BE0100081 - Digital Fabrication Workshop
EXPERIMENT NO: 02
Use of Digital Storage Oscilloscope and Function Generator
Objective: To get familiar with the functions and working of Digital Storage
Oscilloscope and Function Generator.
Digital Storage Oscilloscope:
In 1985, the Walter was first person to introduce the first digital oscilloscope, a computerized
version of the analog machine which process the signal digitally. Digital oscilloscopes in the
21st century uses a memory and digital processing technique to represent voltages in the
manner easy to understand.
Digital storage oscilloscope commonly known as DSO is not only the displaying device
but it also stores the waveform.
Rather than processing the signals in an analog fashion, the DSO converts them into a
digital format using an analog to digital convertor (ADC).
Since the waveform is stored in a digital format, the data can be processed either within
the oscilloscope itself, or even by a PC connected to it.
Fig.1 Block Diagram of Digital Storage Oscilloscope
(Image Source: https://resources.altium.com/p/oscilloscope-basics-beginner-guide)
Front panel of 2 Chanel, 50 MHz RIGOL DSO is shown in the Fig.2 below for the reference.
CONTROLS
Vertical controls:
CH 1 & CH 2 MENU: Displays the vertical menu selections which move the waveform
vertically.
VOLTS/DIV (CH 1 & CH 2): Selects vertical scale factors.
Horizontal controls:
POSITION: Adjust the horizontal position of waveform. The resolution of horizontal
control is a time function.
MENU: Sets the horizontal position to zero.
SCALE: Selects the horizontal time/div (scale factor) which set the horizontal gain
Electrical Engineering Department, Dr. S. & S. S. Ghandhy G.E.C., Surat
BE0100081 - Digital Fabrication Workshop
Trigger controls:
The trigger determines at what time should Oscilloscope starts to acquire data and to a
display a waveform. The trigger must set properly otherwise the wave form display is not
stable and sometimes the screen goes blank due to synchronization of trigger pulse.
Fig. 2 Front Panel of DSO
(Image Source: https://resources.altium.com/p/oscilloscope-basics-beginner-guide)
Input Connectors
CH1 & CH2: Input connectors for waveform display.
Run and Stop Button
With the help run and stop button the experimenter can stop the wave which enhance the
accuracy of fluctuating wave.
Auto Button
This button is used to automatic adjustment of waveform on display panel of DSO.
Measure Controls
Digital storage oscilloscope is employed to measure:
Voltage of the applied signal
Frequency of the applied signal
Time period of applied signal
Amplitude of applied signal
Average RMS value of applied signal
Duty cycle of applied signal
Cursors Knob- Push this knob select cursors from the menu, rotates the knob to adjust the
selected cursor position.
Cursor key- Press this key to open a menu that make experimenter to select the cursors
mode and source.
Measure key- Press this key to access a set of predefined measurements
Measurement Technique
The objective of observing a signal on the oscilloscope screen is to make voltage and time
measurements.
Electrical Engineering Department, Dr. S. & S. S. Ghandhy G.E.C., Surat
BE0100081 - Digital Fabrication Workshop
These measurements may be helpful in understanding the behavior of a circuit
component, or the circuit itself, depending on what has to be measure.
The oscilloscope screen consists of the grids which can be external or internal to the
screen of CRO, which divides both the horizontal axis (voltage) and the vertical axis
(time) into divisions which will be helpful in making the measurements.
These values are determined by two variables namely the time/div and the volt/div both
of which can be adjusted from the relevant buttons available on the front panel of the
oscilloscope.
Measurement of A.C. voltage:
Measurement of peak-to-peak voltage and peak voltage:
1. To measure the ac. voltage of sinusoidal waveform. The input ac. signal is applied from
the signal generator to a channel of CRO. The voltage/div switch (Y-plates) and time base
switch (X-plates) are adjusted such that a steady picture of the waveform is obtained on
the screen.
2. The vertical height (l) that is peak-to-peak height is measured. When this peak-to-peak
height (L) is multiplied by the voltage/div (voltage deflection sensitivity ‘n’) we get the
peak-to-peak voltage (2Vo). From this we get the peak voltage (Vo). The rms voltage
Vrms is equal to Vo/ 2. This rms voltage Vrms is verified with rms voltage value,
measured by the multimeter.
Measurement of D.C. voltage:
The trace (horizontal line) is adjusted such that it lie on the X-axis of the screen. The dc input
voltage to be measure is then fed to the input channel of the CRO in the dc mode. The shift of
trace from the horizontal line occurs which gives the measure of the magnitude of the dc
voltage.
Electrical Engineering Department, Dr. S. & S. S. Ghandhy G.E.C., Surat
BE0100081 - Digital Fabrication Workshop
Measurement of frequency using time-period:
Suppose that the time period of the input signal is T. As we know frequency is the reciprocal
of time period.
Then, the frequency of the signal =1/T
Measurement of frequency using Lissajous figure:
1. When two signals having some frequencies are applied to input terminal of CRO and get
superimposed perpendicularly (when A/B or B/A is pressed), then a pattern of closed
figure is obtained which is known as LISSAJOUS FIGURE.
2. This is easily done on an oscilloscope in XY mode.
3. The signal whose frequency to be measured is given on vertical plate and signal whose
frequency is given to horizontal plate.
Now the known frequency is adjusted such that a Lissajous pattern can be obtained, which
depends on the ratio of the two frequencies.
Let fy be the frequency of unknown signal (applied at vertical plate) and f x be the frequency
of known signal (applied at horizontal plate).
Then tangents are drawn on horizontal and vertical side of the Lissajous pattern, which gives
the measure of:
f x no . of ∩at ℎorizontal side of Lissajous pattern
=
fy no . of ∩at vertical side of Lissajous pattern
Electrical Engineering Department, Dr. S. & S. S. Ghandhy G.E.C., Surat
BE0100081 - Digital Fabrication Workshop
Measurement of phase difference:
If two or more signals are being monitored simultaneously, a time delay may occur between
the signals (that is one signal may lead the other or vice-verse), called as phase difference.
Two waves that have the same frequency, have a phase difference that is constant
(independent of t).
When the phase difference is zero, the waves are said to be in phase with each other.
Otherwise, they are out of phase with each other.
If the phase difference is 180º (radians), then the two signals are said to be in anti-phase. If
the peak amplitudes of two anti-phase waves are equal, their sum is zero at all values of time,
t.
The phase difference is expressed in terms of radians or degrees. In Dual Mode, the phase
difference can be calculated as follows it depicting the two signals having the same
frequency:
The phase difference between the signals can also be determined in XY mode of the dual
slope oscilloscope. In the XY mode, the x-axis data is taken on one channel, y-axis data is
taken on the other. In that way, Channel I is related with Channel II which is presented by
means of graph, so that the variation of a signal with respect to another can be observed. In
XY mode, the two signals having a constant phase difference.
Electrical Engineering Department, Dr. S. & S. S. Ghandhy G.E.C., Surat
BE0100081 - Digital Fabrication Workshop
Function Generator:
A function generator is a very versatile instrument that is used in electronics, mechanics,
bioengineering, physics and many other fields. A wide variety of synthesized electrical
signals and waveforms can be created for testing, repairing and diagnostic applications. It
produces different types of waveforms such as sine, square, triangle and sawtooth over a wide
range of frequencies.
This is a specialized signal generator in which the frequency is controlled by varying the
magnitude of current which drives the integrator where in other common instruments,
frequency is controlled by varying the capacitor in the LC or RC circuit.
Fig. 3 Block diagram of a Function Generator
The frequency-controlled voltage regulates two current sources shown in block diagram. The
upper current source supplies constant current to the integrator whose output voltage
increases linearly with time. According to the equation of the output signal voltage:
V −1
o=¿
C
∫ i dt ¿
An increase or decrease in the current increases or decreases the slope of the output voltage
and hence controls the frequency. As the output of integrator reaches at a pre-determined
maximum level on the positive slope of the output waveform the voltage comparator changes
state. This change of state cuts of the upper current supply and switches on the lower current
supply. When output reaches a pre-determined minimum level on the negative slope of the
output waveform the voltage comparator again changes state it switches on the upper current
source and cuts off the lower current source. The lower current source supplies a reverse
current to the integrator, so that its output decreases linearly with time. Hence, triangular
waveform is obtained at output. The comparator delivers a square wave voltage of the same
frequency. The resistance diode network alters the slope of the triangular wave as its
amplitude changes and produces a sine wave with less than 1% distortion. The output circuit
of the function generator consists of two output amplifiers that provide two simultaneous,
individually selected outputs of any of the waveform function. Hence, waveforms- triangular,
square and sine is obtained.
Electrical Engineering Department, Dr. S. & S. S. Ghandhy G.E.C., Surat
BE0100081 - Digital Fabrication Workshop
Types of function generator
There are various types of generators who generates frequency, but specially function
generator is of two types:
1. Analog
2. Digital
Analog function generator:
(Source: https://www.aimtti.com/product-category/legacy-products/aim-tg550)
The analog function generators do not have the high frequency limitations on non-sinusoidal
waveforms such as triangles and ramps as do the digital function generators. Analog function
generators are simple and easy to use.
Digital function generator:
(Source: https://rigolshop.eu/function-generator-dg1022.html)
It utilizes digital technology to generate the waveforms. There are a number of techniques to
do this, but the most versatile and most widely used technique for digital function generators
is to use direct digital synthesis, DDS.
Application
Where there is a requirement of signals, function generator is used. They provide a variety of
waveforms for testing electronic circuits at low powers. It is used to study the frequency
response of any circuit.
Electrical Engineering Department, Dr. S. & S. S. Ghandhy G.E.C., Surat
BE0100081 - Digital Fabrication Workshop
Lab Exercise 1:
Perform the calibration process of DSO and draw the waveform on graph paper.
Frequency Offset
V(peak-peak) VS (Vertical Sensitivity)
V(Peak) HS (Horizontal Sensitivity)
V(RMS) Time Period
Lab Exercise 2:
Generate a sine wave with 5 V (peak to peak) and Frequency = 1 kHz from function
generator and observe the waveform on DSO. Note down the following readings. Draw the
waveform on graph paper.
Frequency Offset
V(peak-peak) VS (Vertical Sensitivity)
V(Peak) HS (Horizontal Sensitivity)
V(RMS) Duty Cycle
Lab Exercise 3:
Draw the waveform of Exercise 2 with 1 volt dc offset. Set dc offset from function generator.
Lab Exercise 4:
Generate the Triangular Wave with V (Peak) = 5volts, Frequency = 1KHz and Offset = 2Volts
from Function Generator then draw the waveform of the DSO on a graph paper.
Time Period Offset
V(peak-peak) VS (Vertical Sensitivity)
V(Peak) HS (Horizontal Sensitivity)
V(RMS) Duty Cycle
Lab Exercise 5:
Generate the Square Wave with V (Peak) = 1volts, Frequency = 1KHz, Duty cycle = 90% and
DC Offset = 3Volts from Function Generator then draw the waveform of the DSO on a graph
paper.
Time Period Offset
V(peak-peak) VS (Vertical Sensitivity)
V(Peak) HS (Horizontal Sensitivity)
V(RMS) Duty Cycle
*******
Electrical Engineering Department, Dr. S. & S. S. Ghandhy G.E.C., Surat
