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When the square wave generator switching frequency is much higher than the either
signal frequency, bits of each signal are alternately presented to the oscilloscopes vertical
input to reproduce the two signals on the screen.
R, controls the position. The signals on the screen can be overlapped, for the e a s ) ,
co IIIpa rison.
Dual trace CRO Dual beam CRO
1. One electron beam is used to generate two Two electron beams are used.
traces.
2. One vertical amplifier is used. Two vertical amplifiers are used.
3. The two signals are not displayed The two signals are displayed simultaneously.
simultaneously in real time but appears to bedisplayed simultaneously.
4. Same beam is shared between the two Signals Two separate beam~ are used hence easy to
hence difficult to switch quickly between the switch between the traces.
traces.
5. As two signals are displayed separately, the The two signals must have same frequency or
signals may have different frequencies. their frequencies must be integer multiples of
each other.
6. The size and weight is less. The size and weight is more.
7. Cannot be operated at fast speeds hence two Can be operated at very high speed hence two
separate fast transient signals can not be separate fast transient signals can be easilygrabbed. grabbed.
8. The cost is less due to single beam. The cost is more due to two beams.
9. The two different modes of oeration are The two different types are using double gun
alternate and chop. tube or split beam using single electron gun.
1. It is used to measure a.c. as well as d.c. voltages and currents. It is useful to
"/ calculate the parameters of the voltages as peak to peak value, r.m.s. value, duty
cycle etc.
2. In laboratory to measure the f requency, period, phase relationships between the
~ signals and to study periodic as well as nonperiodic signals.
:Y-1n radar, it is used for giving the visual representation of target such as aeroplane,
ship etc.
4/ln radio applications, it is used to trace and measure a signal through out the RF, IF
and AF channels of radio and television receivers. It provides the only effective
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is useful to
value, duty
the RF, IFy effective
way of adjusting FM receivers, broadband high frequency RF amplifiers and
automatic frequency control circuits.
5. In medical applications, it is used to display the cardiograms which are useful for
,/ the diagnosis of heart of the patient. Similarly electromyograms are useful t,o study
muscle condition of the patient.
6. In industry, it is used for many purposes. It is used to observe B-H curves, P-V
diagrams and other effects. Used to study the response of various transducers
which measure strain, pressure, temperature etc. It is used to observe the radiation
pattern generated by transmitting antenna.
7. I t is used to determine the modulation characteristics and to detect the standing
waves in transmiss.ion lines.
8. Curve tracers use the oscilloscope technique for testing the acti ve devices such as
\'acuum tubes, transistors and integrated circuits.
9. It is used to measure capacitance, inductance and also used to check the dIodes. It
can be used to check the faulty components in the various circuits.
1. 01 '(11 (1IIlld expllllll the s tructu re I Il1 d mlllll compOII ' ll ts of (o1l1'ell t lol ll ll cothode ral / tul lC.
2. W i lY phos pho r s cr ee ll Is pro vi de d w ith 111 1 I I lumll llum layer 7
3. st ll te the l 'I Irlous phosphors I I IIUlllg di fferel l t perslstellce I I ll d co lours . S tat e t h"l r appl /ca tio ll a reas.
4 . S ta te the un rio us charac ter is ti cs o f P31 phosphor .
.J. Draw the b lock d iagram o f ge ll e ra l purpose CR.a. Explal l l the fUl lctlolls of ( ' ( IrIOIIS /Jlocks.
6. D ra w a lld ex p la l ll t he b lock d iag ra m o f th e v er tical ampl if ie r u sed III oscilloscopes.
7. E xp la i ll t he fUllc ti on o f d elay lille i ll o sc il lo scopes . W l lI ch are t he two t ypes o f delay l il ie s 7
8. Sta te a nd I!xplain v or lo us fr on t pane l con tro ls o f a S imp le CR.a.
9. Wllllt I~ z -ax is I n tensi ty cOll tro l ?
10 . ll lfhat I s t he r ol e o f a t i1l1e base generator 7 I ii /hat are the basic t l ll1e base requfr( 'mel l ts 7
11. D ra w alld expla il l t he b lock diagram o f t ml e v as e u se d III
Ilo rm al CR.a.12 . Explaill the follo w ll 1g m o de s o f o p er at io ll o f time base generator
I) Free run mod e
I I) A u to mode
Iii) sIngl1 ! sw ee p 1Ilod e
13. Draw the b lock d iagram of a trigg er ge l/eratoI'. E xp la in t he uar lous cont ro l s a ssoc ia ted W i th I t .
14 . What is th e us e of A Cs a nd A CF c ontrols?
15 . W h ic h a re t he h ipic al t ri gg er s OI/rce s 7 E x pl ai n t he ir sigl1lficol/cl'.
16 . E x pl ai n t he u s e o ff ol lo w in g c on tr ol s
I) INT
11 ') EX T
III) LINE
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------------------------------
I
Special Oscilloscopes III
In many ,1pplications it is necessary to investigate the wilveforms hilving verv high
trt'quL'nC\' or the sigrh1ls which Me nonrepetitive and single event. In sonw ,1ppllclllon'>,
tht' dat.l I~, required to be stored and to be used later whencver neces~cilln"cope'>
,1 I"L ' necessary to perform such specia I functions. The various specie11 oscilloscope'>
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on the normal time base generator output. Due to this additinoal time base, any part of
the waveform can be brightened when oscilloscope is running on a normal time base. The
delayed time base then can be used to fill the screen completely with the brightened part
of the waveform. The user then can study that part of the waveform in great detail.
In c 1 delayed time base oscilloscope, a variable time delay circuit is used in the basIC
time base circuit. This allows the triggering of sweep time after the delay time. Thus the
delay time is variable. This time is denoted as td. After this, the sweep is triggered for the
time t,. Then the portion of the waveform for the time t x gets expanded on the complete
()scillo~cope screen, for the detail study.
If inpu,t is pulse waveform and leading edge is used to trigger the delay time, then
bgging edge can be displayed to fill the entire oscilloscope screen. This is shown in the
Fig 5.2(a). Similarly jf the lagging edge is used to trigger the delay time then leading edge
Gln be displayed on the entire screen for the time tx. This is shown in the Fig. 5.2 (b). I f
the time delay is perfectly adjusted, then any portion of the waveform can be extended to
fill the entire screen. This is shown in the Fig. 5.2 (c).
Delay A ,- Sweep . Atime is is triggeredtriggered I
I
I
I
I BI
Input ~I t..-I I I
pulse ,td I tx'
Portion A-B
is enlargedon the screen
(a) Studyof lagging
edge
(b) Studyof leading
edge
0----- tx
Fig. 5.2 Use of additional time delay
5.2.1 Block Diagram of Delayed Time Base Oscilloscope
The Fig. ').3 shows the block diagram of the delayed time base oscilloscope which use
Ill'lin time base (MTB) and delayed time base (DTB).
I I
I I
I I
I I
I I
I I
I I'--I t I I. d tx
B (c) Studyof any portion
of waveform
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MTB
unblanking
circuit
Main time
base
MTB
Ramp output
of MTB
Summation
of
unblanklng
pulses
Potentiometer
for trigger
level control
Summing
circuit
To CRT
grid
Horizontal
deflection
amplifier
Fig. 5.3 Delayed time base oscilloscope
The normal time base circuit is main time base (MTB) circuit which functions same as
c 1 conventional oscilloscope. The function of MTB blanking circuit is to produce an
unblanking pulse which is applied to CRT grid to turn on an electron beam in the CRT,during the display sweep time. The ramp output of MTB is given to the horizontal
deflection amplifier via switch S. It is also given as one input to the voltage comparator.
The other input to the voltage comparator is derived from the potentiometer whose level is
adjustable.
Key Point : Whcl / the levels of ramp ou tput o f M TB a nd trigger lev el set by
potel/tio m ete rs a re e qual, th en tire vo lt ag e c om p a mto r p ro du ccs a ncga tiv e o r positiv e output
sp ik e a t t h at i nstan t.
This spike is used to trigger the delayed time base (DTB) circuit. The time required by
the ramp output to reach the level set by potentiometer is the delay time Td, which is
adjustable.
Similar to MTB, DTB also has a blanking circuit which produces an unblanking pulse,
during the ramp time of DTB.
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The unblanking pulses from MTB and DTB a re added by summing circuit and given
to the CRT grid. The unblanking pulse of MTB produces a trace of u
