The document discusses various types of signal analyzers including cathode ray oscilloscopes, wave analyzers, harmonic distortion analyzers, and spectrum analyzers. It provides details on the working principles, components, and applications of general purpose cathode ray oscilloscopes, dual beam oscilloscopes, sampling oscilloscopes, analog and digital storage oscilloscopes, frequency selective and heterodyne wave analyzers, and fundamental-suppression and heterodyne harmonic distortion analyzers.

1. Unit-2
CATHODE RAY OSCILLOSCOPE &
SIGNAL ANALYZERS
EI8692 Electronic Instrumentation
Dr. T. Babu
Prof & Head
Department of ICE
St. Joseph’s College of Engineering

2. Unit II Syllabus
• General purpose cathode ray oscilloscope
• Dual trace, dual beam
• sampling oscilloscopes
• Analog and digital storage oscilloscope
• wave analyser – frequency selective and
heterodyne
• Harmonic distortion analyser
• Spectrum analyzer.
2

3. Books
• TEXT BOOKS:
• A.D. Helfrick and W.D. Cooper, Modern Electronic Instrumentation and
Measurement Techniques, Prentice Hall India Private Ltd., New Delhi, 2010.
• David A Bell, “ Electronic Instrumentation and Measurements”, Ox for
University Press, 2013.
• Jerome J., Virtual Instrumentation using Lab VIEW, Prentice Hall India Private
Ltd., New Delhi,2010
.
REFERENCES:
• H.S. Kalsi, Electronic Instrumentation, Tata McGraw-Hill, New Delhi, 2010.
• J.J. Carr, Elements of Electronic Instrumentation and Measurement, Pearson
Education India, New Delhi, 2011.
• M.M.S. Anand, Electronics Instruments and Instrumentation Technology,
Prentice Hall India, New Delhi, 2009.
• Sanjay Gupta, Virtual Instrumentation using Lab view, Tata McGraw-Hill
Education, 2010. 3

4. Cathode Ray Oscilloscope
(CRO)
• Used to
– Display and analyze the waveforms
– Measurement (Voltage, phase angle, frequency)
– Display the waveform with respect to time
– Compare two waveforms (Dual Oscilloscope)
4

5. Types
 Dual beam- Dual Trace CRO
• Sampling oscilloscope
• Storage oscilloscope
Analog
Digital
5

6. 6
Block diagram of CRO
1. CRT
2. Vertical amplifier
3. Delay line
4. Time base generator
5. Horizontal amplifier
6. Trigger circuit
7. Power supply
Parts of CRO

7. 7
Cathode Ray Tube (CRT)

8. 8
A cathode ray tube (CRT) contains four basic parts:
• Electron gun – (Produces sharply focussed electron beam)
Cathode
Accelerating anode
Focusing Anode
• Deflecting systems
Vertical
Horizontal
• evacuated glass envelope with a phosphorescent screen
that glows visibly when struck by the electron beam.

9. 9
Deflection Plates:
Vertical
Horizontal
Time base Generators (sawtooth wave ) - Horizontal
CRO is used to display the signals with respect to
time, hence it requires a horizontal constant velocity beam.
A deflecting voltage linearly increase and rapidly
decrease called Sawtooth. (Sweep)

10. 10
Vertical Deflection plates
it’s the principal factor of sensitivity and bandwidth
• V/div
• Bandwidth (range of frequencies that can be accurately
reproduced on the CRT screen).
Screen
Inner side of CRT screen – Phosphor (P31)- green
Phosphor material decides the colour of the beam
CRT graticule – grid of lines on the scale when making
measurements of time and amplitude of any signal.
Aquadag:
A layer pasted inside the CRT, to collect the secondary
emitted electrons.

11. 11
Applications of CRO
• Measurement of Voltage and current
• Measurement of phase and frequency (Lissajous Pattern)
When sinusoidal voltages applied to both vertical and horizontal
plate simultaneously
.Measurement of Voltage

12. Measurement of phase
Two equal voltages of equal
frequency and phase
displacement are applied to a
CRO, the trace on the screen
is a straight Line.
Two equal voltages of equal
frequency but with 90' phase
displacement are applied to a
CRO, the trace on the screen
is a circle
12

13. 13
When two equal voltages of same frequency and phase shift Φ
2
1
2
1
X
X
Y
Y
Sin 

14. 14

15. Measurement of Frequency
15
Lissajous pattern with frequency ratio 2 : 1, Lissajous pattern with frequency ratio 1 : 2

16. 16
Multi Input Oscilloscopes
• Two or more number of Inputs can be viewed at a time
• Compare any two or more wave forms
• Dual Beam CRO
• Dual trace CRO
This oscilloscope uses a single electron gun and produces
multiple traces by switching the Y deflection plates from one
input signal to another (this means that the Y channel is time
shared by many signals). The eyes interpret this as a
continuous simultaneous display of the input signals although it
is a sampled display.

17. 17
Dual Beam CRO
• Beam splitter arrangement
• Separate vertical system for two channels

18. Dual trace oscilloscope -2 Channels
18

19. Dual trace CRO
19

20. Dual trace modes (Alternate)
20

21. Dual trace modes (Chop)
21

22. 22

23. Sampling Oscilloscope
23
• To Examine very fast signals (10ps/div)
• To View Higher frequency waveform, Particularly more than
50- 500 MHz even upto 10 Ghz
• It collects samples from several successive waveform and
construct the complete waveform from the sampled data.
• Combined waveform is amplified by low band pass filter and
then displayed on the screen
• The frequency of the waveform to be displayed should be
more than the sampling frequency of oscilloscope.

24. 24
• The display may be made up from as many 1000 dots of
luminescence.
• The horizontal deflection of the electron beam is obtained
by a staircase waveform to X deflection plates.
• The vertical deflection for each dot is obtained from
progressively later points in each successive cycle of the
input waveform
• Only for repetitive waveform.(Disadv) cannot be used
for the display of transient waveforms.
• sampling techniques
• Real time sampling
• Equivalent sample method

25. 25
Sampling Method
• Before sampling, a trigger pulse activates an oscillator and linear
voltage
• When the amplitude of two voltages are equal, the stair case move up
one step and a sampling pulse is generated to open the gate for
sample the voltage.
• The resolution of the waveform depends on the dimensions of the
steps of the stair case generator.

26. 26
Sampling Oscilloscope

27. Storage Oscilloscope
Analog Digital
• Variable persistence
• Bistable Storage oscilloscope
27

28. 28
1. There is a finite amount of time that the storage tube can
preserve a stored waveform. Eventually, the waveform will be lost.
The power to the storage tube must be present as long as the
image is to be stored.
2. The trace of a storage tube is, generally, not as fine as a normal
cathode ray tube. Thus, the stored trace is not as crisp as a
conventional oscilloscope trace.
3. The writing rate of the storage tube is less than a conventional
cathode ray tube, which limits the speed of the storage
oscilloscope.
4. The storage cathode ray tube is considerably more expensive
than a conventional tube and requires additional power supplies.
5. Only one image can be stored. If two traces are to be compared,
they must be superimposed on the same screen and displayed
together.
Disadvantage of Analog storage Oscilloscope

29. •Conventional analogue cathode ray oscilloscope
•Measured signal converted to digital format and stored in
computer memory within the instrument.
•This stored data can then be reconverted to analogue form at the
frequency necessary to refresh the analogue display on the screen.
•Some digital oscilloscopes compute signal parameters such
as peak values, mean values and R.M.S. values.
• They are also ideally suited to capturing transient signals
when set to single-sweep mode.
DSO
29

30. DSO
30
output analogue signals to
devices like chart recorders
and output digital signals in a
form that is compatible with
standard interfaces like
IEEE488 and RS232.
Some even have disk drives to
extend their storage ability.

31. Digital Storage Oscilloscope
31

32. 32
wave analyzer
Wave analyser is an instrument to measure relative
amplitudes of single frequency components in a complex
waveform
Types of wave analyser:
1. Basic Wave analyser
2. Based upon the frequency ranges
(a) Frequency selective wave analyser
(frequency ranges from 20 Hz to 20 kHz)
(b) Heterodyne wave analyser
(frequency ranges from 10 kHz to 18 MHz)

33. 33
Principle
Basically the instrument acts as a frequency-
selective voltmeter which is tuned to the frequency of one
signal component while rejecting all the other signal
components. The amplitude is indicated either by a
suitable voltmeter or a CRO.
Primary Detector: This is a simple LC circuit. It’s adjusted for
resonance at the frequency of the particular harmonic component
to be measured.
(b) Full-wave rectifier: It is an intermediate stage of the basic
wave analyser. It obtains the average value of the input signal.
(c) Indicating Device: The indicating device is a simple dc
voltmeter that is calibrated to read the peak value of the
sinusoidal input voltage.

34. 34
Working:
The LC circuit is tuned to a single frequency of the input signal and rejects all other
frequencies. The full wave rectifier provides the average value of the input. A
number of tuned filters are connected to the indicating device thorough a selector
switch.

35. 35
Frequency Selective Wave Analyser

36. 36

37. 37
Applications of wave analyser
1. Measure relative amplitudes of signal frequency
components in a completer waveform.
2. Measure the signal energy with well defined bandwidth.
3. The wave analysers are applied industrially in the field of
reduction of sound and vibrations generated by rotating
electrical machines and apparatus.
4. Measure the harmonic distortion of an amplifier.
5. Measure the amplitude in the presence of noise and other
interfering signals.
6. Use in harmonic analysis.

38. 38
Harmonic distortion analyser
The distortion caused due to nonlinear behaviour of the critical
elements is called harmonic distortion. Harmonic distortion
measurement is used for testing of amplifiers and networks as
to what they distort the input signal.
• Heterodyne Harmonic Distortion Analyser
• Fundamental-Suppression Harmonic Distortion
Analyser
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22
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39. 39
• Heterodyne Harmonic Distortion Analyser

40. 40
The input signal is mixed with output of variable frequency oscillator in a
mixer circuit. The balance mixer consists of a balanced modulator and it
eliminates original frequency of the harmonic. After successful mixing,
output of mixer supplies the sum and the difference of each harmonic
beating against the oscillator frequency. Now for each harmonic
component either the sum or difference of frequencies is made equal to
the frequency of the filter by varying the frequency of oscillator. The
quartz crystal type highly selective filters can be used as each harmonic
frequency is converted to a constant frequency. This allows selecting
constant frequency signal related to a particular harmonic and passing it
to the metering circuit.
• Heterodyne Harmonic Distortion Analyser

41. 41
Output of mixer has rms value which is proportional to the rms
value of that harmonic component. So when output of mixer is
supplied to a true rms reading voltmeter through amplifier, the
voltmeter reads the rms value of that harmonic component. This
instrument is also called carrier frequency voltmeters and
selective level voltmeters.
Let us assume, for example a 50 Hz distorted sinusoidal
signal for analysis. The oscillator has a frequency range of 50-60
kHz and the filter has a frequency of 50 kHz.

42. 42
Now harmonic components occure at frequencies of 50, 100,
150, 200 Hz and so on. Now we take one harmonic at a time
and the difference of two frequencies.
i.e., the frequency of an oscillator and that of harmonic equals
filter frequency. Now let us suppose the oscillator frequency is
adjusted to 50.05 kHz. Output of mixer contains the sum and
differences of each harmonic beating against the oscillator
frequency. But only mixer output signal, whose frequency is 50
kHz, which is the result of 50 Hz frequency signal beating with
oscillator frequency of 50.05 kHz, passes through the filter.

43. 43
All other mixer output signals are of frequencies above or
below 50 kHz. So voltmeter reads the rms value of 50 kHz
signal. Since rms value of 50 kHz signal is proportional to the
rms value of 50 Hz harmonic component or fundamental of
input signal, so the voltmeter can be calibrated to read directly
the rms value of the 50 Hz fundamental wave.

44. 44
Fundamental-Suppression Harmonic Distortion
Analyser

45. 45
This instrument is used when the total harmonic distortion rather
than the harmonic distortion of each component. The input is applied
to a network of filters that suppresses or rejects the fundamental
frequency but passes the harmonic frequency components.
1. Input circuit with impedance converter: The impedance
converter offers a low-noise, high-impedance input circuit,
independent of the signal source impedance placed at the input
terminals to the instrument.
2. Rejection amplifier: The rejection amplifier rejects the
fundamental frequency of the input signal and passes the
remaining frequency components on to the metering circuit where
the harmonic distortion is measured.
3. Metering circuit: The meter circuit provides a visual indication
of total harmonic distortion in terms of a percentage of total input
voltage

46. 46
Voltmeter Mode:
With the function switch in the voltmeter position, the instrument operates
as a conventional ac voltmeter, a very convenient feature. In this mode the
input signal is applied to the impedance converter circuit through the 10/1
or 100/1 attenuator, which selects the appropriate meter range. The output
of the impedance converter then bypasses the rejection amplifier and the
signal is impresses directly to the metering circuit. The voltmeter section
can be employed separately for general-purpose voltage and gain
measurements

47. 47
Distortion Mode:
With the function switch in the distortion position, the rejection
amplifier is included in the circuit and distortion is measured. In this
mode the input signal is applied to 1 MW attenuator that provides
50db attenuation in 10db steps, controlled by a front panel switch
marked sensitivity. When the desired attenuation is selected, the
signal is supplied to the impedance converter, which is a low-
distortion, high-input impedance amplifier circuit whose gain is
independent of the source impedance placed at the input terminals.
The overall negative feedback in this amplifier results in unity gain
and low distortion. Signals having high impedance can be measured
accurately and the sensitivity selector can be used in high-impedance
positions without distorting the input signal.

48. 48
For frequencies other than the fundamental, the Wien bridge offers a
varying degrees of phase shift and attenuation, and the resultant is
connected through a post-attenuator to the meter circuit and displayed
on the front panel meter. The attenuator limits the signal level to the
meter amplifier to 1 mV for full-scale deflection on all ranges. The
meter amplifier is a multistage circuit designed for low drift and low
noise, and with flat response characteristics. The meter is connected
in a bridge-type rectifier and reads the average value of the signal
impressed on the circuit. The meter scale is calibrated to the rms
value of a sinusoidal wave.
1. The harmonic distortion generated within the instrument is very
small and can be neglected
2. Only the fundamental frequency component must be suppressed