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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.
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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. |
