DESIGN AND CONSTRUCTION OF A TWIN FLUORESCENT FITTING TO REDUCE STROBOSCOPIC EFFECT IN WORKSHOPS SULEIMAN A. A SALIFU 01052249D ISHMAEL QUAYSON MBIR 01052206D SUBMITTED IN PARTIAL FULFILMENT FOR THE AWARD OF HIGHER NATIONAL DIPLOMA IN ELECTRICAL/ELECTRONICS ENGINEERING
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DESIGN AND CONSTRUCTION OF A TWIN FLUORESCENT FITTING TO REDUCE STROBOSCOPIC
EFFECT IN WORKSHOPS
SULEIMAN A. A SALIFU 01052249D
ISHMAEL QUAYSON MBIR 01052206D
SUBMITTED IN PARTIAL FULFILMENT FOR THE AWARD OF HIGHER NATIONAL DIPLOMA IN ELECTRICAL/ELECTRONICS
ENGINEERING
DEPARTMENT OF ELECRICAL/ELECTRONICS ENGINEERING ACCRA POLYTECHNIC
SEPTAMBER 2008
CERTIFICATION BY SUPERVISOR
I hereby certify that this project work was carried out under my
supervision. I therefore approve that the work is adequate in scope
and quality for the partial fulfillment of the requirement for the award
of a Higher National Diploma (HND) in Electrical/Electronics
Engineering.
SUPERVISOR:
SIGN…………………………….
DATE……………………………
I
DEDICATION
This project is dedicated to
II
DECLARATION
I ………………………………………………….. Declares that the work
was undertaken whilst in Accra Polytechnic.
I further affirm that, this work so far as I know has not been
submitted to any institution for the award of any certificate and the
source of information has been fully acknowledged
NAME………………………………………..
SIGN…………………………….
DATE……………………………
III
ACKNOWLEDGEMENT
IV
ABSTRACT
The project in question is a Twin Fluorescent Fitting to Reduce
Stroboscopic Effect in Workshops.
The report is to investigates and solve the visual illusions caused by
the stroboscopic effects of lighting on rotating and reciprocating
machinery. The lamps studied were fluorescent, mercury vapor, and
incandescent. The results from the experimentation showed
stroboscopic effects for the fluorescent and the mercury vapor
lamps. No stroboscopic effects were observed from the
incandescent lamps.
The lights are powered by the same source of a power, but are
timed to a different frequency to create variation in movement of the
rotating part of the machine.
V
TABLE OF CONTENTS
CONTENT PAGE
CHAPTER ONE
1.1 INTRODUCTION 1
1.2 BACKGROUND 2
1.3 DEFINATION 3
1.4 OBJECTIVES 4
1.5 SIGNIFICANCE OF STUDY 5
1.6 METHOLOGY 6
CHAPTER TWO
2.1 7
VI
CHAPTER THREE
3.1
CHAPTER FOUR
4.1 GENERAL MODE OF OPERATION
4.2 IMPORTANT
4.3 PRECAUTIONS
4.4 SUMMARY
4.5 RECORMENDATIONS
REFERNCE
VII
CHAPTER ONE
1.1 INTRODUCTION
In an installation where rotating machinery is present and where
discharge lamps are used, there is a risk that, the raotating parts
may appear stationary. This effect is known as stroboscopic effect.
It only occurs on discharge lamp, because their discharge is being
extinguished twice every cycle, which causes them to flicker 10ms.
This does not happen in incandescent lamps because their filament
does not cool fast enough to show any signed of cycle variation.
The simplest way to understand stroboscopic effect is to consider
the spoke of rotating wheel. At the moment in time the discharge
lamp is receiving zero voltage, a spoke is always in the position that
was occupied by another spoke whose particular time difference is
equal to one half-cycle of the supply frequency.
1
1.2 BACKGROUND
With the achievement of technological aspect, the present
inventions are relative to stroboscopic effects. These effects can be
minimized by two methods.
If a three phase supply is available this effect can be reduced by
connecting the lamps to alternate phase. As the lamp attain their
maximum and minimum values of light output in sequence, the
overall illumination is kept practically constant thereby keeping the
stroboscopic effect to minimum.
If a single-phase supply is available the head-lag circuit can be
used. In this case we are not going to deal with the single-phase.
The construction of a twin circuit these lamps A and B are supplied
by an oscillating source with frequency different from that of the
phase supplied to the machine.
2
1.3 DEFINITION
The mentioned project is a twin fluorescent light which is oscillated
to different frequency as compared to the frequency of the supply
power to the rotating machine to make a rotating part of a machine
visible.
Even though most industrial machine uses three phase supply,
there’s no guarantee that the problem could be solved by giving the
lighting system to a single phase out of the three. Lamps like
filament bulbs could had been used to solve this problem because
the coil in the bulbs does not cool down, but because of the high
power loss, heat and power consumption it also has become
impossible that type of light to be approved for our industries.
The best way so far is to construct a twin fluorescent lighting system
which is powered with power supply with different frequency from
the main supply.
3
1.4 OBJECTIVES
The main objective of this is to keep stroboscopic effect in Ghana in
to minimum such as our industries and local workshop where there
is so much revolving machines operating all the time.
The aim of this project is to minimize the dangerous situation which
could let ignorant people come in contact with these rotating parts.
4
1.5 SIGNIFICANCE OF STUDY
The main significance of this project is that:
1. the lighting system is easy to operate
2. the system is lass expensive as compared to hazards that
this project helps to avoid
3. it consumes less expensive and consumes less power.
5
1.6 METHODOLOGY
The required electronics components for this project shall be
acquired from a market at hand and the rest imported via Maplin
Electronics UK.
All important information needed for this project to takeoff was
acquired form two main source namely primary and secondary
sources.
Primary source were sources were the personal interactions with my
supervisor and workers of a well equipped and well knowledgeable
on this project.
Secondary sources were the research at the library and the internet.
6
CHAPTER TWO
2.1 TEMPORAL ALIASING
Temporal aliasing is the term applied to a visual phenomenon also
known as the stroboscopic effect. It also accounts for the "wagon-
wheel effect", so called because in video or motion pictures, spoke
wheels on horse-drawn wagons sometimes appear to be turning
backwards.
Temporal aliasing is one example of a range of phenomena called
aliasing that occur when continuous motion is represented by a
series of short or instantaneous samples. It occurs when (a) the
view of a moving object is represented by a series of short samples
as distinct from a continuous view, and (b) the moving object is in
rotational or other cyclic motion at a rate close to the sampling rate.
Rectifier diodes are used in power supplies to convert alternating
current (AC) to direct current (DC), a process called rectification.
Bridge rectifiers
There are several ways of connecting diodes to make a rectifier to
convert AC to DC. The bridge rectifier is one of them and it is
available in special packages containing the four diodes required.
Bridge rectifiers are rated by their maximum current and maximum
reverse voltage. They have four leads or terminals: the two DC
outputs are labelled + and -, the two AC inputs are labelled .
The diagram below shows the operation of a bridge rectifier as it
converts AC to DC. Notice how alternate pairs of diodes conduct.
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c. The Smoothing Capacitor
The full-wave bridge rectifier however, gives us a greater mean d.c. value (0.637Vmax)
with less superimposed ripple while the output wveform is twice that of the frequency
of the input supply frequency. We can therefore increase its average d.c. output level
even higher by connecting a suitable smoothing capacitor across the output of the
bridge circuit as shown below.
The smoothing capacitor converts the full-wave rippled output of the
rectifier into a smooth d.c. output voltage.
20
Two important parameters to consider when choosing a suitable a
capacitor are its Working Voltage, which must be higher than the no-
load output value of the rectifier and its Capacitance Value, which
determines the amount of ripple that will appear superimposed
ontop of the d.c. voltage. Too low a value and the capacitor has little
effect. As a general rule of thumb, we are looking to have a ripple
voltage of less than 100mV peak to peak.The main advantages of a
full-wave bridge rectifier is that it has a smaller a.c. ripple value for a
given load and a smaller reservoir or smoothing capacitor than an
equivalent half-wave rectifier. The fundamental frequency of the
ripple voltage is twice that of the a.c. supply frequency (100Hz)
where for the half-wave rectifier it is exactly equal to the supply
frequency (50Hz). The amount of ripple voltage that is
superimposed on top of the d.c. supply voltage can be virtually
eliminated by adding an an improved π-filter (pi-filter) to the ouput
terminals of the bridge rectifier. This type of low-pass filter consists
of two smoothing capacitors, usually of the same value and a choke
or inductance across them to introduce a high impeadance path to
the alternating ripple component.
21
3.2 Converting 0Hz to 50Hz (DC to AC).
The DC to AC converter also known as power inverter operates in
four stages namely (a) Regulating (b) Pulse generation (oscillating),
(c) Amplification and (d)Stepping Up.
(a)Regulating
Since the amplitude of the oscillator is determined by the Vcc. or the
power supplied to it, is very important to regulate it to match the
Gate to Source voltage of the Mosfets which would be used to
amplify the signals from the Oscillator.
The simplest voltage regulator uses just a resistor and a zener
diode. In the circuit diagram you can see a resistor (R1) and a zener
diode (ZD1) connected across a power supply. The resistor is
connected to the positive (+ve) supply wire and the zener diode
anode is connected to the zero volt (ground) wire. At the junction of
these two components the voltage is clamped by the zener diode to
its specified voltage - in this case 5.6 volts but can be changed to
9.1 or any voltage to suit the Vbe of the transistor(Mosfets) in the
amplifier.
This method is OK for low currents but the resistor becomes too hot
if larger currents are needed. To cope with this problem we can add
the NPN transistor (Q1) .
22
Now the transistor passes the current required at the output.
What is the output voltage?
It is easy to calculate. The voltage at Q1 base connection is 5.6
volts.
The voltage between base and emitter of a silicon transistor is
always 0.6 volts if the transistor is "on".
So the voltage at the Q1 emitter (Vout) must be 5.6 - 0.6 = 5.0 volts.
The output voltage will remain at a constant voltage of 5.0 volts
provided that the input voltage from the supply is more than 6 volts
(the zener voltage plus a little to compensate for that "lost" across
the resistor).
23
In fact the input voltage can be swinging up and down between, say,
6 volts and 12 volts and the output voltage at Q1 emitter will still be
a steady 5.0 volts.
The limiting factors are the amount of heat generated by R1, ZD1
and Q1 since all excess voltage must be shed as heat. The
"wattage" ratings of the individual components must be calculated to
suit:
1. The average input current (through R1 and ZD1) and the output
current (through Q1). can be calculated from Ohms Law and is
decided by whatever the regulator is to supply voltage to.
Ohms Law I = V/R
V = Volts
I = Amps if R = Ohms or
I = mA if R = k½
Let's assume the following:
The circuit which this regulator is driving needs 9.0v at a current of 200A.
A TIP41 transistor is suitable since it can handle current up to 15 A.Its gain at 40 is listed as 40 (typ) so it's easy to see that it will need at least 1mA into its base to allow 15A to flow from collector to emitter.
24
Watts = Volts x Amps milliWatts = Volts x milliAmps
Volts x Amps = Watts
Since the regulating voltage is 9volts and the maximum current from
the transistor is 15A
9volts x 15A = 135watts.
25
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(b) Pulse Generation (oscillating)
Since the DC power haves no frequency, there’s a need for an
introduction of an oscillator such as an astable multivibrator to
change the frequency from zero to 50Hz.
A multivibrator is an electronic circuit used to implement a variety
of simple two-state systems such as oscillators, timers and flip-flops.
It is characterized by two amplifying devices (transistors, electron
tubes or other devices) cross-coupled by resistors and capacitors.
The most common form is the astable or oscillating type, which
generates a square wave - the high level of harmonics in its output