CRT Monitors

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16 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

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CRT Monitors


Stands for Cathode Ray Tube


The first cathode ray tube scanning device was invented
by the German scientist Karl Ferdinand Braun in 1897
.



The first commercial computer equipped with a CRT
monitor was Digital Equipment's PDP
-
1 from 1959.


The dot pitch (Spacing between each pixel of the same
colour) is typically 0.24mm


60Hz to 100Hz



Phosphor is generally a fluorescent substance coated
on the front of the screen which glows when struck by
electron beams


Black and White monitor


Use white pixels


Made up of one phosphor


Colour

monitor


Uses three primary
colours
: Red; Green; and Blue (RGB)


Made up of three phosphors, so close that the human
eye sees the image as one single pixel


Black and White/Coloured
Monitors

CRT Operation

CRT operation (1 of
2)


Electron gun generates an electron beam


The yoke is an electromagnet. Varying the magnetism
in the yoke causes the electron beam to focus in
particular areas of the screen


The shadow mask is a metal screen with holes in it.
The metal blocks the electron beam but the holes will
let the electron beam through when it will strike a
pixel, and only one pixel. Makes sure the image is
sharp


The phosphor screen is made up of the phosphors that
glow when hit by the electron beam. An image is
formed by turning on some phosphors but not others.


CRT operation (2 of 2)


The electron beam sweeps over the phosphor
screen, making some phosphors glow, so fast that
the user sees a stable image on the screen.


Other components such as the panel glass, funnel
glass and the inner magnetic shield provide the
structure of the CRT


Types
of pixel shapes


Triad


Three electron guns arranged with
overlapping circles in a triangle


Circular holes in shadow mask


Used in smaller screens (e.g.
monitors)


Trinitron


Three electron guns arranged in one
line


Three parallel slots


Oval slots in shadow mask


Used in large screens (e.g. televisions)


Interlaced Video


Only CRT
and
ALiS

plasma
displays are capable of displaying
interlaced signals, due to the
electronic scanning and lack of
apparent fixed
-
resolution
.


Image on screen is created in two
halves


First the odd numbered lines then
the even numbered lines


Cheaper


Produce a flickering image and
jerky video motion


Mostly found on older PC
monitors


Non
-
interlaced Video


Entire screen is created in one go


Less flicker


Smoother video motion


More commonly found


Produces a higher quality image

Radiation


Whenever an electric current passes through a conductor
(such as a wire or a copper track on a circuit board) it gives
off an electro magnetic field


The electron gun, electromagnet and coil inside a CRT
monitor produce magnetic fields that radiate from the
monitor


Most of this radiation is exposed from the rear of the
monitor


The amount of radiation escaping the front of the monitor
is widely considered
unharmful

References


http://
www.bit
-
tech.net/hardware/2006/03/20/how_crt_and_lcd_mo
nitors_work/2


http://
www.ehow.com/how
-
does_4965497_crt
-
monitor
-
work.html


http://
www.theavguide.co.uk/view_page.php?page=2