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CCTV Guide
 
   
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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