tech training electronics english

8/9/2019 Tech Training Electronics English

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www.easymind.co.ccproblems simplified with ease & its all free!!


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INTRODUCTION

Electron flow

The Atom

Induction

Electric circuit

Resistance

Static electricity

The conductor

Ohms law

Cable nomogram

Kirchhoffs laws

Circuits

Joules law

Measuring

Multimeter

TRMS

Meter resistance

Circuit conditions

Relay

Fuse

Circuit breaker

Resistor

Inductive switch

Diode

LED

Zener diode

Capacitor

Transistor

Work tasks


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THE ATOMIs the basic unit of matter.

The smallest particle that we can find in a chemical substance is the atom. There are about 115 different

atoms, and by combining them to different molecules we can construct all kind of substances.

When a substance consists of one or more equal atoms it is called an element.

The atom consists of a central, positively charged core, the nucleus, and negatively charged particles called

electrons that are found in orbits around the nucleus. Protons and Neutrons are contained in the centre or

Nucleus of the Atom. For a neutral atom, the number of electrons is equal to the atomic number. Protons

have a positive charge. Neutrons have no charge. Electrons have a negative charge.

Ordinary electric current is the flow of electrons through a wire conductor. The electron is one of the basic

constituents of matter. An atom consists of a small, dense, positively charged nucleus surrounded byelectrons that whirl about it in orbits, forming a cloud of charge. Ordinarily there are just enough negative

electrons to balance the positive charge of the nucleus, and the atom is neutral. The outermost electrons of

an atom determine its chemical and electrical properties.


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THE ATOMElectrons in each shell has a defined energy. The further

the electron is distanced to the nucleus, the higher is theenergy in that electron shell.

Electrons in the outer shell are not strongly bonded to the

the nucleus, and the atom may give up these electrons.

Because metals have few outermost electrons and tend to

give them up easily, they are good conductors of

electricity or heat.

In substances like metals, electrons in the outer shell are

basically moving freely. Connecting an electric voltage to

the metal exposes the charge carriers (electrons) with a

force, causing the electrons to relocate according to the

polarity.

In a conductor, the electrons will move towards the positive pole.

This movement of electrons is called electric current.

Si

Nucleus Electrons

Shell 3Shell 2

Shell 1

The electrons are tightly held in shells that containits maximum number of electrons. If it takes 8

electrons to fill a shell but it has fewer than 8

electrons, the atom will let the electrons come and go

with very little force. This is the reason that some

elements will conduct easily (their outer valence

shell is not full). Copper has a single electron in an

outer shell that can hold as many as 32 electrons.


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THE ATOMElectric current is defined by electrons moving in a

material.

Conductor

Electric conductors are materials where the electrons can

move between different atoms. Good conductors of electricity areelements containing less than 4 electrons in their outer rings.

Semi conductors

In a semiconductor there is a limited movement of

electrons, depending upon the crystal structure of thematerial used. The substances first used for semiconductors

were the elements germanium, silicon, and gray tin.

There are few free electrons compared to conductors.

Insulators (dielectric)

Is a substance that does not readily conduct heat, sound, or

electricity. The electrons are bound and cannot travel

between the atoms.

Glass, porcelain and plastics are commonly used insulators.

Much

Current

Little

Current

No

Current

= Electron


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INDUCTIONElectromagnetic induction. is the production

of an electromotive force (emf) in a conductoras a result of a changing magnetic field about

the conductor.

Variation in the field around a conductor may

be produced by relative motion between the

conductor and the source of the magnetic

field, as in an electric generator, or by varying

the strength of the entire field, so that the field

around the conductor is also changing. Since

a magnetic field is produced around a current-

carrying conductor, such a field can be

changed by changing the current.

On figure A and C, the magnet is standing

still, the induced voltage (and current) is

equal to zero.

A

D

C

E

B

I = 0

I 0

I = 0

I 0

I 0

N

N

N

S

S

S


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INDUCTIONBy changing the magnetic field about the

conductor, there will be produced anelectromotive force (emf) in the conductor.

The direction on the voltage (and current) isdepending on if the magnetic field is

increasing or decreasing.

The level on the induced voltage is dependingon how fast the magnetic field is changing.

The level on the induced voltage is dependingon how strong the magnetic field is.

The direction on the induced voltage isdepending on the direction of the magnetic

field, (in case it is the north/south pole that is

closest to the coil.


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INDUCTION

1 cycle


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ALTERNATOR

Cycle


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THE ELECTRIC CIRCUIT

The battery

Generates a direct current (DC) by a chemical process. The

current is in one direction only, and the battery electrodes may

therefore be marked with (+) and (-).

The alternator

By revolving the coil in a magnetic field, an alternating current

(AC) is being induced. The polarity will alternate.

The technical direction of current is from plus to minus

If the direction of current is defined in a el. schematic, this

direction will be in force.

The actual direction of current, (electron current flow) is on the other

hand from minus to plus.

The electrons move from a negative charged area to a positive charged

area.

A simple electric circuit consists of one power source and one consumer.

Example of power sources are:


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RESISTANCEResistance

-property of an electric conductor by which it

opposes a flow of electricity and dissipates electrical

energy away from the circuit, usually as heat.

Optimum resistance is provided by a conductor that

is long, small in cross section, and of a material that

conducts poorly.

There is always a certain resistance in a conductor.

There will always be a power loss due to a voltagedrop during net movement or flow of electric charge

from one point to another or across some boundary.

The voltage drop will increase the greater the lineresistance is. Usually we are aiming at a low line

resistance by choosing the appropriate cable size and

material.


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STATIC ELECTRICITY-CHARGES

Positive and negative charges behave in interesting ways. Two things with opposite, or different

charges (a positive and a negative) will attract, or pull towards each other. Things with the same

charge (two positives or two negatives) will push away from each other.

A charged object will also attract something that is neutral. Think about how you can make a

balloon stick to the wall. If you charge a balloon by rubbing it on your hair, it picks up extra

electrons and has a negative charge. Holding it near a neutral object will make the charges in that

object move. If it is a conductor, many electrons move easily to the other side, as far from the

balloon as possible. If it is an insulator, the electrons in the atoms and molecules can only movevery slightly to one side, away from the balloon. In either case, there are more positive charges

closer to the negative balloon. The balloon sticks. (At least until the electrons on the balloon slowly

leak off.) It works the same way for neutral and positively charged objects.

As you walk across a carpet, electrons move from the rug to you. Now you have extra electrons.

Touch a door knob and ZAP! The door knob is a conductor. The electrons move from you to the

knob. You get a shock.

We usually only notice static electricity in the winter when the air is very dry. During the summer,

the air is more humid. The water in the air helps electrons move off you more quickly, so you can

not build up as big a charge.

As you walk across a carpet, electrons move from the rug to you. Now you have extra electrons.

Touch a door knob and ZAP! The door knob is a conductor. The electrons move from you to theknob. You get a shock.

We usually only notice static electricity in the winter when the air is very dry. During the summer,

the air is more humid. The water in the air helps electrons move off you more quickly, so you can

not build up as big a charge. OBS! Things with the same charge repel each other. So the hairs try to

get as far from each other as possible.

Static electricity is the imbalance of positive and negative charges.


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STATIC ELECTRICITY-ESD

Electronic components are susceptible to damage from Electrostatic

Discharge (ESD), when an ESD event occurs across their terminals or when electronic parts are exposed to electrostaticfields. Electrostatic Discharge Susceptibility (ESDS) parts can be destroyed by an ESD event regardless of their

electrical and ground connections. Components found to be susceptible to ESD include microelectronic devices, film

resistors, resistor chips, discrete semiconductors, other thick- and thin-film devices, and piezoelectric crystals. Some

common ESDS component types and their relative sensitivities are listed below. Subassemblies and modules containing

ESDS parts are usually as sensitive as the most sensitive ESDS part they contain.

Device Type Range of Susceptibility (Volts)

VMOS 30 to 1800

MOSFET 100 to 200

GaAsFET 100 to 300

EPROM 100 +JFET 140 to 7000

SAW 150 to 500

OP AMP 190 to 5000

CMOS 250 to 3000

Schottky Diodes 300 to 2500

Film Resistors (Thick, Thin) 300 to 3000

Bipolar Transistors 380 to 7800

ECL (PDC Board Level) 500 to 1500

SCR 680 to 1000

Schottky TTL 100 to 2500


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STATIC ELECTRICITY-ESDElectrostatic Discharge (ESD)

Electrostatic discharge is a single, fast, high current transfer of electrostatic charge that results from:

Direct contact transfer between two objects at different potentials, or a high electrostatic field

between two objects when they are in close proximity. The prime sources of static electricity are

mostly insulators and are typically synthetic materials, e.g., vinyl or plastic work surfaces, insulated

shoes, finished wood chairs, Scotch tape, bubble pack, soldering irons with ungrounded tips, etc.

Voltage levels generated by these sources can be extremely high since their charge is not readily

distributed over their surfaces or conducted to other objects. The generation of static electricity

caused by rubbing (or squeezing) two substances together is called the triboelectric effect.Examples of sources of triboelectric electrostatic charge generation in a high RH ( 60%)

environment include:

Walking across a carpet 1000 V1500 V generated.

Walking across a vinyl floor 150 V250 V generated.

Handling material protected by clear plastic covers 400 V600 V generated.

Handling polyethylene bags 1000 V1200 V generated.

Pouring polyurethane foam into a box 1200 V1500 V generated.

ICs sliding down an open antistatic shipping tube 25 V250 V generated.

Note: For low RH (10 those listed above.

What can be done?

Treat floors with static dissipative treatments (benefit of this will probably wear off after a

while.)

Raise air humidity to 40-50% rh with a humidifier

Use an antistatic wrist strap, which connects to your AC ground.Use different Shoes and clothing


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THE CONDUCTOR


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THE CONDUCTOR

Materials which have loosely held electrons are called conductors

Which variable makes an influence on the cable resistance?

Length of the conductor. The longer, the greater the resistance. That is because the electrons have to

travel further and this takes more energy so the resistance

is greater.

The cross sectional area. A large cross section will have many more electrons that are able to movethrough it at the same time.

Material specification. Silver,Copper,Gold and Aluminium are all good Conductors of Electricity

because they have less than 4 electrons in their outer rings.

Temperature. The temperature effects different materials in different ways.

Other: (Number of strands, cooling effect, insulation, external interference, etc.

Resistivity ( ), is the material specific resistance. The Resistivity in a conductor is given at 20 C.

L = conductor length (m)

A = cross-sectional area for the conductor (m2 ) = Resistivity (m) Find the factor from a table

R = Resistance ()

R = x L/AU

ILAcabletwinondropVoltage

=

2:

OHMS LAW


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Ohms law is stating that the electric current i

flowing through a given resistance r

is equal to the applied voltage e

divided by the resistance, or i=e/r.

Ohms is the unit of resistance or how hard a

conductor resists the flow of electrical current.

For any circuit the electric current

is directly proportional to the voltage,

and is inversely proportional to the resistance.

OHMS LAW

U = R x I

R = U / I

I = U / R

U = Voltage, measured in Volt (V)

R = Resistance measured in ohm ()

I = Current, measured in Ampere (A)

OHMS LAW


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OHMS LAW

CABLE NOMOGRAM


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CABLE NOMOGRAM

In order to avoid to calculating the

correct cross section on a cable, we canuse this nomogram.

Ex. 1 is illustrating a connection of a 240

W consumer in a 6V installation, and

cable length is to be 4 meters. Thenomogram shows a 16 square mm cable,

so we choose this cable.

Ex. 2 is illustrating a connection of a 480

W consumer in a 6V installation, and

cable length is to be 0,5 meters. The

nomogram shows a 4 square mm cable,

so we choose this cable.

The nomogram is based on a voltage drop:

0,15V on 6V installation



(if based on a copper conductor with Resistivity: 0,017 /m)

Ex.: 240W, 6V, 4m, 16mm2: I= 240/6 = 40A

U= (0,017 x 4) x 40 / 16 ~ 0,15V

KIRCHHOFFS LAW


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KIRCHHOFF S LAWKirchhoff's laws [for Gustav R. Kirchhoff], pair

of laws stating general restrictions on the current

and voltage in an electric circuit.

The first of these states that at any junction of

paths, or node, in a network the sum of the

currents arriving at any instant is equal to the

sum of the currents flowing away.

[ I= 0 ]

[ I1 + I2 + + In = 0]

The second states that at any given instant the

sum of the voltages, (electromotive forces)

around any closed path, or loop, in the network is

zero.[ E + U = 0]

[U = U1 + U2 + + Un]

When voltages are opposing as seen

above, the difference is the voltage

applied to the circuit. In this case 4

volts must be dropped by the

resistors to equal the appliedvoltage.

E = e l ect r om ot i ve fo r ce , (emf), difference in electric potential, or voltage, between the terminals of a source of electricity, e.g., a battery

from which no current is being drawn. When current is drawn, the potential difference drops below the emf value.

SERIES CIRCUIT


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SERIES CIRCUIT

In a closed loop, the sum

of all voltage drops isequal to the supplied

voltage.

The current is the same in

each component

throughout the circuit.

When two circuit elements

are connected in series,

their effective resistance is

equal to the sum of the

separate resistances.

(U1 + U2 + + Un) = U

I = I1 = I2 = = In

Reff. = R1 + R2 + + Rn

U

R1 R2

I I1 I2

U

U

U1 U2

SERIES CIRCUIT VOLTAGE DROP


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SERIES CIRCUIT VOLTAGE DROP

Voltage drop is a condition that occurs in all circuits. Voltage drop occurs when current

flows through a resistance producing work. When there are two or more resistances in onepath, the supply voltage divides itself across them.

PARALLEL CIRCUIT


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PARALLEL CIRCUIT

The elements of a parallel

circuit are connected so thateach component has the

same voltage across its

terminals.

The current flow is divided

among its parts, and the

total current is equal to the

sum of the currents in the

individual branches.

The total resistance is less

than that of the element

having the least resistance.

U = U1 = U2 = = Un

(I1 + I2 + + In) = ITot

U U2

U1

U I2

I1 IT

U R2

R1

===+= 67,66

0150,0

10150,0

200

1

100

11T

T

RR

Ex. Find the total resistance for

the circuit. R1=100 and R2=200

n21T R

1....

R

1

R

1

R

1+++=

PARALLEL CIRCUIT


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PARALLEL CIRCUIT

A Parallel circuit has more than one path

for current to flow through. The loads maybe side by side and operate independent of

each other but are connected to the same

power source. In this way each component

can have a different current flow through it

while operating at full source voltage.

An advantage of parallel circuits

is that there is no voltage dropbetween loads and if one load is

disconnected the others will

continue to operate.

JOULES LAW


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JOULE S LAW

The relation between effect (power), current and voltage is called Joules law, and given by

the formula P = U x I.Watt [for James Watt], (W),

Unit of power, or work done per unit time, equal to 1 joule per second. It is used as a

measure of electrical and mechanical power.

One watt is the amount of power that is delivered to a component of an electric circuit when

a current of 1 ampere flows through the component and a voltage of 1 volt exists across it.

P = power, measured in Watt (W)

U = Voltage, measured in Volt (V)R = Resistance measured in ohm ()

I = Current, measured in Ampere (A)

Q = Electric charge in Coulumb (C)

t = Time (s)

P = U x I

IUt

tIUP

t

WP

tIUQUW

=

=

=

==

1 W = 1 Nm/s = 1 J/s = 1,35962 x 10-3 HP (metric)

1 HP = 735,499 W

1 HP (US/UK) = 745,700 W

JOULES LAW


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JOULE S LAW

MEASURING


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MEASURINGVoltmeter

Measuring the voltage in a circuit, we use a volt meter.

Always clamp your test pins parallel to the component you

wish to measure. The measurement can be made anywhere

on the circuit without affecting the voltage level. (Provided

that you have a multimeter with good quality).

Ammeter (Amp meter)

To measure the current in a circuit, we use a Ammeter.

Always clamp your test pins in series to the components

you wish to measure. (Except an clip-on ammeter).

Ohm meter

Instrument used to measure the electrical resistance of a

conductor. It is usually included in a single package with avoltmeter, and often an ammeter. Always clamp your test

pins in series to the components you wish to measure.

Whenever testing resistance, the circuit must be without

voltage!

MULTIMETER


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MULTIMETERMost modern multimeters are digital and traditional analogue types are destined to become obsolete.

Here is how a typical measurement are made in typical digital multimeter nowadays:

DC voltage: The A/D circuitry in the multimeter is designed to directly show DC voltage values typically in few volts range.

For higher voltages the input voltage is divided by a voltage divider network. For lower voltages the voltage is amplified with

amplifier.

AC voltage: Basically same idea as the DC measurement, except that the input voltage is rectified somewhere in the process.

DC current: Input current is run through a known low ohm resistance, which converts the input current to a small voltage drop.This voltage is fed to the DC voltage measurement circuitry.

AC current: This is measures in the same way as DC current, except that the voltage is fed to the AC voltage measurement

electronics.

Diode test: A low current (typically less than 1 mA) is fed to the measurement leads (output voltage limited to few volts). The

voltage between measurement leads is measurement with DC voltage measurement electronics.

Resistance measurement: An accurately known low current (varied depending on ohms range) is fed to the measurement leads.

The voltage (directly proportional to the resistance connected) between measurement leads is measured.

Some multimeters can have some of the following functionalities in addition to the basic ones described above:

Continuity tester: Works like the resistance measurement, if the voltage between measurement leads is lower than a specified

value (usually 50 to 300 ohms) it would make the beeper to signal. Frequency: Input signal is converted to square wave first. The multimeter has either pulse counter (count pulses for one second

gives output in Hz) or frequency to voltage converter.

Capacitance: Feed known frequency low amplitude signal through the capacitance. Measure the AC current which go through

the capacitor. Other option is to measure the capacitor charge and discharge times.

Temperature: Voltage from thermocouple sensor is amplified and processed. Then the result is fed to DC voltage measurement

electronics.

METER RESISTANCE


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METER RESISTANCE

All meters have resistance.

The value of this resistance depends upon the voltagerange selected.A typical moving coil meter has aSENSITIVITY of 20,000 ohms per volt.This meansthat when the 1 volt range is selected the meter hasa resistance of 20,000 ohms.When the 10 volt rangeis selected it has a resistance of 200,000 ohms andso on.When the meter is connected to a circuit tomeasure voltage, this resistance will affect the circuitand therefore the accuracy of the measurement obtained.In Fig.1 the voltage across each resistor can be calculated. (see the page on voltage dividers).However, it can be shown that since the resistors are of the same value then the battery voltage divides equally across

them, and the voltage across each will be 15 volts.Now if we set the meter to the 20 volt range to measure thisvoltage, its resistance will be 20 x 20,000 = 400,000 ohms = 400k.

If we connect it across the top resistor, as in Fig.2 then we have two 400k resistors in parallel. Calculating the result ofthis gives us 200,000 ohms and the circuit looks like Fig.3 The voltage will now divide to give 10 volts across the topresistor and 20 volts across the lower resistor.The meter will indicate 10 volts when we know that it should indicate 15volts.Similarly, connecting the meter across the lower resistor will again indicate 10 volts.It appears that there is 10v +

10v = 20 volts across the two resistors, when in fact there is 30 volts.To obtain the most accurate results, set themeter on the highest range possible.This means that its resistance will be highest and have least effect on the circuit.

Digital meter have a very high resistance, typically 10 Mega ohms on all ranges, and the readingsobtained are more accurate than those obtained using a moving coil meter.When buying a new

meter look for a sensitivity greater than 20,000 ohms/volt.

THE EFFECT OF METER RESISTANCE

TRMS


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True RMS (True Root Mean Square) = True effective value

Definition of TRMS:In a circuit whose impedance consists of a pure resistance,

the rms value of an AC wave is often called the effective

value. For example, if an AC source of 100 volts rms is

connected across a resistor, and the resulting current

causes 50 watts of heat to be dissipated by the resistor,

then 50 watts of heat will also be dissipated if a 100-volt

DC source is connected to the resistor.

Remember that an average responding multimeter willexhibit substantial errors when measuring other wave

forms as sine waves, as shown below.

The RMS voltage of a pure sine

wave is Peak voltage /2

The approx. parameters of a 230VAC waveform are

summarized in the table below

6503252300

Peak to

Peak

Voltage

(2V)

Peak

Voltage

(V)

RMS

Voltage

Averag

e

voltage

Calculating Actual RMS Voltage:

If you have a 'true RMS' voltmeter, the meter measures the instantaneous voltage at

regular time intervals. On a graph, the little vertical lines along the sine wave

represent the points in time where the voltage is measured. The microprocessor in

the voltmeter then 'squares' all of the voltages at each point and adds the squared

values together. It then calculates the average (mean) from the squared values. And

finally... it calculates the square root of the average (mean) value.

AC resistance Z = U/I

AC resistance in the coil = XL

ZXL

R

222

RXZL+=

CIRCUIT CONDITIONS


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There are a number of terms used to describe various circuit conditions, some are normal

and some refer to specific circuit faults.These terms are:

Closed circuit

Open circuit

Shorted circuit

Short to ground

1. Closed Circuit

When the circuit provides a continuous path from a power source to an electrical load and

back to the power source, it is called a closed circuit (or a completed circuit).

CIRCUIT CONDITIONS


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2. Open Circuit

If a circuit is broken by any means, such as opening a switch or cutting a wire, it is calledan open circuit and current will cease to flow. This is a normal condition for most circuits

since they need to be switched OFF at various times. It can also be an abnormal condition

such as when a wire is damaged or a switch fails to close properly.

CIRCUIT CONDITIONS


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3. Shorted (Short) Circuit

A short circuit means that the original circuit has been shortened to some degree.An example of this would be when the insulation in the windings of a coil has broken down

causing the windings to touch together or become shorted. This will cause a greater than

normal current flow, resulting in an increase in operating temperature and a reduction in the

effectiveness and life of that coil.(A fuse may also blow).


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RELAYS


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A relay is a switching device operated by a low current circuit which controls the opening

and closing of another circuit of higher current capacity. Relays allow a high current

consuming component to operate with minimal voltage drop by keeping the length of the

high current carrying circuit to a minimum.

Applying voltage to the relay coil causes a electromagnetic action to occur. This action

changes the contacts from their normal position.

Relays may be divided into four types

1.Normally open

2.Normally closed

3.Transfer types

4.Mixed types

RELAYS


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1. A normally open (N.O) relay will not allow current to flow through its contacts.

2. The contacts of a normally closed (N.C) relay are closed in the rest position, allowing

high current to flow through the contacts.

3. A transfer relay has two operational states, it will allow current to flow from one circuit

to another when its windings are not energised and then redirects current to another

circuit when energised. In the relay schematic below, SW1 is open and the windings

are switched OFF. Current will flow from terminal # 3 through the contacts and out of

terminal # 4.

4. A mixed relay is used to open and close two separate circuits.

SW 1 Battery

Flow

1 2

34

5

SW 1 Battery

Flow

Flow

Mixed type Transfer type

FUSE


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A fuse is generally inserted into an electrical circuit for 1 of 2 reasons, either to protect the

power source which includes the wire that connects the power supply to the electrical

device, or to protect the electronic equipment. The electronic equipment manufacturers

specify a fuse rated to open the electrical circuit before damage can be done to the device or

open the circuit if the electronic device fails in some way (electronic devices may pull

excessive current when they fail). If a fuse larger than the specified fuse is used, a small

mistake when installing the equipment may cause catastrophic failure of the equipment.

WHEN, not if, WHEN you're thinking of replacing a blown fuse with a higher rated fuse

ask yourself if you know more than the engineer who designed the equipment. Don't get in

a hurry when installing electronic equipment. Take the time to go get the right fuse. 50

cents for a fuse is better than $50 labour plus the cost of the replacement parts for a repairjob.

Fuse Opening Time

A fuse does not blow when the current reaches its rated current. It is designed to pass itsrated current without opening. A fuse will take varying times to blow under different

conditions. A fuse will pass significantly more than its rated current for a very short time. It

may take 10 minutes or more to blow a fuse at 25% over its rated current.

CIRCUIT BREAKER / FUSE


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When a fuse blows (even one that

has been perfectly capable of

handling the current requirements

of a given piece of equipment),

many people will replace it with a

fuse of equal size without thinking(which isn't necessarily a bad

thing). Then, if it instantly blows

again, they go to the next larger

fuse size (now, that IS a bad thing).

They don't think for a minute that

the fuse that just blew was the

same as the one that worked fine

for a long time. They don't think

that something just might have

changed which is now causing the

equipment to pull significantly

more current.

A circuit breaker's function is, like a fuse, to break a circuit path when a

predetermined amount of current is passed. The picture shows the simplified

version of a self-resetting circuit breaker. In this device, the current flowsfrom the battery terminal, through the bi-metal strip and then to the other

terminal. The bi-metal strip is made of two different types of metal, which

have different coefficients of expansion. This means that one will expand

more than the other when the rise in temperature is the same for both pieces.

In this case, the two metals are bonded to each other. (Now keep in mind

that this is a simplified diagram). When the strip heats up from the current

flow through it, one type of metal expands more than the other. In this case,

the black metal expands more than the red and the strip tends to bend

upward and disconnect the contacts. You can see that the metal starts to

bend as the current increases. When the temperature reaches a given point,

the piece will snap into the open position and the current flow will stop. The

bi-metal strip is stamped into a special shape, which causes the 'snap' action.

This will assure that there is EITHER a solid connection OR a complete

disconnect. You can see a similar snap action in the top of some soda cans.If you push down on the top it starts to bend downward. After the pressure

reaches a certain point, the top will snap down. If you release the pressure

slowly, the top will snap into its original position. This is what happens

when the bi-metal strip cools in the breaker.

RESISTOR


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The resistance value can be printed on the component as a numeric character, or marked on

with different colour rings around the resistance.

The value is given by for rings. The first two rings, states a number, 1 99.

The third ring states the number of zeros that has to be added to the first two numbers.

The fourth ring states the tolerance value, from 1 10%.

Band 1 Band 2 Band 3 Band 4 Band 5 Band 6

Color 1st Digit2nd Digit3rd Digit Multiplier ToleranceReliabilit

Black 0 0 1

Brown 1 1 1 10 1% 1%

Red 2 2 2 100 2% 0.10%

Orange 3 3 3 1,000 3% 0.01%

Yellow 4 4 4 10,000 0.00%

Green 5 5 5 100,000

Blue 6 6 6 1,000,000

Violet 7 7 7 10,000,000

Gray 8 8 8 100,000,000

White 9 9 9 1,000,000,000

Gold x 0.1 5%

Precis ion Resistor Color Codes

Read the resistance value by means

of the colour codes.

Verify the value with an ohmmeter.

Band 1 Band 2 Band 3 Band 4 Band 5

Color 1st Digit2nd Digit Multiplier Tolerance Reliability

Black 0 1

Brown 1 1 10 1%

Red 2 2 100 0.10%

Orange 3 3 1,000 0.01%

Yellow 4 4 10,000 0.00%

Green 5 5 100,000

Blue 6 6 1,000,000

Violet 7 7 10,000,000

Gray 8 8 100,000,000

White 9 9 1,000,000,000

Gold x 0.1 5%

Resistor Color Codes

INDUCTIVE SWITCH


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Proximity Switches allow the user to detect

the presence of material without having to

make physical contact. Inductive sensors are

used when the target is metal. These are the

most widely used switches in industry today.

Proximity switches are available in either

Shielded or Unshielded versions. Shielded

versions will detect metal only at the sensing

face. Unshielded versions usually have a

larger sensing range, but the drawback is that

they will detect metal around the sensinghead. This means that the surrounding area

(normally 3 times the switch diameter, and

twice as deep as the sensing range) must be

free from metal objects.An inductive proximity switch consists of 4 main components: coil, oscillator, detection circuit and solid state switching device (transistor in

DC switches, thyristor in AC switches). The oscillator creates a high frequency field that is emitted from the sensing face. When a metal

target enters that field, eddy currents are induced in the metal target (hence the term INDUCTIVE). Energy is required from the oscillator to

maintain the eddy currents in the target. As the target enters the sensing range of the sensor, the energy required becomes too great for the

oscillator, and it stops. The detection circuit senses this and signals the switch to change state. After the metal target leaves the sensing

range, the oscillator resumes functioning, and the switch returns to its normal state (either Normally Open or Normally Closed).

Inductive proximity switch:

NBN4-12GM50-E0 (Easy Ramp)

This is a NPN element:

(Gives a negative signal)

Neg. Signal on (4).

Operating current: 0200mAOperating voltage: 1030V

Power supply to L+ and L-

No load supply current: Max. 17mA

DIODE


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The Diode is a two-terminal electronic device that permits current flow predominantly in

only one direction.

A diode has a low resistance to electric current in one direction and a high resistance to it in

the reverse direction. This property makes a diode useful as a rectifier, which can convert

alternating current (AC) into direct current (DC). When the voltage applied in the reverse

direction exceeds a certain value, a semiconductor diode breaks down and conducts

heavily in the direction of normally high resistance. When the reverse voltage at which

breakdown occurs remains nearly constant for a wide range of currents, the phenomenon is

called avalanching. A diode using this property is called a Zener diode. It can be used to

regulate the voltage in a circuit. (See Zener diode).

When voltage is applied to a diode and current is

flowing through the diode, there will be approximately

a 0.6 volt drop across the diode.

Anode Cathode

Conducting direction

Rectifier

LED


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A light-emitting diode (LED) produces light as current passes through it; some LED's can

act as the light source of lasers. The emitted colour selection is somewhat limited. The most

commonly available colours are red, green, amber, yellow, blue and white. The red, green,

yellow and amber have a working voltage of approximately 1.8 volts. You can refer to the

data sheet for each LED to find the exact value. The actual working voltage is determined

by the breakdown voltage of the particular semiconductor material.

When using an LED in a circuit, the exact working

voltage is not extremely important. The most

important thing is the current flow through the

LED. A series resistor must limit the current

through the diode. An LED has a specifiedmaximum continuous current rating. Most LEDs

can pass 20 milliamps continuously without

damage but it is not necessary to use the maximum

rated current. An LED will light with much less

current. The difference between high current andlow current will be the brightness of the LED. To

decide what resistor value is needed, you subtract

the working (forward) voltage from the power

supply voltage and divide that number by the

desired current flow.

ZENER DIODE 1


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Zener diodes are generally used for voltage regulation.

The diodes are used with reverse polarity when

compared to their rectifier counterparts (you hook

them up backwards to make them work properly).

All diodes have a point at which they will conduct

current when sufficient reverse voltage is applied.

Most diodes are damaged when the reverse voltage

reaches the breakdown (or avalanche) voltage. Zener

diode circuits have a current limiting resistor in series

with the diode as part of their design. The other end

of the resistor is connected to the cathode of the zener.The other end of the zener, the anode, is connected to ground. If the zener diode is a 5.1 volt

zener, the voltage on the cathode of the zener will be very close to 5.1 volts. The voltage is

going to be close the rated zener voltage. You can sometimes get the voltage very close to its

rated zener voltage by varying the value of the resistor. This changes the current flowthrough the diode.

Symbol

ZENER DIODE 2


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If you look at the curve,

you can see that a

change in current (near

the breakdown voltage)

corresponds to a smallchange in the

breakdown voltage.

This type of circuit is

good for use as a

voltage reference but it

is not very good to

supply regulated

voltage to circuits that

draw a large amount ofcurrent.

CAPASITORA i i l i d i hi h i f l ( l i ll d i i l) d


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A capacitor is an electronic device which consists of two plates (electrically conductive material) separated

by an insulator. The capacitor's value (its 'capacitance') is largely determined by the total surface area of the

plates and the distance between the plates (determined by the insulator's thickness). A capacitor's value iscommonly referred to in microfarads, one millionth of a farad. It is expressed in micro farads because the

farad is such a large amount of capacitance that it would be impractical to use in most situations. A

capacitor works basically as a resistor that is depending.

The capacitor is used to store charge in an electrical circuit. You may also say that it is used to limit sparksor remove unwanted electrical pulses in a circuit. A capacitor functions much like a battery, but charges

and discharges much more efficiently (batteries, though, can store much more charge). Some capacitors are

called electrolytic, meaning that their dielectric is made up of a thin layer of oxide formed on a aluminium

or tantalum foil conductor. A capacitor has a value of one farad when it can store one coulomb of

charge with one volt across it.

These capacitors are often used to

stabilize a pulsating direct current. The

capacitors have a defined conducting

direction and are marked positive and/or

negative, (as a battery).

Electrolytic capacitor

r

nl

A

U

QC

0

)1(

=

==

C = Capacitance F

Q = Electric charge CU = Voltage V

= Permittivity F/m

0 = Permittivity vacuum F/m

CAPASITORN l i d fi d it


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Non-polarized fixed capacitor

A non-polarized ("non polar") capacitor is a type of capacitor that has no implicit polarity - it can beconnected either way in a circuit. Ceramic, mica and some electrolytic capacitors are non-polarized. You'll

also sometimes hear people call them bipolar capacitors.

Polarized fixed capacitor

A polarized ("polar") capacitor is a type of capacitor that have implicit polarity -it can only be connectedone way in a circuit. The positive lead is shown on the schematic (and often on the capacitor) with a little

"+" symbol. The negative lead is generally not shown on the schematic, but may be marked on the

capacitor with a bar or "-" symbol. Polarized capacitors are generally electrolytic.

Note that you really need to pay attention to correctly hooking a polarized capacitor up (both with respect

to polarity, as well as not pushing a capacitor past its rated voltage). If you "push" a polarized capacitor

hard enough, it is possible to begin "electrolyzing" the moist electrolyte. Modern electrolytic capacitors

usually have a pressure relief vent to prevent catastrophic failure of the aluminium can (but don't bet your

eyesight on this).Plates

Insulator

TerminalTerminal

Unit table

1pF = 10-12F = 1/1000 000 000 000

1F = 10-6F = 1/1000 000

1mF = 10-3 F = 1/1000

TRANSISTOR

Th i ll h 3 i l Th l


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The transistor generally has 3 terminals. The control

terminal is called the base. The other 2 terminals are

known as the emitter and the collector and they carry

virtually all of the current flowing through the transistor.

PNPNPN

b b

k k

ee

There are 2 basic configurations of bipolar transistors,

one is an 'NPN' the other is a 'PNP'. The two are very

similar. The biggest difference is the direction ofcurrent flow through the collector and emitter.

On an NPN transistor, the base must have a positive

voltage with respect to the emitter.

By varying IB , we can control a large current throughIK .The transistor uses a small current to control a

larger current, a little like a relay.

The transistor function can also be looked on as todiodes connected together like on the picture to the

right. A transistor needs to have a small amount of

voltage difference between the base and the emitter.

The required voltage is usually about 0.6 volts.

+

-+

+ -

-

TRANSISTOR

Th i t l l h th di ti f th t


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The pictures clearly shows the directions of the current.

- +

-+

+ -

TRANSISTOR

The transistor is being sed in man different electrical applications The transistor ses a


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The transistor is being used in many different electrical applications. The transistor uses a

small current to control a larger current, a little like a relay. Some of the advantages with

the transistor, is that it works much faster compared to a relay, has no moving parts, and no

breaker contacts that can get burned. You can also adjust the conductance, (not only

ON/OFF). Compared to the relay, the transistor doesnt take overcharges very well and it is

not as flexible regarding the size

of the control current in relationto the working current.

In order to use a weak signal,

for handling a high working

current, there are often beingused several transistors

connected to each other.

The NPN transistor to the right isused as a switch. UKE

ULOAD

UB

RB

WORK TASKS


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WORK TASKSAND

TEAMWORK

DEVIDE INTO TEAMS

2-3 PERSONS ON EACH TEAM

THE LEARNING PYRAMIDE

A l i F


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Lectures

Reading

Audio visual (see/hear)

Demonstration

Discussion group

Learning by doing (practice)

Teach others / Immediate use of knowledge

Average learning Factor

5%

30%

50%

75%

90%

10%

20%

BREAK

CORRECT PROCEDURE FOR THE


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CORRECT PROCEDURE FOR THE

RECTIFICATION OF ELECTRICAL PROBLEMS

THEORY & PRACTICE


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Theory put into

practice

You will be

making practical

lab tasks,

makingelectrical

circuits

combined with

theoreticalcalculations on

different

circuits.

WORK TASKS -INSTRUMENTS


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If you connect the multimeter to the circuit, according

to the picture on the right, what can be measured?

How do you hook up an ammeter in a circuit?

Which value does the instrument show?

4,7 kU = 14 V

If you connect a multimeter to this circuit, what can

be measured?

How do you hook up the voltmeter in the circuitshown to the right?

Which value does the instrument show?

U = 14 V

R1

= 4,7 k

R2 = 1 k

R1

R2

Multimeter

WORK TASKS RESISTANCE

Connect according to the figure. Measure the voltage over the bulb.


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Connect according to the figure. Measure the voltage over the bulb.

Unscrew the bulb. What is the voltage over the bulb now?

What can we learn based on this experience?1k ohm

12V/0,2A

12V

WORK TASKS SERIES

Connect according to drawing A, use a 12V/0,2A bulb, and change the A


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g g , , , g

voltage between 0 and 10V. What happens?

Connect according to figure B, E = 10V. How strong is the lightilluminating when using:

Why?

Connect according to figure C, U = 10V. How strong is the light

illuminating now, and why?

What do we name this kind of circuit and which rule applies for the totalresistance.

C

B

A

47 100 470

R

100

470

WORK TASKS SERIES

Set the input voltage to exactly 12,00


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p g y ,

Measure and calculate every part voltage and make the

note in the table below.

Sum up all part voltages and note this on the bottom of the

table.

U Measured U Calculated

UAD -----

UAB

UBC

UCD

Total: U AB + U BC + U CD =

470

1 k

4,7 k

A

B

C

D

WORK TASKS PARALLEL

U = 10V R1 = 47 R2 = 100 R3 = 470 Bulb = 12V/0,2A


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1 2 3

Make the connection, and use only the 470 resistance. Howdoes the lamp illuminate?

Add only the 100 resistance. How strong is the light illuminating

now?

Now, add on the 47 resistance. How strong is the lightilluminating now?

Why?

What do we name this kind of circuit and which rule applies forthe total resistance.

R1 R3R2

WORK TASKS PARALLELSet input voltage to exact 16,00 V

16 00


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Measure and calculate each part current and make the

note in the table below.

Sum up all part currents and note this on the bottom of

the table, IR1, IR2 and IR3 .

IMeasured ICalculated

UR

UR1

UR2

UR3

Total: IR1 + IR2 + IR3 =

R1 R3R2

R

UAC = 16,00 V

R = 1 k

R1 = 4,7 k

R2 = 470

R3 = 1 k

A

B

C

WORK TASKS POWER

What is the heating effect for the total circuit?

EAC = 16,00 V


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Which heating effect is produced by each part resistance?

What is the voltage supplied, when the 20 k hot-wire emitsapprox. 5 mW?

a) What is the resistance when it emits 9W and we havesupplied 30V to the circuit?

b) Connect the resistance, calculated from task a) into the

circuit, turn on the power. What happens to the resistance?

R1 R3R2

R

AC ,

R = 1 k

R1 = 4,7 k

R2 = 470

R3 = 1 k

A

B

C

WORK TASKS THERMIC RESISTANCE

U = 12,00 V


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100

,

Bulb = 12V/0,2AMeasure and fill in the missing values.

Calculate and fill in the resistance of the bulb

and the three resistances.

A) Why is there a difference between themeasured and the calculated resistance?

B) Why is it important to understand thisphenomena, and can you come up with

practical examples for this.

100

47

Bulb Resistances

IMeasured

Rcalc

RMeasured

WORK TASKS RELAY

Based on what you have learned about induction,


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Explain why, on some relays that a diode isconnected in parallel to the relay coil.

Explain the process and what will happenwhen we turn the power on, (activate the

relay) and then off (deactivate the relay).

Connect the multimeter to 85 and 86. Set

the multimeter on Min/Max record, 1ms and

set the range to 4000V (1000V). Connect

and disconnect the power plug(set the powersupply to 12V). Read the Min/Max values

recorded. Explain your findings.

WORK TASKS TRANSISTOR

NPN transistor as a switch


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Given information:HFE = 100 Iload = 1 A

UKE = 0,5 V UB = 10 V

UBE = 0,5 V

Calculate and fill in the missing values.

URL = ?RL = ?

Ib = ?

RB = ?

PRL = ? (Load effect on RL)

UB

UKE

RB RL

HFE =IK

IB

WORK TASKS TRANSISTOR

NPN transistor as a regulator


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Estimate a serial resistance between baseand source to protect the transistor.

U source = 10V, Imax (load) = 0,2A

Connect a 12V/0,2A light bulb and use theNPN transistor to adjust/variate the light

intensity on the bulb.

U source = 10V

Use the multimeter and measure the

resistance when there is no illumination.

What is the Max/Min resistance?

WORK TASKS ZENER DIODE

Connect according to fig. 1 and set the power totl 4 5V V if th t th b i t


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exactly 4,5V. Verify that the buzzer gives a tone.

Turn off the power and connect according to figure 2.Set the power to exactly 4,5V. Does the buzzer sound

now?

Increase the voltage to 5,5V. Does the buzzer soundnow?

Explain the results and your findings from task 1, 2 and3.

Fig. 1

Fig. 2

NOTES


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TRMS


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