اصطلاحات دوربین مدار بسته

 

CCTV Guide

 

AGC

    

ALC

    

Amplitude

    

Block diagram

CCD

    

Chroma

    

Colour bar signal

    

Camera
Loop-through cable connectors

    

Mistermination

    

Noise

    

PAL

Pixel

    

Scene illumination

    

AC Adaptor

    

Alarm
Input

Angle of View

    

Auto
Electronic Shutter

    

Auto Iris Control

    

Auto Gain
Control

Auto White Balance

    

Back Light

    

Cable

    

CCD

Day&Night

    

DVR

    

Dome Camera

    

Iris

Lens

    

Motion Detection

    

MPEG

    

Outdoor Camera

PTZ Camera

    

S/N
ratio

    

Varifocal
Lens

    

Video
Gain

Auto Pan

    

C-mount

         

AGC(Automatic Gain Control)

This
control is applied to the gain of the video amplifier stage/s
following the
imaging device. It is usually related to ALC in that if the iris
is fully open
and video output is low, the gain of the amplifier stage is increased. So to is
the noise generated by the stage itself and preceding devices
which is then
visible as grain or snow on the screen. As 'useable sensitivity'
indicates the
minimum illumination at which a 'picture' can be discerned amongst
this noise,
it is useful to know the illumination level at which AGC switches
on or off and
how much noise (S/N ratio) you have

 

ALC(Automatic Light Control/auto-iris)

A servo control system applied to the iris of a camera/lens
system to ensure a constant output level from the camera under varying light
conditions by opening/closing the iris as required. This is usually
contained in the lens body for power and video output sample from the camera. Other
systems exist where the servo electronics are contained in the camera and a 4
wire connection is made to the lens.





Amplitude

Normally refers to the magnitude of a signal voltage ie.
the video signal is produced and distributed at an amplitude of one volt peak
to peak (p-p). Can also refer to the peak of a voltage above or below the base
line





Block diagram

Simple diagramatic drawing of a system indicating
its various components - cameras, switchers, monitors etc. - and their
interconnections





CCD

Charge coupled device - Image sensor which is a large scale
integrated circuit containing hundreds of thousands of photo-sites (pixels)
which convert light energy to electronic signals.





Chroma

The
part of the video signal which conveys colour information on the
scene to be
televised. This information is encoded into the video signal ie. not transmitted
in its original form.





Colour bar signal

A test signal
for video systems which when displayed on a colour monitor screen
consists of 8
vertical bars - white, yellow, cyan, green, magenta, red, blue,
black - giving
indication of the systems ability to display colour information
correctly. Many
other types of test signal are used to properly assess a system's performance





Camera

NA camera may produce geometric distortion on a
perfectly scanned monitor if its own deflection circuits are non linear (tube
type camera) or if geometric distortion is introduced by the lens. Low cost
pinhole and wide angle lenses are most notable for this





Loop-through cable connectors



Twin sets of connectors on a switcher or monitor enabling that device to
use that signal without affecting other equipment on the same signal line. A
means of enabling a 75 ohm termination is sometimes provided allowing that
equipment to be at the end of the transmission line and to terminate it, or to be at some
mid point in the line and represent a high impedance to the signal.





Mistermination

The incorrect
signal level resulting when a transmission line is not terminated
by its characteristic
impedance





Noise

Noise in a video signal, the grainy or snowy effect on the
displayed picture. Noise in a picture can have a great number of causes but is commonly
apparent when the camera is working in very low light levels with its
amplifiers at maximum gain.





PAL

A colour encoding/transmission system developed largely by
Walter Bruch of Telefunken. PAL stands for Phase Alternate Line. In the PAL
encoding system, colour information is represented by a sub carrier which has a
particular amplitude and phase relationship to the reference burst signal, depending
on the colour to be transmitted. Every second line, the phase of the signal is
reversed by 180 degrees and by virtue of the decoder processes in the PAL
system, any phase or amplitude errors introduced by the transmission path are
averaged out and minimised. In Australia, we use a variant of the PAL transmission
system as classified by the CCIR. PAL B is used on both VHF and UHF terrestrial
transmissions.



Pixel

The microscopic
photo-sensitive sites on a CCD image sensor of which there are
hundreds of
thousands.



Scene illumination

The amount of light incident to a particular scene and measured in lux
although sometimes foot-candles are stated. Lux values are nearly 10 times the value in
foot-candles. The luminous intensity of a light source is measured candelas (cd)
and the amount of light that will fall upon an object is dependant upon the
intensity of the illuminator and the distance of the object from it as in the
formula lux = cd---d2 where d2 is the distance in meters between source and object.



AC Adaptor

This is also called a power supply.? CCTV devices need
power in order to run.? Each device has its own power requirements (usually 12
volts.)? The power coming out of the wall(in the USA)is 110 to 120 AC.? The AC
adaptor converts the AC to DC powera and will adjust it to a specified amperage.



Alarm Input

An input connection to a security VCR or CVR that
triggers the unit to start recording the images if the alarm is triggered



Angle of View

When referring to security cameras, this refers to the angular
range in degrees that
you can focus the camera on without distorting?the image.??When focusing close
up, you can generally see a wide angle of view. If the focus is distant, the
angle of view is narrower



Auto Electronic Shutter

The
ability of the camera to compensate for moderate light changes in
indoor applications
without the use of auto iris lenses



Auto Iris Control

lens which the
aperture automatically opens or closes to maintain proper light
levels on the
faceplate of the camera pickup device



AGC(Automatic Gain Contol)

An
electronic circuit used by which the gain of a signal is
automatically adjusted
as a function of its input or other specified parameter



Auto White Balance

A color camera
feature that constantly monitors the light and adjust its color to
maintain white areas



Back Light Compensation

A feature on newer CCD cameras which electronically compensates for
high background lighting to give detail which would normally be silhouetted



Cable

The
wiring used to connect electronic devices. Cables transmit
different kinds of
signals such as video, power, data, and audio



CCD

Charged-coupled device. It was first invented in the 1970's,
this technology uses a shift register combined with photodiodes to create the
modern day imaging device. Used in cameras, scanners, and fax



Day&Night Camera

Regular cameras with an especially sensitive CCD chip that allows a good image to
be captured in very low ambient lighting.? These are not to be confused with
NIGHT VISION cameras



DVR(Digital Video Recorder)

A DVR
is basicallya computer that converts the incoming (analog) signal
from the cameras to
digital, and then compresses it, and stores it. The DVR replaces the function of a
multiplexor (quad or switcher)and security VCR



Dome Camera

A camera with a domed shape.? This type of camera is
usually used inside of the premise.? Some come with infrared lighting and some
are designed to be tamper-proof



Iris

The iris (on some lenses) controls how much light is let
into the camera lens



Lens

The lens of the camera determines the angle of view and
the focus of the captured image



Motion Detection

Feature of some
VCRs and DVRs to only record video if something in the image moves
or changes.
Therefore you don't have to look through hours of taped video
looking for
something to happen.? It also saves a lot of space on the tape or
hard drive



MPEG

Motion
Picture Experts Group who designed the standard.? This is a
standard way of
compressing audio and video files



Outdoor Camera

Come in special
weatherproof housings that allow them to stand up well in tough
weather and
temperature conditions



PTZ(Pan-Tilt-Zoom) Cameras

PTZ
cameras allow you to adjust the position (pan is side to side,
tilt is up and
down) and focus (zooming in) of the camera using a remote
control.? Due to this
added function, these cameras tend to cost much more than non PTZ? models



S/N ratio

Signal
to noise ratio.This number represents how much signal noise the
camera can tolerate and
still provide a good picture.? The higher the number the better



Varifocal Lens

Camera lens in which the focus is not fixed, it can be manually or automatically
adjusted



Video Gain

An increase in video signal power by an amplifier, expressed as
the ratio of output
to input. Also known as amplification



Auto Pan

Automatic back and forth camera motion



C-Mount

Former industrial standard lens mounting format

 

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[تهران]
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