Glossary of terms
Auto-terminating
Feature whereby the equipment automatically selects the correct termination depending on whether the video output BNC is connected.
Auto White Balance
Feature on colour cameras whereby the camera constantly monitors the light and adjusts its colour to maintain white areas.
ATM (Asynchronous Transfer Mode)
A high-speed cell-switching network technology that handles data and real-time voice and video. ATM is defined in the Broadband ISDN (BISDN) standard and provides "bandwidth on demand" by charging customers for the amount of data they send. Data rates are scalable, starting as low as 2.048 Mbps with intermediate speeds of 25,51 and 100 Mbps, to high speeds of 155,622 Mbps and up into the gigabit range.
Asynchronous Transmission
Transmission in which time intervals between transmitted characters may be of unequal length. Transmission is controlled by start and stop bits at the beginning and end of each character. Compare with synchronous transmission.
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 decrease barrel distortion on wide angle lenses.
Archive
Long term storage of digital files to a removable media. At this time DAT is the most common media for archiving of digital recordings.
Aperture
The ‘opening’ of a lens, a measure of its light gathering capability. Relative Aperture is a ratio between its focal length and effective aperture, measured in F numbers, generally the lower the better.
Anti-Passback
An arrangement where the software flags a card as either 'in' or 'out' when it is used at designated readers. Anti-passback can be either local or global i.e. per controller or per system. Anti-passback can also be timed.
Angle of View
This is what alters (not the focal length) when you use a lens designed for one format on another format. It decreases with format size.
Analogue
A signal in which any level is represented by a directly proportional voltage; not digital.
Ambient Light Level
Background or general light level of a given area.
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.
Alarm Bypass Relay
A relay in the controller that is used to shunt or bypass the door alarm contacts of a central alarm system to allow authorised access without causing an alarm.
AIT2 (also see AIT)
Second generation “Advanced Intelligent Tape” drive, with a larger memory capacity of 50Gb native.
AIT (also see DDS3/DDS4)
Advanced Intelligent Tape. First generation tape drive that will replace DDS technology. AIT has several advantages over DDS drive range: 30,000 tape passes; regular head cleaning not required; larger memory capacity - 20Gb or 35Gb native. An in-built memory chip (MIC) to increase the speed of data searches.
Ah
Ampere hours. e.g. 1A for 6 hours = 6Ah. Always de-rate the battery capacity by 66%
ADSL (Asymmetrical Digital Subscriber Line)
A telephone line with uneven transmission rates; half the transmission can attain speeds up to 640 kbps; the other half can attain speeds of 2.048 Mbps or greater in the opposite direction.
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.
Access Authorisation
Permission granted to a card number enabling the cardholder to enter a location based on a programmed time schedule.
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 detail in shadows.
A.I. (Auto Iris)
An electronic circuit fitted to the iris of a lens to help compensate for large changes in light levels.
A.G.C. (Automatic Gain Control)
An electronic circuit that tries to keep signals at a constant level; more useful in cameras at low light levels. The higher the number the better, typical values 12 - 20dB i.e. a gain of approx 4x - 10x.
