LOW VOLTAGE SYSTEMS
CHAPTER 15.1
TELEVISION
By
Dinesh Kumar Sarda

WHO INVENTED TELEVISION ???
Electronic television
was first successfully
demonstrated in San
Francisco on Sept. 7,
1927. The system
was designed
by Philo Taylor
Farnsworth, a 21-
year-old inventor
who had lived in a
house without
electricity until he
was 14.

Pixel
it is the smallest
controllable element of a
picture represented on the
screen.
The image that is displayed on
the screen is composed of
thousands (or millions) of small
dots; these are called pixels; the
word is a contraction of the
phrase "picture element".

Aspect Ratio
The aspect ratio of the image is the ratio of
the number of X pixels to the number of Y
pixels.

Resolution
The number of pixels that can be displayed on the
screen is referred to as the resolution of the image
It is the number of distinct pixels in each dimension
that can be displayed.
It is usually quoted as width × height, with the units
in pixels: for example, "1024 × 768" means the
width is 1024 pixels and the height is 768 pixels.

TV IS MADE OF ???
CATHODE
RAY TUBE

CATHODE RAY TUBE(CRT)
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. The image may represent
electrical waveforms (oscilloscope), pictures
(television, computer monitor), radar targets
and others.

BASIC CATHODE RAY TUBE
The CRT uses an evacuated glass envelope which is
large, deep, heavy, and relatively fragile

BASIC WORKING OF CRT
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.

PHOSPHORESCENCE
Phosphorescence is emission of light from a
substance exposed to radiation and persisting
as an afterglow after the exciting radiation has
been removed

PHOSPHEROUS PERSISTENCE
Various phosphors are available depending upon the
needs of the measurement or display application. The
brightness, color, and persistence of the illumination
depends upon the type of phosphor used on the CRT
screen. Phosphors are available with persistence's
ranging from less than one microsecond to several
seconds. For visual observation of brief transient
events, a long persistence phosphor may be desirable.
For events which are fast and repetitive, or high
frequency, a short-persistence phosphor is generally
preferable.

ADAVNATAGES OF CRT
1.The cathode rayed tube can easily increase the monitor’s
brightness by reflecting the light.
2.They produce more colours
3.The Cathode Ray Tube monitors have lower price rate than the
LCD display or Plasma display.
4.The quality of the image displayed on a Cathode Ray Tube is
superior to the LCD and Plasma monitors.
5.The contrast features of the cathode ray tube monitor are
considered highly excellent.

DISADVANTAGES OF CRT
1.They have a big back and take up space on desk.
2.The electromagnetic fields emitted by CRT monitors constitute a health hazard to the functioning of living
cells.
3.CRTs emit a small amount of X-ray band radiation which can result in a health hazard.
4.Constant refreshing of CRT monitors can result in headache.
5.CRTs operate at very high voltage which can overheat system or result in an implosion
6.Within a CRT a strong vacuum exists in it and can also result in a implosion
7They are heavy to pick up and carry around

THANK YOU...