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Common CCTV Terminology
Common CCTV Terminology
Common CCTV Terminology & Frequently Asked Questions
Automatic Gain Control (AGC)
Keeps the strength of the output signal constant, even when the light level changes. In other words, it boosts the signal strength at low light levels and caps it at higher light levels.
Automatic Iris (AI)
The ability to compensate for large variations in light levels which is particularly useful for cameras that need to compensate for changes from bright sunlight to dark shadows. The auto iris circuitry is normally linked to a motorized iris drive that physically opens and shuts the iris on the lens. Closing a physical iris is a much better way to protect a camera from being damaged by bright sunlight than simply using electronics to reduce the signal strength.
Automatic White Balance (ATW)
Automatically adjusts the color settings to maintain the quality of the white areas of the image.
Back Light Compensation (BLC)
Automatically adjusts the image to compensate for bright sunlight or bright lights to give more detail on the darker areas of the image.
An accessory which enables the transmission of video using unshielded twisted pair wire instead of coaxial cable by transforming an unbalanced signal into a balanced signal. When video signal is transmitted through coaxial cable, the distance traveled by the signal is limited because the signal is in the form of an unbalanced signal that is susceptible to Radio Frequency Interference or noise. Coax cable incorporates special shielding to minimize noise while Video Baluns transform the video signal into a balanced form in which each wire in the twisted pair transmits an identical signal with opposite polarized magnetic fields. Noise affects each signal equally. When the signals are combined, the noise is cancelled out. By using a balun, an unshielded twisted pair wire can transmit video for much longer distances than coax cable and with a lower cable cost.
A bayonet style connector for coaxial cable that is most commonly used for CCTV installations.
Charge Coupled Device (CCD)
One of the two main types of image sensors used in security cameras. When a video is recorded, light that come through the camera's lens is converted from light into electrons by the CCD. The number of electrons is then measured and converted to a digital value.
A type of cable typically used in CCTV installations that has a central conductor, surrounded by a shield which can be made of various metallic material such as copper, sharing the same axis. There are various standards for different types of co-axial cable. The cable used for normal CCTV installations is called RG59 or RG6.
Digital Video Recorder (DVR)
A DVR is a device that is similar to a VCR but records television data in digital on a hard drive as opposed to a VCR tape. A DVR has all of the same functionality of VCR (recording, playback, fast forwarding, rewinding, and pausing) plus the ability to skip to any part of the program without having to rewind or fast forward the data stream.
The distance between the center of a lens, or its secondary principal point and the imaging sensor. Lower lengths give a greater field of view and less magnification. Longer lengths give a narrower field of view and greater magnification.
IP Network Camera
A camera that is designed to record and transmit the images that are encoded in one of the standard compression techniques, such as MPEG4, MJPEG or H.264, through a network or internet connection to allow for remote viewing and monitoring. Network cameras normally do not have any analogue video outputs.
Low frequency light below the visible spectrum to the human eye. This is often used for covert or semi-covert surveillance to provide a light source for cameras to record images in dark or zero light conditions. Infrared is produced by LEDs (Light Emitting Diodes).
Measuring unit used to indicate the amount of light striking a surface, that is, the luminous flux density at a surface. The lower the LUX rating of a camera, the better the camera will see in a dimmer environment.
On Screen Display (OSD)
A method of displaying set-up information and/or instructions on a display monitor.
Television Lines (TVL)
Measuring unit used to decipher the resolution quality of a video device. Higher TVL means higher resolution. 380 TVL is considered as medium resolution; 480 TVL or greater is considered as high resolution; and 560 TVL is considered as ultra high resolution.
Type of lens that allows adjustment of the magnification and field of view of the camera through its capability to change its focal length.
CCTV FREQUENTLY ASKED QUESTIONS
Question: What is the difference between 1/4” and 1/3” Charged Coupled Devices (CCD’s)?
Answer: 1/4” and 1/3" are both common sizes of CCD’s. The difference is that the larger the CCD the more sensitive the device is to light and that it provides a wider angle of view.
Question: What are the benefits of using a Varifocal Lens over a Fixed Lens?
Answer: Varifocal Lens often makes installation of cameras much easier as Fixed Lens requires an installer/user to have an accurate and precise knowledge of the field of view; whereas, with the Varifocal Lens, the installer/user can adjust the focal length to achieve the desired field of view.
Question: What is a “Sony Super HAD”?
Answer: Sony Super HAD is a leading type of charged coupled device (CCD) that is used for CCTV cameras made by Sony. The image quality of Sony CCD’s is generally very high.
Question: What are Infrared LED’s used for?
Answer: Infrared (IR) LED’s are used in conditions where there is no light or very low and limited lighting. IR’s light up the area covered by the camera with lighting that is invisible to the human eye, yet is clearly seen through the CCTV cameras.
Question: What is Resolution?
Answer: Resolution is measured in Television Lines (TVL). Usually the higher the TVL means the higher resolution which means the image would be clearer and sharper.
Question: What is X-Y-Z bracket?
Answer: X-Y-Z brackets allow dome cameras to be installed sideways on a wall without having the video to look like it is sideways; therefore, eliminating the need to install a separate wall mount with the camera.
Question: Can a Bullet Camera be used or installed in indoor environments?
Answer: Yes, Bullet Cameras may be used or installed in both indoor and outdoor environments.
Question: What is a Multiplexer?
Answer: Multiplexers allow the input of more than one camera to display on one monitor. They might have other functions such as motion detection and can output up to 16 cameras at once on one screen.
Question: What are the benefits of 24VAC over 12VDC?
Answer: When using 24VAC, the voltage drop is less severe than 12VDC; therefore, allowing for better power stability when cameras are installed at further distances from the power source. Also many GSI cameras that run on 24VAC have built-in “Line-Lock” which helps prevent picture rolling on the monitors. “Sync” pulses are emitted from the cameras to allow a video monitor to synchronize the picture on the screen.
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