4. Oscilloscopes contain a vacuum tube(-
a vacuum tube in which a hot
cathode emits a beam of electrons that
pass through a high voltage anode and
are focused or deflected before hitting a
phosphorescent screen)
with a cathode (negative electrode) at
one end
to emit electrons and
an anode (positive electrode)
to accelerate them so they move
rapidly down
the tube to the screen.
WHAT IS ELECTRON GUN?
5. The electrons are called cathode rays
because they are emitted by the
cathode and this gives the
oscilloscope its full name of cathode
ray oscilloscope or CRO
The tube also contains
electrodes to deflect the electron
beam up/down and left/right.
6. 1. measurement of A.C. signals. So
essentially the oscilloscope can be
used to make quantitative and
qualitative measurements.
2. For example if we are looking at an
incoming sine wave, from the CRO one
can assess the signal amplitude,
frequency and quality.
Use Of An Oscilloscope
7. 3. Some may argue that the best solution to
the problem of measuring a D.C. signal
would
be to use a DMM, this is true in most cases,
but if the purity of the D.C signal is an
important factor
a CRO would also be useful to check for any
A.C ripple in the signal.
4. In general the biggest use for the Oscilloscope
is for the accurate
10. Front panel controls
Focus control
This control adjusts CRT focus to obtain
the sharpest, most-detailed trace. In
practice, focus needs to be adjusted
slightly when observing quite-different
signals, which means that it needs to be
an external control.
11. Intensity control
This adjusts trace brightness. Slow
traces on CRT oscilloscopes need
less, and fast ones, especially if not
often repeated, require more.
12. Dual-trace controls
Dual-trace oscilloscopes have a mode
switch to select
either channel alone, both channels, or (in
some) an X-Y display, which uses the
second channel for
X deflection.
13. Time base generator
The TIME/DIV control determines the
horizontal scale of the graph which
appears on the oscilloscope screen.
14. The VOLTS/DIV controls determine the
vertical scale of the graph drawn on
the oscilloscope screen.
Check that VOLTS/DIV 1 is set at
1 V/DIV and that the adjacent controls
are set correctly.
Volts/Div Control
16. Vertical Position
This knob controls the vertical
position of the trace. You will find it
very convenient when you are setting
or reading voltages.
17. Beam finder
If you do not find a trace, push this
button. The screen will display what
quadrant the trace is in.
AC - DC - Gnd
Selects desired coupling for incoming
signal, or grounds amp input.
DC couples signal directly to amp.
AC connects via a capacitor. (Blocks DC)
Gnd = no signal. Gnd connects Y input
to 0 volts.
Checks position of 0v on screen.
18. Bandwidth
A 10MHz CRO does not mean it
will correctly measure signals at
10MHz.
Vertical Amps are not so wide-
band as to amplify all signals.
10MHz is the 3dB point.
A 10MHz signal of 1v will measure
0.707v on the screen.
20. Voltmeter
CRO can be used to measure
potential differences and to see how
they vary.
We can determine the maximum
value (max voltage) of the signal
and peak to peak voltage when you
observe the signal on an
oscilloscope.
The oscilloscope can show the shape
21. Display of Waveforms
We can display waveforms by
using CRO.
As we apply ac voltage to y- input
of CRO , then waveform is
displayed on screen, depending on
the shape of applied wave.
This waveform is displayed with
respect to time.
24. Measurement of Short Time Inter
WE can measure a very small time
interval, e.g. measurement of sound
speed in a metal rod by using CRO.
25. Measurement of Frequency
We can measure the frequency of an
unknown signal using CRO.
Initially, the unknown frequency
signal is applied to the vertical
inputs of CRO.
Horizontal sweep is turned on and
the display appearing is on the
screen is adjusted by the varying
different control knobs provided on
the front panel of CRO.
26. After obtaining the display of good
deflection, count the number of
horizontal division for a complete
cycle.
From the counted horizontal divisions,
the time period is computed as,
T=m*n
where, m=no. of division in one cycle
n=setting of time base =
Time/division
From the measured time period of the
signal , the unknown frequency is
