MASINDE MULIRO UNIVERSITY OF SCIENCE AND

TECHNOLOGY DEPARTMENT OF ELECTRICAL AND

COMMUNICATIONS ENGINEERING NAME: WEFWILA

JOHN SHILENZO

REG. NO.: TET/D/01-

54304/2018 COURSE CODE:

DEE070

COURSE TITLE: WORKSHOP

PRACTICE TITLE: WORKSHOP

REPORT

DATE OF SUBMISSION: ----------

1
Contents
DECLARATION 4
ABSTRACT 7
ACKNOWLEDGEMENT 10
PREFACE 11
CATHODE RAY OSCILLOSCOPE 18
CRO CONTROLS: 19
1. Focus - Focus the spot or trace on the screen. 19
2. Intensity – Regulates the brightness of the spot or trace. 19
3. Position – Controls the position of trace on the screen. 19
4. Trigger – selects the timing of the beginning of the horizontal sweep. 19
5. Coupling – Selects whether trigger occurs at specific DC or AC level. 19
6. Sensitivity – Selects the sensitivity of the vertical amplifier in
calibrated steps. 19
CONNECTIONS FOR THE OSCILLOSCOPE:

19 RESISTORS….

21
INTERGRATED CIRCUITS...........................................................................................................25

CAPACITORS................................................................................................................................27

TRANSFORMERS........................................................................................................................31

SEMICONDUCTORS.....................................................................................................................35

TRANSISTORS................................................................................................................................36

SOLDERING AND DESOLDERING...............................................................................................38

ELECTRICAL MACHINES..................................................................................................................42

ELECTRICAL INSTALLATION..........................................................................................................44

Factors to be considered during installation.........................................................44

2
 Steps of installation

44 Types of installation (wiring)

46

INSTALLATION EXERCISE 51
Exercise one:

51 Exercise two.

53 Exercise three

54
Exercise four: 56
Exercise five:
59 Exercise six
...............................................................................................................................................
60

MECHANICAL WORKSHOP 64
Workshop safety 64
Machine shop safety
64
Welding process 67
BRAZING: 73
Arc welding:

73 Gas welding

74
INDUSTRIAL VISITS...........................................................................81
DOSHI GROUP OF COMPANIES(METSEC)

81 KINDARUMA POWER STATION

88

3
 TONONOKA GROUP........................................................................................................91

COMMUNICATION AUTHORITY OF KENYA......................................................................98

CONCLUSION...............................................................................................................................102

RECOMMENDATION.....................................................................................................................102

REFERENCES...................................................................................................................................103

4
DECLARATION
I, WEFWILA JOHN SHILENZO declare to the best of my knowledge that this report is
my original work and has not been presented in any university.

SIGN………………………………………

DATE……26/7/2018…………………………………

ABSTRACT
This report gives details of all the activities that were undertaken during the internal attachment

5
(Workshop practice) in Masinde Muliro University of Science and Technology
between September 2020 to January 2021

What was learned in the industrial visits. Basic skills in Engineering were acquired
and practical work site in the industries was a great achievement. I appreciate.

DEDICATION

6
I dedicate this report to my dear parents, friends and everybody else who in one
way or the other played a role to ensure all the activities undertaken during the
workshop practice were a success. Moreover, I highly appreciate all the technicians
from all the departments of the Engineering Faculty for making it easy during the
internal attachment.

ACKNOWLEDGEMENT
I would like to express my sincere gratitude to God for His unending grace and
mercy to ensure that the practice was conducted safely without fear and any injury
reported.

7
I also thank Masinde Muliro University fraternity for providing a conducive
environment to ensure that the practice was done in an environment that is
student friendly and learning friendly.

The organizers of the practice more specifically the various technicians from the
three departments of the of school of Engineering in Masinde Muliro University of
Science and Technology should feel appreciated.

Again, I thank the managers of Metsec company, Communication Authority of

Kenya, Kindaruma hydroelectric power station and Tononoka Group Company for
allowing us to use their resources during the industrial visit in their various
companies.

PREFACE
This report is intended primarily to indicate the skills learned during the workshop practice and

8
arouse the interests of the undergraduate engineers in the technical aspect of
electrical and communications engineering. The content of the report mainly
focuses on the practical experience acquired during this period. It aims at helping
the student understand engineering more comprehensively through solving field
related problems. Each chapter of the report represents a range of worked out
exercises performed in different workshops for various engineering disciplines, and
a comprehensive report on what was learned in various companies visited. The
student engineer will also find the report very useful in his /her career while
preparing designs and layout for fifth year project and other application-oriented

Project.

1. DEPARTMENT OF ELECTRICAL ENGINEERING

In the department of Electrical and communications engineering, workshop practice
was divided into sections under which we performed various activities as outlined
under the following sub- titles:

 Electrical installations

 Electronics workshop

 Electrical machines

 Civil engineering workshop

 Mechanical engineering workshop

9
1.1 SAFETY PRECAUTIONS

 Avoid contact with energized electrical circuits

 Disconnect the power source before servicing or repairing electrical equipment

 Never use metallic pencils or wear rings while when repairing

electrical equipment’s

 Wear nonconductive gloves, protective clothes and shoes with insulated soles

 Nobody is allowed to make jokes or playing in the laboratory

 After electrical machines they should be switched off

 Make sure environment around workplace is clean before and after work

 Make sure the cable used fulfills its rating and having suitable

insulations ELECTRONIC WORKSHOP

ELECTRONICS

INTRODUCTION
Electronics is the discipline that deals with the development and application
of devices and systems involving the flow of electrons in a vacuum.

OBJECTIVES
i. To know the various symbols used in electronics,
ii. to know how measuring instruments such as multimeter works and
how to test various components found in electronics.
iii. To work with various electronic components such as transistors in
order to enforce what was learned in class.
iv. To find out about bread boarding, types of bread boarding and
various types of breadboards.
v. To investigate how circuit diagrams can be drawn from breadboard connections.
vi. To know how soldering and de-soldering can be done

10
ELECTRONIC DESIGN

Involves designing an electronic circuit to achieve a specified

objective. DESIGN PROCEDURE

A) Come up with an idea.

B) Block diagram.

C) Implementing the block diagram.

D) Testing the results and analysis of the circuit.

E) Conclusion and recommendation.

TYPES OF MEASURING INSTRUMENTS

Several measuring instruments were studied in electrical lab.

They include: Multi-meters,

CROs,

Tachomet

ers,

Ammeters,

Millimetre

s,

Micrometr

es, Clamp

meter,

Voltmeter

s,

Power factor

meters,

Frequency
11
meters,

Signal generators etc.

12
MEASURING SYSTEMS AND SYMBOLS
Various components are used in electronic circuits to achieve specific
functions or solve particular problems. These components are identified by
their distinct universal symbols and each has its function in an electronic
circuit.

13
14
15
MEASURING INSTRUMENT
Meter
Meters are important devices for quantifying various electrical
parameters.: Ammeter- used to measure current
Voltmeter- used to measure
voltage Ohm meter- used to
measure resistance
Multimeter - used to measure voltage, current and resistance
A. Multimeter

Types:
Analog multimeter This is also called VOM; (Volt Ohm Meter). It has a
moving coil meter whose pointer indicates the value being measured on a
well graduated scale. By changing the selection switch, various values of
quantities can be measured well.

Digital multimeter
Uses logic circuits to perform accurate, precise and well displayed easy to
read measurements.
The value of quantity being measured is displayed on a screen.

Limitations of a multimeter:
They integrate input signals using root mean square method and will
correctly read the voltage of an input signal even if it is not a perfect sine
wave.
16
Safety precaution when using multimeters

17
  Ensure that the test leads and rotary switch are in correct position for
the desired measurement.
 Never use damaged meters.
 Never touch the probes of a voltage source when the lead is
plugged in a 20A/20mA/20μA Jack.
 Never measure resistance in a circuit when power is supplied.
 Never apply more than the ratio voltage between the input jack and the ground.
 Be cautious when working on voltages on above 50V dc and 30V ac.
 To avoid damage or injury to the meter it should not be used for
circuit ratings that exceed 4500W.
Uses of multimeters
1. To measure current intensity
Place black lead in the ‘COM’ jack and red lead in 20A jack.
Ensure the rotary switch is pointing on maximum current (for ac 20Aand
dc 20A) Place the ammeter in series (in loop) to make a measurement.
Record the current value in
amperes. Turn OFF the
multimeter
2. To Measure voltage
Potential difference is measured in volts.
Place the black lead in the COM jack, the Red jack in VΏ
Jack. Turn the rotary switch to point maximum voltage.
Place the voltmeter in parallel with the component across which voltage is to
be to be determined.
Record your measurement in
Volts. Turn OFF the device.
3. Resistance measurement
Place the black lead in the COM
jack. Place the red lead in VΏ

18
jack.

19
Turn the rotary switch to measure the highest available resistance then
change rotary switch slowly to measure until the right value is obtained.
Remove the resistor from the circuit
completely. Measure the resistance across
a given resistor. Turn OFF the device.
Exercise
Measurement of voltage, current in branches, and resistance values

CATHODE RAY OSCILLOSCOPE

The CRO is a multipurpose instrument used for taking measurements of various
signals, waveform analysis, phase angle measurement, period and duty cycle. The
cathode ray is a beam of electronics which are emitted by heated cathode and
accelerated towards the fluorescent screen. The assembly of the cathode, intensity
grid, and accelerating anode is called the electron gun. Its purpose is to generate
the electron beam and control its intensity and focus.

CRO CONTROLS:

1. Focus - Focus the spot or trace on the screen.

2. Intensity – Regulates the brightness of the spot or trace.

3. Position – Controls the position of trace on the screen.

4. Trigger – selects the timing of the beginning of the horizontal sweep.

5. Coupling – Selects whether trigger occurs at specific DC or AC level.

6. Sensitivity – Selects the sensitivity of the vertical amplifier in calibrated steps.

CONNECTIONS FOR THE OSCILLOSCOPE:

Vertical Input: These are pairs of jacks for connecting the signal under study to the Y
or vertical amplifier.

20
Horizontal Input: These are pair of jacks for connecting external signal to the
horizontal amplifier.

External Trigger Input: Input connector for external trigger signal.

Using an oscilloscope.
 Set the trigger to AUTO D.C coupling CH 1
 Set the horizontal mode A.
 Set the vertical mode- both/dual.
 Set the sweep speed (time/div).
 Set vertical coupling to ground.
 Turn up the intensity.
 Wiggle vertical position till a horizontal line
appears.
 Set vertical coupling to a.c / d.c

Pic 1: Photo of a CRO

SIGNAL GENERATOR

It is also referred to as function generator. It is a device that produces simple

repetitive waveforms such as sine, square and triangular waves. They generate
signals at various frequencies and amplitudes. They are used to stimulate a circuit
under test where an oscilloscope is then connected to measure the circuits output.

21
Operating Instructions

o Set the DC offset control to read 0v.

o Choose the right function I.e. sine, square or triangular wave.

o Choose required frequency range.

o Adjust to the required frequency using the frequency knob.

o Connect the output from the signal generator to the vertical input of oscilloscope.

o Establish a steady trace of this input signal on the oscilloscope.

o Adjust the horizontal sweep time/cm and trigger to the appropriate positions.

o To determine the voltage signal appearing at the output of the signal

generator, the peak value on the oscilloscope is read.

ELECTRONIC CIRCUIT COMPONENTS

BREADBOARD
A breadboard is a construction base for prototyping of electronics It
composes of connected conductors in rows and power rail behind a plastic
block with rows of sockets. It is made up of plastic case which has holes
through which connecting wires and circuit components are inserted.
It preferred for making temporary circuits since it does not involve soldering,
simply it is ideal for prototyping (the process of implementing an idea by
creating preliminary model from which other forms are copied).
Outside appearance

22
 RAVINE ROWS COLUMNS
Internal anatomy

POWER RAIL TERMINAL STRIPS

Terminal strips
Composes of metal strips on the bottom of the breadboard, then on top of
the metal strips there are little clips that hid behind the plastic holes. This
holes allows one to stick wire or leg of components into the holes in the
breadboard which then hold it in place.
Once inserted the components will be electrically connected to anything else
placed in that raw.

Power rails
Aside from horizontal rows there is also a power rail that run vertically along the sides.

23
This rails identical to the ones that run horizontally except that they are
typically all connected but not on the either sides
They are usually labeled red and blue/black at their top on the
plastic block Ravine
There is also a ravine that isolate the two sides of the breadboard which
is of great importance mostly when dealing with ICs to avoid short circuiting
the legs.
COMMON USES
It preferred for making temporary circuits
Another common use of bread board is testing electronic component i.e.
when testing how a component works it eliminates the work load of soldering
and disoldering.
COPPER STRIP BOARD
Copper strip board is a board where circuits are primed permanently after
testing on a bread board. It is a horizontal strip of lines made of copper
conductors on a board where permanent building of circuit is done.
Components are mounted on the plane side while terminals are passed
through the holes in the board and pins are soldered on the rare side.

Advantage of a copper strip board

It’s easy to make alteration on the circuit after it has been built than in
PCBThey are passive components that limit the flow of current producing a
voltage drop between its terminals (from Ohms law)
It is a non-polar component therefore easy to use.

Symbols for a Resistor

or

24
Types of resistors
 Fixed resistors
This are resistors whose values cannot be changed as it is set at a
particular value

Under this category we can have

Carbon resistor

They have carbon which provides the resistive element of the component

Metal film resistor

They have a metal piece which provide resistive element of the component

Wire wound resistor

It is a resistor in which the resistive element exists out of an insulated

metallic wire that is winded around a core of non-conductive material.

25
Surface mounts resistors (SMR)

They are devices that are used at surface mount technology (SMT).

They were developed to meet the ongoing desire for printed circuit
board to meat manufacturer desire of developing small components

SMR on motherboard
SMR code
In this system of coding, the value of resistance of a resistor are written on
the surface of the device as shown below.

Properties:
a. Have high accuracy

26
b. Have low tolerance
c. Power resistors
d. They are high power resistors

Variable resistors

This are resistors which their resistance value can be

adjusted Under this there are

Rheostat

This is a type of variable resistor that that is used to control the flow of
current by manually increasing and decreasing the resistance.

Light dependent resistor

This are variable resistors that their resistance changes with the
change in light intensity i.e. their resistance decreases with increase in
light intensity.
27
Function of a resistor.
 Limits the flow of current
 Protects components that is before it, example
the LEDS. Color coding
Resistor values can easily be obtained by use of indicated color codes.
There exists various color coding basing on number of bands as
describe below. o 4 bands
o 5 bands
o 6 bands

Color Code

Color Numbe Multiplie toleranc Temp.

r r e coefficient
Silver _ 0.01 +/- 10% ¬¬_

gold _ 0.1 +/- 5% _

Black 0 1 _ _

Brown 1 10 +/- 1% 100ppm

Red 2 100 +/- 2% 50ppm

Orang 3 1K _ 15ppm
e
Yellow 4 10K _ 25ppm

Green 5 100K +/- 0.5% _

Blue 6 1M +/- _
0.25%
Violet 7 10M +/- 0.1% _

28
 Grey 8 ¬¬_ _ _

White 9 _ _ _

Bands have functions as

below Four bands
1st band-gives first digit
2nd band gives second
digit 3rd band gives
multiplier value 4th band
gives the tolerance Five
bands
1st band gives first digit.
2nd band gives the second
digit. 3rd band gives the
third digit.
4th band gives the
multiplier. 5th band gives
the tolerance. 6 bands
1st band gives first digit.
2nd band gives second
digit. 3rd band gives the
third digit. 4th band gives
the multiplier. 5th band
gives the tolerance.

29
6th band gives the temperature band

30
2.5 INTEGRATED CIRCUITS – ICs

An integrated circuit or monolithic integrated circuit is a set of electronic circuits on

one small plate or “chip” of semiconductor material normally silicon. This can be
made much smaller than a discrete circuit made from independent components.

Integrated circuits are used in virtually all electronic equipment today and have
revolutionized the world of electronics.

IC’s normally come in any of the three forms below;

a)Dual-in-Line Package (DIP) – it is sometimes abbreviated as DIP. This is an electronic

component package with a rectangular housing and two
parallel rows of electrical connecting pins. The
package may be
through- hole mounted to a PCB or inserted in a socket. A
DIP is usually referred to as DIPn, where n is the total number of
pins. E.g. DIP14.

DIL Package.

b) Single-in-Line Package (SIL) – has one row of connecting pins. It is not as

popular as DIP but has been used for packaging RAM chips and multiple resistors
with a common pin.

c)Quad-in-line Package (QIL) – this has the same dimensions as the DIL
package, but the leads on each side are bent into an alternating zigzag
configuration so as to fit 4 lines of solder pads, instead of 2 as it is in DIL. The QIL
design increased the spacing between solder pads without increasing package size.

31
Advantages of integrated circuits

(i) Miniature size – as fabrication process is used for the integration of active
and passive components onto a silicon chip, the IC becomes much smaller,
when compared to discrete circuit.
(ii)Due to small size, the weight of the IC also reduces when compared to discrete circuit.
(iii) To produce hundreds of discrete circuits on a PCB for the same
logic takes more time and increase the cost factor. But for the production of
hundreds of ICs the cost will be very low and less time consuming.
(iv) The PCB consisting soldered joints will be less reliable. This
problem is omitted in IC’s because of No-soldered joints, with fewer
interconnections and thus highly reliable.
(v)The small size of IC causes lesser power consumption and lesser power loss.

Disadvantages of integrated circuits

1. Some complex IC’s may be costly.

2. The power rating of most of IC’s does not exceed over 10watts. Thus it is
not possible to manufacture high power IC’s
3. Some components like transformers and inductors cannot be integrated
into IC due to their bulky nature hence have to be connected externally.
4. High grade P-N-P assembly is not possible.
5. It is not possible to fabricate capacitors that exceed a value of 30pF.
Higher value capacitors are connected externally to IC.
6. There is a large value of saturation of transistors.

CAPACITORS

A capacitor is a passive two-terminal electrical component that stores charge. Some

capacitors have polarity i.e. electrolyte capacitors while others don’t have i.e.
ceramic capacitors.
Capacitors are also used in rectification or dc filtering.

Symbols of a capacitor

32
TYPES OF CAPACITORS

They are divided into two broad categories;

1) Polar Capacitors-Those that have negative and positive terminal.

2) Non-polar capacitors-those with no polarity. Examples of such are the

ceramic capacitors. These are used to store charge. The insulating or dielectric
material is the ceramic. They are disc shaped. Ceramic capacitorTheir values are
interpreted as in examples below;

e.g. 102 => 10 x 10² pF

= 1000pF

= 0.001 µF

434J => 43 x 10^4 ± 0.5% pF =430000 ± 0.5% pF = 0.43 µF ± 0.5%

Fig. Ceramic capacitor.

Other types of capacitors are;

Electrolytic capacitors

They have positive and negative terminals (two polarities). Its insulated in a

di-electric material that helps in making sure no shorting while charging. These
capacitors have temperature ratings and also voltage rating.

They are majorly used in power blocks for smoothing DC output from a bridge, smoothing

33
signals and are also used in power factor correction methods.

Polyester capacitor

It is a capacitor made of polyester material.

Paper capacitors

It is a capacitor whose terminals are held in a foil of paper that is not conductive.
This is made of flat thin strips of metal foil conductors that are separated by waxed
paper (the dielectric material).

Aluminum /metallic capacitor

It is mostly found in DVD drives and pc motherboards. They have polarities and are
generally small in size. Have aluminum casing. These capacitors store from 1uF to
100000uF. They have tolerance of 1 - 50%.

However, they have high leakages and are used for low frequencies.

Tantalum capacitors

They are rated from 0.5uF to 100uF. They do not have polarities and are used in
small voltages. A tantalum capacitor typically consists of a pellet of tantalum metals
as anode, covered by an insulating oxide layer that forms the dielectric, surrounded
by a conductive material (electrolyte) as cathode.

34
They are preferred because they have less leakage.

Air/ variable capacitors

This has metallic plates and is separated by paper plates between. They are used
for frequency change in radios

. symbol of a variable capacitor

Trimmer capacitors/preset

Have two terminals and are adjustable components. They are used in precision circuitry.

Mica capacitors

These are made of metal foil plates that are separated by sheets of mica (the
dielectric). They don’t have polarity.

TESTING OF CAPACITORS

Capacitors can either be tested by, Cold test or hot test.

Cold test is by observations, whereby a defective capacitor may be observed

having bulged out, leaking (oozing out of) some fluids or looking charred.

In Hot test, we use a meter.

Capacitor can develop any of the following defects;

 Open circuit

 Shorted capacitor

 Leaking capacitor

35
Before testing, a capacitor is discharged first, to avoid damage on the meter hurting oneself.

Using an analogue multi-meter

 Use a 1MΩ resistance on the meter.

 Put the red lead on the positive terminal and the black lead on
the negative terminal of the capacitor.

 If the capacitor is good, the pointer should deflect to the right side
(low range side) and then moves slowly to the left hand side. It should
cover more than half distance deflected.

 If it is shorted, the pointer will deflect on the low range side and
never comes back at all.

 If open, the pointer will not deflect at all.

 If it is leaking, the pointer will deflect to the right (low range) and
will cover half distance it deflected.

Using a digital multi-meter

 set the range knob to 20kΩ

 For a good capacitor, after connecting the probes, the continuity should read
from 1- 20k and then back to 1.

 If it is open, the number displayed on the meter is 1.

 If shorted, the number displayed on the meter is 0.

If leaking, the meter will come from 1 but will not reach 20.

TRANSFORMERS

It is an electrical device that changes the alternating potential difference from one
level to another through electromagnetic induction.

It can be either a step up or a step down transformer.

36
 a) Step up transformer -Have more secondary winding than the primary.
Primary windings are thicker than the secondary windings hence lower
resistance in the primary side. The primary windings are either yellow or red
in color whereas the secondary are blue in color.

b) Step down transformer-have primary winding that are more than the
secondary winding. Primary windings are thinner hence higher resistance in
primary than the secondary.

TYPES OF TRANSFORMERS

i) Air core transformer

The air passes through the core for cooling purposes. These are used for high
frequency work. The lack of a core means very low inductance. Such transformers
may be nothing more than a few turns of wire soldered onto a PCB.

ii) Iron dust core transformer

In between the windings is “dust” which is iron-like fillings. A core made by

mixing finely powdered magnetic material with an insulating binder and moulding
under pressure to form a rod-shaped core that can be moved into or out of coil or
transformer to vary the inductance or the degree of coupling for tuning purposes

iii) Iron core transformer

Most power transformers are of the iron-core type. As the name suggests, their core
where the windings are done is Iron. They are used at low frequencies, such as 50Hz
and 400Hz hence require a core of low-reluctance magnetic material usually iron.

37
 iv) Chopper transformer

It is also known as switch-mode power supply transformer (SMPST) used in

computer memories, colored screens, again used in universal power
transformers. We input primary voltage and get several voltages as outputs.

v) Fly back transformer

Is also called Extra High Tension transformer (EHT)

or Auto-transformer. It is used in computer monitors and

CRTs.

It delivers the final anode of cathode in CRT.

EHT transformer has two windings on its primary side;

a) Switching winding

b) Current-sensing winding

On its secondary side, it has several windings. These windings may carry up to 25kV.

vi) Radio frequency transformer

They are transformers for Frequency Modulated (FM), Short Wave (SW) and
Medium Wave (MW).

Used in radios for tuning the

frequency. Used for oscillations.

vii) Line filter transformer

This transformer has got two windings. The live line goes through one winding while
the neutral winding goes through another winding, before they go to capacitor
filters.

38
viii) Intermediate frequency transformer

39
These are mostly found on radio sets. They are mostly tuned transformers,
containing a threaded ferrite slug that is screwed in or out to adjust Intermediate
Frequency tuning.

ix) Audio transformer

Also known as Audio frequency transformers work at frequencies between 20Hz and
20 kHz and are used in audio amplifier circuits. Audio transformers usually perform
several functions at once; where used, they allow the AC audio signal to reach the
loudspeaker whilst preventing any DC from the amplifier affecting the operation of
the loudspeaker. Audio transformers can also be used for matching microphones to
amplifier inputs.

LOSSES IN A TRANSFORMER

a) Iron losses-this is as a result of eddy currents and hysteresis

b) Copper losses-due to resistance of the windings, I²R losses

TESTING TRANFORMERS

When testing the transformers; the primary winding always has the higher
resistance, for step- down transformer and lower resistance for a step-up
transformer.

When using a digital multi-meter;

0 value indicates short-circuit in transformer.

Value close to 1 indicates leaking in a

transformer. 1 value indicates an open

circuit in a transformer. ppm/°C.)

40
 SEMICONDUCTORS

Semiconductors are materials whose electrical conductivity lies between that of a

good conductor and an insulator. A good conductor is like copper and an insulator is
like polythene.

DIODES
A diode is a device which only allows unidirectional flow of current if
operated within a rated specified voltage level.
A diode acts as valve in electronics basing on whether it is forward biased or
reversed biased

WORKING PRINCIPLE OF A DIODE

N-side will have a significant number of electrons, and very few holes
whereas the p side will have a high concentration of holes and very few
electrons. Due to this, a process called diffusion takes place. In this
process free electrons from n side will diffuse into the p side and
recombine with holes present there, leaving positive immobile ions in n
side and creating negative immobile ions in p side of the diode.
Therefore, there will be uncovered positive donor ions in the n-type side near
the junction and there will also be uncovered negative acceptor ions in the p-
type side near the junction edge. Due to this, numbers of positive ions and
negative ions will accumulate on n-side and p-side respectively. This region
so formed is called as depletion region due to the “depletion” of free carriers
in the region. Due to the presence of these positive and negative ions a
static electric field called barrier potential is created across the p-n junction
of the diode. It is called "barrier potential" because it acts as a barrier and
opposes the transfer of holes and electrons across the junction.
FORWARD BIAS
In a PN junction diode when the. Positive terminal of a source is connected to
the p-type side, and the negative terminal of the source is connected to the
n-type side, the diode is said to be in forward biased condition. We know that
there is a barrier potential across the junction. This barrier potential is
directed in the opposite of the forward applied voltage. So a diode can only
allow current to flow in the forward direction when forward applied voltage is
more than barrier potential of the junction. This voltage is called forward
biased voltage. For silicon diode, it is 0.7 volts. For germanium diode, it is
41
0.3 volts. When forward applied voltage is more than this forward biased
voltage, there will be forward current in the diode, and the diode will become
short circuited. Hence,

42
there will be no more voltage drop across the diode beyond this forward
biased voltage, and forward current is only limited by the external resistance
connected in series with the diode. Thus, if forward applied voltage increases
from zero, the diode will start conducting only after this voltage reaches just
above the barrier potential or forward

biased voltage of the

junction. REVERSE
BIASED
If the positive terminal of the source is connected to the n-type end, and the
negative terminal of the source is connected to the p-type end of the diode,
there will be no current through the diode except reverse saturation current.
This is because at the reverse biased condition the depilation layer of the
junction becomes wider with increasing reverse biased voltage. Although
there is a tiny current flowing from n-type end to p-type end in the diode due
to minority carriers. This tiny current is called reverse saturation current.
Minority carriers are mainly thermally generated electrons and holes in p
type and n type respectively. Now if reverse applied voltage across the diode
is continually increased, then after certain applied voltage the depletion
layer will destroy which will cause a huge reverse current to flow through the
diode. If this current is not externally limited and it reaches beyond the safe
value, the diode may be permanently destroyed. This is because, as the
magnitude of the reverse voltage increases, the kinetic energy of the
minority charge carriers also increases. These fast-moving electrons collide
with the other atoms in the device to knock-off some more electrons from
them. The electrons so released further release much more electrons from
the atoms by breaking the covalent bonds. This process is termed as carrier
multiplication and leads to a considerable increase in the flow of current
through the p-n junction. The associated phenomenon is called an avalanche
breakdown.

43
Types of diodes:
LED
This are special type of diode that emit light when they are forward biased

PIN DIODE
A pin diode with a wide undoped intrinsic semiconductor region between a
p type semiconductor and n type semiconductor.

PHOTO DIODE
A photo diode is a diode that convert light into electrical current when
photons are absorbed into the photodiode

44
SCHOTTKY DIODE
It’s a diode in which a semiconductor metal junction is formed
between a semiconductor and a metal thus creating a Schottky
barrier

VARACTOR DIODE
It is a reversed biased pn junction diode whose capacitance can be varied electrically

PN JUNCTION DIODE
The standard which used for voltage rectification

Fig 2.15 Sourced from

electrical

ZENER DIODE
Used for voltage regulation and make use of breakdown property.

Testing of diode
Fig 2.17 Sourced from electrical
Using analogue meter
Set the meter to ohms’ range
Connect the cathode terminal of multimeter to P side and anode to N side.
The reading should be very low resistance.
Reverse the connection. The reading should be very high for a working diode.
Using digital meter
Set the meter to continuous range

45
Connect lead to ends of diodes. The meter should produce a sharp sound if the diode is

46
good or it should read some values
Cold test
Check for discoloration or deformation

TRANSISTORS

It is a semiconductor device, made of two diodes placed back to back, and is used in
building of amplifiers.

It has two connections; PNP, or

NPN. Construction of transistor

from diodes.

When testing, the Base-Emitter combination should measure a higher value of

resistance than the Base-Collector combination.

Testing the BJT transistor, the Base terminal is used as the reference

terminal. Steps;

 Adjust the meter to diode range.

 Place the red probe on the Base terminal, and the black probe on the
Emitter terminal. One is expected to get a number in range of 300-
1200, for forward bias.

 One should get a similar value when they place a black probe on the
Collector terminal and the red probe on the Base terminal.

In reverse bias condition, you should get 1, and if you get 1 in both cases, it means
the transistor is shorted.

47
TYPES OF TRANSISTORS

1.Bipolar Junction Transistors (BJTs)

A BJT is a type of transistor that relies on contact of two types of

semiconductors for its operation. They have two types of charge carriers; electrons
and holes. They can be classified as NPN or PNP type.

2.Darlington pair transistors.

It consists of two transistors.

i) There are two BJTs that contain a miniaturized circuit.

ii) Testing it can be complicated. This is because of number of circuits

contained in it. Darlington is found in monitor circuits of a TV or Computer CRT.

3.Field Effects Transistor (FETs)

When testing the FETs, you should know the gates to test between the Drain and
the Source. Before testing it, you should short its terminals first.

If you place the red probe on the SOURCE and the black on the DRAIN, you

should get the FETs characteristics.

If you interchange the probes, you should get a value of 1.

If you get a 0 even after interchanging the probes, then it is an

internal short. If you get a 1 even after interchanging the probes,

then it is an internal open.

4.Regulators

It is used in regulation. It has three terminals, one Earth terminal, and two
Positive/Negative terminals.
48
  78- Series regulates Positive, (LA78) – positive DC Regulation.
e.g. 7805 means its voltage is +05V

 79-Series regulates Negative, (LA79) – negative DC regulation.

5.High Power Transistor

It is a high power NPN Silicon transistor, and is designed for use in industrial-military
power amplifier switching circuit applications

Types by functions

This is classifying them according to what they are designed to do. Some
transistors are used for switching while others are for amplification.

These are primarily used to amplify low level signals but also function as

switches. Hfe value ranges from 10 to 500 with maximum IC from 80 to

600mA.

1. Small switching transistors

Used to amplify low level signals but can also function well as switches. Hfe value
ranges from 10 to 200 with Ic from about 10 to 1000mA.They come in NPN and PNP
forms.

2. Power transistors

They are used where a lot of power is being used (current and

voltage) Power rating range from around 10 to 300W with

frequency from 1-100MHZ.

3. High frequency transistors

They are used for small signals that run at high frequency for high speed switching

applications. They are used for high frequency signals and are able to switch on and

off at high speeds.

49
They are used in HF, VHF, UHF, CATV and MATV amplifiers and oscillator applications.

50
4. Phototransistors

These are light sensitive transistors.

They have two terminals instead of the usual three.

5. Unijunction transistors

These are three lead transistors that act as electrically controlled switches. They
are not used for amplification.

2.6 SOLDERING AND

DESOLDERING

SOLDERING

Method of joining metal parts using filler metal of low melting point and a

soldering gun. Process of Soldering

 General Preparation.

The circuit boards should be cleaned prior to soldering. Oxidation should be

removed by methods that do not damage leads or parts and do not hinder solder
wetting. The solder tips should be cleaned to ensure proper heat transfer and avoid
transfer of impurities to the solder connection. Component leads should be applied
with solder prior to soldering. Excess solder should be removed from the circuit
board so that it does not interfere with the proper placement of a new component.

 Placement and Heating of the Component Leads.

The component leads should be placed in the holes in the circuit board.
For heat sensitive components like transistors heat sinks should be used.

 Application of Solder.

The part being soldered must be held in place until the solder solidifies.
The solder should be applied at the upper portion of joint so that the
work surface and not the iron will be responsible for melting the solder.

Soldering gun/iron.

51
Precautions to be taken when soldering

1. Solder as far as possible from the body of a semi-conductor.

2. Never apply molten solder to leads or terminals for long.

3. Keep the surface and solder tip clean to enable the connection to be made quickly.

4. Use lead free elements when soldering.

5. Never touch the element tip of the soldering iron since they are usually very
hot and give one a serious burn.

6. Always work in a well ventilated area since the smoke produced is irritating.

DESOLDERING

DE soldering is a process of removing soldered components by melting solder and

having it removed by either a solder sucker or wick/solder braid or by pulling out
component. Solder sucker is useful when there is a lot of solder to remove.

Rules to be followed while desoldering;

1. Avoid peeling off the strip.

2. The DE soldered face should be very smooth.

3. There should be no continuity between the strip being tested and the adjacent strip.

4. Ensure the tip of the soldering iron should not be greater than the pad to
prevent burning of the board.

52
DE soldering of Surface Mount Components Using a Blower Gun

A blower gun contains three variable controls, two irons, and two ON and OFF switches gun.

Blower Gun.

3. Variable controls.

The Air-control;

This determines the magnitude of the pressure at the output of the blower gun.

The Heater-Control;

This determines the amount of heat to be generated at the element of the blower gun.

The Temperature-Control;

This is used to determine the temperature of the fixed gun at which it operates.

53
ON and OFF Switches;

Have one switch for fixed gun, and the other for blower

gun. ELECTRICAL MACHINES

In this section, different methods of starting a motor were

learnt MOTOR STARTING

Motor starter is an electrical circuit composed of electromechanical and electronic

devices which are used to start or stop an induction motor.

Motor starting methods include:

 Direct On-Line method

 Reversing Direct online method

 Star delta method

Direct On-Line method

A direct online starter connects the motor terminals directly to the power supply
hence the motor is subjected to the full voltage of the power supply. Consequently,
high starting current flows through the motor. This method is suitable for small
motors below 5 HP.

54
Fig 2.7. Circuit diagram of DOL starter

55
 FIGURE: DOL STARTER

Star delta method

The motor windings are connected in star during starting; the connection is changed
to delta when the motor starts running. When starting a motor, it should be started
slowly to prevent the rotor overheating and drawing an enormous current. When the
windings of a three phase motor are connected in star, the current is reduced to
square root of three of the normal running
current that is
taken when
it's connected
in delta. When
the motor
picks up
speed, the
connection is
changed to
delta so that
the motor runs
at full speed
and torque
from then on.

56
Fig 2.8 Circuit diagram of star delta starter

FIGURE: DELTA-STAR STARTER

57
ELECTRICAL INSTALLATION:

Electrical installation is the electrical wiring and associated devices such as

switches, meters and light fittings used in buildings. The following information is
important to understand well electrical installation.

Electricity generation and distribution

Electrical energy is produced from its various sources i.e. Water, steam, coal and
petroleum or nuclear plants. These sources are used to turn turbines which intern
rotate coils in a magnetic field which then produces electricity.

Produced voltage is then stepped up and down respectively using transformers to

be transmitted over large distances and enable consumers to get power in the
required amounts.

Power is produced mostly at 11Kv. It is then stepped up to 132Kv and the power is
transmitted over large distances to a substation. Here, power is stepped down to
66Kv then fed to another substation that steps down to 33Kv. From 33Kv, it is
stepped down to 11Kv in another substation. From 11Kv; power is stepped down to
415V which is then stepped down to 240V.

The voltage between phases is 415V while that between a phase and a neutral is
240V.The voltage is stepped up during transmission to reduce transmission losses.
The line on top of the pylons used to transmit power in high voltage is basically
used as lightening arrestor thus preventing the lines from destruction by lightening.

Factors to be considered during installation

a)Type of building- whether installation work is for a permanent or temporary
or for extension to an existing building.
b) Durability – a good installation should be durable.
c)Cost – a good installation should be less expensive but reasonably cheap.
However, an electrical engineer should make a good installation as expected
of him.
d) Safety- an engineer should make safety the first factor to be satisfied
as it is the most important aspect of installation.
e)Earthing- provides safety required as far as installation is concerned.
f)Flexibility- if the wiring system should be one that can be easily extended in future or not.
g) Installation state- if the installation might be subjected to mechanical
damage, moisture, fumes, abnormal temperatures, inflammable or explosives.
h) Appearance –if the installation should be exposed or concealed
i)Flexibility- if the wiring system should be one that can be easily extended in future or not.
j)Installation state- if the installation might be subjected to mechanical
damage, moisture, fumes, abnormal temperatures, inflammable or explosives.
k) Appearance –if the installation should be exposed or concealed

58
Steps of installation
 The schematic diagram is drawn
 The wiring diagram is drawn

NB:
Conventionally, in installation, neutral does not pass through the switch and also the
red cable is considered live.

Precautions:
i. Before wiring is done, testing should be done by use of DMM.
ii. Cables connecting the live, neutral and earth should be laid.
iii. An engineer should familiarize the symbols before and during wiring
process to avoid confusion and/or misinterpretations.
iv. Terminations and markings should be identified
v. Layout of the circuit should be well understood
vi. Wiring should be done carefully to avoid wastage of cables and other apparatus
vii. Before powering the circuit, it should be tested for continuity

The following are commonly used symbols in electrical installation.

59
The tools and equipments used in installation include the following:

 Consumer control unit

A component of an electrical power system within which on electrical power feed
provides supply to subsidiary circuits

 Junction boxes
A container for electrical connection with the intension of protect also this is used
for joining wire to electrical switches or sockets
 Meter box
They contain electrical meter which measures the amount of power consumed
 Distribution board
A component of an electricity supply system which divides an electrical power feed
into subsidiary circuits while providing a protective fuse or circuit breaker
 Circuit breakers
An automatically operated electrical switch designed to protect an electrical
circuit from damage caused by overload or short circuit

 Tools and apparatus

1. Pliers 7. Hammer
2. Nails 8. Screws
3. Screw drivers 9. Spirit level
4. Cutter 10. Hack saw
5. Meter rule 11. Clips

60
Types of installation (wiring)
 Surface wiring
 Concealed wiring
Surface wiring-In this type of wiring, the wires run on the surface of the wall
instead of conduits/wall studs. The electric wires are held in position using metal
clips. This type of wiring prevents the creation of wall studs which will require to be
filled again after the wiring process. The electrical wires used are Copper sheathed
wires which are well insulated.
The procedure for surface wiring included:
e) The circuit to be laid is first interpreted
f) The cable size to be used is determined depending on the loads.
g) An overview, demonstration and lying of the necessary components was also
done such as:
 Laying of the isolators,
 Fixing of the distribution board,
 How to engage the consumer control unit in the circuit?
 Connecting of the circuit breakers,
 Fixing of the sockets, lamps other lighting elements in the circuit,
 Correct positioning of the junction boxes, socket holders, bulb
holders and lying of the cables relative to the wall by use of the spirit
level.
In addition, the emphasis was given to the circuit breaker and the importance
attached to it. For instance, the rating of the circuit breaker necessitates its usage
in the circuitries.
The total power demand of each circuit determines the circuit breaker to be used.
The following are some of the loads with varying rating of the circuit breaker and
the preferred cable sizes

LOAD RATING CABLE SIZE

CIRCUIT OF
BREAKER
Lighting 5A 1.0/1.5mm2

61
Sockets 10A/13A/20A 2.5mm2

62
 Cooker 20A 4mm2

Water heater 20A 4mm2

It is the process of connecting different electrical components to the mains supply in

a building. The process depends largely on;

-ratings of the components

-materials of the components

-area of

installation

OBJECTIVES:

*to learn safety precautions taken during installation.

*to learn different types of wiring.

*to learn how power is distributed from the power station to the consumer.

*to learn various types of cables and their applications.

*to learn on how to install different electrical components.

*to learn on how to correct on different faults.

Socket connection

Sockets are wired; in two

ways Radial

This involves looping only once. It has no alternative route of power thus in case of
a cut, power goes off.

Fig 2.1 Radial socket wiring

63
Ring

This involves looping to and back to the supply. It provides an alternative route
of power and therefore in case of a cut at any position of the cable, power will
still be available at the socket.

The only disadvantage of this method is that it quite expensive as it consumes more cable.

Fig 2.2: Ring socket wiring

This connection involves a ring connection and then a radial at the final

connection. Cut a circuit from being destroyed by over rated current.

It consists of a high resistant wire that melts away when more than rated current
flows thus creating an open circuit.

Fuse element is made of zinc, copper, silver, aluminum and alloys to provide and
predictable characteristics.

FUSES:

Types of fuses

64
They are classified in to two major categories i.e. low voltage and high voltage fuses.

Low voltage

(i) Semi enclosed or rewindable type (KIT-KAT type)

(ii) Totally enclosed or cartridge type.

Cables

Cables are classified in different

ways; According to the area of

application Overhead cables.

Underground

cables. Submarine

cables.

According to

insulation Rubber

insulated

Polyvinyl chloride (PVC)

insulated Paper insulated

Silk and cotton

insulated Enamel

insulated

Vulcanized bitumen insulated

cables Gutter perch

According to the voltage it can support

Low tension up to

1000volts High tension

up to 22kv Super

tension 22kv-33kv EHT

65
33kv-66kv

Oil filled and pressure and gas cables for 66kv-132kv

66
Extra super tension- for above

132kv. According to their sizes

1.031 mm-used for lighting circuits

2.5mm used for socket circuits

4.0mm-used for cooker and water heater

circuits 6.0mm-used as earth cables.

The installation should meet the following;

1) Economy-The circuit should obey the law of engineering economics. Cables

should be the best quality.

2) The installation should be neat and smart i.e. good appearance.

3) Lifespan-Check on the expected life span to suit the purpose for the
installation i.e. either temporal or permanent.

Types of wiring systems

Conceded Wiring-This uses steel conduit or plastic conduits. The appliances are
the ones visible only.

Surface wiring-applied mainly on timber houses (trunking system)

Sheathed Wiring-Includes PVC insulated and armored cables.

Installation
Exercises
Exercise one

Using PVC insulated cable TWE; Install the following circuit such that the
TWO lamps can be controlled from ONE position. (Surface wiring ) CCU

67
 L

L2

From the above circuit diagram, the two lamps (L1 and L2) are controlled
from a single switch as shown. The mode of wiring used is the surface wiring,
whereby the cables are fixed on the surface of may be a wall or ceiling or
any other surface in which wiring is being done. The live line and the neutral
are taken from the CCU to the lamps with the live line passing via the switch
first before going to bulb. There is no Earth wire to the lamp.

Exercise Two

Using PVC insulated cable, Install the following circuit such that lamp L1, L2
and L3 L4, are controlled individually by switch S2. Switch S1 is a master
switch. (Surface wiring system)

68
 L2

L1

S1 S2

L3 L4

In
the above exercise, the four lamps are controlled by switch S2, which is a two-
gang-one-way switch. Lamp L1 and L2 are controlled by one gang of the
switch while lamps L3 and L4 are controlled by the other gang of the switch.
Switch S1 is a Master switch and it controls the entire circuit of the lamps
and switch S2 except the CCU operation. The live line passes through master
switch first before proceeding to the lamps via S2. The neutral is also present
but not connected to the switches. There is no earth wire.

Exercise Three

Using PVC TWE Insulated cable, Install the following circuit such that lamp L1
and L2 is controlled from switch S1 individually and lamp L3 is also controlled
from switch S2 and lamp L4 is controlled from two positions. (Concealed
wiring system-use conduit pipes)

69
 L1 L2

S4
JB

S1
S2

L3
L4 S3

Exercise Four

Using PVC Insulated cable, Install the following circuit such that lamp L1 is
controlled from THREE positions by switches S1, S2 and S3, lamp L2 is
controlled from TWO positions by switches S4 and S5. Install the sockets,
S01 and S02 in radial system (Concealed wiring system-use mini-trunking).

70
Exercise Five

Using single core PVC insulated cables, Install the following circuit using
conduit Pipes for the Power circuit and mini trunking for the Lighting circuit,
such that lamp L2 is controlled by switches S1, S2 and S3, Lamp L1 is
controlled by switch S4. The sockets outlets SO1 and SO2 are connected in
radial connection while SO3 and SO4 are connected in ring connection with a
Spur. CCU

71
Exercise6: COMPLEX
WIRING Objective
To install a sub circuit for lighting and power
circuit Use PVC conduit for both lighting and
power circuit. Condition
Switch S1 is dimmer switch to control L1, S2 to control L3 and switch S3, S4
and S5 to control L2 the socket outlets are connected in ring with a spur.
Design the circuit and implement it.

72
Schematic diagram

The circuit diagram above is a complex wiring diagram. It consisted of an

Energy meter, distribution board, the consumer control unit (CCU), an
Isolator, socket outlets, fluorescent fittings, incandescent lamps, switches,
bell & bell-switch.

From the supply, power was taken to the Distribution board, from where it
passed through the meter before proceeding to the other components. From
the distribution board, power was taken to the CCU and the other line to the
Isolator. Isolator is meant in case there occurs a three-phase machine which
may need a power supply from the system. The CCU is meant to serve and
control the other part of the circuit. From the CCU, three live lines are taken
out for different loads. One live wire (and its neutral) serves the lighting
system and the bell. This live line carried a maximum of 5Amps as per the
73
circuit-breaker. This system has no earth wire. The fluorescent fitting L2
is

74
controlled by three switches, S4 (an intermediate switch), S3 and S5.
Another live wire carrying 30Amps (connected to 30A Circuit-breaker) was
taken from the CCU to serve the sockets system. In this system, along the
live wire are also the Neutral and the Earth wires. The sockets were
connected in Ring method, with a spur. Also we obtained the third live wire
from the CCU, and this one was connected to a 30Amps rated circuit breaker,
to serve the cooker socket and also water heater socket. This system also
must have the 3-wires, live, neutral and earth wire. In the sockets and the
cooker systems, a high rating circuit-breaker is used because some
appliances and gargets which are used in those sockets have ratings of
13Amps or more.

75
76
CIVIL AND STRUCTURAL ENGINEERING

DEPARTMENT SURVEY
Definition: surveying is the technique and science of making
measurements of relative positions of natural and man-made feature on
earth’s surface. In order to accomplish their objectives, surveyors use
elements of geometry, engineering, trigonometry, mathematics physics
and laws.
Surveying techniques and equipment
Varieties of means that are more precise have been developed for surveying.
Levels are calibrated to provide a precise plane from which differentials in
height between the instrument and the point in question can be measured.
The basic tools of planer surveying are:
1. A tape measure- for measuring shorter distances
2. A lever- for determining the height or the elevation differences
3. A theodolite-is a set on a tripod with which one can measure angles
(vertical and horizontal) combined with triangulation.
4. Total station- is a more modern instrument. It is a theodolite with an
electronic distance measurement device (EDM) and can also be used
for leveling when set to the horizontal plane.
Branches of surveying
Engineering surveying/construction surveying: It involves survey work for the
purposes of construction and engineering design. It is the process of
establishing and making the position and detailed layout of new structures
such as roads or buildings for subsequent construction.
Hydrographic surveying: It is conducted for the purposes of mapping the
coastline and seabed navigation, engineering and resource management
purposes.
Topographic surveying: It is a form of survey that measures the elevation of
points on a particular piece of land and presents them as contour lines on a
plot.
Photogrammetric surveying: A survey done by satellite imagery or aerial
photography used base where no map exists.
Geographic information systems (GIS): It involves mainly digital database.
: Used in electrical engineering to show grid
77
network. Leveling

78
Leveling refers to the determination of elevation points above the earth’s surface.
A level instrument is an optical instrument or telescope complete with a build
in spirit level that is mounted on a tripod

Objectives
To determine the relative heights of points on the earth’s surface
Here, an experiment was carried out to determine the differences in height
between points and subsequently the reduced levels of the various points in
particular to determine the reduced levels of the center line of the road from
water lab to the main gate in MMUST for the purposes of plotting profile.
Equipment used in
surveying Level
Tape
Tripod
stand A
theodolite
Leveling

staff
Calibrated
rod

Parts

79
The basic setup of a transit level consists of the actual transit level

80
Procedure
The level was set at a convenient point and then temporal adjustment done
on the level. The staff was being held at the first point benchmark and
reading taken on staff (back sight). The staff is then moved to the next
position and reading taken (intermediate sight). This is repeated for the third
and fourth positions at interval of 20m. With the staff in the last position, the
level is moved forward and set up at the second position and reading taken
in the last position as back sight. This is known as the change point. The
whole process is repeated till the required line is covered.
Setting up
Tripod should be set up such that the tripod head is approximately horizontal judging by
81
the eye then the level is attached to the tripod. The tripod shoes are then
threaded firmly to the ground.

Leveling the instrument

The circular bubble is positioned between foot screens. This is done by
rotating the two foot screws in opposite direction until the bubble is in
central position
Terms used in leveling
Back sight- is the first reading taken after setting up the level. If it at the
beginning of operation, it is taken when the staff is placed on the bench mark
Intermediate sights- readings taken on the leveling staff in between the
back and foresight
Foresight- is the last position taken at the station before the instrument
is shifted to a new station
Change point- is a point at which the leveling staff is held when the level is
shifted from one position to another

82
MECHANICAL & INDUSTRIAL ENGINEERING
Objectives
1. To know the types of machines in Mechanical and Industrial
Engineering workshop and their uses
2. To learn and practice different types of welding processes

Workshop rules, regulations and safety

a. Keep the shop clean. Metal scraps should be placed in a scrap bin
rather than allowing them to remain on the floor as scraps can knock
down persons working in the workshop.
b. Do not machine any material until you know what it is and how it
should be handled because some materials are very dangerous under
some conditions e.g. magnesium chips burn with great intensity under
some conditions and can damage machines beyond repair.
c. Compressed air should never be used to remove chips and cutting oil
from machines because the flying chips may cause serious eye
injuries. Vaporized oil may ignite and cause painful burns and
property damage.
d. Oil rags must be placed in a closed container. Rags used to clean
machines become imbedded with metal chips. Be sure to place
them where they can be used again-this will reduce the probability
of spontaneous combustion (self- ignition caused by chemical
action).
e. Use care when handling long pieces of metal stock.
f. Dress properly. Avoid loose clothing.
g. Avoid wearing materials that can be caught by moving parts of machines.
h. Keep your sleeves rolled up. No neckties.
i. Maintain adequate ventilation where dust and fumes are hazard.
j. Always protect your eyes when doing jobs that produce flying
chips, such as grinding.
k. Do not operate any machine until you are sure about its operation and controls.
83
 l. Stop the machine before making measurements and adjustments. Do
not touch machine surfaces when it’s moving.
m. Keep the floor around the machine clear of chips metal scraps and oils.
n. Concentrate on your work during machine operations.
o. Do not remove chips with your hands or when the machine is
running. Instead, use a brush or pliers to remove long chips.
p. Do not carry sharp tools or for that matter any tools in your pocket.

Metal arc welding safety:

a. Welding gloves should be worn and no part of the body should be
exposed to the rays from the arc otherwise burning will result.
b. Welding aprons should be worn to protect body and clothing.
c. Filter glasses should be chosen according to BS recommendations.
d. Do not weld in a position where other personnel may receive direct
or reflected radiation.
e. If possible, do not weld in buildings with bright colored walls
(white). As this increase reflected light and introduces greater eye
strain.
f. Do not chip or deslag metals unless glasses are worn.
g. Do not weld while standing on a damp floor.
h. Switch off apparatus while not in use.
i. Make sure that welding return leads make good contacts, thus
improving welding conditions and reducing fire risks.
j. Avoid having inflammable material in the welding workshop.
k. Degreasing using chemical compounds such as Trichloroethylene,
Perchloroethylene, carbon tetrachloride, methyl chloride should be
carried out away from the welding operations and the chemicals
allowed evaporating completely from the surface of the component
before beginning welding.
Saws and cut-off machines safety:
a. Clean oil and grease from the floor around work area.
b. Burrs on cut pieces are sharp. Use special care when handling
pieces lest they cause you serious cuts.

84
c. Do not clean chips from the machine with your hands. Use a brush. Stop the

85
 machine before cleaning.
d. Keep your hands clear of moving parts.
e. Stop the machine before making adjustments.
f. Handle band saws with extreme care. They are long and springy and
can uncoil at high speeds causing serious cuts.
g. Do not operate the machine unless all guards are in place.

WELDING PROCESS
Welding is a fabrication process that joins materials, usually metals or
thermoplastics, by causing coalescence. This is often done by melting the
work pieces and adding a filler material to form a pool of molten material
(the weld pool) that cools to become a strong joint, with pressure sometimes
used in conjunction with heat, or by itself, to produce the weld. This is in
contrast with soldering and brazing, which involve melting a lower-melting-
point material between the work pieces to form a bond between them,
without melting the work pieces. Welding methods can broadly be
categorized as;

 Pressure welding; in which the parts are headed to a plastic

condition and the weld is formed by mechanical pressure.

 Fusion welding; in which the parts are melted and ran into each
other giving a continuous joint.

There are eight welding processes which are divided into three categories
shown below.

1. ELECTRIC
Electric Arc -MMA (manual metal
arc) MIG (metal inert gas)
TIG (tungsten inert
gas) Submerged Arc
Electro-Slag

2. RESISTANCE
• Spot
• S
eam
GAS
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• Oxy-Acetylene

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3. ELECTRIC ARC WELDING
Operation of the electrode
The weld pool is protected from oxidation by the gasses produced by melting
the chemicals on the electrode coating. This wire electrode also acts as a
filler material to fill the gap between the two parts being joined. Its third
function is to form a slag which protects the weld area form cracking as it
allows the joint cool slowly and protect it from oxidation.
Applications
This has many operational uses such as repair work to constructional steel.
It is ideal for outdoor uses as the gasses needed to form the shield are not
blown away.
Principle of operation
Electricity is passed through an electrode which jumps between the
electrode and the work piece. This causes an arc which produces great heat
melting the electrode and the work piece causing the edges to fuse together
(Consumable electrode)
Welding process
This is the localized joining of metals by heating them to a suitable
temperature with or without application of pressure or the use of filler metal
The welding process is used in fabrication and erection of steel structures in
industrial construction and civil engineering, for example the construction of
steel reservoirs, boilers and pipelines. Welding is also applied in concrete
reinforcement, fastening panels and members in automobile and aviation
industry.
Advantages of welding
1. A good weld is as strong as a base metal
2. Most welding facilities are portable
3. Welding permits considerable freedom in design
4. Welding can be mechanized
5. Large number of metals both similar and dissimilar be joined
by welding Shortcomings of welding
1. It gives a harmful radiating fumes and spatter
2. It results into residual stresses and distortions of the work piece
3. Jigs and fixtures are generally rigid to hold

88
4. Edge preparation of work pieces is generally required before welding them

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 5. Heat from the weld produces metallurgical changes

Classifications of welding
process Pressure
processes
The parts to be joined are heated to plastic state (fusion may occur to
limited extent) and forced together with external pressure to make the joint.
Fusion process
The material at the joint is heated to the molten state and allowed to solidify
to make the joint without the application of pressure. A filler metal is added
to the weld to fill the space between the parts welded. The filler metal
deposited should ordinarily be at some as the base metal e.g. gas welding,
electric arc welding etc.
Types of welds

Types of weld
joints The
Tee- joint

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TYPES OF WELDING
Electrical arc welding
Electric arc welding is a process in which fusion is achieved by heating with
an arc with or without application of pressure and with or without the use of
a filler material.

Welding machine electrode holder electrode

+ Workpiece
Work cable

-
Schematicdiagram showing electric arc welding

An electric arc is a continuous stream of electrons flowing through some sort

of medium between two conductors of an electric circuit and accompanied
by heat generation and radiation. The arc is obtained from consumable and
non-consumable electrodes and the work piece.
Striking an arc
The electrode is brought in contact with the work piece at the point where
welding is to be started after connecting the work piece to welding circuit.
After a light contact, the electrode is immediately withdrawn to a distance
equal to the diameter of the electrode from the work piece.
The voltage available at the output terminals of a welding set before the arc
is struck is called open circuit voltage. The voltage falls after the arc is
established to about less than half the open circuit voltage. The arc length is
the distance between the end of the electrode and the surface of the molten
metal on the work piece.
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Formation of an arc
When the electrode is in contact with the job a large current flow. When the
electrode is withdrawn, current continues to flow in form of a spark across
the air gap. The air gap gets ionized and conducts as a result current is able
to flow across the gap inform of an arc.
Arc welding electrodes
There are two main types of electrodes:
1. Non-consumable electrodes: when these electrodes are used the filler
materials are added separately, since the electrode is not consumed, the arc
length remains constant so that it’s stable and easy to maintain. They are
mainly made from carbon, tungsten or graphite.
2 .Consumable electrodes: they provide the filler material. They
should have same composition as the base metal. They are of three
kinds; i.e. bare electrodes, fluxed electrodes and coated or shielded
electrodes.
Electrodes are mainly coated in order to:
 Improve arc stability by ionizing arc path.
 Provide protective gaseous atmosphere to prevent oxygen,
hydrogen and nitrogen pickup by the molten metal
 Provide protective slug over hot metal.
 Reduce spatter of weld metal; when coating burns off slower than the core.
 Add alloying elements
 Slow down the cooling rate of weld to prevent hardening.

Commonly used arc welding

processes Metal arc welding
Inert gas arc welding
Carbon arc welding
Submerged arc welding
Atomic hydrogen
welding Shielded metal
arc welding
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Arc welding procedure
Thoroughly clean and prepare the edges for proper deposition of the metal
Select the electrode of proper material and size according to dimensions of
the work piece
Adjust the voltage to proper value
Layout the work piece and connect with a
earth romp Strike the arc at the right position
Take a proper run of the welding if needed take
another run Clean the weld and chip off.

Safety issues
Heat and sparks-Because many common welding procedures involve an
open electric arc or flame, the risk of burns is significant.
Eye damage-The brightness of the weld area leads to a condition called arc
eye in which ultraviolet light causes inflammation of the cornea and can burn
the retinas of the eyes.
Inhaled matter-Welders are also often exposed to dangerous gases and
particulate matter. Processes like flux-cored arc welding and shielded metal
arc welding produce smoke containing particles of various types of oxides
Gas welding
Oxy fuel gas welding (OEW) is a group of welding processes which join
metals by heating with a fuel gas flame or flares with or without the
application of pressure and with or without the use of filler metal.
Commercial fuel gases have one common property: they all require oxygen
to support combustion. To be suitable for welding operations, a fuel gas,
when burned with oxygen, must have the following:
 High flame temperature

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  High rate of flame propagation
 Adequate heat content
 Minimum chemical reaction of the flame with base and filler metal
Types of Flames
There are three basic flame types: neutral (balanced), excess acetylene
(carburizing), and excess oxygen (oxidizing).
The figure below shows the flames:

Gas welding
techniques Leftward or forehand welding: In this process the torch is held
in the right hand at an angle 40-50 degree and the welding rod in the left
hand at an angle of 30-40 degree from the work piece. The flame is given
circular rotational or side to side motion to obtain uniform fusion
throughout. This method is more efficient for welding materials up to 6mm
thickness
Rightward or backhand welding: It differs from the leftward welding in the
direction of movement of the torch. In this system moves from left to right.
The torch is held at an angle of 30-40 degree. The cone of flame rightward
welding is deeper than the flame in leftward welding hence this process is
more suitable for welding plates above 6mm thickness.

94
Forehand welding

Backhand Welding

MIG welding

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Operation
MIG uses an inert gas such as Argon or CO2 to shield the weld
The bare wire electrode is fed continuously to the weld - semi-automatic
process Can be used on light and heavy plate
Does not produce a slag and can be used for multi run welds and by
robots. Applications
This is one of the most common ways of welding. It can be used to weld
sheet metal as well as heavy plates. As the electrode is fed automatically
and no slag is formed it is ideal for robotic welding for example car
production.
D. TIG welding

Principle of operation
Two separate currents flow in the circuit in this welding process. One is for
the arc and is similar to MAGS, the other is a high frequency current used to
start the arc. This
96
means an arc is not stuck by touching the work piece as
before. Operation
The arc melts the two edges to be joined as well as the filler rod forming the
weld pool. The gas is pumped through the nozzle protecting the weld pool
from oxidation. The electrode is only to maintain the arc supplying the heat.
A consumable filler rod fed by the operator gives the extra metal necessary
for the weld pool.
Applications
TIG is suitable for welding most metals. However, when welding aluminium
AC is used. This is necessary to breakdown the oxide layer on the outside of
the aluminium which has a high melting point. It is also suitable for stainless
steel.
OXY-ACETYLENE
Types of flames
There are three basic flame types:
1. Neutral (balanced),
2. Excess acetylene (carburizing), and
3. Excess oxygen (oxidizing)
Types of oxy-acetylene gas
a. Neutral flame – Fusion welding of steel and cast iron.
b. Oxidizing flame - Used to weld copper and brass.
c. Carburizing flame - Used to weld aluminium and alloy steel

97
Principle of operation
In a fusion welding process, heat is concentrated on the joint edges until
the metal melts and starts to flow. The molten metal fuses as the joining
edges meet.
Operation
Oxygen and acetylene gas are burned at the tip of the nozzle on the welding torch.
Oxidation of the joint faces is prevented by an envelope made up of the
products of combustion. A filler metal, in rod form, can be added.
Storage
Acetylene is dissolved in a porous material called acetone, which will absorb
25 times it’s own volume of Acetylene. Acetylene would explode if it were
stored under pressure.
Operation
Oxygen and acetylene gas are burned at the tip of the nozzle on the welding
torch. Oxidation of the joint faces is prevented by an envelope made up of
the products of combustion. A filler metal, in rod form, can be added.

BRAZING
98
This is the process of joining two metal pieces heated to suitable temperature by using

99
a spelter. The spelter is distributed between the closely fitted surfaces of the
joint by capillary action. A flux is used to clean the oxide from the metal
surface; it’s usually applied by dipping the heated end of the rod into the tin
of flux. In this method, any suitable heat source can be used e.g. a blow pipe,
oxy-acetylene etc.
The filler material melts at lower temperature than the base metal hence it’s
a non- fusion process.
Brazing techniques
Torch brazing Silver
brazing Furnace brazing Blaze welding
Cast iron welding Vacuum
brazing Dip brazing
Disadvantages of brazing:
Brazing does not melt the base metal of the joint; it allows much tighter
control over tolerances and produces a clean join without the need for
secondary finishing.
Brazing produces less thermal distortion than welding due to the uniform
heating of a brazed piece.
The lack of joint strength as compared to a welded joint due to the softer
filler metals used.
Brazed joints can be damaged under high service temperatures
Some brazing applications require the use of adequate fluxing agents to
control cleanliness.
The joint color is often different than that of the base metal, creating an
aesthetic disadvantage.

Advantages of brazing:
Complex and multi-part assemblies can be brazed cost-effectively.
The brazing can be coated or clad for protective purposes. Finally, brazing is
easily adapted to mass production and it is easy to automate because the
individual process parameters are less sensitive to variation.
WELDING EXERCISE.
Practical work

10
0
Use arc weld to join these two steel sheets;
Two pieces of steel sheet measuring 50*50 are cut out of a larger sheet
using grinding machine
The piece edges are smoothen using a file to have smooth
edges Then they are placed on workbench for welding
Arc weld method is applied to join the two

FIGURE: cutting of
samples using grinder

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1
 INDUSTRIAL VISITS
The industrial visits were conducted on the last week of the workshop
practice duration. This is where we were able to visit various firms in the
industry and familiarize with how they carry out their production or service
activities.

Below are the places and firms we visited during the industrial tours period:

 Tononoka steel limited Company

 Data cables

 Telephone cables

 Aluminium conductors

 Welding cables

 Concentric cables

 Aerial bundle conductors

 Overhead cables

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2
  Stay wire

Properties of conductors

 Low electrical resistance

 Mechanically strong and flexible

 Must be relatively cheap

Examples of conductors: Silver, copper, Aluminium, Tin, Lead, Iron etc.

7.1.1.2 Insulation
The insulation in a cable is designed to cater for the voltage level of the
cable i.e. the higher the voltage of the cable, the thicker the insulation needs
to be. All conductors in the one cable are insulated with the same material.
An insulator should have the following properties;

 Must have high resistance

 Must be capable to with-stand mechanical stress, i.e. bending and compression.

Examples of insulators : PVC, Rubber, etc.

7.1.2Protection
The cable requires protection from the environment in which it is to operate.
This can take the form of a metallic shield such as lead or steel wire armor,
or a polymeric such as PVC.
During our visit to Doshi (Metsec) company, we were taken through the
following main copper wire manufacturing process:

7.1.3Determining the size of the cable

The conductor, (either single or stranded) determines a size of a

cable. The size of a cable is the total cross section area of

conductor(s).

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3
The size of a cable is determined from the following formula;

3.14 X d² X No.of strands

Cable size (mm²) = 4

Whereby; d is the diameter of the individual conductor in (mm).

7.1.4Types of Cables

1.PVC Insulated & Sheathed Cables

Single core wiring cables – ranges from 1.0mm² -

120mm² Single core sheathed – ranges from

1.0mm² – 4.0mm²

PVC insulated & sheathed twin flat – ranges from 1.0mm² - 16mm²

2.Low Voltage Armored Cables –

600/1000V 2-core, 3- core, 4-

core

3. 6.35/11kV (High Voltage) XLPE Insulated

Armored Cable 3 Core cables – sizes range

from 50mm² - 95mm²

4.PVC Un-armoured Cables

2 core, 3 core and 4core range from 1.5mm² - 50mm².

5.PVC Insulated Screen Flexible Cable (Braided)

2 cores, 3 cores and 4 cores with size ranges from 0.5mm² - 2.5mm²

6.Welding Cables

16mm², 25mm², 35mm², 50mm², 70mm², 95mm², 120mm²

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4
7.PVC Insulated Cords

10
5
 23/0.15

 40/0.15

 70/0.15

 100/0.15

8.Automobile Cables

Ranges from; 0.5mm², 0.6mm², 0.75mm², etc. All the way to 16mm²

9.Battery Cables

Sizes, (16, 20, 25, 30, 40, 50, 60, 75) mm²

11. Special Cables

 Double sheathed round submersible cables

 3 core flat submersible cables

 Electrode cables

 Audio cables

 Microphone cables

 Speaker cables

 Alarm cables

 Under gate cables

 Coaxial cable

 Bell wire –flat

 XLPE insulated Armoured Auxiliary control cable

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6
  XLPE/PVC Un-armoured Auxiliary control cable

 L.V XLPE Insulated Aerial bundled cable – aluminium

 Galvanized stay wire – stranded

7.1.5Cable Manufacturing Process

During their manufacturing, the cables undergo the following;

I. Copper mining –testing is done

II. Wire drawing –copper strip is drawn

III. Rewinding is done

IV. Stranding is done, after which testing is done

V. Insulation – then the cable is tested on a very high voltage to determine

strength of the insulator.

VI. Twisting of cores – testing

VII. Insulation of cores – testing

Also, during the visit to Doshi (Metsec) company, we were taken through the
following main copper wire manufacturing processes.
Drawing process
EC Grade Continuous Cast Copper rod of 8 mm diameter is taken for
drawing on wire so as to different gauge wires.

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7
Annealing Process

After drawing operation, the coils of drawn wire are put in Electric Furnace
in a pot for getting it annealed soft wire.

Bunching / Stranding Process

After the wire is annealed, it is wound on reels and is put for bunching /
Stranding on the wire Stranding / bunching machines for getting different
size range of bunched
/Stranding wires and then passed through nuzzling process for better surface of wire.

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8
TONONOKA GROUP

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9
 SINGLE POWER LINE DIAGRAM

11kv incoming supply (KENYA POWER)

KPLC METERING BREAKER 11KV/630AMP

HV BREAKER (O.C.V)11KV/630AMP

MAIN TRANFORMER1.6MVA,11KV/433V,50HZ

2500A MAIN BREAKER

300kw HF welder

E.O.T. cranes 250kw HF welder

8’’tube mill G.I PLANT/WELD MESH

Guard rail mill/open section+comp & 10 TON.CTL/20TON.CTL

Wire drawing/BRC
2.5” mill OTO

OLD SLITTING LINE NEW

SLITTING LINE

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0
MAIN OFFICE 700KVAR P.F.
PANEL

FIGURE: Programmable logic circuits

11
1
 PROCESS FLOW CHARTS

A. COLD ROLLED STEEL SECTIONS

RAW MATERIALS ROLLING PACKING DESPATCH

Raw materials: mild steel ribbons

DESPATCH
B. STEEL WATER PIPES

RAW MATERIALS ROLLING ENDFACING STRAIGHT ENING HYDRO GALVANISING

DESPATCH
DESPATCH THREADING

Raw materials: mild steel ribbons

11
2
Figure1: Hydro testing machine

Figure 2: mild steel ribbons

C. CUT TO LENGTH SHEETS AND PLATES

RAW MATERIALS SHEARING PILING DISPATCH

D. SLITTING(HOOPS)

RAW MATERIALS
Steel coils: SLITTING 9
RECOILING TO
ROLLI
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DESPATCH
 FIGURE: Slitting machine

E. GALVANISED PIPES

RAW DE-
RINSIN PICKLING
MATE GREASIN FLUXING DRYING
G GALV
RIA LS G Billing
Spectr RINSING AN
ISING
um Inter notific Internati
95 Licenses manage ment
planni n onal
n ation coordin
al ation
QU
EN
CH
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NG