1
UNESCO-NIGERIA TECHNICAL &
VOCATIONAL EDUCATION
REVITALISATION PROJECT-PHASE II
NATIONAL DIPLOMA IN
ELECTRICAL ENGINEERING TECHNOLOGY
ELECTRICAL/ ELECTRONIC
INSTRUMENTATION (II)
COURSE CODE: EEC 236
YEAR II- SEMESTER III
2
PRACTICAL
Version 1: December 2008
TABLE OF CONTENTS
Department
Electrical Engineering Technology
Subject
Electrical Electronics Instrumentation 11
Year
2
Semester
3
Course Code
EEC 236
Credit Hours
2
Theoretical
1
Practical
2
3
WEEK 1:
Measurement
of
AC
voltage
using
oscilloscope………………………1-4
WEEK 2
Measurement of DC voltage using oscilloscope…………………………………58
WEEK 3:
Measurement of frequency using calibrated time base……………………………911
WEEK 4:
AC power measurement in single phase circuit………………………1215
WEEK 5:
Three phase power measurement by two wattmeter…………………………..16-17
WEEK 6:
Three phase power measurement by two wattmeter…………… ………….18-19
WEEK 7:
DC power measurement……………………………………………………..20-21
WEEK 8:
Temperature coefficient of resistance………………………………………..22-28
WEEK 9:
4
Effect of temperature on diode……………………………………….2936
WEEK 10:
Semi conductor diode recognition……………………………………………37-40
WEEK 11:
Transformer efficiency using single phase wattmeter………………………..40-43
WEEK 12:
Determine the Resistivity of Materials………………………………………4447
WEEK 13:
Thermal effect on resistance……………………………………………………4849
WEEK 14:
Effect of temperature on semi conductor diode……………………………….50-51
WEEK 15:
Basic electrical quantities measurement……………………………...5254
5
6
PRACTICAL
Week 1
Title:
Measurement of AC using oscilloscope.
Objective:
To measure the peak voltage of an alternating signal using an oscilloscope.
Introduction:
When an AC is applied to the oscilloscope a sine wave appears on the screen.
7
The magnitude of the unknown voltage can be found by using the following formular:
Volts(unknown) = Voltage sensitivity(V/div) X Deflection AB(div)
V(p-p) = Volt/div X div.
Equipment to be Used:
1. Oscilloscope.
2. DC voltmeter.
3. 100KΩ Potentiometer.
4. Variable output DC power supply.
Circuit Diagram
8
Procedure:
Step 1: Set up circuit as shown in fig. above.
Step 2: Test for correct ground level and adjust the controls for correct display.
Step 3: Apply an AC voltage to the oscilloscope and measure the peak to peak
deflection of the signal, adjust the oscilloscope’s V/div, if necessary to get a clear signal.
Record the measure deflection in the table below.
Step 4: Vary the applied voltage and repeat step 3.
Step 5: Repeat step 4, until table is completed.
9
PRACTICAL
Week 2
Tittle:
Measurement of DC voltage using oscilloscope.
Objectives:
To measure a direct voltage using an oscilloscope
Introduction:
When a D.C. voltage is applied to the oscilloscope, the spot moves and then rests at a
position above or below the zero voltage position.
10
The distance OA indicates the size of the applied voltage, which can be found from the
following formula.
Applied voltage = Deflection sensitivity (div.) x Deflection sensitivity (div.)
Vdc = OA (div) x V/div.
Equipments:
i.
Oscilloscope.
ii.
DC voltmeter.
iii.
100KΩ potentiomter.
iv.
Variable output DC Supply.
Circuit Diagram
11
Procedure:
Step 1: Set up the circuit, as shown in fig. above.
Step 2: Test for correct ground level and adjust the controls for correct display.
Step 3: Apply a D.C. voltage to the oscilloscope and measure the vertical deflection in
(Cm), adjust the volt/div. if necessary to get a clear signal. Record the measure deflection and
the v/div. in table below.
Step 4: vary the voltage and repeat step 3.
Step 5: Repeat step 3, until the table is completed.
12
PRACTICAL
Week 3
Tittle:
Measurement of frequency using calibrated time base.
Objective:
To measure the frequency of calibrated of a sinusoidal waveform using an oscilloscope.
Introduction:
The frequency can calculated on the CRO by first measuring the periodic time (T), then
applying the formula:
F = 1/T HZ
To calculate the periodic time, consider the waveform shown in fig. below.
The periodic Time = Number of (cm), for one cycle x horizontal amplifier (sec/cm)
T = Cm x Sec/cm.
13
Equipment:
-
Oscilloscope.
Signal generator.
Procedure:
Step 1: Set up circuit as shown in fig. below
Step 2: Test for correct ground level and adjust the controls for correct display.
Step 3: Apply a 1.5 AC. Signal of 100HZ to the CRO. Set the vertical amplifier
switch
at 0.5V/div.
Step 4: Adjust the frequency of the time base to get a complete cycle.
Step 5: Record in table the signal generator frequency, the number of “cm” for one
cycle and the horizontal amplifier sensitivity value (sec/cm).
Step 6: Repeat step 3 to 5 for the following frequencies 500HZ, 1KHZ, 2KHZ.
14
15
PRACTICAL
Week 4
Tittle:
AC power measurement in single phase circuit.
Objective:
Transformer Power Factor
 Introduction:
The transformer is a device for transferring energy from one AC circuit to another
through electromagnetic coupling. The operation of the transformer is based on the
property of mutual induction, which is the name given to the influence exercised on the
electric condition in a conductor by an electric current in a neighboring conductor. To
calculate the power factor of the primary and secondary winding connect the transformer
as shown in figure (1-7).
Where
P.fp=
Pp
Ip X Vp
P.fs=
Ps
Is X Vs
 Apparatus
- one power supply
- AC instrument group
- Transformer single phase
- Single phase wattmeter
16
Single phase Transformer
L
A
Supply
0- 220
Vac
V
A
W
W
W
W
V
Variable
Load
N
Fig. 4.1
Procedures :
1. Connect the circuit as shown in fig.(4.1) with out the load.
2. Turn on the power supply.
3. Record the instruments reading in both primary and secondary winding at no- load
condition in table(4.2).
4. Connect the load with circuit
5. Vary the load in five steps and record the instruments reading for each step in the
table(4.2).
6. Turn off the supply and disconnect the circuit.
Step
Primary
Primary
Primary
no.
Voltage(Vp)
Current(Ip)
power(Pp)
1
2
3
4
5
Table (4.2)
17
Secondary
Secondary
Secondary
Voltage(Vp) Current(Ip) power(Pp)
Note:
- Never swith ON the power supply without your teachers
permission.
Worksheet 04
Solve the following questions:
1) The following steps are used for carrying out a turns ratio test on transformer.
Number these steps to obtain the correct sequence.
( ) Connect the voltmeter with primary.
( ) Connect the power supply to primary winding.
( ) Read the ohmmeters reading.
( ) Select the instruments and components.
( ) Connect the ohmmeter with primary winding.
( ) Connect the voltmeter with secondary winding.
( ) Read the voltmeters reading.
( ) Connect the transformer to supply.
( ) Calculate the ratio.
2)
Use the measuring values in table 1-3 , to calculate the power factor, power
losses and efficiency at each step. Record the calculated results in the table 4.1
Step
no.
Primary P.f
Secondary P.f
1
2
3
4
5
Table (4.1.1)
18
Power losses
Efficiency η
PRACTICAL
Week 5
Title:
Three-phase power measurement by two wattmeter.
Characteristics
It is possible to use two single phase wattmeter to measure the active power delivered to a
three-phase load as shown in fig. 5. To do this, the current coil of one of the wattmeter’s is
connected in series in line A and the current coil of the other wattmeter is connected in line C.
The total power delivered to the load is always the algebraic sum the two wattmeter readings.
However when the power factor of the load is lower than 100%, the readings of the two
wattmeter’s are different from each other. When the power factor is lower than 50%, the pointer
of one of the meters will tend to go in the opposite direction. In order to read this power, the
direction of the current in that meter must be reversed and the total power in the circuit will then
be algebraic sum of the two readings.
Equipment:
One power supply
One three- phase wattmeter
One AC instrumentation group
One variable resistive load
One variable inductive load
One variable capacitive load
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CIRCUIT DIAGRAM
Fig. 5
Procedure 1
a. Connect the circuit shown in fig. 5.
b. Place all switches of the resistive load in the position “OFF”.
c. Turn “ON’ the power supply and adjust the voltage so that E1 = 380 volts.
d. Set the resistive load to 586 ohms per phase.
e. Record all your readings in table 1.
f. Turn “OFF” the power supply
Result
1. From the result of procedure, calculate:
Apparent power:
= √3V1I1 = 1.73 X 380 X 0.375 = 246VA
Real power: = (𝑤1 ± 𝑤2)
𝑟𝑒𝑎𝑙 𝑝𝑜𝑤𝑒𝑟
Power factor = 𝐴𝑝𝑝𝑎𝑟𝑒𝑛𝑡 𝑝𝑜𝑤𝑒𝑟 x 100 = 100%
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PRACTICAL WORK
Week 6
Procedure 2
a. In fig. 5 change the resistive load for the inductive load.
b. Place all the switches of the inductive load in their “ OFF” positions.
c. Turn “ON” the power supply and adjust for E1 = 380V.
d. Set the inductive load to 586 ohms per phase.
e. Record all your readings in table below.
f.
Turn ”OFF” the power supply.
Result:
From the result, calculate:
Apparent power
E1 ……………… X I1……………… X √3. = ……………………..VA
Real power:
(±𝑤1)……………… + (±𝑤2) …………….. = ………………...Watt
POWER FACTOR:
𝑅𝑒𝑎𝑙 𝑝𝑜𝑤𝑒𝑟
× 100%
𝐴𝑝𝑝𝑎𝑟𝑒𝑛𝑡 𝑝𝑜𝑤𝑒𝑟
Reactive inductive power:
√𝐴𝑝2 − 𝑝𝑅 = ……………VAR
Procedure 3:
a.
In fig 5. Change the inductive load for the capacitive load.
b.
Place all the switches of the capacitive load in their “OFF” positions.
c.
Turn “ON” the power supply and adjust for E1 = 380V.
d.
Set the capacitive to 586 ohms per phase.
21
e.
Record your readings in table
f.
Turn “OFF the power supply.
Result:
From results in this procedure, Calculate :
Apparent power:
E1……………. X I1 ……………….. X √3 = ………………..VA
Real power:
(±𝑤1) …………… + (±𝑤2) ……………… = ………………Watts
Power factor:
𝑅𝑒𝑎𝑙 𝑝𝑜𝑤𝑒𝑟
a𝐴𝑝𝑝𝑎𝑟𝑒𝑛𝑡 𝑝𝑜𝑤𝑒𝑟 X 100% = …………………………%
Reactive capacitive power:
= √𝐴𝑝2 − 𝑅𝑝2
= √… … … . 𝑉𝐴2 − ⋯ … … … … 𝑊2 = ………………Var
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Practical
Week 7
TITLE:Experimental determination of power in a d.c circuit
OBJECTIVE:To determine the power in a d.c circuit.
BACKGROUND INFORMATION
The power of a resistor can be determined in a dc circuit under any of the following
conditions:
(1)
if the resistance of the resistor is unknown, but the voltage (V) across the resistor
and current (I) through the resistor can be measured.
i.e Power P = IV, watts.
(2)
if the resistance (R) if the resistor and the current through it are known to give,
P = I2R (watts).
(3)
if the resistance (R) of the resistor and the voltage across it are known to give
P = V2/R (watts)
PROCEDURE:
(1)
Connect the circuit shown in fig 14.1 with the voltmeter V across the resistor R
and the ammeter A in series with it.
(2)
Use the ammeter to record the current, I (Ampere) through the resistor and the
voltmeter to record the P.d. (volts) across the resistor.
(3)
Determine and record the value of R (in ohms) before the commencement of the
experiment.
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Voltmeter
V
R
E
A
Ammeter
R
Fig 7.1
RESULT ANALYSIS:Calculate the power P, across the resistor using each and all the formulae stated above.
24
PRACTICAL
Week 8
Title:
Temperature coefficient of resistance.
7.1 Introduction:
You might have noticed on the table for specific resistances that all figures were
specified at a temperature of 20o Celsius. If you suspected that this meant specific resistance of a
material may change with temperature, you were right!
Resistance values for conductors at any temperature other than the standard temperature
(usually specified at 20 Celsius) on the specific resistance table must be determined through yet
another formula:
The "alpha" (α) constant is known as the temperature coefficient of resistance, and
symbolizes the resistance change factor per degree of temperature change. Just as all materials
25
have a certain specific resistance (at 20o C), they also change resistance according to temperature
by certain amounts. For pure metals, this coefficient is a positive number, meaning that
resistance increases with increasing temperature. For the elements carbon, silicon, and
germanium, this coefficient is a negative number, meaning that resistance decreases with
increasing temperature. For some metal alloys, the temperature coefficient of resistance is very
close to zero, meaning that the resistance hardly changes at all with variations in temperature (a
good property if you want to build a precision resistor out of metal wire!). The following table
gives the temperature coefficients of resistance for several common metals, both pure and alloy:
TEMPERATURE COEFFICIENTS OF RESISTANCE, AT 20 DEGREES C
Material
Element/Alloy "alpha" per degree Celsius
==========================================================
Nickel -------- Element --------------- 0.005866
Iron ---------- Element --------------- 0.005671
Molybdenum ---- Element --------------- 0.004579
Tungsten ------ Element --------------- 0.004403
Aluminum ------ Element --------------- 0.004308
Copper -------- Element --------------- 0.004041
Silver -------- Element --------------- 0.003819
Platinum ------ Element --------------- 0.003729
Gold ---------- Element --------------- 0.003715
Zinc ---------- Element --------------- 0.003847
Steel* --------- Alloy ---------------- 0.003
Nichrome ------- Alloy ---------------- 0.00017
Nichrome V ----- Alloy ---------------- 0.00013
Manganin ------- Alloy ------------ +/- 0.000015
Constantan ----- Alloy --------------- -0.000074
* = Steel alloy at 99.5 percent iron, 0.5 percent carbon
26
Let's take a look at an example circuit to see how temperature can affect wire resistance,
and consequently circuit performance:
This circuit has a total wire resistance (wire 1 + wire 2) of 30 Ω at standard temperature.
Setting up a table of voltage, current, and resistance values we get:
At 20o Celsius, we get 12.5 volts across the load and a total of 1.5 volts (0.75 + 0.75)
dropped across the wire resistance. If the temperature were to rise to 35o Celsius, we could easily
determine the change of resistance for each piece of wire. Assuming the use of copper wire (α =
0.004041) we get:
Recalculating our circuit values, we see what changes this increase in temperature will bring:
27
As you can see, voltage across the load went down (from 12.5 volts to 12.42 volts) and
voltage drop across the wires went up (from 0.75 volts to 0.79 volts) as a result of the
temperature increasing. Though the changes may seem small, they can be significant for power
lines stretching miles between power plants and substations, substations and loads. In fact, power
utility companies often have to take line resistance changes resulting from seasonal temperature
variations into account when calculating allowable system loading.

REVIEW:

Most conductive materials change specific resistance with changes in
temperature. This is why figures of specific resistance are always
specified at a standard temperature (usually 20o or 25o Celsius).

The resistance-change factor per degree Celsius of temperature change
is called the temperature coefficient of resistance. This factor is
represented by the Greek lower-case letter "alpha" (α).

A positive coefficient for a material means that its resistance increases
with an increase in temperature. Pure metals typically have positive
temperature coefficients of resistance. Coefficients approaching zero
can be obtained by alloying certain metals.

A negative coefficient for a material means that its resistance
decreases with an increase in temperature. Semiconductor materials
(carbon, silicon, germanium) typically have negative temperature
coefficients of resistance.

The formula used to determine the resistance of a conductor at some
temperature other than what is specified in a resistance table is as
follows:
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
a) Resistivity
"Resistivity" is the resistance of a piece of the conductor with unit
length and unit cross- sectional area .
The resistivity is related by:
R =
ρL
A
Where R: the value of the conductor resistance in ohm (Ω).
L: the length of the conductor in meters (m).
A: the cross-section area of the conductor, in square meters (m²)
ρ : resistivity (Ω.m ).
Example 4-1
Calculate the resistance of 1000 m of copper conductor, cross-sectional
area is 4 mm2 and the resistivity is 1.78 × 10-8 Ω.m ?
Solution:
ρ L
R =
R =
A
1.78 × 10-8 × 1000
4 × 10
L = 1000 m
ρ = 1.78 × 10-8 Ω.m
-6
A = 4 mm2
= 4 × 10-6 m2
R = 4.45 Ω
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b) Conductivity
"Conductivity" is the degree of ease by which an electric current
passes through the material.
The Conductivity is related by:
τR ==
Where
ρ1L
ρA
τ : Conductivity (1/ Ω.m)
ρ : resistivity (Ω.m ).
c) Temperature coefficient
Change of temperature can affect the resistance of a conductor.
If the temperature increase, the dimensions of the conductor increase, thus increase their
resistance.
The following formula gives the value of the resistance as a function of a temperature
R2 = R1[ 1+ α (t2-t1)]
where
R1 : the resistance of the conductor at first temperature.
R2: the resistance of the conductor at second temperature.
α : temperature coefficient.
t1 : the first temperature.
t2 : the second temperature.
Example 4-2
The resitance of conductor is 20 Ω at temerature 30oC ,calculate the
resistance at 60 oC? assume α = 0.00396
Solution:
R2 = R1[ 1+ α (t2-t1) ]
R2 = 20 [ 1+ 0.00396 (60-30)]
R2 = 22.376 Ω
30
PRACTICAL
Week 9
Title:
Temperature effect on diode.
Objectives:
1. to study the effects of forward and reverse bias on both the germanium and
silicon junction diodes.
2. to observe the effects of the diode potential barrier.
3. to consider the advantages of using silicon rather than germanium diodes
where temperature is a factor.
4. to study the reverse-bias leakage characteristics of the germanium and silicon
diodes.
Materials required
Power source:8-12V regulated or variable low-voltage dc-regulated source.
Equipment: Electronic voltmeter,0-to 5mA and 0-to 50 A meters, ohmmeter, curve
tracer.
Components
Potentiometer: 1kΩ and 2.5 kΩ, 0.5 W.
Diodes: Germanium 1N34 or equivalent, Silicon 1N914 or equivalent.
Background information
Junction diode is one of the most elementary solid-state device, but it is called
upon constantly to do its simple tasks as shown:
1- to allow current to move in a forward direction with little opposition.
2- To prevent reverse current
3- To give an inexpensive means of voltage division in the (ON) direction.
4- To provide a means of thermal protection for other devices.
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Forward Bias
When a diode is connected into a circuit with the source voltage applied. As
shown in the figure below, its said to be biased in a forward direction. That is, the
source voltage is applied so that the negative terminal is attached to the cathode of the
diode while the positive terminal is attached to the anode. This type of connection will
cause electrons to move forward through the diode and complete the circuit when the
voltage of the source is greater than the internal potential barrier of the diode.
The potential barrier of germanium diode is a little more than 0.1 V, but for a
silicon diode it is more than 0.5 V. The amount of forward current that will pass
through either type of diode depends upon the amount of forward voltage applied
across the diode. Notice in the figure shown that there is a resistance in series with the
diode. This allows prevents full voltage from being placed across the diode. The diode
voltage VF will increase to about 0.2 V for germanium and 0.6 V for silicon and then
remain near this value as the current increases. The figure below shows a comparison
of the Volt-Ampere characteristics of the germanium and silicon diodes. Note that the
curve for the silicon diode rises sharply once potential barrier of about 0.6 V is passed
but that the forward voltage does increase somewhat.
32
Reverse Bias
When the diode is placed in a circuit such as that shown below (reverse of the
forward bias figure), it's considered to be reverse biased. Ideally, no current should flow
in this bias condition. In reality a tiny current seems to leak through, depending on the
temperature of the diode; for this reason , the current is called leakage current.
For the silicon diode leakage current is extremely low at room temperature- a few
nano-amperes; however, for the germanium diode the leakage may amount to several
microamperes. If the operation of the circuit is observed carefully, it will be noted that
the meter needle moves very slightly. A very sensitive meter of a good curve tracer is
required to measure the leakage a accurately.
33
Leakage current is caused by the movement of minority carriers that are generated
as a function of the absolute temperature. A good rule of thumb is that the amount of
leakage current will approximately double for each 10C rise in temperature; of course, it
will be reduced by one-half when the temperature drops 10C.
Junction voltage
The forward bias junction voltage for the silicon diode at room temperature is
about 0.6 V. As the temperature rises, however, this voltage tends to drop, a factor related
to the carrier mobility. This property allows the diode to be used in many circuits,
especially power amplifiers, to provide voltage divider action that changes with
temperature. For instant, the forward junction voltage for the silicon diode at 25C is
about 0.6 V when it drops to 0.5 V at 45C.
Experimental Procedure
Forward Bias
1. Study the circuit illustrated below. Observe the direction of the diodes as well as
the polarities of the meters and the voltage source.
2. obtain the necessary equipment and materials.
3. observe the silicon diode for markings. If the diode symbol is not marked on the
diode, there should be other markings. Generally, a band placed nearer one end
than the other to identify the cathode of the diode.
4. connect the circuit as it shown above, be certain that the diode is in the proper
direction and that the meters are connected correctly with the proper range and
34
polarity. If a variable power supply is available, the 2.5 kΩ potentiometer needs to
be used. If a fixed supply or a 9 V transistor battery is used, the potentiometer
provides a simple means of variable voltage.
5. Turn on the supply voltage and adjust the output to the circuit to 0 V. In the table
below, record the forward voltage VF across the diode and the forward current IF
through the diode.
6. complete and record the measurements of VF for the values of IF given in the
table below.
IF ,
mA
0.0
0.1
0.2
0.3 0.4 0.5 0.6 0.8 0.1
2.0
4.0
5.0
VF,
Silicon
V
Diode
RF,
Ω
VF,
Germanium
V
Diode
RF,
Ω
7. Remove the power from the circuit and replace the silicon diode with the
germanium diode, placing it in the same direction as the silicon diode.
8. repeat step 5 and 6 and record the data in the table.
9. plot the values of voltages and current just measured on the graph paper below, the
two curves plotted should resemble those of the diode characteristic curves.
35
10. From the values of voltage and current in the table above, compare resistance for
each value and record your results in the table.
Remember
In Forward bias, the diode should give when examined a low resistance. In the other
hand, high resistance will be read by the ohmmeter in the reverse bias.
Reverse Bias
1. connect the circuit shown below. Since this experiment is designed to check the
reverse characteristics of the silicon and germanium diodes, the diode is placed in
the circuit in a direction that is the reverse of the previous procedure. Insert the
silicon diode in the circuit and check all polarities and ranges of meters carefully.
2. turn on the power supply and set to the first voltage given in the table provided.
Record any observable current. The amount of current is extremely small, and so
the power supply lead may be disconnected and then reconnected while observing
the micrometer.
VR, V
Silicon
Diode
Germaniu
m Diode
0
1
2
3
4
5
6
7
8
IR, nA
IR, A
3. Measure and record the reverse current IR for each value of reverse voltage
indicated in the table.
36
4. Remove the power and replace the silicon diode with a germanium diode and
repeat the experiment.
37
PRACTICAL
Week 10
Title:
Semiconductor Diode Recognition
Objectives:
To recognize their practical shape, check for forward bias and reverse bias in open
and short circuit tests.
Introduction:
The diode is the simplest semiconductor devices but it plays a very vital role in
electronic systems, with its characteristics that closely match those of a simple switch.
Tools and Equipment:
1. Multi-meters.
2. Power Supply.
3. Diodes of different types and shapes.
Procedure:
Step1. Recognize all diodes given to you, see the figure below.
Step2. Draw them, marking P and N terminals.
38
Title:
Diode Test
Objectives:
To use multi-meter to check the diode for:
Forward bias & Reverse bias.
A. Open Circuit.
B. Short Circuit.
Tools and Equipment:
4. Multi-meters.
5. Power Supply.
6. Diodes of different types and shapes.
39
Procedure:
(A) Forward bias and Reverse bias
Step1. Connect the circuit as shown above.
Step2. If the reading is low; this indicates that the diode is forward biased and has a low
resistance.
Step3. If the reading is high, this indicates that the diode is reverse biased and has it has
high resistance.
Step4. If steps 2 and 3 were correct, then the diode is properly operating and therefore in
good condition.
(B) Open Circuit
Step1. Connect the circuit as shown above, for forward bias test.
Step2. Infinity () reading indicates open circuit.
Step3. Connect the circuit as shown above, for reverse bias test.
Step4. Infinity () indication means that the diode is open circuit.
(C) Short Circuit
Step1. Connect the circuit as shown above.
Step2. If the Ohmmeter indicated zero, then the diode is short circuited and the diode is
in the forward direction.
40
Step3. Connect the circuit as shown above.
Step4. If the Ohmmeter indicated zero reading, then the diode is short circuited and the
diode is in the reverse bias direction.
41
PRACTICAL
Week 11
Title:
Transformer Efficiency using single phase wattmeter
 Introduction:
The transformer is a device for transferring energy from one AC circuit to another
through electromagnetic coupling. The operation of the transformer is based on the
property of mutual induction, which is the name given to the influence exercised on the
electric condition in a conductor by an electric current in a neighboring conductor.
η=
Ps
Pp
To determine the transformer efficiency, connect a transformer as shown in fig.(1-8).
 Apparatus
- one power supply
- AC instrument group
- Transformer single phase
- Single phase wattmeter
Procedures :
7. Connect the circuit as shown in fig.(1-8) with out the load.
8. Turn on the power supply.
9. Record the instruments reading in both primary and secondary winding at no- load
condition in table(1-8).
10. Connect the load with circuit
11. Vary the load in five steps and record the instruments reading for each step in the
table (1-8).
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12. Turn off the supply and disconnect the circuit.
L
Supply
0- 220
Vac
W
W
W
W
Variable
Load
N
Fig. (1-8)
Step no.
Primary power(Pp)
Secondary power(Pp)
1
2
3
4
5
Table (1-4)
Note:
- Never swith ON the power supply without your teachers permission.
Worksheet 03
Solve the following questions:
1) Give the definition of the transformer efficiency
2) Use the measuring values in table 1-8 , to calculate the power losses and efficiency
at each step. Record the calculated results in the table 1-9
43
Step
no.
Power losses
1
2
3
4
5
44
Efficiency η
PRACTICAL
Week 12
Title:
Determine the Resistivity of Materials
Introduction:
The purpose of this investigation is to expose the factors responsible for affecting the
resistance of a wire in an electrical circuit. Many factors will have to be investigated prior to
experimentation. A prior knowledge of electrical circuits and the factors of resistance will be
required. The conclusive objective will be that research on the subject matter is pro
Objective:
To verify the resistivity of a material.
Theory
If all of the experiments to be practiced could be based on a single setup it would be very
useful because this would save time and make the results easier to relate to.
This experiment set up would have to be able to test the following factors for
differentiation of resistance in a wire.
Equipment
-.Material
-.Length
-.cross-sectional width
A variance of material will have to be tested to confirm that resisting capacities are
different with different materials. The only wires that can be accessed are made from copper and
nichrome. The results given by these wires should be interesting because copper is renowned for
its low resistance as it is primarily used for electrical cabling. Nichrome however, is renowned
45
for its high resistance as it is primarily used as a heating element. With this prior knowledge of
these two materials it will help making an accurate hypothesis and it should also be obvious
when problems occur.
Wires of differing lengths will have to be tested to confirm that resistance is in proportion
to length. This should simply involve testing different lengths of one type of wire. There is no
range limit to how long the lengths could be but it is doubtful that they will exceed 1m for
practicality.
Wires with different diameters or SWG (standard wire gauge) need to be tested to prove
that the resistance of a wire is inversely proportional to its area. The only widths of wire that can
be accessed are SWG 26, SWG 32 and SWG 36
The experiment will obviously require an electrical circuit as the resistance of a wire in
an electrical circuit is being calculated. To calculate the resistance of the wire using Ohms Law,
both an ammeter and a voltmeter will be required:
Voltage / Current = Resistance
The wire in question will have to be attached in this circuit in series so that the current
flows directly through it. Power will need to be supplied through a DC power pack that enables
the power to be changed easily and accurately.
Circuit diagram
46
Procedure:
Step 1. Measure the length of the given resistance wire.
Step 2. Measure the diameter of the material by a micrometer gauge.
Step 3. Compute the cross-sectional area using the formular A =𝜋𝑑2/4.
Step 4.
Set the digital multi-meter to a suitable ohmmeter range and connected across the
resistance wire at various length.
Step 5. Complete the table below.
It does not matter about the power being supplied because voltage or current does not affect
resistance. The voltage supplied by the power pack cannot be regarded as accurate, that is also a
reason why a voltmeter is used.
It may be necessary to alter the power supplied if problems arise with temperature. As
was noted earlier, resistance in conductors rises with temperature. This would give inaccurate
results.
Results of the highest accuracy are required because the conclusion will be based on the
results mainly in graphical format.
0.05
0.25
5
0.1
0.52
5.2
0.2
1.05
5.25
0.3
1.59
5.3
0.5
2.94
5.88
1
6.90
6.90
1.5
13.61
9.07
47
PRACTICAL
Week 13
Title:
Thermal effects on resistance.
Objective:
To measure the temperature using thermometer.
Equipment:

Glass bottle, 1-pint size

Rubber stopper with 1 hole

Glass tubing to fit hole, 24" long

Water

Dye or colored ink

Sealing wax or paraffin

Scotch or masking tape

Cardboard strip, 10" x 2'

Ordinary thermometer
Procedure:
Place the glass tubing, sealed at one end, through the stopper. Fill the tube full of water colored
with the dye. Quickly invert the tube, placing the lower end in a bottle about one-fourth full of
the colored water. Press the stopper firmly in the bottle. Adjust the liquid in the tube by
loosening the stopper or pressing it further into the bottle until the liquid is about half way along
the exposed portion of the tube above the stopper. Then use the wax to seal the tube in the
stopper and the stopper in the bottle. Tape the cardboard to the tube above the stopper.
48
Note the temperature on an accurate thermometer. Record this temperature on the cardboard,
which will act as a temperature scale. Place the thermometers in a different temperature situation
and leave them for a few minutes to allow the thermometers to register the new temperature.
Note the new reading and mark on the scale. Carefully measure the distance between the two
readings on the scale, and mark other degrees of temperature on it, as all other changes will be in
the same proportion.
49
EFFECT
OF
TEMPERATURE
ON Week 14
SEMICONDUCTOR DIODE
Title:
Effect of temperature on semiconductor diode.
Objectives:
To verify the effect of temperature on semiconductor diode
Equipment:
1. Breadboard.
2. Diode.
3. Voltmeter
Procedure:
The diode was placed on a heating device, which was connected to a variac which was
used to control temperature; a thermocouple was used to moderate temperature. Also the diode
was placed on ice, which was also connected to a thermocouple.
Results
This project was exactly as predicted the output of the device decreased in a linear
fashion as the
Temperature varied from room temperature. The average output correlated with the average
temperature except for a few exceptions. All four diodes had relatively the same output for a
given temperature.
Conclusions/Discussion
The experiment did not proceed entirely without problems. The temperatures of the
heating pad were never stable, and the instability grew with the temperature thus making testing
difficult. Also twice during the experiment wires were displaced and had to be fixed before
testing was resumed.
The hypothesis that the change in temperature will be equivalent to the increase in
degradation caused by leakage current was supported. The higher or lower the temperature the
diode was exposed to, the greater degradation was present.
50
What is the impact of different temperatures on semiconductor diodes?
51
PRACTICAL
Week
15
TITLE:Basic Electrical Quantities Measurement
It is necessary knowing how to measure voltage, current, and resistance. Special
types of instruments are used to measure these basic electrical quantities. The instrument
used to measure voltages is a voltmeter, the instrument used to measure current is a
ammeter, and the instrument used to measure resistance is a ohmmeter.
Commonly, all three instruments are combined into a single instrument such as a
multimeter or AVO meter ( Ampere- Volt-Ohmmeter), in which you can choose what
specific quantity to measure by selecting the switch setting.
Figure (1) shows typical portable multimeters, part (a) from figure shows analog
multimeter with pointer, and part (b) shows a digital multimeter with digital screen.
(a) Analog multimeter
(b) Digital multimeter
Figure (1) Typical portable Multimeter
52
+
V
+
A
_
Ω
_
+ V _
_
0.00
+
General scheme symbols are used to indicate placement of meters in circuit when
value changes need to be shown. Figure (2) shows meter symbols used to present the
different meters, as voltmeter, ammeter and ohmmeter.
(a) Voltmeter
0.00
+ A _
(b) Ammeter
0.00
+ Ω _
(c) Ohmmeter
Figure (2) Meter symbols
How to use Analogue meter:
Figure (3) shows a typical multimeter. This device can measures the three electric
quantities. The following step shows how to obtain readings from a multimeter.
1.Set the range of the desired quantity to be measured to the highest value.
2.Connect the leads to the right terminals at the meter
3.Switch on the circuit if necessary.
4.Adjust the range until you get clear readings.
5.Apply the following formula to obtain the measured quantity.
Re ading 
Range
Full  Scale
For example, referring to figure (3),the reading was 3.5 from a full-scale value of 5V, as
shown in the small box.The range was set to X300V.So the measured voltage is
3.5 
300
 210
5
53
6
8
10
12
4
14
2
20
30
10
0
200
500
ADC
100
1k
0
VDC
50
50
5k
20k
2
1
Scale
15
40
0
3
4
0
5
Ω
VAC
3
4
Reading =3.5
Pointer
Range
Off
DC VOLT
600
300
600
300
60
12
0.3
60
12
3
x1
x10
0.06
1.2
DC Current
12
120
x100
x1k
X100k
Common
AC VOLT
A
Ω
OHMS
V
Figure (3): Multimeter
Note:
The scale has to be viewed from an angle perpendicular to it.
54