Please use this page to find descriptions of words, acronyms or phrases you may not be familiar with.  If there is something you are after that you cannot see listed, please contact us by clicking here

A

AGC (AUTOMATIC GAIN CONTROL) - Electronic circuitry to increase the video signal in low light conditions. This usually introduces 'noise' in the picture giving a grainy appearance. Camera specifications must always be considered with AGC off.

ALC (AUTOMATIC LEVEL CONTROL) - This is a manual adjustment you will find on Auto Iris lenses, and is also known as peak/coverage control. Adjusting this control allows the auto iris circuitry to either take bright spots into greater consideration (peak), bringing out the detail in bright areas, or to take them into less consideration (average) bringing out detail in shadows.

AMBIENT LIGHT LEVEL - The background or general light level of a given area.

ANALOGUE SIGNAL - In video terms, the representation of a camera scene by varying voltages in the video signal, the voltage being directly proportional to the light level.

ANGLE OF VIEW - Angle of view is the angle covered by a picture for a particular lens and camera combination. The higher the number, the wider the area that can be covered by the camera-lens combination. However, the angle will decrease with the format size, of either the camera or the lens. For example with lenses: - 1/3" 2.6mm lens on a 1/3" camera will give a 75 deg angle of view - 1/2" 2.6mm lens on a 1/2" camera will give a 90 deg angle of view

APERTURE - The light gathering area of a lens. The iris controls the size of the aperture.
 
ARMOUR - Extra protection for a cable that improves resistance to cutting and crushing. The most common material used is steel.

ASPECT RATIO - The ratio of the vertical to the horizontal dimension of an image. This is normally 3:4.

ASPHERICAL LENS - These types of lenses are specially shaped to better focus the light rays entering the lens. This allows approximately 25% more light onto the sensor. This will in turn improve the overall lux level, enabling the camera to perform better at lower light levels.

ATTENUATION - A term that refers to signal loss in a transmission system.

AUTOMATIC IRIS - An electronic circuit fitted to the iris of a lens to help compensate for large changes in light levels. This type of lens is recommended for use where there are low light or changing light conditions, for example external use. An Auto Iris lens adjusts the aperture automatically dependent on the light level, very much like the human eye.

AUTO-TERMINATING - Feature whereby the equipment automatically selects the correct termination depending on whether a BNC video output is connected.

AUTO WHITE BALANCE - Feature on colour cameras whereby the camera constantly monitors the light and adjusts its colour to maintain white areas.

AUTO-FOCUS LENS - Automatically adjusts the lens focus from surrounding scene and keeps a moving object in focus.

 AGC (AUTOMATIC GAIN CONTROL) - Automatically adjusts the video quality in low light condition. 

 ALC ( AUTOMATIC LEVEL 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.  

 

B

BACKBONE - A high-capacity network that links together other networks of lower capacity. A local backbone network would typically be an FDDI network acting as an in-building backbone to link together multiple LANs.

BACK FOCUS - A mechanical adjustment in a camera that moves the imaging device relative to the lens to compensate for different back focal lengths of lenses. An important adjustment when a zoom lens is fitted.

BALANCED SIGNAL - A video signal converted to a balanced signal, usually to enable it to be transmitted along a 'twisted pair' cable. Used in situations where the cabling distance is too great and which would produce unacceptable losses in a coaxial cable.

BAUD - A unit of measurement that denotes the number of bits that can be transmitted per second. For example, if a modem is rated at 9600 baud it is capable of transmitting data at a rate of 9600 bits per second.

BALUN - A transformer that levels out impedance differences, so that a signal generated on to a coaxial cable can be transferred on to a twisted pair cable.

BANDWIDTH - The range of frequencies a transmission line or channel can carry: the greater the bandwidth, the greater the information-carrying capacity of a channel. For a digital channel this is defined in bit/s.

BIFURCATOR - An adaptor with which a loose tube containing two optical fibres can be split into two single fibre cables. (See loose tube).

BIT - Abbreviated with small "b". Binary Digit. The smallest unit of data in a computer.

Bps (BITS PER SECOND) - The rate at which individual bits are transmitted across a communications link or circuit; written bit/s. One thousand bit/s is 1 Kbit/s, and one million bit/s is 1 Mbit/s.

BLANKING - The process whereby the beam in a CRT is cut off during the retrace period.

 C

CAMERA FORMAT - Video camera's CCD chips format; 2/3", 1/3", 1/4", etc. Camera Sensor: Video image sensor. CCD or C-MOS chip.

CATEGORY 5 - Cabling standard specified by EIA/TIA 568 for use with speeds up to 100Mbit/s including FDDI (TP PMD), 100BaseT and 100BaseVG-AnyLan, and potentially ATM at 155Mbit/s.
 
CCD (Charge coupled device) - A flat thin wafer that is light sensitive and forms the imaging device of most modern cameras. Size is measured diagonally and can be 1/3"-1/2" or 2/3". There are two types, frame transfer and interline transfer.

CCIR - The European 625 line standard for the video signal.

CCTV (Closed Circuit Television) - Is a Television system that sends a signal to one or more monitors rather than broadcasting over a public network, hence closed-circuit. A standard CCTV system will normally include a CCTV camera (for capturing video), transmitters and receivers (to transfer the video from the source to where it is recorded), a recording system (for video playback), and a monitor (for video monitoring). CCTV systems are primarily used for security purposes inside and outside buildings. However, they can also be used for specialist applications such as mobile police use and interrogation.

C-MOUNT - The standard screw mounting for 2/3" and 1" camera lenses. The distance from the flange surface to the focal point is 17.526mm. A C-mount lens can be used on a camera with a CS-mount by adding an adaptor ring to reduce this distance to 12.5mm (See CS mount).

CS MOUNT - A new generation of lenses designed for 2/3", 1/2" and 1/3" cameras incorporating CS-mounts. The distance from the flange surface to the focal point is 12.5mm. CS mount lenses cannot be used on cameras with a C-mount configuration. These lenses are more compact and cheaper than the C-mount equivalents.

CO-AXIAL CABLE - Any cable that has a conductor and shield sharing the same axis. Also known as RG59.

COLOUR SATURATION - The degree of mixture of a colour and white. High saturation means little or no white.

COMPOSITE SYNC - A signal comprising of both Line and Field sync pulses but without any video information.

COMPOSITE VIDEO - A complete video signal, comprising of sync and video information. The sync pulse should be 0.3 volts and the video signal should be 0.7 volts.

CORE - The central region of an optical fibre through which a signal carrying infrared is transmitted. Manufactured from high-density silica glass.

CROSSTALK - Unwanted interference from another adjacent communications channel.

CRT - Cathode Ray Tube. The vacuum tube part of a monitor or television. 

 

D

DB (DECIBEL) - a logarithmic ratio between two signals. It is used as the unit of noise or signal strength.

DC Power - Direct Current Power; can be derived from an AC adapter or from a battery. Among DC voltages of 6, 9, 12, 24, 28, 12VDC is most common in the CCTV industry.

DEPTH OF FIELD - The proportion of the field of view that is in correct focus. The depth of field in focus DECREASES when: the focal length is longer, the f number is smaller, or the object distance is shorter.

DIGITAL SIGNAL - An analogue signal that has been converted to a digital form so that it can be processed by a microprocessor.

DIP Switches - Dual Interface Poll switches usually allow you to change the configuration of a circuit board to suit your application.

DIRECT DRIVE LENSES - This is an Auto-Iris lens, which has a motor or galvanometer coil moving the iris vanes in the lens, driven directly by the camera. There are no active electronics in the lens, hence they are simpler, smaller and cheaper than the equivalent auto-iris lenses.

DUPLEX - Used in multiplexing terminology, whereby two single (simplex) units are assembled in one unit enabling the system to record all camera images onto the VCR and display them on the monitor simultaneously.

DSL (Digital Subscriber Line) - A technology for bringing higher-bandwidth information to homes and businesses over ordinary copper telephone lines.

DVR (Digital Video Recorder) - records video pictures digitally.

DWELL TIME - The length of time a switcher will hold a camera before moving onto the next camera in the sequence.

 

E

EI (Electronic Iris) - Automatically varies a CCD camera's shutter to mimic Auto Iris control. Allowing fixed or manual iris lenses to be used in a wider range of areas.

ELC (Electronic Light Control) - Compensates for moderate light changes in indoor applications without the use of auto iris lenses. Select this mode when a fixed iris lens or manual iris lens is used.

Electronic Shutter - Compensates for moderate light changes in indoor applications without the use of auto iris lenses.

ETHERNET - The most widely used LAN transmission network. Based on a bus network topology, it runs at a maximum speed over 100 meters of 10Mbit/s. It operates over conventional co-axial cable, thin wire co-axial cable and unshielded twisted pair cabling. This has several implementations - 10Base5 for use over conventional co-axial cable, 10BaseF for use over optic fibre, and 10BaseT for use over Unshielded Twisted Pair (UTP) cabling.

F

FAST ETHERNET - Proposed 100Mbit/s technology for workstation LANs.

F-number (f-stop) - Optical or lens speed. Smaller f-number means faster lens.

Flash Memory Or Flash RAM (Random Access Memory) - A type of constantly powered non-volatile memory that can be erased and reprogrammed in units of memory called blocks.

FOCAL LENGTH - The distance between the secondary principal point in the lens and the plane of the imaging device (focal point). The longer the focal length, the greater the magnification the narrower is the angle of view.

FOCAL POINT - The point on the axis of a lens to which parallel rays of light will meet.

FRAME - One complete TV picture made up of approximately 625 lines. 25 frames are transmitted every second.

FRAME STORE - An electronic method of capturing and storing a single frame of video. All slow scan transmitters include a frame store that holds the picture at the moment of alarm, while the control is being dialled up. When the link is confirmed, the picture is transmitted.

FRAME TRANSFER - A type of CCD imaging device in which the entire matrix of pixels is read into storage before being processed by the electronics of the camera. This method helps to eliminate the vertical streaking caused by, for example, car headlights.

FULL PICTURE UPDATE - This technology enables a transmission system to update a full, high quality picture at very fast speeds.

FTP (File Transfer Protocol) - A way to exchange files between computers on the Internet.

G

Gamma - Degree of contrast in a video picture between output magnitude and input magnitude.

GB - Gigabyte.

GEN LOCK - Also called external sync. A separate coaxial cable is run to each camera and carries sync pulse information to ensure that all cameras are producing fields at exactly the same time. This eliminates picture bounce during switching and can improve quality and update time in multiplexers.

GROUND LOOP - An alternating current (AC) that can be produced in a cable. This is usually caused by parts of the system being fed from different electrical sources resulting in different earth potentials at each end of the signal path. This results in interference of the video pictures in the form of a black shadow bar across the screen or as a tearing effect in the top comer of a picture.

GROUND LOOP TRANSFORMER - An isolation transformer. There is no direct connection between input and output.

H

HARDWIRED - Direct cables connected from one electronic product to another. Can be labour intensive to install and is only used in simple systems with short cable runs.

Hz (HERTZ) - The number of variations per second (e.g. picture frames, alternating of the current, etc).

HUB - The centre of a star topology network or cabling system. A multi-node network topology that has a central multiplexer with many nodes feeding into and through the multiplexer or hub. The other nodes do not usually directly interconnect. LAN hubs are increasingly popular with the growth of structured cabling and the need for LAN management.

I

ILLUMINANCE - The measurement of light in lumens per square metre, the unit of which is the lux.

IMAGE SENSOR FORMAT - Size of the CCD element in the camera.

IMPEDANCE - A measure of the total opposition to current flow in an alternating current circuit, measured in Ohms (O).

INFRA RED LIGHT - The wavelength of light produced above the visible part of the spectrum.

INFRA RED TRANSMISSION - A method of transmitting video and telemetry signals across free space along an infrared beam. This opens possibilities for using CCTV where it had been previously impossible to run cables. Distance can be limited and the signal can be degraded in adverse weather conditions.

INTERLACE - The accurate combining of two fields, one odd one even, into a single frame. For standard video picture make up, you would have 50 fields per second interlaced, which equates to 25 frames per second.

INTERLEAVING - Method used with alarms or activity detection which allows extra frames of video, from alarmed cameras, to be added to a time multiplexed sequence whilst a state of alarm exists.

INTERLINE TRANSFER - Another type of CCD imaging device in which the rows of charge are stepped down one at a time and processed straight away.

INTERNAL SYNC - The internal generation of sync pulses in a camera without reference to external sources. This uses a crystal-controlled oscillator within the camera, which is typically used on non-mains powered cameras.

IP (INTERNET PROTOCOL) - The TCP/IP standard protocol that defines the IP datagram as the unit of information passed across an Internet and provides the basis for connectionless packet delivery service.

IP ADDRESS - The 32-bit address assigned to hosts that want to participate in a TCP/IP Internet.

IP DATAGRAM - The basic unit of information passed across a TCP/IP Internet.

IP RATING - This is used as an index of environmental protection. The number combination defines the protection from outside influences afforded by an enclosure. The minimum rating for most external housings for cameras is IP65. Please click here to view the IP Rating Chart

IR - Infrared

IRIS - The mechanism within a lens that is adjusted to vary the amount of light falling upon the imaging device. If this is an Auto Iris lens for example, then the mechanism would close when it is very bright, and open as it becomes darker, to give a good usable picture.

IR SHIFT - The difference in the field of view in focus between daylight and infrared light.

J

JPEG - A popular compression standard for still images. Native to most web browsers, this is the preferred image standard for many Network cameras.

JPEG2000 - A new compression medium but as yet uncommon standard, based on Wavelet technology.

K 

Kb - Kilobyte,

Kbps (Kilobits per second) - A measure of bandwidth

L

LAN (Local Area Network) - A communications system that links computers into a network, usually via a wiring based cabling scheme. LANs connect PCs, workstations and servers together to allow users to communicate and share resources like hard disk storage and printers. Devices linked by a LAN may be on the same floor or within a building or campus. It is user-owned and does not run over leased lines, though a LAN may have gateways to the PSTN or other, private, networks.

LED (LIGHT EMITTING DIODE) - An electronic component that produces light when stimulated by electricity. This is the cheapest and most common type of transmitter for infrared light along an optical fibre.

LENS MOUNT - See C-Mount and CS-Mount.

Lens Speed - Optical speed, expressed by f-number. Smaller f-number means faster lens.

LINE AMPLIFIER - A device to make good the loss of signal strength and quality due to long cable runs.

LINE FEED CAMERA - A camera that receives its power along the same cable that is used to send its picture back to the monitor. Makes for ease of installation, but cabling distances can be restricted and connections to other equipment can cause problems.

LINE LOCKED - The sync pulses of cameras that are locked to the AC mains frequency.

LINE POWERED - A camera in which the power is supplied along the same coaxial cable that carries the video signal. Makes for ease of installation, but cabling distances can be restricted and connections to other equipment can cause problems.

Linux - An UNIX-like operating system. Very efficient and fast-performing system.

LL (Line Lock mode) - LUX Lumens per Square Meter; unit of illumination amount.

LUMINANCE - The brightness element of a video signal.

LUX - Density of light measured in lumens/sq metre. This is used to define the sensitivity of camera imaging devices.

 M

MATRIX SWITCHING - This is an advanced method of switching video signals where there can be any number of inputs directed to any number of outputs. These are generally associated with larger systems where it is necessary to have several control positions, each of which can be programmed to control different groups of cameras.

MB - Megabyte

Mbps (Megabits per second) - A measure of bandwidth.

Mini-DIN - Multi-wire cable with Mini-DIN connectors at both ends. Usually has four inner wires.

Monochrome Signal - Black and White signal.

Motorised Lens - A camera lens equipped with small electric motor that enables focusing lens, opening or closing the iris diaphragm, or changing the focal length.

MJPEG - This compression standard generally refers to JPEG images shown at high frame rate, generally 30 frames per second. It gives high quality video images, but the comparatively large file sizes of each individual image does put demands on the transmission bandwidth.

MODE - (In fibre optics) The path taken by a light ray as it travels along a fibre.

MONOCHROME - A black and white picture. Recommended for use with external cameras, as they have better picture resolution at night.

MPEG1 - The video standard that typically delivers 30/25 (NTSC/PAL) frames per second. With many variations, this format provides low-resolution images but places low demand on the transmission medium.

MPEG2 - Compression offers higher resolution images and same frame rates as MPEG1. Only modern computers can decode this format, as it generally demands high computing capacity.

MPEG4 - A video compression standard that offers high performance video with good resolution and moderate demand on transmission bandwidth. Most MPEG4 solutions today, however, are focused on high-end applications, since they are very costly.

MULTIMODE FIBRE - An optical fibre that allows the signal carrying light to travel along more than one path.

MULTIPLEXER - An electronic system that can accept a number of camera inputs and record them virtually simultaneously. Most also provide many other features such as multi screen displays with four, nine, sixteen etc. cameras on the screen at once. Most have alarm inputs that trigger several pre-programmed functions. Multiplexers can be used to transmit up to sixteen pictures down a single video line whether it is a coaxial cable, microwave, infrared link etc. However, this requires a multiplexer at each end of the line.

MUX - Combines two or more video/audio signals into one channel. Usually accepts 10 or 16 video inputs and displays them in various formats.db

N

NOISE - This is inherent in all electronic circuits. In a video signal this appears as snow or graininess in the picture.

NTSC (National Television System Committee) - formulates standards for American colour television system. NTSC system has 525 horizontal scan lines and 30 frames per second.

P

PAL (Phase Alternating Line system) - A colour television system used in Europe, Australia, parts of Africa and the Middle East. It has 625 horizontal scan lines and 25 frames per second. 

Pan - Rotating or scanning a camera side ways to view an area in a horizontal direction.

PAN & TILT - A device that can be remotely controlled to provide both vertical and horizontal movement for a camera.

PEAK-TO-PEAK - The measurement of a video signal from the base of the sync pulse to the top of the white level. For a full video signal this should be one volt.

PHASE ADJUSTABLE - The ability to delay the line locking process so as to align cameras fed from AC voltages of different phases.

PHOTOCELL - A device that automatically switches on the infra-red lights when light levels fall to a pre-set level.

PHOTO DETECTOR - A device at the receiving end of an optical fibre link that converts light to electrical power.

Picture Element (Pixel) - Photo sensor site in an image sensor like CCD chip; converts the input light image to an electronic signal.

Pinhole Lens - A lens with a relatively small front opening so it can be used in covert application.

Pixel Picture Element - Photo sensor site in a image sensor like CCD chip; converts the input light image to an electronic signal.

PPP (Point-to-Point Protocol) - For communications between two computers using a serial interface.

PPPoE (Point-to-Point Protocol over Ethernet) - Presets The pre-positioning of pan, tilt and zoom cameras by the use of potentiometers in the moving parts of the camera head. These allow the control equipment to store and move to a set reference point when the controller dictates or when an alarm exists.

PSTN (Public Switched Telephone Network) - Quad Splitter Combines up to 4 video inputs into one channel and displays them on one monitor screen split into 4.

PRESETS - A function contained within a telemetry system that, on receipt of a signal, causes a particular camera to pan (left to right), tilt (up and down) and zoom (lens) to a predetermined field of view. Most systems can accommodate up to 16 pre-set positions for each camera. This is an especially useful feature on larger systems with alarmed areas.

Q

QUAD SPLITTER - A product that can display the views from 4 cameras simultaneously on one monitor. It is also possible to select any individual camera for full-screen display on real time monitoring, dependent on model.

R

RAM (Random Access Memory) - The place in a computer where the operating system, application programs, and data in current use are kept temporarily so that they can be quickly reached by the computer's processor.

REFLECTED LIGHT - Scene illumination multiplied by reflectance. This is the amount of light returned to the camera and determines the quality of picture.

REMOTE SWITCHER - A video switcher to which the cables from the cameras are connected and which contains the switching electronics. This unit may be remotely located and connected to a desktop controller by a single cable for each monitor.

RESOLUTION - There are a number of resolutions available, each dependant upon the camera that you install on the DVR.  For Analogue cameras the common resolutions are CIF, 2CIF, 4CIF and VGA whilst for IP Cameras the Reolutions go much higher through HD (High Definition) and upwards to multiples of HD.  Another way of looking at resolution is by looking at TVL (TV Lines) the traditional Home Television (Not HD) runs at 625 TV Lines, this is the number of lines running down the right hand side of the screen to make up the picture.  HD Televisions run at 720 or 1080 TV Lines, whilst some High Definition Cinemas run at 2 HD or 2160 TV Lines.  The easiest way to compare TV Lines and Resolution outputs is to look at them visually, we have therefore put here two pictures that show the same images displayed at varying resolutions or TV Lines.  You can clearly see the difference in the pictures against each other.

For facial detection we have uploaded another picture with a similar difference.

           

Another Example

       

RG59/U Cable - One of coaxial cables suitable for video transmission in CCTV system

RJ11 - Popular name for the standard four-wire modular connector for phone connections.

RJ45 - Popular name for the eight-pin modular connector in the 10BaseT standard for UTP connections to workstations or smart wiring hubs.

ROUTER - Router Network interconnector device. A router can be used to link LANs together

RS-232 Port - A communication port with 15 pins.

S

S-Video - Transmits luminance and colour portions separately, using multiple wires, thus avoiding the colour encoding process and its inevitable loss of picture quality.

S/N RATIO (SIGNAL TO NOISE) - a measurement of the noise level in a signal expressed in dB (decibels). In a video signal, values from 45dB to 60dB produce an acceptable picture. Less than 40dB is likely to produce a 'noisy' picture.

SCART - A standard European 20 pin connector, used for carrying both audio and video signals in domestic TV appliances. The majority of modern televisions and VCRs have a scart connector on them.

SENSITIVITY - Of a camera, usually specified in LUX, should be the amount of light falling upon an imaging device to produce a video signal of 1-volt peak to peak. Confusingly, it is often referred to as the amount of light at the lens, which is not technically accurate and can be misleading unless the lens specification is provided in detail, including its light transmission value.

SHEATH - The outer finish of a cable. Usually this consists of an extruded layer of PVC or polyethylene.

SIMPLEX - This is a type of multiplexer. There is only one PCB inside a Simplex unit, so it can only do one of the three functions at a time. It can either record all cameras simultaneously, playback all cameras or display all cameras onto a monitor at the same time. It is mainly used on multiple camera systems, but because of its limitations, it tends only to be used on an un-named installation.

SINGLE MODE FIBRE - An optical fibre constructed in such a way that light travelling along the core can only follow one path. (Also called mono-mode).

S.V.H.S. (Super Video Home System) - New format high-resolution VHS video recorders, capable of giving greatly improved picture if all features are used. VHS compatible.

SWITCHER - A video switcher to which the cables from the cameras are connected and which contains the switching electronics. This allows the user to switch between the pictures given by the different cameras, either manually or automatically after a preset time. Many switchers also have the facility that, if an alarm is activated, the switcher will switch to the camera covering the area where the alarm has been activated.

SWIVEL MOUNT - Used on a tower or bracket to enable the housing to be pointed at any angle, vertically or horizontally.

 

T

TCP (Transmission Control Protocol) - A set of rules to exchange messages with other Internet points at the information packet level.

TCP / IP (Transmission Control Protocol / Internet Protocol) - The basic communication language or protocol of the Internet.

TELEMETRY - The system by which a signal is transmitted to a remote location in order to control the operation of equipment. In CCTV systems this may include controlling pan, tilt and zoom functions, switch on lights, move to pre-set positions etc. The controller at the operating position is the transmitter and there is a receiver at the remote location. The signal can be transmitted along a simple twisted pair cable or along the same coaxial cable that carries the video signal.

TELEMETRY TRANSMITTER - The unit that is at the control position of a CCTV system and contains the keys, joysticks etc. for the remote control of pan/tilt/zoom cameras.

TERMINATION - The video cable requires an impedance of 75 ohms at normal video signal bandwidth. This is often called 'low Z'. There is a switch on the back of the monitors to select either 75 ohm or 'high Z' (sometimes 'high/low'). If a signal is looped through more than one monitor all should be set to 'high' except at last, which should be to 'low' or 75 ohm.

TIGHT BUFFERED - A type of cable in which the optical fibres are tightly bound.

Time / Date Generator - Installed between a CCTV camera and a monitor, it generates the information of Date, Time and camera ID.

TFT (Thin-Film Transistor) -  Is a variant of Liquid Crystal Display (LCD) which use's Thin-Film Transistor (TFT) technology to improve their image quality. TFT LCDs are one type of active matrix LCD, though this is usually synonymous with them. They are used in both flat panel displays and projectors. In computing, TFT monitors are rapidly displacing competing CRT technology, and are commonly available in sizes from 30 to 77 cm (~12 to 30 inches). As of 2006, they have also made inroads on the television market. There is no, or minor effect on the eyes, if we use TFT-LCD monitors.

TOUCH SCREEN CONTROL - A system that allows all the camera controls to be displayed on the screen of a special monitor. Controlling any function simply requires the screen to be touched at the appropriate symbol to select a camera or pan, tilt and zoom. The system is computer driven and can include maps, diagrams, etc. that are automatically displayed according to the alarm received.

TRIPLEX - Multiplexer feature that gives you the ability to simultaneously view both playback and live cameras within the same multi-screen, while still recording.

TVL (Television Lines) - The maximum number of changes between light and dark on a picture, across 3/4 of the width, dictates the resolution of a CCTV product, measured in TVL.

TWISTED PAIR - A cable, often screened, that consists of two conductors twisted together along their length.

U

UNBALANCED SIGNAL - A composite video signal, transmitted along a coaxial cable, is an example of an unbalanced signal. (See balanced signal).

UNTERMINATED - Video input of a piece of equipment, wired so as to allow the video signal to be fed to further equipment. Does not necessarily include extra sockets for the extra cables.

UPS (Uninterruptible Power Supply) - A battery, attached to a piece of hardware, for example a server that provides back up power for conducting an orderly shutdown if the server's normal power supply fails.

UTP (Unshielded Twisted Pair) - The standard cabling used for telephone lines. The standard IEEE 802.3, 10BaseT, defines use of Ethernet over UTP for rates up to 10Mbit/s. The general LAN medium of choice for the 1990s.

V

VARIFOCAL LENS - A type of lens that enables a manual selection between two focal lengths, to give the desired picture view. A good option for customers, who are unsure of angle or distance, as it saves having to try multiple lenses.

VHS (Video Home System) - Name given to ½" tapes, used with domestic video recorders.

Video Band - The frequency band used to transmit a composite video signal.

VIDEO LAUNCH AMPLIFIER - An interface between the video source and distribution cable. This is used where the video signal requires to be processed before being launched over coaxial or balanced lines.

VIDEO SWITCHER - A device to enable different cameras to be selected to a monitor. The switching is normally arranged to take place during the blanking period of the video signal to prevent a picture bouncing when a new one is selected.

VCR (Videocassette Recorder) - A device that accepts signals from a video camera/microphone and records video/audio on magnetic tape in a cassette. The VCR can play back recorded video/audio on a television set or CCTV monitor.

VMD (VIDEO MOTION DETECTION) - a method of detecting movement in the view of the camera by electronic analysis of the change in picture contrast.

W

WAN (Wide Area Network) - A network that covers a larger geographical area than a LAN and where telecommunications links are implemented, normally leased from the appropriate PTO(s). Examples of WANs include packet switched networks, public data networks and Value Added Networks.

WAVELET - Compression that is optimised for images containing low amounts of data. The relatively inferior image quality is offset against the low bandwidth demands on transmission mediums.

WHITE LEVEL - The brightest part of a video signal corresponding to approximately 1.0 volt (0.7 volts above the black level).

Web Server - The computer program (housed in a computer) that serves requested HTML pages or files.

Z

Zoom Lens - A lens of continuously variable focal length.