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A
Access Card – A coded card, about the size of
a credit card, that grants a user access to a particular
area or building—usually by being submitted to a card
reader. It can also be used for photo identification of
the cardholder and for other data collection purposes. Card
technologies include magnetic strips, Wiegand-effect, proximity
(active/passive), barium ferrite, and smart/intelligent
cards.
Access Code – A code that’s entered manually
on a keypad to give an individual access to a particular
area through a door or gate in an access controlled system.
Access Level – The door or combination of doors
and/or barriers an individual is authorized to pass through.
Access Relay – An electrically operated switch
that is activated to unlock a door.
Access Time – The amount of time that an access
door is unlocked for entry.
Alarming – The ability of CCTV equipment to
respond to an input signal, normally a simple contact closure.
The response varies depending on equipment type.
Amplifier – Electronic system used to boost,
or increase, the gain of signals.
Amplitude Distortion – An unwanted change in
signal amplitude.
Analog-to-Digital Converter – A device that
converts incoming analog signals into digital information.
Angle of View – The angular range that can be
focused within the image size. Small focal lengths give
a wide angle of view, and large focal lengths give a narrow
field of view.
Annunciator – An audible and/or visual signaling
device that gives notice of a door being open.
Aperture – The opening of a lens, which controls
the amount of light reaching the surface of the pickup device
(CCD). The size of the aperture is controlled by the iris
adjustment. By increasing the f-stop number (f1.4, f1.8,
f2.8, etc.), less light is permitted to pass to the pickup
device.
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.
Attenuation – The loss of signal strength as
it flows through a cable. Usually expressed in decibels
(dB).
Audit Trail – A listing that may be used to
monitor the progress of a person through protected areas.
Can be created in real time.
Authentication – Verification of a user’s
identity when the user logs onto a network.
Automatic Frequency Control (AFC) –
An electronic circuit used in which the frequency of an
oscillator is automatically maintained within specified
limits.
Automatic Gain Control (AGC) – An electronic
circuit in 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
opens or closes automatically to maintain proper light levels
on the faceplate of the pickup device (CCD).
Automatic Level Control (ALC) – Assigns the
amplifier’s output level automatically to ensure a
consistent paging level. It keeps loud voices from booming
out of the paging system’s speakers and enables people
with weak voices to be clearly heard. It also makes it easier
to understand people in noisy environments.
Auto White Balance – A feature on color cameras
that constantly monitors the light and adjusts its color
to maintain white areas.
AWG (American Wire Gauge) – A method of measuring
wire-conductor diameter. The number refers to the number
of steps involved in drawing the wire. The more a wire is
drawn or sized, the smaller the diameter is. For example,
24 AWG wire is smaller than 19 AWG wire.
B
Back Focal Distance – The distance from the rear-most
portion of the lens to the image plane.
Back Light Compensation (BLC) – A feature on newer
CCD cameras that compensates electronically for high background
lighting to give detail that would normally be silhouetted.
Badge – To use a card key in a reader to gain
access to protected areas.
Balun – A device used to match or transform an
unbalanced coaxial cable to a balanced twisted-pair cable.
Bandwidth – A measure of the carrying capacity
of information over a network. Video, for example, takes more
bandwidth to transmit over a network than text does.
Baseband – The frequency band occupied by the
aggregate of the signals used to modulate a carrier before
they combine with the carrier in the modulation process. In
CCTV, the majority of signals are in the baseband.
Bend Loss – Increased attenuation in a fiber that
results from the fiber’s being bent or from minute distortions
within the fiber.
Bend Radius – A measurement of a cable’s
flexibility, it’s the radius of the smallest circle you
can form with the cable without damaging it.
Biometrics – Refers to readers that identify human
attributes such as fingerprint, hand geometry, voice recognition,
or retinal analysis.
Black Level – The level of the video signal that
corresponds to the maximum limits of the black areas of the
picture.
BNC (Bayonet-Neill-Concelman) – A commonly used
connector for coaxial cable. After insertion, the plug is
turned, tightening the pins in the socket.
Boot Sector Viruses – Computer viruses that infect
the boot sector on a floppy disk or the Master Boot Record
(MBR) on a hard drive by overwriting the original boot code
with its own code. The boot sector, or MBR, generally resides
on the first sectors of a hard disk and controls the boot
sequence when a computer is started up. A virus that infects
the these sectors is especially dangerous because, every time
the computer is started up, the virus is loaded into memory
from where it can spread to other parts of the hard disk or
to another disk. Boot sector viruses frequently cause a complete
system failure in which a PC can’t start up or find its
hard drive.
Broadband – A technique for sending data, voice,
and video traffic over long distances by transmitting high-frequency
signals over coaxial or fiber optic cables.
Buffer Capacity – Refers to the amount of information
the system can store. This may include the users, time of
day, and specific door.
C
CATV (Community Antenna Television or Cable Television)
– A publically or privately owned system that uses coaxial
cable to transmit broadcast television programming received
by a central antenna to subscribers.
CCD (Charged Coupled Device) – A chip that picks
up the image and converts it to an electrical signal.
CCTV (Closed Circuit Television) – A private television
system in which video signals are transmitted over a privately
owned cable.
Candela – In the International System of Units
(SI), the candela is the base unit of measuring luminous intensity.
Candlepower – The unit measure of an incident
light.
Channel Balance – In a stereo system, the level
balances between left and right channels. Properly balanced,
the audio should be centered between the left and right speakers.
Cladding – The plastic or glass sheath that’s
fused and surrounding the core of an optical fiber. It keeps
the lightwaves inside the core and adds strength to it.
Clamping Voltages – The “sustained”
voltage held by a clamp circuit at a desired level.
Coaxial Cable – A type of cable that can pass
a range of frequencies with low loss. It consists of a hollow
metallic shield in which one or more center conductors are
put in place and isolated from one another and from the shield.
CODEC (Code/Decode) – An encoder plus a decoder.
It’s an electronic device that compresses and decompresses
digital signals. CODECs usually perform analog-to-digital
and digital-to-analog conversion.
Composite Video Signal – A signal in which the
luminance and chrominance information has been combined using
one of the coding standards: NTSC, PAL, SECAM, etc.
Conditional Refresh – A technique used in slow
and fast scan transmission equipment, where only small screen
changes are transmitted. Up to a certain percentage of the
on-screen picture can be updated before a full picture update
is required.
Control Panel – A set of utilities that change
various aspects of the system’s behavior, such as the
color of the background, the port to which printer data is
sent, the speed of the mouse cursor, etc.
Crosstalk – Signal interference from one cable
pair to another pair (or other pairs) in the same cable sheath.
Cycles per Second – The frequency of an electrical
signal or soundwave. Measured in Hertz (Hz).
D
Database – A collection of data used and produced
by a computer program. The files created at the host of
the access control system forms its database.
Data Encryption Standard (DES) – An encryption
technique that scrambles data into an unbreakable code for
public transmission.
Decibel (dB) – A measure of the power ratio
of two signals. It is equal to ten times the logarithm of
the ratio of the two signals.
Demilitarized Zone (DMZ) – A separate network
used to isolate public services from your private network.
Both users from the Internet and users from the secure network
may access servers in the DMZ. Traffic may not travel from
the Internet or the DMZ directly to the secure network without
first going through a proxy server (usually a firewall).
Denial-of-Service – Attacks that bombard a Web
server with more requests for connections than it can handle,
causing it to become so slow as to be unusable or even crash
entirely.
Depth of Field – The front-to-back zone in the
field of view that is in focus in a televised scene. With
a greater depth of field, more of the scene is in focus.
Digital Certificates – An electronic document,
provided by a trusted third party, made up of a public key,
digital signature, owner identity, serial number, issuer,
and expiration date. Used in private and public key encryption.
Digital Disc Recorder – A system that enables
recording of video images on a digital disc.
Digital Signature – An electronic code that
is unique and virtually impossible to copy or transfer.
Distortion – The unwanted changes in signal
or signal shape that occur during transmission between two
points.
Distributed Intelligent Device – An access control
device that makes its own access decisions, uploads event
messages periodically, and periodically saves this information.
Distribution Amplifier – A device that accepts
a signal and sends it out to a number of independent outputs.
Door Open Time – The time allowed for a controlled
door to remain open after a valid entry.
Duplex – To perform two functions simultaneously.
For example, a DVR can record video while playing back video
at the same time.
DVI (Digital Visual Interface) – A connector
that provides bandwidth needed for devices as well as plenty
of headroom for the future. (See DVI-D and DVI-I.)
DVI-D – Digital-only connector.
DVI-I – Supports both digital and analog connections.
Dwell Time – The length of time a switcher holds
on a camera before moving on to the next camera.
E
Electronic Access and Control – Used to control
who is allowed into an area of a building, the building itself,
or even a campus. It can also control when access is allowed,
and it can track when and where each user enters. An electronic
credential—a magnetic card, a PIN, or even a biometric
scan—is provided to a user. The user presents this credential
to a reader to gain entry. The door controller, which contains
the programming for who has access, allows entry.
Electronic Shuttering – The ability of the camera
to compensate for moderate light changes in indoor applications
without the use of auto iris lenses.
Encoding/Decoding – The process of organizing
information into a format suitable for transmission and recovery.
Encryption – The rearrangement of a previously
digitally encoded signal’s bit stream in a systematic
fashion to make the information unrecognizable. Information
is only restored on receipt of the necessary authorization
key. This technique is used for securing information transmitted
over a communication channel with the intent of excluding
all other than authorized receivers from interpreting the
message. Can be used for voice, video, and other communications
signals.
Encryption Algorithms – Mathematical formulas
used to scramble information.
Equalization – The process of correcting losses
of certain components in a signal.
F
f-number – The f-number indicates the brightness
of an image formed by the lens, controlled by the iris. The
smaller the f-number, the brighter the image.
f-stop – A term used to measure the size of a
lens aperture.
Feedback (Acoustic) – Unwanted interaction between
the output and input of an acoustical system, for example,
between the loudspeaker and the microphone of a system.
Fiber Loss – The amount of signal attenuation
in a fiber optic transmission.
Fiber Optics – Flexible glass fibers used to conduct
energy. Ideal for secure transmissions. If someone tries to
tap fiber, light leaks and transmission fails, so a tap can
be detected instantly.
Field – One half of a frame, consisting of either
the odd or the even numbered lines; 60 fields are transmitted
every second.
File-Infecting Viruses – Common computer viruses
that infect executable files by adding their own code to that
of the original file. When a user opens an infected file,
the virus attaches itself to other executable files. When
infected files are transferred to another computer, the virus
travels with them and finds more files to infect. Because
they require the transfer of an executable file, which most
people know not to open, common file-infecting viruses tend
to spread relatively slowly and don’t cause the wildfire
infections across the Internet that worms do.
Firewall – A network node set up as a boundary
to prevent traffic from one segment to cross over to another.
Firewalls are used to improve network traffic, as well as
for security purposes. The most common application for a firewall
is to control traffic between a private network and the Internet
to intercept outsiders trying to break into the private network.
A firewall exerts this control by applying rules to information—primarily
IP addresses and port numbers—found in incoming network
packets.
Focal Length – The distance from the center of
the lens to the pickup device (CCD). The focal length determines
the size of the image and the angle of the field of view seen
by the camera through the lens.
Foot-Candle (FC) – The light intensity (illumination)
of a surface one foot distant from a source of one candle.
It is equal to one lumen per square foot. (1 FC = 1 lm/sq.
ft.). The foot-candle is the unit used to measure incident
light.
Frame – The total area of the picture that is
scanned while the picture signal is not blanked.
Frequency – The measure of the rapidity of alterations
of a periodic signal, expressed in cycles per second or Hz.
Front Porch – The portion of the composite video
signal that lies between the leading edge of the horizontal
blanking pulse and the leading edge of the corresponding synchronizing
pulse.
Full-Motion Video – Video transmission that changes
the image 30 frames per second (fps).
G
Gain – Amount of signal amplification, usually
expressed in decibels. The relative increase in voltage, current,
or power from the input signal to the output signal.
GB (Gigabyte) – Unit of computer memory consisting
of about one thousand million bytes (one thousand megabytes).
Actual value is 1,073,741,824 bytes.
Gen-lock – A method used to synchronize one or
more cameras by external means such as Composite video, Composite
sync, horizontal sync or vertical sync.
Ghost – A shadowy or weak image in the received
picture, offset either to the right or to the left of the
primary image. It is the result of transmission conditions
in which secondary signals are created and received earlier
or later than the primary signal.
GHz (GigaHertz) – One billion cycles per second.
Ground – An electrical connection point that is
common to either a metal chassis, a terminal, or a ground
bus.
Ground Fault – The temporary current in the ground
line, caused by a failing electrical component or interference
from an external electrical source such as a thunderstorm.
Ground Loop – Caused by different earth potentials
in a system. Seen on a video transmission as a black shadow
bar across the screen or as tearing in the top corner of a
picture.
H
Hacker – A person who maliciously breaks into
networks, breaks the security on application software, or
creates viruses. Hackers often use known security holes in
operating systems to penetrate networks. They find security
holes to exploit by pinging a network to find an open IP address
and then probing to find an open port. Many corporate firewalls
are probed thousands of times a day by hackers looking for
a security hole.
Headend – The electronic equipment at the start
of a cable system; usually switches, multiplexors, and digital
recorder equipment.
Horizontal Resolution – The maximum number of
individual picture elements that can be distinguished in a
single scanning line.
I—K
Image Size – The size of an image formed by the
lens onto the pickup device (CCD). The current standards are
1", 2/3", 1/2" and 1/3" measured diagonally.
Impedance – The resistance to the flow of current
in a circuit.
Incident Light – The light that is falling directly
over an object.
Insertion Loss – The signal strength loss that
occurs when a piece of equipment is inserted into a line.
Interlace – A process where every other horizontal
line is scanned in one field while the alternate lines are
scanned in the next field to produce a complete picture frame.
Interleaving – A method used in alarms or activity
detection, which allows extra frames of video from alarmed
cameras to be added to a time-multiplexed sequence while a
state of alarm exists.
Iris – A means of controlling the size of a lens
aperture and therefore the amount of light passing through
the lens.
L
Lag – The image retention of an object after the
object has been scanned; can cause a smearing effect.
LCD (Liquid-Crystal Display) – A display technology
that uses rod-shaped crystals that flow like liquid and bend
light.
Lens – An optical device for focusing a desired
scene onto the imaging device in a camera.
Level Control – Main iris control. Used to set
the auto-iris circuit to a video level desired by the user.
After setup, the circuit adjusts the iris to maintain this
video level in changing lighting conditions. Turning the control
towards High opens the iris and towards Low closes the iris.
Line of Sight – An unobstructed view from one
location to another that is used to send a video signal wirelessly
between two locations.
Link Lock – To lock the field frequencies of multiple
cameras to the same AC power source frequency for the purpose
of having the cameras share a common power source.
Looping – Occurs when a high impedance device
has been permanently connected in parallel to a video source.
Loudspeaker – An electroacoustical
transducer that changes electrical energy to acoustical energy.
Lumen (lm) – A unit of measuring light intensity
produced by the luminosity of 1 candela (cd) in one radian
of a solid angle.
Lux (lx) – A unit of measuring the intensity of
light on a surface (10.764 lx = 1 footcandle [FC]).
M
Macro Viruses – Viruses written in the internal
macro language provided with many applications. Macro viruses
are extremely common—especially within Microsoft®
Excel® and Microsoft Word files. They spread easily because
they travel in documents that are often shared and also because
many of them, in wormlike fashion, e-mail themselves to everyone
they find in an address book. Because macro viruses are so
easy to write and modify, new ones pop up all the time. Additionally,
because macro viruses spread within an application, they may
spread between operating systems—for instance from a
PC to a Mac®.
Mail Bomb – A form of denial-of-service attack
that shuts down e-mail servers by swamping them with more
e-mail than they can handle.
Manual Iris Lens – A lens with a manual adjustment
to set the iris opening (f-stop) in a fixed position. Generally
used for fixed lighting applications.
Matrix Switcher – A switcher able to route any
of its inputs (cameras) to any of its outputs (monitors);
matrix switches often include telemetry control.
Mbps – Megabits per second (bps).
Mechanical Focus (Back Focus) – The mechanical
aligning of the imaging device with the focal point of the
lens; it is most important on zoom lenses to be sure the image
stays in focus throughout the zoom range.
Megahertz (MHz) – A unit of frequency equal to
1,000,000 cycles per second.
Modulate – To change or vary a parameter, such
as the amplitude of a signal for amplitude modulation or the
frequency of a signal for frequency modulation.
Multimode Fiber – An optical fiber with a core
diameter of 50 to 100 microns. Its core causes some distortion
and provides less bandwidth than single-mode fiber.
Multipartite Viruses – The hybrids of the virus
world, most commonly a combination of boot sector viruses
and file infecting viruses. They commonly infect both system
sectors and files. These viruses are fairly rare because they’re
difficult to write but tend to be particularly nasty when
they occur.
Multiplexing – Transmitting multiple signals over
a single communications line or computer channel.
N
Network – Computers connected together to share
information. Two types of networks are Local Area Networks
(LANs) and Wide Area Networks (WANs).
NEXT (Near-End Crosstalk) – Signal interference
from one cable pair that adversely affects another pair on
the same end.
Noise – Random spurts of electrical energy or
interference.
NTSC (National Television System Committee) –
An organization that formulated the standards for the current
United States color television system. This system is used
in most countries of the Americas, as well as other parts
of the world. NTSC uses 525 lines per frame, 29.97 frames
per second, and 59.94 fields per second.
O
Opto-Isolator – A small device that converts the
input of electrical signals to light signals and converts
them back to electrical signals on the output side.
Overscan – A video-display effect in which the
image is enlarged so that its edges are off the screen.
P
PAL (Phase Alternation Line) – A European color
TV system featuring 625 lines per frame, 25 frames per second
and 50 fields per second. PAL is used mainly in Europe,
China, Malaysia, Australia, New Zealand, the Middle East,
and parts of Africa.
Passive Device – A device that must draw its
current from connected active equipment. A balun, for example,
is a passive device.
Peak-to-Peak – The amplitude difference between
the highest and lowest parts of a signal.
PIN (Personal Identification Number) – A code
number used to restrict access to a service to the person
authorized to use it.
Pixel – Stands for picture elements. Pixels
are the tiny dots of information that make up a digital
image. The more pixels there are on the camera’s image
sensor (CCD or CMOS), the higher the image resolution is.
The higher the resolution, the clearer a video image or
an enlarged print is.
Policy Routing – Routing method that forwards
packets to specific interfaces based on user-configured
policies.
Polymorphic Virus – A virus that attempts to
defeat virus-scanning software by using an algorithm to
encrypt itself each time it infects a new host. The encrypted
virus escapes detection by the antivirus software and then
decrypts itself to infect the computer. This virus is very
difficult to detect because its signature is different every
time it infects a new host. More sophisticated polymorphic
viruses vary their encryption methods, making them even
more difficult to detect.
Power – The rate at which electrical energy
is applied to or taken from a device. It is expressed in
terms of watts, milliwatts, or microwatts.
Pre-position Lenses – Zoom lenses that use a
variable-resistor (potentiometer) to indicate zoom/focus
position to the lens controller. After initial setup, this
enables the operator to view different preset areas quickly
without having to readjust the zoom and focus each time.
Private and Public Keys – Mathematical codes
used for encryption of transmitted data. A secret private
key and a mathematically related public key are generated
for each party in a transmission. When someone wants to
send a secure message, they use the public key of the recipient
to encrypt the message. The recipient then uses his/her
private key to decrypt it. It is virtually impossible to
deduce the private key from the public key.
PTZ Camera – Pan, tilt, and zoom camera.
PVC (Polyvinyl Chloride) – The
type of plastic from which cable jackets and wire insulation
are usually made.
Q
QoS (Quality of Service) – Measure of performance
for a transmission system that reflects its transmission quality
and service availability.
R
Radio Frequency (RF) – Any of the electromagnetic
wave frequencies that lie in the range extending from below
3 kilohertz to about 300 Gigahertz.
Random Interlace – A scanning technique commonly
used in CCTV systems in which there is no external control
over the scanning process. There is no fixed relationship
between adjacent lines and successive fields.
Range Finder – Used to determine the focal length
needed and what the picture will look like on a monitor.
The user looks through the device and adjusts the range
finder to the desired picture. Numbers on the outside of
the range finder indicate the focal length needed.
Reflected Light – The scene brightness or the
light being reflected from a scene. Usually it represents
5 to 95 percent of the incident light, and it is expressed
in foot-lamberts.
Resolution – A measure of the ability of a camera
or television system to reproduce detail. It is the number
of picture elements that can be reproduced with good definition.
Retained Image (Image Burn) – A change produced
in or on the target of the pickup device (CCD), which remains
for a large number of frames after the removal of a previously
stationary light image and that yields a spurious electrical
signal that corresponds to that light image.
RG11 – A video coaxial cable with 75 ohms impedance
and much thicker diameter (around 12 mm) than RG59. RG11
provides at least twice the distance of RG59 cable and is
most commonly used in large CCTV systems.
RG58 – A coaxial cable designed with 50-ohm
impedance; not suitable for CCTV.
RG59 – A type of coaxial cable that is most
common in small to medium-size CCTV systems. It is designed
with an impedance of 75 ohms, and it has an outer diameter
of around 6 mm.
Roll – A loss of vertical sync
that causes the picture to move up or down on the TV screen.
S
Saturation (Color) – The vividness of a color.
It is directly related to the amplitude of the chrominance
signal.
Scanning – The rapid movement of the electronic
beam in a pickup device of a camera or in the CRT of a television
receiver. It is formatted line by line across the photo-sensitive
surface that produces or reproduces the video picture. When
referring to a video surveillance field, it is the panning
or the horizontal camera motion.
Sensitivity – The amount of responsiveness to
an incident light on the pickup device (CCD) on a camera,
indicating how much the device is affected or changed by light.
Shielding – The process of protecting a cable
with a grounded metal surrounding, so electrical signals from
outside the cable cannot interfere with transmission inside
the cable.
Signal-to-Noise Ratio – The ratio between a useful
video signal and unwanted noise.
Simplex Multiplexor – A multiplexor that enables
the user to look at multiscreen images or perform time-multiplex
recording. It cannot record multiplexor pictures while showing
multiscreen pictures.
Single-Mode Fiber – An optical glass fiber that
consists of a core of very small diameter. A typical single-mode
fiber used in CCTV has a 9-µm core and a 125-µm outer diameter.
Single-mode fiber has less attenuation and therefore transmits
signals at longer distances than multimode fiber.
SMPTE (Society of Motion Picture and Television Engineers)
– A professional group whose committees set standards
in television and motion picture industries. The RS-422 SMPTE
serial interface is used on video equipment.
Sound Pressure Level (SPL) – The expression of
loudness or volume; measured in decibels (dB). A 10 dB increase
in SPL represents a doubling in volume.
Spam – Internet junk e-mail that clogs servers
and in-boxes with offers for dubious products, links to pornographic
sites, chain letters, hoaxes, and scams of all kinds. At best,
spam is a nuisance, but if you’re not paying attention,
spam can also be dangerous.
Spot Filter – A small insert used in a lens to
increase the f-stop range of the lens.
Stealth Viruses – These are computer viruses that
actively hide themselves, often in a PC’s memory. They
can fool the operating system by modifying and forging the
results of calls to functions in the infected file, so the
system believes it’s reading the original file. A stealth
virus can even hide the fact that it’s consuming memory.
Stealth viruses hide themselves so well, they can sometimes
fool antivirus products into thinking a computer is virus
free.
STP (Shielded Twisted Pair) – Cabling that is
a twisted-pair cable with a foil and/or braided shield to
minimize EMI/RFI.
Surge Protector – A device that protects computers
from excessive voltage and current in the power line.
Sync – Electronic pulses that are inserted in
the video signal for the purpose of assembling the picture
information in the correct position.
T
TDG (Time and Date Generator) – A function that
enables the time and data to be recorded on a tape used in
a video surveillance operation.
Telemetry – Remote controlling system used to
control digital encoded data. Used for pan, tilt, zoom, focus,
preset positions, wash, wipe, etc. Because the data used to
control these functions is digital, it’s usually sent
via twisted-pair or coaxial cable with the video signal.
Terabyte (TB, Tbyte, or Ter) – 1,099,511,627,776
bytes.
Time-Lapse Video Recording – The intermittent
recording of video signals at intervals to extend the recording
time of the recording medium.
Time Multiplexing – The technique of recording
several cameras onto one time-lapse VCR by sequentially sending
camera pictures with a time interval delay to match the time-lapse
mode selected on the recorder.
Tracking – A zoom lens’ ability to remain
in focus during the entire zoom range from wide angle to telephoto
position.
Transceiver – A hardware device that links a node
with a baseband network backbone, enabling transmitting and
receiving capabilities.
Transformer – An electromagnetic device that can
increase (step up) or decrease (step down) the voltage of
alternating currents.
Trojan Horse – A virus program disguised as a
legitimate program. A Trojan horse does not replicate itself
but depends on its users to spread. It’s often a game
or utility that seems to do one thing but has incorporated
within itself another, secret function that will cause damage,
pass on information about your computer, or enable its sender
to hijack your computer. Trojan horses are often part of hybrid
or multipartite viruses. For instance a Trojan Horse may be
“planted” in an application by a worm or it may
incorporate a virus within itself.
Twisted Pair – A cable composed of two insulated
conductors twisted together. Because both wires have nearly
equal exposure to any interference, the differential noise
is slight.
U
Unbalanced Signal – In CCTV, this refers to a type
of video signal transmission through a coaxial cable. It is
called unbalanced because the signal travels through the center
core only, while the cable shield is used for equating the
two voltage potentials between the coaxial cable ends.
Unity Gain – In broadband networks, this is the
balance between signal loss and signal gain through amplifiers.
UTP – Unshielded twisted pair. A cable with one
or more pairs of twisted insulated copper conductors bound
in a single sheath.
V
Vertical Interval – The time it takes for vertical
retrace.
Vertical Retrace – The return of the electron
beam to the top of a television picture tube screen or a pickup
device (CCD) at the completion of the field scan.
Video Motion Detection – A system that uses the
video signal from a camera to determine if there is any movement
in the picture and set off an alarm.
Video Type Lens – An auto-iris lens without an
internal circuit to control the iris. All iris control voltages
come from a circuit located within the camera.
Virus – Software code—usually disguised as
something innocent—that replicates itself in PCs. Some
viruses need help to reproduce, some replicate all by themselves,
but all reproduce without your permission or knowledge. Viruses
often have an infection phase where they reproduce and an
attack phase where they do damage. The ability to infect varies
from virus to virus, as does the damage they can cause. Viruses
are roughly categorized into subgroups such as common file-infecting
viruses, worms, Trojan horses, macro viruses, and others.
VLAN (Virtual Local Area Network) – A network
of computers that behave as if they were connected to the
same wire even though they may be physcially located on different
segments of the LAN—or even on a different LAN entirely.
VLANs are configured through software rather than hardware,
which makes them extremely flexible. The advantages of VLANs
include increased performance, improved management, simplification
of software configurations, and increased security.
Volt – The unit of measurement of electromotive
force. One volt is the force required to produce a current
of one ampere through a resistance of one ohm.
VPN (Virtual Private Network) – A means of segmenting
a network and prioritizing traffic based on a selected set
of users. Tunneling encapsulates the data on these networks;
encryption protects it.
W—X
Watt – The measurement of electrical power that
equates to one watt and is equal to one ampere of current
flowing at one volt.
White Balance – An electronic process used in
video cameras to retain true colors. It is performed electronically
on the basis of a white object in the picture.
Wide Angle Lens – A lens that may be effectively
used for a wide angle of view.
Worm – Self-replicating computer viruses. Unlike
an ordinary virus, which depends on the transfer of a host
file in order to replicate, a worm is an independent entity
that usually spreads itself without needing a computer user
to transfer a file. Most travel primarily by e-mail but some
also spread through nontraditional means through the IRC,
peer-to-peer networks, or even Web sites. Worms tend to spread
very rapidly and can cause a lot of damage.
Y
YUV – Describes the analog luminance and color-difference
signals in component video systems. Y is for luminance; U
and V are the two subcarrier modulation axes used in the PAL
color-coding system.
Z
Zoom Lens – A lens system that may be effectively
used as a wide angle, standard, or telephoto lens by varying
the focal length of the lens.
Zoom Ratio – The ratio of the starting focal length
(wide position) to the ending focal length (telephoto position)
of a zoom lens. A lens with a 10X zoom ratio magnifies the
image at the wide-angle end by 10 times. |
