B1.1M03 Presentation V1.0 Dated 02.02.09

MODULE 3 : ELECTRICAL

FUNDAMENTALS

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

IONISATION

FACTORS AFFECTING IONISATION:

HEAT

LIGHT

ELECTRIC FIELDS

MAGNETIC FIELDS

CHEMICAL ACTION

PRESSURE

CAN BE:

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

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

CONDUCTION OF ELECTRICITY

IN SOLIDS – ELECTRONS

IN LIQUIDS – POSITIVE IONS OR NEGATIVE IONS

IN GASES – ELECTRONS AND IONS

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

CONVERSION OF ENERGY:

- CHEMICAL ENERGY CONVERTED TO ELECTRICAL ENERGY - ELECTRICAL ENERGY CONVERTED TO LIGHT ENERGY - LIGHT ENERGY CONVERTED TO HEAT ENERGY

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

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)

EASA Ref : 3.3 PREFIXES: 0.1 Amp = 100 milliamp 0.010 Amp = 10 milliamp 0.001 Amp = 1 milliamp 0.000001 Amp = 1 microamps 3 TYPES OF CURRENT: - DIRECT CURRENT (DC)

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

FREQUENCY:

1 HERTZ = 1 CYCLE PER SECOND

UNIT FOR FREQUENCY = HERTZ (Hz)

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)

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

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

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

ELECTRIC CHARGES:

ELECTRIC CHARGES GIVES A MATERIAL ITS ELECTROMAGNETIC

PROPERTIES

PROTON - POSITIVE CHARGE

ELECTRON - NEGATIVE CHARGE

2 TYPES OF CURRENT FLOW:

ELECTRON FLOW - ELECTRONS FLOW FROM NEGATIVE TO POSITIVE

CONVENTIONAL CURRENT FLOW - HOLES TRAVEL FROM POSITIVE TO NEGATIVE

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.

6 BASIC MEANS OF GENERATING ELECTRICITY - FRICTION - PRESSURE - HEAT - LIGHT - MAGNETISM GENERATON OF ELECTRICITY ( EASA Ref : 3.4 )

FRICTION:

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

ONE BECOMES POSITIVE AND THE OTHER WILL BE NEGATIVE

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

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

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 )

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.

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)

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

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

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)

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

CLASSES OF CELLS

PRIMARY CELL = NOT RECHARGEABLE = CAN BE USED ONLY ONCE

SECONDARY CELL = RECHARGEABLE = CAN BE REUSED MANY TIMES

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

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

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

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

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

EASA Ref : 3.5

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 distilled water (70%)

- the 2 plates are separated by plates known as separators - purpose of the porous separators is to prevent short circuit

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

EASA Ref : 3.5

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

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

EASA Ref : 3.5

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

EASA Ref : 3.5

ALKALINE BATTERIES - positive plate, nickel hydroxide , NI(OH)2 - negative plate, metallic cadmium (Cd) - electrolyte, potassium hydroxide (KOH) - plates are made by sintering process

EASA Ref : 3.5

Alkaline Battery

Nickel cadmium battery

Connections of

cells

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

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.

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

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 )

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

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

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.

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.

– 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

EASA Ref : 3.5

Temperature versus

Voltage

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

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

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

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

Sources of DC power supply: - battery

- DC generator - rectifier output

3 components associated with a circuit: - voltage => unit volts

- current => unit amperes or amps

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

Series circuit

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

schematic

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

parallel

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

When the series circuits and the

parallel circuits are connected together,

they are said to be a combination.

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:

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.

Using the equation

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

calculated.

voltage = current x resistance

current = voltage / resistance

– To find resistance:

R = V / I = 6V / 2A = 3 Ω

I = E / R = 1.5V / 10Ω = 0.15 Amp

= 150mA

ANALOGY:

E = I X

R (constant)

(constant) E

= I X R

(constant)

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

EASA Ref : 3.6

i

i

i

i

i

i

SUM:

i

+ i

+i

+ i

= i

+ i

=> 5A + 5A + 5A + 4 A = 8A + 11A => 19A = 19A

ALGEBRAIC:

i

=5amp, i

=5amp,

i

=8amp, i

=5amp,

i

=4amp, i

=11amp

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

6V 6V 6V

2K _ ₊ 2K ₊ 2K

+ _ _

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

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 I =0.5 Amp

EASA Ref : 3.6

RESISTORS and RESISTANCE COMES IN MANY - SHAPES - SIZES - VALUES - WATTAGES

SYMBOLS

SI UNIT for RESISTANCE – Ohm

1 OHM = 1 VOLT OF PRESSURE THAT CAN PUSH 1 AMP OF CURRENT

THRU’ A RESISTOR IN A SECOND

18

1 AMP OF CURRENT = 6.24150629 X 10 ELECTRONS PER SEC

MULTIPLES:

Ex:

1K Ω = 1000 Ω

1M Ω = 1000000 Ω = 1 X 10

_Ω

170K Ω =170000 Ω

1M5 = 1500000 Ω

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

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

VARIABLES AFFECTING ELECTRICAL RESISTANCE LENGTH

RESISTANCE INCREASES WITH LENGTH CROSS-SECTIONAL AREA OF THE WIRE

RESISTANCE DECREASES WITH INCREASE IN AREA THE RHO OF THE MATERIAL

DIFFERENT MATERIALS HAVE DIFFERENT RESISTANCE (CONDUCTIVE ABILITY) RESISTIVITY:

DEPENDS ON THE MATERIALS ELECTRICAL STRUCTURE AND ITS TEMPERATURE

TEMPERATURE

MOST MATERIALS USED AS CONDUCTORS INCREASE IN RESISTANCE VALUE AS TEMPERATURE INCREASES.

BUT THERE ARE MATERIALS THAT THEIR RESISTANCE DECREASE AS

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 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

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)

EASA Ref : 3.7

SELECTION OF WIRE

- IF THE PROPER WIRE IS NOT SELECTED, THERE CAN BE A SEVERE DAMAGE TO 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?

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.

BUSBAR (ALUMINUM)

3CM 4CM 125CM

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

SPECIFIC RESISTANCE:

R = p L / A

2.65 µ

Ω

-cm x 125cm / 12cm²

EASA Ref : 3.7

RESISTOR COLOUR CODE

4 COLOUR BANDS

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

THE 3rd _{BAND AS MULTIPLIER ( NUMBER OF ZEROES )}

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

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

5 BAND RESISTORS

FOR MILITARY USE

- 1st_{, 2}nd _{AND 3}rd _{BANDS DETERMINE THE FIRST 3 DIGITS}

- 4th _{BAND IS THE MULTIPLIER}

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_{, 2}nd _{AND 3}rd _{DIGITS ARE THE VALUE}

- 4th _{BAND IS THE MULTIPLIER}

- 5th _{BAND IS THE TOLERANCE}

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

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

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.

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)

RESISTORS CIRCUIT PATTERNS

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

-PARALLEL

-SERIES PARALLEL COMBINATION

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

SERIES CONFIGURATION

V1=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

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

FORMULA

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

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

PARALLEL CONFIGURATION

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

EASA Ref : 3.7

COMBINATION CONFIGURATION (SERIES PARALLEL)

FORMULA:

Req = (R1 // R2) + R3

= R1xR2 +R3

COMBINATION

R

RTOTAL= RAB

x R3

R

1/R

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 1.125 Therefore RCD = 1/1.125 = 0.889 Ohms

EASA Ref : 3.7

RTOTAL = RAB + R3 + RCD

= 2.857 + 3 + 0.889 = 6.7 Ohms

EXAMPLE 2

R

= R1 +R2

= 1 + 2

= 3 Ohms

R

= 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

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

TOLERANCES AND LIMITATIONS

RESISTANCE IS PROPORTIONAL TO LENGTH AND Rho OF THE MATERIAL AND INVERSE TO THE X-SECTIONAL AREA

-OHM’S LAW APPLIES

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

POWER RATING

2 WATTS 1/4 WATT

STABILITY

-THE ABILITY TO MAINTAIN THE RESISTANCE OF THE CIRCUIT -CHANGES VERY LITTLE WITH CHANGE OF TEMPERATURE

-IMPORTANT IN ELECTRONIC PRECISION CIRCUITS

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 SIDES

CHIP TYPE – COMES UP TO 6 LAYERS

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

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 A LAMP OR TO VARY THE CHARGING OF A CAPACITOR

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

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 SMALL SCREWDRIVER

-CHEAP AND VERY ACCURATE

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

.

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

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 )