© 2014 IJIRT | Volume 1 Issue 6 | ISSN: 2349-6002
CATHODE RAY TUBE AND IT’S APPLICATIONS
Shubham Gupta,Vishal Sharma, Parshant Sharma
Electronics & Communication Department,
Dronacharya College of Engineering
ABSTRACT
In this paper we would be studying about Cathoderay
tube.We would be focussingon the construction and working
of cathode ray tube. The main idea behind this paper is that
to study moreabout cathoderay tube. We will be having basic
overview of cathode ray tube and also study about various
applications of cathod ray tube. Also in this paper we will be
studying about components of CRT.
INTRODUCTION
The German scientist Karl Braun invented the cathode ray tube
with a fluorescent screen making up one end of the tube in 1897.
It rapidly became a research tool for scientist such as Thomson.
Braun discovered that a stream of electrons would make a screen
coated with fluorescent material glow with light. Braun was the
developer of the cathode ray oscilloscope. He demonstrated the
first oscilloscope tube in 1897, after research work on high
frequency alternating currents. Cathode ray tubes previous to
Braun's work had produced uncontrolled cathode ray streams.
Braun succeeded in producing a narrow stream of electrons
directed by means of alternating voltages that could trace patterns
on a fluorescent screen.
The cathode ray tube or (CRT) is a vacuum tube containing one
or more electron guns, and a fluorescent screen used to view
images. It has a means to accelerate and deflect the electron
beam(s) onto the screen to create the images. The images may
represent electrical waveforms (oscilloscope), pictures
(television, computer monitor), radar targets or others. CRTs have
also been used as memory devices, in which case the visible light
emitted from the fluorescent material
(if any) is not intended to have significant meaning to a visual
observer (though the visible pattern on the tube face may
cryptically represent the stored data). The CRT uses an evacuated
glass envelope which is large, deep (i.e. long from front screen
face to rear end), fairly heavy, and relatively fragile. As a matter
of safety, the face is typically made of thick lead glass so as to be
highly shatter-resistant and to block most X-ray emissions,
particularly if the CRT is used in a consumer product.
experiments, was able to deflect cathode rays, a fundamental
function of the modern CRT. The earliest version of the CRT was
invented by the German physicist Ferdinand Braun in 1897 and is
also known as the Braun tube.It was a cold-cathode diode, a
modification of the Crookes tube with a phosphor-coated screen.
In 1907, Russian scientist Boris Rosing used a CRT in the
receiving end of an experimental video signal to form a picture.
He managed to display simple geometric shapes onto the screen,
which marked the first time that CRT technology was used for
what is now known as television.
The first cathode ray tube to use a hot cathode was developed by
John B. Johnson (who gave his name to the term Johnson noise)
and Harry Weiner Weinhart of Western Electric, and became a
commercial product in 1922.
TYPES OF CATHOD RAY TUBES
CRTs are divided into two major groups based on how the
electron beam(or beams) are directed to the desired location on
the tube's screen.
1. CRTs where the electron beam is deflected electrostatically or
by electric fields. This system
of electron beam deflection is used primarily for oscilloscopes
where great speed is required to position the electron beam to a
desired location on the screen in order to follow rapidly changing
waveforms.
2. CRTs where the electron beam is electromagnetically
deflected. This type of CRT is used almost universally in
television, computer
displays and radar.
Therefore following are further classifications of CRT’s :
1. Cat’s eye
2. Charactrons
3. Nimo
4. William’s tube
5. Zeus thin CRT
HISTORY OF CATHOD RAY TUBE
The experimentation of cathode rays is largely accredited to J. J.
Thomson, an English physicist who, in his three famous
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BASIC COMPONENTS OF CRT
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The basic CRT consists of four major components.
1.
2.
3.
4.
Electron Gun assembly.
Deflection plate assembly.
Screen for CRT.
Glass body and base.
DIAGRAM OF CATHOD RAY TUBE
The end wall of CRT ,called the screen of CRT is coated with
phosphor. When electron beam strikes the CRT screen, a spot of
light is produced on the screen. The phosphor absorbs the kinetic
energy of the bombarding electrons and emits energy at a lower
frequency in a visual spectrum. Among the fluorescent materials
used are zinc orthosilicate, calcium tungstate and zinc sulphide.
The intensity of light emitted from screen of CRT is called
luminance.
4 GLASS BODY AND BASE
The whole assembly is protected in a conical highly evacuated
glass housing through suitable support’s. The inner walls of CRT
between necks and screen are usually coated with a conducting
material known as aquadag and this coating is electrically
connected to the accelerating anode. The coating is provided in
order to accelerate the electron beam after passing between the
deflection plate.
WORKING OF CATHODE RAY TUBE
1 ELECTRON GUN ASSEMBLY
It is used for producing a strain of electrons.The electrongun
assembly consists of an indirectly heated cathode,
A control grid surrounding the cathode, a
Focusing anode and an accelerating anode.
The solo function of it is to provide a focused electron beam which
is accelerated towards the phosphorus screen. The rate of emission
of electrons or say intensity depends on magnitude of
Cathode current which is cantrolled by
the control grid.
2 DEFLECTION PLATE ASSEMBLY
The electron beam passes through the two pairs of deflection
plates. One pair of deflection plate is mounted vertically and
deflects the beam horizontal and called horizontal deflection
plate. And the other pair mounted horizontally deflects beam in
vertical direction and therefore is called vertical deflection
plate.The electron beam will be deflected to left or right of the
tube axis according to the conditions that whether the plates are
charged.
3 SCREEN FOR CRT
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Heater element is energized by alternating current to obtain high
emission of electron from cathode. Control grid is biased negative
with respect to cathode it controls the density of electron beam to
focus the electron beam on the screen focusing anode is used. the
focusing anode operate at a potential of twelve hundred (1200 V)
and accelerating anode at 2000 V to accelerate the electron beam.
Two pairs of deflection plates provided in the CRT these
deflection plates are mounted at right angle to each other to
provide electron beam deflection along vertical and horizontal
axis of the screen. The screen consists of a glass which is coated
by some florescent material lie zinc silicate. Which is
semitransparant phosphor substance. When high velocity electron
beam structs the phosphorescent screen the light emits from it.
The property of phosphor to emit light when its atoms are excited
is called fluorescence.
An electron beam source and beam intensity control mechanism.
• One or more accelerating electrodes. These increase the
electron’s velocity so that when the electrons hit the screen they
have enough
energy to ensure appropriate light output from the screen. The
faster the electrons are travelling, the brighter the fluorescence
produced by the screen.
• A focusing section consisting of electric fields that bring the
electron beam to a sharp focus precisely at the screen. Most CRTs
have a
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curved front screen so that the focusing mechanism required by
the television produces a focused beam at the same distance from
the filament, no matter where on the screen the electron beam hits.
• A deflection system consisting of magnetic coils that positions
thebeam to a desired location on the screen or is used to scan the
beam across and down the screen in a repetitive pattern.
• A phosphor screen that converts the kinetic energy of the
electrons in the invisible electron or cathode ray beam into visible
light.
color (red, blue, and green). Examples of monochromatic CRTs
include black and white TVs and old computer terminals.
4. Oscilloscopes, devices used to measure and display voltages,
also use CRT displays. In this case, the persistence of the
phosphor is more important than the color.
5. The CRTs in televisions and computer monitors bend the
electron beams with magnetic deflection, while oscilloscopes rely
on electrostatic deflection.
REFRENCES:-
• A mechanical structure known as the envelope or tube outer that
allows a vacuum state ( the glass tube). This must also provide a
location for electrical connections to the various electrodes, and
must insulate those connections and components from each other.
[1]
[2]
[3]
[4]
[5]
Basics of electronics - J S katre
www.wikipedia.com
www.google.co.in
Electronic and instrumentation – J.B. Gupta.
Albert Abramson, Zworykin, Pioneer Of Television,
University of Illinois Press.
[6] Telefunken, Early Electronic TV Gallery, Early
Television Foundation.
[7] Measurement Systems - McGraw Hill Professional.
[8] Analog circuit design: art, science, and Personalities.
BLOCK DIAGRAM OF CRT
.
APPLICATIONS OF CRT
1. The primary components of a cathode ray tube (CRT) consist
of a vacuum tube containing an electron gun and a screen lined
with phosphors. CRTs are used to produce images.
2. The phosphors in a CRT's screen are the materials that directly
produce the photons generated by the CRT. These phosphors are
struck by incoming electrons from the electron gun, absorb
energy, and then re-emit some or all of that energy in the form of
light.
3. CRT technology used to be common in televisions and
computer monitors. Colour CRTs contain three electron guns
corresponding to three types of phosphors, one for each primary
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