CCTV Glossary of Terms "A"

A.L.C. (Automatic Level Control)

On AI lenses, also known as the peak/average control. Adjusting this control allows the auto iris circuitry to either take bright spots more into consideration (peak), bringing out detail in bright areas, or less into consideration (average) bringing out

Activity Detection

A feature of the Generation 3 video multiplexer range that uses video motion detection techniques to improve the camera update times. It also gives a relay closure.

Alarming

The ability of CCTV equipment to respond to an input signal, normally a simple switch closure. The response varies depending on equipment type, most common is for switcher to ‘hold’ on the camera corresponding to the alarm input.

Analog

A signal in which any level is represented by a directly proportional voltage; not digital.

Angle Of View

The maximum scene angle that can be seen through a lens.

Aperture

The lens opening that controls the amount of light reaching the pickup device (imager).

Aspect Ratio

The ratio of the picture frame width to the picture frame height in standard TV systems. It is 4 units horizontal over 3 units vertical.

Aspherical Lens

A lens designed with a non spherical shape so that it refracts the light passing through it to either lower the lens aperture so that it passes more light or decreases barrel distortion on wide angle lenses.

Attenuation

A decrease or loss in a signal. Reduction of signal magnitude (loss) normally measured in decibels.

Auto White Balance

Feature on color cameras whereby the camera constantly monitors the light and adjusts its color to maintain white areas.

Automatic Frequency Control (AFC)

An electronic circuit used whereby the frequency of an oscillator is automatically maintained within specified limits.

Automatic Gain Control (AGC)

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

Automatic Iris Lens

A lens in which the aperture automatically opens or closes to maintain proper light levels on the camera's pickup device.

Auto-Terminating

Feature whereby the equipment automatically selects the correct termination depending on whether the video output BNC is connected.