The cathode ray oscilloscope (CRO) is an electronic device that uses a cathode ray tube to visually display signal waveforms. It can be used to study the wave shapes of alternating currents and voltages, and to measure voltage, current, frequency, power, and phase shift. The CRO contains an electron gun that produces a focused beam of electrons, a cathode ray tube with a fluorescent screen, vertical and horizontal deflection plates to move the beam, amplifiers, a time base generator, and a power supply. The CRO allows users to view the waveform of electrical signals and to analyze their characteristics.

1. CATHODE RAY
OSCILLOSCOPE (CRO)

2. Using a CRO , the wave shapes of alternating currents and voltages can be
studied. It can also be used for measuring voltage, current, power, frequency
and phase shift.
 Introduction
The cathode Ray Oscilloscope or mostly called as CRO is an electronic
device used for giving the visual indication of a signal waveform.
It is an extremely useful and the most versatile instrument in the electronic
industry.
CRO is widely used for trouble shooting radio and television receivers as well
as for laboratory research and design.

3. Block Diagram

4. Electron Gun Assembly
The electron gun assembly consists of an indirectly heated cathode, a control
grid, a focussing anode and an accelerating anode and it is used to produce a
focused beam of electrons.
 Cathode Ray Tube
It consist of following parts as
Glass Envelope
It is a conical highly evacuated glass housing which maintains vacuum inside
it and supports various electrodes.
The inner wall of CRT between the neck and screen are usually coated with a
conducting material known as aquadag. This coating is electrically connected
to the accelerating anode so that the electrons which accidentally strike the
walls are returned to the anode. This prevents the walls from charging to a
high negative potential

5. Screen
The screen is coated with some fluorescent materials such as zinc
orthosilicate, zinc oxide etc and is the inside face of the tube.
When high velocity electron beam strikes the screen, a spot of light appears
at the point of impact. The colour of the spot depends upon the nature of
fluorescent material.
Deflection Plate Assembly
It consists of two sets of deflecting plates within the tube beyond the
accelerating anode and is used for the deflection of the beam.
One set is called as vertical deflection plates and the other set is called
horizontal deflection plates.
The vertical deflection plates are mounted horizontally in the tube. On
application of proper potential to these plates, the electron beam can be
made to move up and down vertically on the screen.
The horizontal deflection plates are mounted vertically in the tube. On
application of proper potential to these plates, the electron beam can be
made to move right and left horizontally on the screen.

6. Trigger (Sync.) Circuit
A sample of the input waveform is fed to a trigger circuit which produces a
trigger pulse at some selected point on the input waveform. This trigger pulse
is used to start the time base generator which then starts the horizontal
sweep of CRT spot from left hand side of the screen.
 Vertical Amplifier
The input signal is applied to vertical amplifier. The gain of this amplifier can
be controlled by VOLT/DIV knob. Output of this amplifier is applied to the
delay line
 Delay Line
The delay Line retards the arrival of the input waveform at the vertical
deflection plates until the trigger and time base circuits start the sweep of the
beam. The delay line produces a delay of 0.25 microsecond so that the
leading edge of the input waveform can be viewed even though it was used to
trigger the sweep

7. Power Supply
A high voltage section is used to operate CRT and a low voltage section is
used to supply electronic circuit of the oscilloscope.
 Time Base (Sweep) Generator
This produces a saw – tooth waveform that is used as horizontal deflection
voltage of CRT. The rate of rise of positive going part of sawtooth waveform is
controlled by TIME/DIV knob. The sawtooth voltage is fed to the horizontal
amplifier if the switch is in INTERNAL position. If the switch is in EXT. position,
an external horizontal input can be applied to the horizontal amplifier.
 Horizontal Amplifier
This amplifies the saw – tooth voltage. As it includes a phase inverter two
outputs are produced. Positive going sawtooth and negative going sawtooth
are applied to right – hand and left – hand horizontal deflection plates of CRT

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