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HARDWARE COMPRESSION
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Video data compression taking place in specialised purpose built microchips.
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HARD WIRED
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Direct cable connection between one product to another, used for control of equipment in simple systems.
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HAYES COMPATIBILITY
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When a modem complies with the Hayes AT command language used by most communication software packages.
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HELICAL SCAN
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Recording system used by VCR's, a record/playback head used by VCR's whereby the head rotates scanning the video tape in a helical path.
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HORIZONTAL RESOLUTION
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The amount of information that can be displayed upon any VDU (measured in lines).
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HZ
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Hertz Cycles per second. The measure of frequency.
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IDENT
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Camera caption or number displayed on a video signal.
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ILLUMINANCE
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Measurement of light in lumens per square metre, the unit of which is lux.
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IMAGE INTENSIFIER
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A device that uses fibre optics to increase the sensitivity of a pick-up tube.
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IMAGE PLANE
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The surface upon which an image is formed in a camera.
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IMAGE SENSOR FORMAT
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Refers to the size of the image plane within a camera.
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IMPEDANCE
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Measured in ohms, refers to the combined resistance and reactance in an electrical circuit.
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INTERLACE (2:1)
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Refers to the combination of two fields, one odd, one even to produce a single frame.
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INTERLEAVING
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Term used in multiplexing. When a camera is alarmed, be it via external means (PIR) or by activity detection, then it is recorded every other frame.
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INTERLINE TRANSFER
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Type of CCD imager used by some cameras.
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INTERNAL SYNC
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The internal generation of sync pulses in a camera using a crystal controlled oscillator. This is needed on non-mains powered cameras.
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IP RATING
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A rating used to provide an index of protection from elements such as water and dust ingress. (see page 34)
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IR LIGHTING
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Lighting that is above the visible wavelength, used for discrete illumination in CCTV systems.
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IR SHIFT
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Difference in focus of a camera's field of view between white and IR lighting.
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IR TRANSMISSION
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Method of sending video signals and/or data over free space, distance and quality of transmission is affected by environmental conditions such as fog and rain.
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IRIS
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Mechanism within a lens to regulate the amount of light that passes through, and falls upon, the image sensor.
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ISDN
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Integrated Service Digital Network an International standard for voice and data communications offering greatly improved transmission speeds than the older PSTN network (Public Switched Telephone Network).
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ISIT
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Intensified Silicon Intensified Target usually used for extreme low light CCTV or X-Ray machines.
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ISO
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International Standards Organization.
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I/O
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Input/Output.
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I/P
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Input.
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KILO
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Order of magnitude 10 -3.
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LAG
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Retention that occurs in a video image when rapid motion of the camera or viewed object leaves a trail.
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LAN
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Local Area Network Communications network for electronic equipment, limited to usually a single building or site.
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LASER
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A source of exceptionally pure light which can consist of a single wavelength concentrated into a straight beam, used to transmit IR lighting through fibre optic cable.
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LEASED LINE
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A telephone connection giving a permanent point to point link.
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LED
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Light Emitting Diode.
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| Lens calculator |
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LINE AMPLIFIER
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Device that prepares a signal for transmission over extended cable runs by amplifying the signal strength.
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LINE FED
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A camera that is powered down the same cable which it uses to send the video information back to the monitor.
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LINE LOCKED
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A camera that is synchronised to the frequency of its AC power supply.
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LINE POWERED
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See line fed.
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LOOPING
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A piece of video equipment that allows video signals to pass through without being terminated.
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| LOOP FRAME STORE |
The principle is that a series of video frames is compressed and stored in a continuous loop. This records a certain number of frames and then records over them again and again until an alarm signal is received. When this happens it carries on recording for a dozen frames or so and then stops. This means that frames before and after the incident are recorded. This eliminates the boring searching through hours of video tape and concentrates on the period of activity. |
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LUMINANCE
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Y the monochrome element of a video signal.
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LUX
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Unit of light measurement.
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MATRIX SWITCHING
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A video switcher that allows any input to be switched to any monitor output.
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MCL
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Maximum camera length.
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MEGA
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Order of magnitude 10 -6.
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MEGASTREAM
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Communications network comprising many hundreds of individual communication channels.
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MFD
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Mode field diameter fibre optics.
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MI
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Manual Iris.
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MICRO
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Order of magnitude 10 -6 (one millionth).
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MICROWAVE TRANSMISSION
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Method of sending video signals and/or data over free space, longer distances than IR transmission can be achieved. Licencing is usually required.
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MILLI
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Order of magnitude 10 -3 (one thousandth).
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MODE
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Path taken by light rays along fibre optic cable.
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MODEM
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Modulator / Demodulator device used for sending digital signals over an analogue network, i.e.. video transmission over the PSTN network.
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MODULATION
MODULATOR
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Modulation is the impression of a baseband video and audio signal to a Radiowave (RF Frequency) that can be processed (demodulated) by a television tuner. This modulated RF frequency can then be combined with an existing feed of local channels and be distributed to all the televisions on a coaxial network as a new channel.
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MONITOR
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A video display unit used to display images from a camera or computer.
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MONOCRHOME
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A black and white picture.
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MOS
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Metal Oxide Semiconductor a form of CCD imager used in some CCD cameras.
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MTBF
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Mean Time Between Failure the average time between equipment or component failure.
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MTTR
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Mean Time To Repair the average time it takes to repair a piece of equipment.
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MULTIMODE
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An optical fibre that supports more than one propagation mode.
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MULTIPLEXER
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A unit that can accept a number of camera inputs and almost simultaneously display them on a single monitor and/or record them to a single video tape. Multixplexers can also be used to transmit multiple cameras over the same transmission medium.
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MULTIPLEXING
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Process in which multiple cameras are transmitted or recorded.
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MUX
MULTIPLEXER
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An electronic system that can accept a number of camera inputs and record them virtually simultaneously. They can also provide multi screen displays with four, nine, sixteen etc. cameras on the screen at once. 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. This requires a multiplexer at each end of the line.
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NANO
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Order of magnitude 10 -9.
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ND
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Neutral Density.
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ND FILTER
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A glass filter that attenuates the light evenly over the visible spectrum, used to force the iris on a lens to open in order to focus the camera for low light conditions.
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ND SPOT FILTER
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A graduated filter fitted to the centre of a lens, restricting the amount of light that can effectively pass through to the image sensor.
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NEUTRAL COMPUTING
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Powerful software used in motion detection to teach the computer to learn object sizes and shapes.
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NOISE
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Appears on screen as graininess or 'snow' effects on a video image.
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NON-COMPOSITE VIDEO
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A video signal that is complete, except for the synchronisation information.
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NTSC
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National Television Standards Committee. Colour Video Signal, North American and Japanese television standard - 525 Lines, 60Hz.
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N/C
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Normally Closed.
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N/O
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Normally Open.
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O/P
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Output.
more>> P-Z
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