Introduction to the Oscilloscope
Course:
Name(s):
Instructor:
Date:
Section:
Introduction and Objectives:
The oscilloscope is a useful instrument for studying ac circuits. It is often used to display graphs of
voltage versus time.
It is a very fast X-Y plotter and can be used to plot an input signal versus time or another signal. It can
also be used to determine the voltage and frequency of an input signal. It consists of a cathode-ray tube
(CRT) where a beam of electrons emitted from a filament are accelerated and focused on a fluorescent
screen. Deflection plates in the oscilloscope help to move the beam horizontally or vertically.
Equipment Required:
Oscilloscope, signal generator, connecting wires and connectors.
Lab Procedures:
Connect the oscilloscope to the signal generator. An example of an oscilloscope connection is in the
picture below, however your oscilloscope may differ based on the make.
Signal generator
Oscilloscope
Connecting wires
1
Power on the signal generator and oscilloscope. Adjust the signal generator to the desired output
frequency. Adjust the oscilloscope controls till you see a suitable display (for example, see the picture
below).
Time/Div control
(x-axis)
Trace
Volts/Div
(y-axis)
Vertical mode
(set on CH1)
ON/OFF, Intensity, Focus and
Illumination controls
Channel 1
2
Set the signal generator to produce an output as desired using its controls:
Signal frequency
control
Fine control for
signal frequency
ON/OFF switch
Output and ground
leads that go to
oscilloscope
Amplitude (controls the
voltage or height of the
wave)
Sine wave output
3
The period of the wave displayed on the oscilloscope can be measured by counting the number of
divisions required for one wave and then converting this to seconds using the “TIME/DIV” scale setting
on the oscilloscope.
Multiply by this factor to
get the Period in seconds
Count number of
divisions for one
wave
Perform your measurements as directed in the sections below. Enter your results in the tables.
4
For voltage measurements:
Count number of
divisions from
peak to peak
Multiply by this
factor to get the
peak to peak
voltage
The peak voltage is half of the peak to peak voltage. Multiplying the peak voltage by 0.707 gives the rms
(root-mean-square) voltage.
5
Data Tables:
Part 1
Time and Frequency Measurements:
Generator frequency: 90 Hz
No. of divisions
Time sweep/div
Period (s)
Frequency (Hz)
[Reciprocal of
Period]
Percent difference
(compare with 90 Hz as
E1 )
[|E2-E1|/(E2+E1)/2] x 100
Period (s)
Frequency (Hz)
[Reciprocal of
Period]
Percent difference
(compare with (300 Hz as
E1 )
[|E2-E1|/(E2+E1)/2] x 100
Calculations:
Generator frequency: 300 Hz
No. of divisions
Time sweep/div
Calculations:
6
Source -Line: 60 Hz
Set the source to “Line” on the oscilloscope and then adjust the signal generator frequency till you get a
stationary pattern on the screen. Note the actual graduated marking on the signal generator to obtain this
stationary pattern. Calculate the percent error of the marking you find to the accepted value of 60 Hz.
usually, the calibrated markings on the signal generator may have inaccuracies and this experiment lets
you determine this inaccuracy.
No. of divisions
Time sweep/div
Period (s)
Frequency (Hz)
Calculations:
7
Percent error
(compare with (60 Hz)
[|E-A|/A] x 100
Part 2
Voltage Measurements:
To obtain another reading of the voltage, measure the output voltage of the signal generator with a
multimeter. Make sure your multimeter is set to measure an AC signal by pressing on the blue button till a
symbol is displayed.
Generator frequency: 90 Hz
Volts/div
No. of
divisions
(peak to
peak)
Peak to
peak
voltage
(V)
Peak
voltage
(Vo)
rms voltage
(Peak voltage) x
(0.707)
Calculations:
8
Voltage by
multimeter
Percent difference
(compare rms voltage
with multimeter value)
[|E2-E1|/(E2+E1)/2] x 100
Part 3
Lissajous Figures:
Generator frequency: 60 Hz
When two ac voltages are added such that one is on the x-axis and the other on the y-axis, then patterns
called “Lissajous figures” are produced. Depending on the phase and frequency differences between the
two signals, different patterns can be seen. If the signals have the same frequency and phase, then a
diagonal line is produced. When the signals have the same frequency, but a phase difference of 0°, then an
ellipse is produced. If the signals have the same frequency, but a phase difference of 90°, then a circle is
produced.
For this part you will need to connect two signal generators to an oscilloscope as shown in the picture:
Signal applied to y-axis
Signal applied to x-axis
9
Oscilloscope settings for producing Lissajous figures:
Lissajous
Figure
Set control to
“X-Y”
Set control to
“ADD”
10
Use the drawing toolbar in Word to draw the figures you see in the table below:
(In Word 2007: Insert  Shapes  You can use the “Curve,” “line,” “freeform,” “oval” or any other
convenient shape tool to draw your figures below).
X- input
Y-input
Sketch of pattern seen
frequency
frequency
Y
X
Y
X
Y
X
Y
X
11
Answers to questions:
1. What is a cathode-ray tube (CRT)?
2. What is the function of deflection plates in an oscilloscope?
3. How can a graph of voltage versus time be obtained on an oscilloscope?
4. What is the difference between peak voltage and rms voltage?
5. What are Lissajous figures? How are they produced on an oscilloscope?
6. How does the number of wave cycles seen on a screen for a fixed input frequency vary with the SWEEP
TIME/DIV control setting? Why is this?
7. Explain why a 60 Hz Lissajous figure can be varied from a straight line to a circle.
Conclusions:
12