IN SERIES WITH CENTRIFUGAL SWITCH

OPERATION

THE CURRENTS ARE 90 DEGREES OUT OF PHASE, SO MAGNETIC FIELDS ALSO THE SAME.THE TWO WINDINGS ACT LIKE A TWO PHASE STATOR AND PRODUCE THE ROTATING FIELD REQUIRED TO START THE MOTOR.THE SWITCH OPENS AND CUTS OUT THE START WINDING WHEN THE MOTORNEARLY AT FULL SPEED.THE DIRECTION OF ROTATION –REVERSED BY CHANGING OVER THE TWO LEADS OF ANY ONE WINDING.USES FOR VACUUM CLEANERS, WORKSHOP PEDASTAL DRILLS,REFRIGERATOR AND AIR COMPRESSORS.


EASA Ref : 3.18

Single phase induction motor


EASA Ref : 3.18

Capacitor start induction motor


EASA Ref : 3.18

SHADED POLE CONSTRUCTIONSTATOR- PROJECTINGPOLE PIECES – SPLIT INTO TWO - ONE HALF FITTED WITH COPPER OR ALUMINIUM RING ( SHADING )ROTOR- SQUIRREL CAGE

OPERATIONAS THE SUPPLY CURRENT RISES AN INDUCED VOLTAGE IS SET UP IN THESHADING RING.FLUX PRODUCED IN THE RING OPPOSES THE BUILD UP OF MAIN FLUX. MAIN FLUX CONCENTRATES IN THE UNSHADED POLE.AS THE SUPPLY CURRENT DROPS, AN INDUCED VOLTAGE IS SET UP IN THE SHADING RING. FLUX PRODUCED OPPOSES THE COLLAPSE OF THE MAIN FLUX.MAIN FLUX CONCENTRATED IN THE SHADED POLE.THE NEXT HALF CYCLE, THIS IS REPEATED,CREATING FLUX SHIFTING FROM UNSHADED TO THE SHADED POLE, SIMILAR TO A ROTATING FIELD.SPEED IS DETERMINED BY THE INPUT FREQUENCY.CAN BE VARIED WITHIN LIMITED RANGE BY A SERIES RESISTOR ORINDUCTOR.REVERSAL OF ROTATION – BY TRANFERRING THE SHADING RINGS TO THE OTHER HALF OF THE POLEPIECES (NOT PRACTICAL )USE FOR FANS, BLOWERS, CLOCKS AND ENGINE INDICATION INSTRUMENT.


EASA Ref : 3.18

Shaded pole induction motor


EASA Ref : 3.18

Line of flux moves towards the shaded ring (effect of moving field )


EASA Ref : 3.18

CONSTRUCTION OF HYTERESIS MOTORSTATOR – TWO WINDINGS 90° TO EACH OTHER- REFERENCE AND CONTROL PHASEROTOR - COBALT STEEL- HIGH MAGNETIC RETENTIVITY AND LARGE HYTERESIS LOOP.

OPERATIONIF REFERENCE PHASE IS MAXIMUM, CONTROL PHASE NO CURRENT AT THIS TIMEROTOR RETAINS THE FLUX POLARITY WHEN THE REFERENCE PHASE REDUCES.THE CONTROL PHASE NOW BUILDS UP-ROTATING FIELD CREATED.THE ROTOR WILL BE ATTRACTED TO THE STATOR OF THE OPPOSITEPOLARITIES.AS CONTROL CURRENT DIES AWAY, THE CURRENT BUILDS UP ON THEREFERENCE PHASE. ROTOR CONTINUES TO TURN AS THE FIELD ROTATESTHE SPEED OF THE MOTOR DEPENDS ON THE SUPPLY FREQUENCY.DIRECTION OR ROTATION IS DONE BY CHANGING THE PHASE RELATIONSHIP OF THE CONTROL PHASE BY 180 DEGREESUSED AS SERVO MOTORS AND MINIATURE RATE GYROS.


EASA Ref : 3.18

Hysteresis motor


EASA Ref : 3.18

METHODS OF SPEED CONTROL OF INDUCTION MOTOR

1. WOUND ROTOR

- VARYING THE AMOUNT OF EXTERNAL RESISTANCE IN THE ROTOR CIRCUIT.

- USED OF HEAVY DUTY RESISTORS

2. SQIRREL CAGE ROTOR

- TWO SPEED MOTOR WINDING- ELECTRONIC CONYROL UNIT


EASA Ref : 3.18


EASA Ref : 3.18

B1.1M03 Presentation V1.0 Dated 02.02.09

Documents

1m03 presentation

r1 r2

multiplier

rcrl parallel

single phase

magnetic field

aluminum wired

series parallel