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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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). 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.
Coax Cable


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.
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 Access and Control

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.

Fiber Optics

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

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.

J

K

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.

Society of Motion Picture and Television Engineers

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.

Unshielded Twisted Pair

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

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.

X

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.

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