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CCTV Glossary

The following is a list of commonly used terms related to CCTV, with a brief description of the meanings. These terms are not specific to Bolide Technology Group, they are general terms used throughout the CCTV industry. If you don't find the term you are looking for, or you find any error, please contact us.

A B C D E F G H I J L M N P R S T V W

Automatic Gain Control (AGC)
This is a feature of many CCTV cameras that helps keep 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 levels.

Auto Iris (AI)
Cameras with an Auto Iris feature, have the ability to compensate for large variations in light levels. 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 motorised 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 then simply using electronics to reduce the signal strenth.

Alarm Input
Some cameras and video servers have the ability to accept alarm inputs. These are inputs from standard sensor devices such as, Passive Infra-red (PIR) detectors, door contacts, active beams etc. or relay outputs from intruder alarm panels, or access control panels. Alarm input circuits can come in a number of forms. Most commonly they are self powered, so will operate with a passive switch style circuit. However, in some cases, they expect to be provided with power (normally 12V) as the signal of open or closed. In a few cases manufactures only supply TTL (very low voltage) level inputs. In that case, they can only be safely used with normal alarm sensors in conjunction with some additional isolation circuitry. In this case, it is best to contact the manufacturer for advice.

Ambient Light Level
This refers to the amount of background light in any given situation.

Analogue Signal
Most CCTV cameras, although internally working with digital components, produce a standard analogue signal. This is where the image is represented by a variable voltage level and frequency timings. In the UK and Europe, the standard for the analogue signal output from CCTV cameras is called PAL. In the USA, the standard used is called NTSC.

Aperture
The aperture of a lens, is the area that allows the light to pass into the lens. Lenses with large apertures allow more light in than lenses with small apertures.

Aspect Ratio
This is the ratio between the the height and width of an image.

Automatic Level Control (ALC)
This is a feature of some cameras, that allows the camera to either bring out detail in bright areas of the image, or bring out more detail in the darker areas, depending on how it is set up. This is often useful where the view has a window in the background, where the sunlight is causing the image of the room to be much darker than required.

Automatic Terminating (Auto-terminating)
Video signals are normally transmitted along co-axial cable, which require a terminating resistor at either end. If the signal is looped through a piece of equipment that has an input and an output, then it should be terminated if it is the final piece of equipment, but not terminated if it is in between other equipment. Some appliances have a manual switch for this setting, other equipment automatically detects if termination is required and applies the additional resistor as necessary.

Automatic White Balance
This is a feature of some cameras that automatically adjusts the colour settings to maintain the quality of the white areas of the image.