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Access control system:
an electronic system that allows, restricts and tracks the movement of
people through entry/exit points in a site. Programmable electronic
keys, cards etc. with readers are used to achieve this. |
AGC Automatic Gain Control:
is circuitry in a camera which boosts the video signal (including the
noise). It becomes operational when the light level is low. |
Alarm interface:
is a facility which allows external alarms like PIR's, reed switches,
vibration sensors etc. to be connected to the CCTV switcher so that a
nominated camera is switched on when an alarm signal is received. |
ALC Automatic Light Compensation:
is a setting in an auto iris lens to control the iris opening. It can be
adjusted between peak and average to respond to the bright part of the
scene (peak setting) or the average value of the video signal (average
setting). |
Algorithms:
are complex mathematical formulae or rules used to solve problems. In
CCTV, they are used to achieve digital compression of a video picture. |
Alkaline battery:
is a type of DC power source with a longer life compared to the standard
battery. It cannot be recharged. |
Amplitude:
refers to the strength of the video signal at a point and is measured in
volts. |
Angle of refraction:
is the angle of bending of light when it travels from one medium into
another. |
Angle of view:
represents the area of the scene (maximum horizontal and vertical angle)
that can be seen through a lens. It is measured in degrees. |
Aspect ratio:
is the ratio between the horizontal and the vertical lengths of the
video picture. The aspect ratio for NTSC and PAL systems is 4:3. |
Audible detector:
is a device which detects sound. In CCTV, it can be interfaced with a
switcher so that a nominated camera is switched on when the detector is
activated. |
Audio switching:
is a device which can switch between various audio inputs either
manually or sequentially. Many matrix switchers incorporate this
feature. |
Auto balance:
is a system of detecting and automatically correcting errors in the
amplitude of colour signals. |
Auto iris:
is a diaphragm which is inbuilt in a lens to automatically control the
amount of light falling on the chip. The tiny motors in the lens open or
close the diaphragm, depending upon the amplitude of the video signal. |
Automatic pan:
is a feature of a pan tilt or pan only head which allows the head to
continuously move (pan) left and right between two fixed points. These
fixed points can be set by adjusting the limit switches in the head. |
Attenuation:
is a reduction in the strength of light or an electrical signal and is
usually measured in decibels. |
Average video signal:
represents the average light level of the whole picture used to open or
close the automatic iris in the lens. |