Computer Graphics Lab
Department of Computer Science & Engineering
Group 6
1. Rima Datta 36th Batch
2. Shiren Akter 36th Batch
3. Md. Wasim 37th Batch
4. Abuzor Gefary 37th Batch

The Subject of Discussion
 What is cathode ray tube.
 Features.
 How CRT work & display.
 Color CRT.
 Cathode Ray Oscilloscopes.
 Application of CRT.
 Advantages of CRT.
 Disadvantages of CRT.

What is cathode ray tube
 The cathode ray tube (CRT) is a vacuum tube containing an
electron gun (a source of electrons) and a fluorescent screen,
with internal or external means to accelerate and deflect the
electron beam, used to create images in the form of light
emitted from the fluorescent screen.

Features
The features of a CRT can be split into 4 main sections:
 Electron gun.
 Deflection system.
 Fluorescent screen.
 Glass Tube & Base.

Basic Cathode Ray Tube

Electron Gun
 The role of this section is to produce electrons at
a high, fixed, velocity.
 This is done through a process known as thermionic
emission.

Deflection system
 It consists of Two PERPENDICULAR sets of
Electric/Magnetic fields.
This allows control over both horizontal and
vertical axes.
By controlling the Voltage applied to the fields, it is
possible to vary the deflection through Electrostatic
force/Motor effect.

Fluorescent screen
 The role of this part is to display where the electrons
are hitting the CRT.
 It is a screen coated with a material that emits light
when struck by electrons.
 Zinc sulfide or Phosphorus are two commonly used
materials

Glass Tube and Base
 The whole assembly is protected in a conical highly
evacuated glass tube.
 Glass tube is a long, clear tube. The CRT uses an
evacuated glass envelope which is large, deep , fairly
heavy, and relatively fragile.
 Inside the tube's neck is an assembly that produces a
stream of electrons. Electrical connections to these
internal components are made through metal pins that
extend out through the back of the tube's neck, usually
in a circular formation.
 Vacuum is created inside the glass tube 0.001Pa to 133
nPa.

How CRTs work & display
 A CRT monitor contains millions of tiny red, green, and
blue phosphor dots that glow when struck by an
electron beam that travels across the screen to create
a visible image. In a CRT monitor tube, the cathode is a
heated filament. The heated filament is in a vacuum
created inside a glass tube. The electrons are negative
and the screen gives a positive charge so the screen
glows.

How CRTs work & display
A CRT TV works by having the electron beam "scan" the
screen at an rate faster than our eyes can perceive.
 The images we see are actually made from many
fluorescent dots.
 The fluorescence caused by the beam striking the
screen lasts a bit longer so that the next scan can be
made without the previous image disappearing.
 It scans twice each time, first filling in the odd "holes"
then the even ones.
 Each scan is about 1/5 0 of a second.

Color CRTs
 Color tubes use three different phosphors which
emit red, green, and blue light respectively.
 Color CRTs have three electron guns, one for each
primary color, arranged either in a straight line or in a
triangular configuration .
 The three beams in color CRTs would not strike
the screen at the same point without convergence
calibration.

Cathode Ray Oscilloscopes
A Cathode Ray Oscilloscope (CRO) is a diagnostic device that
allows one to “See” voltage.
 It is essential a Cathode Ray Tube with two
perpendicular sets of
deflecting electric plates.
 The vertical set is where an input voltage
is plugged in for the oscilloscope to display.
 However, the horizontal set is connected to
a "sweep generator“
 This is what provides a constant, but
adjustable, time base for the sweeping.
 It essentially creates a “saw tooth voltage”.
 This is what causes the image to be
animated, and measured with a linear scale.

Application of Crt
 In televisions
 In computer monitors
 As a display device in radar
 In cathode ray oscilloscope

Advantages of CRT
 The cathode rayed tube can easily increase the
monitor’s brightness by reflecting the light.
 can produce more colors.
 The quality of the image displayed on a CRT
monitors is superior to the LCD and Plasma
monitors.
 The color features of the cathode ray tube
monitor are considered highly excellent.

Disadvantages of CRT
 monitors causes a health hazard to the functioning
of living cells.
 CRTs emit a small amount of X-ray radiation which
can result in a health hazard.
 Constant refreshing of CRT monitors can result a
headache.
 CRTs operate at very high voltage which can
overheat system or result in an implosion.

References
 https://learn.digilentinc.com/Documents/Digital/D
C06_VGAController/CRT_Monitor.svg
 http//www.slideshare.com
 http://nsb.wikidot.com/pl-9-4-1-9
 http://electronics.howstuffworks.com/tv3.htm