Glossary

Accronym	Description
ADSL	Asymmetrical Digital Subscriber Line. Data service provided over a standard PSTN telephone line that is faster inbound than outbound. Typically the inbound rate is 2 – 8 MB / second. The outbound service is typically 256Kbits – 2 Mbits / second.

AGC	Auto gain control. Electronic circuitry mainly in cameras which increases the sensitivity of the camera. This allows the camera to produce images at lower light levels but has the negative side affect of introducing noise into the video image.

ALC	Auto Level Control. ALC is provided on some cameras and auto iris lenses. It allows the “fine tuning” of the iris level to suppress bright areas or to lift detail in dark areas.

Aperture	The term aperture refers to the ability of a lens to pass light. Aperture is measured in “F stops” and the lower the F stop rating of the lens the more it can pass through to the cameras imager.

API	Application Programming Interface. An API provides a means of communication with the operating system of a device via a third party system at command level. APIs are usually provided by manufacturers of networked CCTV products to allow custom third party software to interact with and control elements of the networked CCTV system.

Archive	A process which allows the copying of video data from a DVR onto a removable media such as CD/DVD/USB devices etc. Also referred to as “Back up”

Aspect ratio	Aspect ratio describes the ratio of the horizontal to vertical size of an image. Most CCTV is displayed in 4:3 aspect, widescreen TV tends to be in 16:9 aspect.

Attenuation	Losses of signal in its transmission media, measured in dB.

Auto iris	Lens type where a motorised iris assembly constantly controls the amount of light allowed through the lens and onto the cameras imager. This provides a correctly exposed image under varying lighting conditions.

AWB	Auto White Balance. AWB constantly monitors light and adjusts the colour balance of a camera to ensure accurate colour rendition under varying light temperatures and levels.

Back Focus	Camera feature which allows the “coarse” setting of focus by moving the imager backwards or forwards in relation to the lens. Proper back focus setting is critical where zoom lenses are being used as it ensures correct focus tracking throughout the range of the zoom lens. Back focus is also referred to as “racking”.

Balanced Signal	Method used for signalling to cancel out interference. Balanced signals also do not rely on Ground as part of the transmission circuit so earth loops do not occur. Balanced signals are normally cabled via twisted pair cable to improve noise and interference rejection.

Balun	Balanced / Unbalanced converter. Most commonly found in CCTV as an analogue video to twisted pair converter, allowing a camera signal to be changed to a balanced signal and transmitted via twisted pair cable. At the control end of the system the twisted pair signal is turned back to the unbalanced video signal and fed to control and recording equipment.

BLC	Back Light Compensation. Feature found on cameras to compensate for strong backlit scenes where objects viewed by the camera would normally just be a silhouette.

BNC	British Naval Connector. The standard connector for video connections on co axially cabled systems.

CCD	Charge Coupled Device. This is the standard type of imager found in CCTV cameras.

CCIR	Comittee Consultatif International Des Radio Communications. This is the monochrome TV standard for all non NTSC areas.

CIF	Common Interchange Format. Refers to a video image displayed in pixels, the standard for CIF is 352 x 288 pixels.

CMOS	Complimentary Metal Oxide Semiconductor. This is the latest camera imager technology, which has a number of benefits over CCD.

Cmount	Old lens standard designed for half inch and one inch format cameras. A CS mount adapter is required to fit a Cmount lens to a modern camera.

Composite Video	Complete video signal comprising of 0.3 volts sync pulse and 0.7 volts video content.

Compression	Techniques employing specialised algorithms that are used to reduce the amount of data before storage or transmission. The same algorithm is used to decompress the data back its original form when recovered from storage or transmission.

Contention Ratio	Refers to ADSL services. The contention ratio of an ADSL service refers to how many users are sharing the upstream bandwidth.

Default Gateway	Networking term that defines where a PC (or other networking device) should look in order to connect to a different network from the local network.

Depth of Field	Refers to the area of useable focus in an image. The wider the iris opens the lower the depth of field is.

Direct Drive	Feature found on cameras where the auto iris lens drive circuitry and adjustment are onboard the camera.

DVR	Digital Video Recorder. A recording device which uses digital video processing to store, display and transmit images.

EI	Electronic iris. A feature found on some cameras where the cameras shutter and circuitry is used to control light level instead of an auto iris lens. Can normally only be used indoors.

EPOS	Electronic Point Of Sale. Refers to cash handling equipment such as cash registers through to sophisticated “back office” PC based centralised systems. It is possible to interface some types of DVRs and CCTV systems to EPOS systems allowing for overlay of transactions onto the camera images. It is also often possible to view, store, and search transactions.

Event Recording	Refers to systems where the recording device is triggered by motion, alarm inputs or other “intelligent” alarm devices. When event recording actual recording only takes place when the recorder is triggered.

Field	A single filed of video consisting on either odd or even TV lines. A PAL standard camera transmits 50 fields per second.

Focal Length	The focal length of a lens defines the view angle of the lens. The longer the focal length the narrower the view angle of a lens, for instance a 16mm lens will have a much narrower view than a 4mm lens.

Frame	One complete TV picture that consists of 2 fields, I even field and one odd field. PAL TV pictures are transmitted at 25 frames per second.

Frame Store	A frame store is the electronic device that holds a single video image in digital format. The larger the capacity of the frame store the higher the resolution and detail of the image that can be held.

Galvanometric lens	Basically a type of auto iris lens where electrical currents cause movement of the mechanical iris assembly.

Gateway	A networking term that describes a piece of equipment that provides a gateway from one network to another. For instance an ADSL router provides a means of allowing a domestic PC to access the Internet. Gateway devices are typically routers or servers.

Hub	A piece of networking hardware that provides an interconnection point for cabling. A hub broadcasts data received on one port out of all ports and thus creates more network traffic than is really necessary, wasting network bandwidth. Now outdated, switches have replaced hubs.

Internet	The World Wide Web. Affectively a public internetwork.

Intranet	Private Network that has the appearance of The Internet and uses the same technologies such as protocols, web browsing and FTP.

IP	Internet protocol. The protocol or “language” of The Internet.

Iris	Mechanism within a lens that controls the throughput of light. When fully open the maximum amount of light is allowed to pass, at the fully closed position minimal (if any) light is allowed through.

ISDN	Integrated Services Digital Network. Digital telephone and date service that is ran over normal telephone lines. ISDN consists of a 64Kbits / sec B (bearer) channel and a 38.4Kbits /sec D (control) channel. It is available with multiple bearer channels from 2 to 30.

ISP	Internet Service Provider. A company that provides access to The Internet on a subscription basis. ISPs also offer services such as web hosting, email accounts and FTP services.

JPEG	Joint Photograhic Experts Group. The body who created the compression standard designed for digital still frame image capture.

LAN	Local Area Network. A network that is generally confined to a geographically confined area, such as a building or office complex.

Line Lock	A means of synchronizing cameras to the AC power source.

Linux	An open source operating system that is developed by a large community of software developers. Linux is supplied in many guises on a free of charge basis. Now commonly used in the CCTV industry as an operating system for DVRs, IP Cameras, PCs and many other devices.

Looping	Term used describe a piece of video equipment that has an output for each video input.

Lux	Lux is the unit used to express the level of light in a scene. The lux unit is also used to express the sensitivity of a CCTV camera.

MAC Address	Media Access Control Address. A MAC address is the physical address that is “burned into” a network control chip. Every MAC address is unique and is used at a low level to define the real address of a PC or other network enable device.

MPEG	Motion Picture Experts Group. The body who created the compression standards designed for digital moving pictures and audio. Subsequent MPEG standards include MPEG2 and MPEG4.

Multiplexing	In electrical terms the ability to send multiple signals via a single transmission media. In CCTV multiplexing refers to the sequential recording of all cameras to a single media (analogue tape or various types of digital media).

NIC	Network Interface Card. An acronym used to describe the network card in a computer or DVR.

NTSC	National Television Standard Committee. TV standard used primarily in the USA. Comprises of 525TV lines per frame delivered at 60 fields per second.

PAL	Phase Alternate Line. TV system used in most areas except the USA. Comprises of 625TV lines per frame delivered at 50 fields per second.

Pan & Tilt Head	Electro mechanical device that provides pan and tilt movement for the attached CCTV camera. Used in conjunction with a telemetry system.

Patrol	Also referred to as a tour. This is a capability that some PTZ units and most domes have. The patrol or tour is programmed into the PTZ or dome as a series of presets or co ordinates. These presets or co ordinates are then recalled as a moving sequence by a single key press or alarm trigger.

PIR	Passive Infra Red. A range of detection devices used in intruder systems and CCTV. PIRs are used to provide triggers to these systems to raise alarm conditions or change recording patterns.

Preset	Term used to describe the capabilities of some pan and tilt systems and most PTZ domes. The PTZ or dome is driven to a required view and the controller then instructs the PTZ or dome to remember that position. The position can then be recalled by a single key press or alarm trigger.

PSTN	Public Switched Telephone Network. Normal analogue telephone system used worldwide. Also referred to as POTS (plain old telephone system)

Router	A piece of networking hardware that is used to route network traffic from one network to another. Routers are generally used with telephone services to link networks via PSTN, ISDN, or ADSL.

Sensitivity	The lowest amount of light that a camera can produce a useable picture. Sensitivity is expressed in Lux.

Switch	A piece of networking hardware that provides an interconnection point for cabling. Switches are intelligent devices that route networking signals on a port to port basis, this ensuring efficient use of the network bandwidth.

TCP	Transmission Control Protocol. One of the suite of TCP/IP protocols. TCP is a connection orientated protocol that provides verified end to end communications and error checking. TCP protocol is used where data must arrive complete with acknowledgements.

Telemetry	Method used in CCTV systems to control movement of PTZ cameras or domes. Telemetry signals can be transmitted via the same co axial cable as the camera signal or via a data cable using RS 232, RS 485 or RS 422 presentation.

Termination	Method used to provide optimum signal conditions across a transmission media. The last piece of equipment is the “end of line” and a resistor is placed between the two transmission media conductors at that point. In the case of video the end of line termination value is 75 Ohms.

Tour	Feature found on some PTZ cameras and most domes. See patrols for a full definition.

TVL	Television Lines. TVL is the measurement used to state the resolution of analogue TV devices. It has long been the benchmark used in CCTV to rate the resolution performance of CCTV cameras and monitors. The higher the TVL rating of a device the more detail it is capable of capturing or displaying.

Twisted Pair	Twisted pair is a cable type that literally has one or more twisted pairs of conductors. Twisted pair cable greatly enhances the noise cancelling properties of balanced data signalling such as RS 485 and RS 422 by ensuring that both conductors are exposed to external influences (noise / induction etc) in equal amounts.

UDP	User Datagram Protocol. One of the suite of TCP/IP protocols. UDP is a connectionless protocol where data is sent and it is simply hoped that it will arrive intact, there is no way of knowing if data did arrive at all and if it did whether I arrived unscathed. UDP is used where integrity of data is not important and fast transmission is the only issue to be considered.

Update Rate	Term used to describe the receive rate of images for CCTV systems capable of remote transmission. Sometimes also known as refresh rate.

VDA	Video Distribution Amplifier. A device that provides multiple video outputs from one video input. Typical VDAs provide 2, 4, or 8 outputs per input. VDAs are normally required where many pieces of CCTV control equipment need to be fed from the same camera signal.

VEXT	Term used to describe a VCRs “head step” connection to another piece of equipment such as a video multiplexer. Ensures that the VCR image capture is synchronized with the images fed to it.

VPN	Virtual Private Network. A secure network that resides within a larger open network. VPNs use encryption and a host of other techniques to secure the network from external exploits and hacking.

WAN	Wide Area Network. A network that is geographically spread.

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