| A.G.C. (Automatic Gain Control) |
An electronic circuit that tries to keep signals at a constant level; more useful in cameras at low light levels. The higher the number the better, typical values 12 - 20dB i.e. a gain of approx 4x - 10x. |
| A.I. (Auto Iris) |
An electronic circuit fitted to the iris of a lens to help compensate for large changes in light levels. |
| A.L.C. (Automatic
Level Control) |
On AI lenses, also known as the peak/average control. Adjusting this control allows the auto iris circuitry to either take bright spots more into consideration (peak), bringing out detail in bright areas, or less into consideration (average) bringing out detail in shadows. |
| ADSL (Asymmetrical
Digital Subscriber
Line) |
A telephone line with uneven transmission rates; half the transmission can attain speeds up to 640 kbps; the other half can attain speeds of 2.048 Mbps or greater in the opposite direction. |
| Alarming |
The ability of CCTV equipment to respond to an input signal, normally a simple switch closure. The response varies depending on equipment type, most common is for switcher to ‘hold’ on the camera corresponding to the alarm input. |
| Alarming |
The ability of CCTV equipment to respond to an input signal, normally a simple switch closure. The response varies depending on equipment type, most common is for switcher to ‘hold’ on the camera corresponding to the alarm input. |
| Ambient Light Level |
Background or general light level of a given area. |
| Analogue |
A signal in which any level is represented by a directly proportional voltage; not digital. |
| Angle of View |
This is what alters (not the focal length) when you use a lens designed for one format on another format. It decreases with format size. |
| Aperture |
The ‘opening’ of a lens, a measure of its light gathering capability. Relative Aperture is a ratio between its focal length and effective aperture, measured in F numbers, generally the lower the better. |
| Aspherical Lens |
A lens designed with a non spherical shape so that it refracts the light passing through it to either lower the lens aperture so that it passes more light or decrease barrel distortion on wide angle lenses. |
| Auto White Balance |
Feature on colour cameras whereby the camera constantly monitors the light and adjusts its colour to maintain white areas. |
| B.L.C. (Back Light
Compensation) |
A feature of modern CCD cameras which electronically compensates for high background lighting to give detail which would normally be silhouetted. |
| Back Focus |
The mechanical aligning of the imaging device with the focal point of the lens. Most important on zoom lenses to ensure the image stays in focus throughout the zoom range. |
| Balanced Signal |
Method of transmitting video, usually over twisted pair cable, that consists of two equal but opposite signals being sent down two conductors. |
| Balun (Balanced Unbalanced) |
A device that connects a balanced line, such as twisted pair, to an unbalanced line, such as coax cable. |
| Base-Band Video |
Unmodulated video signal suitable for display on a monitor but not a domestic TV. |
| Baseband |
A full-channel bandwidth transmission where digital signals are placed onto a transmission line with no change in their modulation. |
| Baud |
Unit of signalling speed. The speed in baud is the number of line changes (in frequency, amplitude, etc.) or events per second. At low speeds, each event represents only one bit condition, and baud rate equals bps. As speed increases, each event represents more than one bit and baud rate does not truly equal bps. |
| Baud rate |
Data transmission speed. |
| Bit (Binary Digit) |
The smallest unit of information in a binary system; a one or zero condition. |
| Black Level |
The level on a video signal, just above the sync pulses, where black portions of the picture are represented. |
| BNC |
Video connector, the most commonly used in CCTV. |
| Byte |
A unit of information, usually shorter than a computer "word." Eight-bit bytes are most common. Also called a "character." Category 1 through 5 cables (CAT 1-5) The following categories are based on their transmission capacity. Categories 1 through 5e are based on the TIA/EIA-568 standard.
CABLE TYPE APPLICATION
1 UTP Analogue Voice
2 UTP Digital Voice, 1-Mbps Data
3 UTP, STP 16-Mbps Data
4 UTP, STP 20-Mbps Data
5 5e UTP STP 100-Mbps Data |
| C Mount |
Long established industrial standard for connecting cameras and lenses, widely used in the CCTV industry. |
| C.C.D. (Charged Coupled Device) |
A ‘chip’ that performs the same function as a camera tube. |
| CD-ROM (Compact Disc Read-Only Memory) |
A compact disk format used to hold text, graphics and hi-fi stereo in excess of 650 MB of data, which is equivalent to about 250,000 pages of text or 20,000 medium-resolution pages.
|
| Composite Video |
The full video signal, including both video data and sync pulses. |
| Compression |
A number of methods to reduce the size of digital information. See J-PEG, M-PEG and Wavelets. |
| CS Mount (Special C mount) |
New standard for connecting cameras and lenses. It has a shorter penetration into the camera, needed for many modern CCD designs. |
| CS to C Mount |
Adaptor 5mm spacer ring used to enable the use of C mount lenses on CS mount cameras. |
| D.D. (Direct Drive) |
An Auto Iris lens requiring a D.C. reference from the camera rather than the traditional video reference. |
| Data cable |
Cable used for transmitting low level signals between system units. |
| dB (decibel) |
A logarithmic unit for comparing two voltages, each 6dB doubles the voltage. |
| Default |
An assumption made by the system when no specific choice is given by the programme or the user. |
| Depth of Field |
The area of acceptable focus of an image. The wider you set the aperture of a lens the lower the depth of field becomes. |
| Dialup Line |
A two way line used in Public Switched Telephone Network (PSTN) |
| Digital |
A signal that levels are represented by binary numbers. These can be kept in a store. |
| Digital Video |
Recorder - DVR See Hard Disk Recorder. |
| Distribution
Amplifier |
A device that accepts a video signal and sends it out over a number of independent outputs. |
| DOS |
A disk operating system in which programmes are stored on disk. |
| Duplex (Multiplexer) |
A multiplexer with two frame stores allowing it to show multi-screen pictures while performing time multiplex recording. |
| DVD (Digital Video
Disk, Digital
Versatile Disk) |
A de facto standard agreed on by the computer, consumer electronics and entertainment industries for storing 4.7 or more GB of data on a single optical disc the size of a CD. |
| Dwell Time |
The length of time a switcher will hold a camera before moving on to the next in sequence. |
| E.I. (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. |
| Ethernet |
A local area network (LAN) developed by Xerox, Digital Equipment Corp. and Intel. Standardised as IEEE 802.3 and ISO 8802.3. Ethernet connects up to 1024 nodes at 10 Mbps over twistedpair, coax and fibre optic cable. When a station is ready to send, it transmits its data packets onto the network, which is common to all nodes. All stations "hear" the data. The station that matches the destination address in the packet responds while the others do nothing. Ethernet is a data-link protocol and functions at the Physical and Data-link Levels of the OSI model (Layers 1 and 2). |
| Ethernet Address |
A unique 48-bit number maintained by the IEEE/ISO and assigned to each Ethernet network adaptor. |
Ext. Sync (external
sync) |
The ability of CCTV equipment, normally cameras, to accept one or more of the standard sync formats so as to align itself to the rest of the system. |
| EXview™ |
The latest interline CCD sensor from SONY that has increased sensitivity across the visible spectrum and the near IR. |
| Fast Ethernet |
Generally refers to 100BASE-T and 100BASE-FX but may also include 100VG. |
| Field |
One half of a frame, consisting of either the odd or the even numbered lines, 50 fields are transmitted every second. |
| Field of View |
The view achieved with a particular lens; varies with the focal length. |
| Firewall |
A network node set up as a boundary to prevent unauthorised traffic from one segment to cross over to another. Firewalls are used to improve network traffic, as well as for security purposes. |
| Flash memory |
A memory chip that holds its content without power but must be erased in fixed blocks rather than single bytes. Block sizes typically range from 512 bytes up to 256KB. |
| Focal Length |
Of a lens, the distance in millimetres, between its secondary principal point and its focal point. The higher the number the greater the magnification and the less the field of view. |
| Focal Point |
The point on the axis of a lens to which parallel rays of light will cover. |
| Format |
How the computer arranges the information onto disk. Can also apply to printers. |
| Frame |
One complete TV picture made up of approximately 625 lines. 25 frames are transmitted every second. |
| Gigabyte (Gb) |
Order of magnitude; 10 9 |
| Hard Disk |
Non volatile digital data storage device used in PCs. Come in various storage sizes, normally measured in giga-bytes. See Hard Disk Recorder. |
| Hard Disk Recorder -
HDR (Digital Video
Recorder - DVR) |
Device that uses digital techniques to record CCTV pictures to a hard disk. The results can be of higher quality than VHS or SVHS, events can be found faster and there is no loss of quality when copies are made. |
| HTML (Hypertext Mark-up Language) |
A standard for defining documents with hypertext links. HTML is a subset of SGML (Standard Generalised Mark-up Language) and is used to establish links between documents on the World Wide Web. |
HTTP (Hypertext
Transfer Protocol) |
The clients/server protocol used for connections to servers on the World Wide Web. Addresses of Web sites begin with an http://prefix. |
| Hub |
A central connecting device in a network that joins communications lines together in a star configuration. |
| Hz (Hertz) |
Cycles per second. |
| I.R. (Infra Red) |
A range of frequencies lower than visible red light used for covert surveillance or as a low cost wireless video link. |
| Internet |
1) Any large network made up of several smaller networks.
2) A group of networks that are interconnected so that they appear to be one continuous large network and can be addressed seamlessly at the OSI Network layer through routers.
3) The industry name for the Worldwide interconnected network. Based upon the original ARPANET network, it’s used as a reference resource, a way of sending e-mail and an online chat room for users around the world. |
| Intranet |
A network connecting a related set of standard Internet protocols and files in HTML format with employees using Internet browsers in an organisation’s network and within the corporate firewalls. |
| IP (Internet
Protocol) |
The protocol used in gateways to connect networks at the OSI Network Layer (Layer 3) and above. IP routes a message across networks. |
Iris (Iris
diaphragm) |
Adjustable diaphragm that regulates the amount of light passing through a lens. |
ISDN (Integrated
Services Digital
Network) |
A digital switched network used to transmit voice, data, images or video. Also see BRI |
| J-PEG |
Joint Picture Expert Group. A popular suite of digital compression tools. Originally for use with "still" pictures but often used in CCTV products. |
| Kb |
Kilobyte, or one thousand bytes or characters of information. |
| Kilo |
Order of magnitude; 10 3 |
| LCD |
Liquid Crystal Display. A type of flat screen display. |
| Line Amplifier (Video line corrector) |
A device to make good the loss of signal strength and quality due to long cable runs. |
| Line Fed Camera |
A camera that receives its power along the same cable that is used to send its picture back to the monitor. |
| Linux |
A freeware, clone version of the UNIX‚ System V release 3.0 kernel that runs on PC x86 machines and other platforms. |
| Local Area Network (LAN) |
A data-communications system confined to a limited geographic area (up to about 10km) with moderate to high data rates (100 kbps to 100 Mbps). The area served may consist of a single building, a cluster of buildings or a campus-type arrangement. The network uses some type of switching technology and does not use common carrier circuits (although it may have gateways or bridges to other public or private networks). |
| Lux |
Metric measure of the light striking a surface. The light available from that surface will depend on how reflective it is. |
| M-PEG |
Moving Picture Expert Group. A suite of digital compression tools specifically designed to video images. |
| Macro |
Feature allowing you to pre-programme frequent system configurations for selection by a single keystroke or optionally by alarm inputs. |
| Mb |
Megabyte, or one million bytes or characters of information. |
| Mechanical Focus
(Back-focus,
racking) |
The mechanical aligning of the imaging device with the focal point of the lens; most important on zoom lenses to ensure the image stays in focus throughout the zoom range. |
| Megabyte (Mb) |
Order of magnitude; 10 6 |
| Micro |
Order of magnitude; 10 –6 |
| Modem |
Used with PSTN telephone lines to connect a fastscan system to the dial up BT network. |
| Modem |
Modulator/demodulator used in data transmission. |
| Modem (Modulator-
Demodulator) |
A device used to convert serial digital data from a transmitting terminal to an analogue signal (carrier) for transmission over a telephone channel or to reconvert the transmitted analogue signal to serial digital data for acceptance by a receiving terminal. |
| Monochrome |
Black and white, not colour. |
| Multiplex (Time
multiplex) |
Using one carrier to send more than one signal. In video multiplexers, achieving this by sending a different camera’s output in each successive field or frame of a video signal, in a form that can later be retrieved as single camera pictures. |
| Multiplexer |
A device that divides a transmission into two or more sub-channels, either by splitting the frequency band into narrow bands (frequency division) or by allotting a common channel to several transmitting devices, one at a time (time division). |
| N.T.S.C. (National
Television
Standards
Committee. See EIA) |
Colour TV system used in the USA. |
| Nano |
Order of magnitude; 10 –9 |
| Network |
A series of points connected by communications channels. |
| NIC (Network Interface Card) |
Board that provides network communication capabilities to and from a computer system. Also called an adaptor.
Noise Unwanted signals present on data lines. |
| Off-line |
Access control system not connected to a central computer. |
| On-line |
Access control system connected to a central computer. |
| OSD |
On-Screen Display. The ability of a camera or a piece of camera control equipment to display its set-up menu on a display monitor. Thereby greatly simplifying installation. |
| P.A.L. (Phase
Alternate Line. See
CCIR) |
Colour TV system used in the UK |
| Password |
A special word, code or symbol that must be presented to the computer system to gain access to its resources. It identifies the user to the computer system. |
| Photocell |
Automatically switches on the infra-red lights when light levels fall to a preset level. |
| Pico |
Order of magnitude; 10 –12 |
| PIN |
Personal Identification Number. |
| PING (Packet
InterNet Groper) |
A utility used to determine if a TCP/IP device is available and responsive on a network or at an Internet site. |
| Plasma |
A type of flat screen display. |
| Port |
That portion of a computer through which a peripheral device may communicate. |
| 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. Special telemetry equipment is required. |
| Protocol |
A standard for sending coded messages between computers and peripherals. |
| Protocol Converter |
Data transmission converter i.e. RS232 to RS485 or vice versa. |
| PSU |
Power supply unit. |
| Pulse |
A positive or negative change in voltage that conveys information to a circuit. |
| Quad Splitter |
Device that uses digital techniques to compress four full pictures onto one monitor screen. Rack Mount (19" rack) An industrial standard housing 19" wide, its height is measured in units (U’s) of 1.75". |
RAM (Random Access
Memory) |
Read/write memory of a computer. Usually a memory chip that can be written to, read from and erased from. |
