Technical notes
Monitors

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In this page you can find the main terms used when specifying monitors,
 useful to select the more suitable product for your application.
 Our technical service will be glad to help you, in case further clarifications will be needed.

Selection table for monitors

Monitor sizeRecommended viewing distance (CCIR standard)
9" (23cm)0.9m
12" (31 cm)1.2m
14" (36cm)1.6m
17" (43cm)1.8m
21" (53cm)2.2m
How does a monitor operate?

Monitor converts the video signal generated by the camera into a visual display image. It consists of a cathode ray tube (CRT) and in some signal processing circuitry.

The CRT is matched at his back with an electronic gun generating a beam of electrons. The electronic beam scans progressively the CRT surface screen. Because the beam strenght is proportional to the video signal level, it restores the picture image on the monitor screen.

In a black/white monitor the signal processing circuits separate the luminance component from the sync signal. Luminance signal is then amplified while the sync signal is splitted in an horizontal (H)and in a vertical (V) sync signal. Both sync signals, after being amplified, are used to control the horizontal and vertical deflection of the electronic beam.

In a colour monitor there are three different electronic guns one for each of primary colours, red, green and blue. The composite video signal has a further chorominance component, besides the luminance and sync components.

Resolution

It is the monitor ability to show details on the screen. The higher is the resolution, the sharper will be the picture details. The resolution value generally shown is the horizontal resolution measured in TV lines. However, differently from cameras its value refers to the center of picture where resolution is higher. In black/white monitors a typical value for resolution is around 700-800 lines, while for colour monitors the standard resolution is normally much lower, i.e. around 350 TV lines.

Linearity

Scanning is not linear at edges and corners of monitor screen and horizontal and vertical lines appear to be bent. Linearity value shown in  monitor specifications is the percentage of this distortion. The smaller is the percentage value shown, the less the picture will be distorted by non linearity and the better thus is the monitor.

Impedance

In order to operate correctly, a monitor (when being the terminal element of the system) must have the same impedance value as the camera and the transmission cable, i.e. 75 ohm. However when other monitor are connected together and the video signal is looped in the next monitor,  only the terminating monitor must have a 75 ohm impedance, while the intermediate monitors must have a high impedance to avoid picture distortions.A switch allows impedance setting between the two values.

Standards

There are presently two different standards in the world:  CCIR (625 lines, 50 Hz) used in Europe and  EIA (525 lines, 60 Hz) used in the USA and in Japan.

Scanning

Scanning of monitor is interlaced: at first odd lines are scanned (1,3, 5 ...) producing one field; then, even lines are scanned creating a second field. Thus, a complete frame of video picture is made of two fields. In this way, the scanning speed is doubled: the display is scanned at a rate of 50 cycles per second (60 with EIA standard), but only 25 frames per second are actually acquired, without any noticeable flickering effect. This is due to the persistence properties of the human eye.

Go to monitors index

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Last modified 10-05-2013
 
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HOME PAGE ENGLISH
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INFO
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SEARCH
 
PRODUCTS RANGE
Security
Surveillance cameras
CCTV lenses
Digital Video Recorders
Monitors
IR and white light lamps
Video signal control devices
Pan & tilts
Housings
Machine vision
Industrial cameras
Machine vision lenses
Lighting for machine vision
Other products
Photographic and medical printers
DISCONTINUED PRODUCTS DATA BANK
 
TECHNICAL NOTES 
Optical calculator
 
HOME PAGE ENGLISH
COMPANY PROFILE
HOT NEWS
OFFERS
INFO
MAILING LIST
SEARCH
 
PRODUCTS RANGE
Security
Surveillance cameras
CCTV lenses
Digital Video Recorders
Monitors
IR and white light lamps
Video signal control devices
Pan & tilts
Housings
Machine vision
Industrial cameras
Machine vision lenses
Lighting for machine vision
Other products
Photographic and medical printers
DISCONTINUED PRODUCTS DATA BANK
 
TECHNICAL NOTES 
Optical calculator