EKT 101 Electric Circuit Theory
Module 2
UNIVERSITY MALAYSIA PERLIS
EKT 101
ELECTRIC CIRCUIT THEORY
LABORATORY MODULE 2
SEMESTER I (2012/2013)
SCHOOL OF COMPUTER AND COMMUNICATION ENGINEERING
SEM I 2012/13
EKT 101 Electric Circuit Theory
Module 2
INTRODUCTION TO LABORATORY II
BASIC LABORATORY EQUIPMENT
OBJECTIVE
1. To introduce student with the basic laboratory equipment
2. Become familiar with the basic operation of a multimeter, oscilloscope and function
generator and to gain skill in handling these equipments.
3. Able to perform simple calibration of an oscilloscope.
A. MULTIMETER
Multimeter is a basic tool in electric and electronic fields. It is a multipurpose device to
measure voltage, current and resistance. Basically there are two types of multimeter used
either in the education or industrial field based on the electronic circuits inside them:
analog and digital meters. The analog meter, broadly known as VOM (volt-ohmmiliammeters) uses a mechanical moving pointer which indicates the measured quantity
on a calibrated scale. It requires the user a little practice to interpret the location of the
pointer. The digital meter broadly known as DMM (digital multimeter) used number or
numerical display to represent the measured quantity. It has high degree of accuracy and
can eliminate usual reading errors compared to the analog meters.
a) Resistance Measurement
For VOM always reset the zero-adjust whenever you change scales. In addition always
choose the range setting that will give the best reading of the pointer location. As an
example, to measure a 500- resistance, choose function switch resistance with a range
setting of X 1k. Finally do not forget to multiply the reading by the proper multiplication
factor. If you are not sure about the value always starts with the highest range and going
downwards until appropriate scale is chosen.
b) Voltage Measurement
When measuring voltage levels, make sure the meter is connected in parallel with the
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EKT 101 Electric Circuit Theory
Module 2
element whose voltage is to be measured. Polarity is important because the reading will
indicate up-scale or positive reading for correct connection and down-scale or negative
reading if reverse connection of the meter test leads to the resistor’s terminals. Therefore
a voltmeter is not only excellent for measuring voltage but also for polarity
determination. Choose the correct function switch for example DCV to measure dc
voltage and turn to the range switch that has slightly bigger value than the voltage to be
measured.
c) Current Measurement
When measuring current levels, make a series connection between the meter and the
component whose current is to be measured. In other words, disconnect the particular
branch and insert the ammeter. The ammeter also has polarity marking to indicate the
manner they should be hooked-up in the circuit to obtain an up-scale or positive
measurement.The connection of the multimeter to measure different electrical quantities
is shown in both schematic diagram and real wiring illustration in the laboratory in Figure
1.
R
Vs
V/
A
Figure 1: Schematic diagram
Figure 2: Real wiring diagram for illustration
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Module 2
B. OSCILLOSCOPE
An oscilloscope or better known as scope is the most versatile piece of equipment that
displays the variation of voltage with time on a cathode-ray tube (CRT). In other words it
can actually draw a graph of voltage direction and amplitude of a signal. The signal can
only be measured if its frequency is within the range of the scope’s frequency.
In all experiment to follow the type of oscilloscope used will be a dual-trace triggeredsweep scope, model GOS-622G, 20 MHz with two (2) vertical inputs at the sensitivity of
1 mV/cm.
The typical scope has four sections/modes as shown in Figure 4. They are vertical;
horizontal; trigger or sync; and display. Let us look at each section to learn its purpose
and adjustments.
Figure 4: Functional block diagram of a general purpose oscilloscope
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Module 2
CONTROL
BUTTONS/SWITCH
INTENSITY
FOCUS
VOLT/DIV
VERTICAL
Y-POSITION
VAR SENS VOLT/DIV
VERTICAL COUPLING
TIME/DIV
HORIZONTAL
X-POSITION
VAR SENS TIME/DIV
TRIGGER LEVEL
FUNCTION
The function of intensity is to control the intensity (brightness) of
light or electron beam suitable to the eyes.
The electron beam is focused through the grid control in the cathode
ray tube. The beam is controlled through this button.
This button controls the sensitivity of the input signal at the vertical
mode so that a wide range of signals can be displayed. Typically the
range varies from a few mV to hundreds of Volts.
This button enables the signal displayed to move upwards and
downwards.
This button enables the adjustment of calibration in terms of
VOLT/DIV to be carried out.
This button determines the way the signal to be measured is input to
the vertical mode. When the switch is set to GND, the signal is
shorted to ground. Therefore the signal is not displayed. With AC
only the ac signal is allowed to pass through and displayed. With DC
both components dc and ac levels are passed to the vertical mode
and displayed on the screen.
This button is associated to the horizontal mode and is the scale
factor for period. As an example if the TIME/DIV is 1 ms means that 1
cm scale on the scope screen is equal to the 1 ms.
This button enables the signal to be moved to the right and left
horizontally.
This button is used to calibrate the period.
This button is adjusted until a moving signal on the screen is made
stationary.
Table 1: Control buttons and its functions of an oscilloscope
(a) Amplitude Measurements (Voltage)
DC levels:
(i)
Place DC/AC/GND switch in the GND position to establish the base-line or zero
level reference on the screen.
(ii)
Then switch the DC/AC/GND switch to DC position to measure dc level. In this
position the input probe has direct coupling to the internal amplifiers.
(iii)
Finally place the scope leads across the unknown dc level and use the following
equation to determine:
DC level (V) = Vert. deflection (div.) X Vert. sensitivity (V/div.) X probe setting
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EKT 101 Electric Circuit Theory
Module 2
AC level:
(i)
Place DC/AC/GND switch in the GND position to establish the base-line or zero
level reference on the screen.
(ii)
Then switch the DC/AC/GND switch to AC position to measure ac level. In this
mode there is a coupling capacitor between the input probe and the internal
amplifiers. This blocks the dc from display and allows the measurement of lowlevel ac signals sitting on the same line as high-level dc voltage.
(iii)
Finally place the scope leads across the unknown ac voltage level to obtain
voltage using the following equation:
Vp-pl (V) = Vert. deflection Peak-Peak (div.) X Vert. sensitivity (V/div.) X probe setting
C. FUNCTION GENERATOR
(i)
A function generator is usually a piece of electronic test equipment or software used to
generate different types of electrical waveforms over a wide range of frequencies. Some
of the most common waveforms produced by the function generator are the sine, square,
triangular and sawtooth shapes.
(ii)
A function generator is a device that can produce various patterns of voltage at a variety
of frequencies and amplitudes. It is used to test the response of circuits to common input
signals. The electrical leads from the device are attached to the ground and signal input
terminals of the device under test.
Figure 5: Function Generator
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Most function generators allow the user to choose the shape of the output from a small
number of options.

Square wave - The signal goes directly from high to low voltage.

Sine wave - The signal curves like a sinusoid from high to low voltage.

Triangle wave - The signal goes from high to low voltage at a fixed rate.
The amplitude control on a function generator varies the voltage difference between the
high and low voltage of the output signal. The direct current (DC) offset control on a
function generator varies the average voltage of a signal relative to the ground.
The frequency control of a function generator controls the rate at which output signal
oscillates. On some function generators, the frequency control is a combination of
different controls. One set of controls chooses the broad frequency range (order of
magnitude) and the other selects the precise frequency. This allows the function generator
to handle the enormous variation in frequency scale needed for signals.
The duty cycle of a signal refers to the ratio of high voltage to low voltage time in a
square wave signal
How to use Function Generator
After powering on the function generator, the output signal needs to be configured to the
desired shape. Typically, this means connecting the signal and ground leads to an
oscilloscope to check the controls. Adjust the function generator until the output signal is
correct, then attach the signal and ground leads from the function generator to the input
and ground of the device under test. For some applications, the negative lead of the
function generator should attach to a negative input of the device, but usually attaching to
ground is sufficient.
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Appendix
CONTROL BUTTONS/SWICHES OF OSCILLOSCOPE
NO
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
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CONTR BUTTONS/SWICHES
Calibration Point, CAL
Intensity, INTEN
Focus
Trace Rotation
Power ON LED Indicator
Power ON/OFF
VOLT/DIV
AC/DC
GND
CH1(X) Input Port
VAR SENS
CH2 (Y) Input Port
SWP. UNCAL
GND
SWP. VAR
SLOPE
EXT TRIG (EXT HOR) input terminal
NO
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
CONTR BUTTONS/SWICHES
TIME/DIV
TRIG/ALT
COUPLING
SOURCE
X-Y
Trigger Mode: NORM/AUTO
LOCK
TRIGGER LEVEL
HOLDOFF
Horizontal Position
X 10 Magnification
CH2 INV
CH2 Vertical Position
Vertical Mode
CH1 Vertical Position
CHOP
SCREEN – each graticule calibrated
in centimeters
EKT 101 Electric Circuit Theory
Module 2
UNIVERSITY MALAYSIA PERLIS
EKT 101
ELECTRIC CIRCUIT THEORY
EXERCISE 2
SEMESTER I (2012/2013)
SCHOOL OF COMPUTER AND COMMUNICATION ENGINEERING
SEM I 2012/13
EKT 101 Electric Circuit Theory
Module 2
A. MEASUREMENT USING MULTIMETER (RESISTANCE IN SERIES AND
PARALLEL)
a) With resistors given, complete Table 1 below. Using multimeter, measure the resistance
COLOR BAND
No.
Band 1
Band 2
Band 3
Band 4
Nominal Value
Measured Value
1.
2.
3.
4.
b) Construct the circuit as shown in Figure 1 on the breadboard. Note that R1= 1.2
k, R2 = 1 k, R3 = 3.9 k and R4 = 4.7 k.
a
R1
R2
R3
R4
b
Figure 1: Resistor in Series
a) Give the equation to CALCULATE of total resistance for the circuit in Figure 1.
b) Using multimeter MEASURE the total resistance.
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EKT 101 Electric Circuit Theory
Module 2
3. Figure 2 show the resistor connected in parallel.
R1
R2
R3
R4
Figure 2: Resistor in Parallel
a) Give the equation to CALCULATE of total resistance for the circuit in Figure 2.
b) Using multimeter MEASURE the total resistance.
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EKT 101 Electric Circuit Theory
B
Module 2
CALIBRATION OF OSCILLOSCOPE
1.
Connect a coaxial input signal probe to the BNC jack CH1.
2.
Obtain a base-line or zero level horizontal trace by setting the vertical coupling switch
to GND and by appropriately adjusting the vertical and horizontal position controls.
3.
Calibrate the sensitivity of the instrument by setting the VOLT/DIV switch to the
required range.
4.
Set the vertical coupling switch to AC (disengage the switch). Set the sweep sensitivity
TIME/DIV [ to 0.5 ms. Next, touch the input probe lead to the calibration point, CAL .
Make sure that the magnification scales at both scope and probe is X1.
5.
OBSERVE the values obtained from the displayed waveform and DRAW the waveform
in Figure 6 indicating the important values such as peak-peak value Vpp, Frequency f,
VOL/DIV button setting and TIME/DIV button setting.
Note: It is very important to make a prior calibration on the scope to ensure a correct
and accurate measurement.
6.
Draw the waveform signal in graph below.
Figure 6: Calibration signal
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