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Simple do it yourself advice |
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Favorite questions |
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AC
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Alternating Current.
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ACTIVITY DETECTION
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A simple form of video motion detection, activity detection merely produces an alarm indication when light levels change. Often used with video multiplexers to increase the update of cameras where activity is occurring.
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ADDRESS
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A sequence of bits, a character or a group of characters that identifies a network station.
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AFC
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Automatic Frequency Control the automatic tracking of an oscillator to a specific narrow range of frequencies.
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AGC
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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 have AGC off.
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AI
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Automatic Iris a function of a lens that automatically adjusts to varying light levels to allow the correct amount of light to fall upon the image sensor.
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ALARM ACTIVATED VCR
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A VCR that is triggered to start recording from the idle position. This can take as long as 20 seconds to spool the tape and start recording for a useable picture. If the VCR is in time lapse mode an alarm trigger can take considerably less for a useable picture.
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ALARMING
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Ability for CCTV equipment to respond to an external alarm input, providing numerous functions such as to switch the relevant camera signal and alarm start a VCR.
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ALC
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Automatic Level Control on AI lenses a manual adjustment also known as Peak/Average, a facility to make the lens respond more to the highlights (Peak), or more to the darker scenes (Average) , providing a user adjustment of information seen in the highlight.
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ALGORITHM
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A rule or procedure for problem solving, a commonly used term in mathematics.
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AM
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Amplitude Modulation.
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AMBIENT LIGHT
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The general light level of any given scene.
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ANALOGUE
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An electrical voltage that is directly proportional to a given input, i.e.. giving a correspondingly variable output.
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ANGLE OF VIEW
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The limits of the viewing area of a camera/lens.
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APD
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Avalanche Photo Diode.
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APERTURE
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The measure of the light gathering capability of a lens. The maximum aperture is the minimum 'f' stop of a lens, generally the lower the 'f' stop the better.
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APERTURE CORRECTION
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Switchable correction circuit which electronically sharpens the image of a picture.
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ARMOUR
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Protection given to a cable to provide resistance to damage that may be incurred from being crushed or cut.
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ASPECT RATIO
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Ratio between the vertical and horizontal image size of a camera sensor, the ratio is 4:3.
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ASYNCHRONOUS DATA
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Most common form of data, where data is passed without any clocks or timing information. Uses start and stop bits to synchronise.
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AT COMMANDS
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A protocol used between a modem and terminal equipment for autodialing and configuration of the modem.
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ATTENUATION
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Term used to describe the amount of loss seen in a video signal when transmitted from one point to another.
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| AUTOMATIC IRIS |
A lens that adjusts automatically to allow the right amount of light to fall on the imaging device. There is a tiny motor and amplifier built in which receives a control signal from the camera to maintain a constant one volt peak to peak (pp) video level. |
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AUX
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Auxiliary.
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BACK FOCUS
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A mechanical adjustment for focusing a camera. It moves the image sensor in relationship to the lens to accommodate for different back focal lengths of lenses. This is important when a zoom lens is fitted.
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BALANCED SIGNAL
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Term generally associated with the transmission of video signals over twisted pair cables. A circuit of two conductors equal to each other in voltage but opposite in polarity.
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BANDWIDTH
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A value expressing the difference between the upper and lower limits through a range of allowable frequencies.
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BAUD
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The speed at which data is transmitted, i.e.. 1 baud = 1 Bit per second.
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BIT
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A binary digit, the smallest element of information in a binary system.
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BLACK LEVEL
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A measure of picture signal level, that matches to a specified maximum limit for black peaks.
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BLANKING PERIOD
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The period of the composite video signal at black level (0.3V) and below when the retrace occurs.
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BLC
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Back Light Compensation - an electronic feature of modern CCD cameras to allow viewing of highlighted scenes that would normally be silhouetted, thus providing more detail.
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BNC
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The most common form of video connector used in CCTV.
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BPS
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Bits per second.
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BROADBAND
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Communications transmission where the signal is impressed on a higher frequency carrier.
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BRIDGING
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The connection of more than 1 electrical circuit or component in parallel.
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BURN
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An image that has become permanently frozen onto the sensitive region of a camera or monitor tube.
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BUS NETWORK
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A topology network where all terminals are attached to a transmission medium serving as a bus.
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BYTE
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A unit of 8 Bits.
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CABLE EQUALISER
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Increases the video signal level by amplification, used on long cable runs to compensate for the loss in video signal level.
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CAD
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Computer Aided Design.
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CAMEO
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Term seen in video multiplexer terminology, represents one sixteenth of the area of a full screen.
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CATV
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Communal Aerial Television.
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CCD
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CCD: Charge coupled device; It is light sensitive and forms the imaging device of most modern cameras. Size is measured diagonally and can be 1/3",1/2",etc". There are two types, frame transfer and interline transfer.
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| What is CCD sensor? |
Our video cameras are piece of technology and at the heart of it is the CCD (charge coupled device) imager chip. A CCD consists of several hundred thousand individual picture elements (pixels) on a tiny 1/2", 1/3", or 1/4" chip. Each pixel responds to light falling on it by storing a tiny charge of electricity. The pixels are arranged on a precise grid, with vertical and horizontal transfer registers carrying the signals to the camera's video processing circuitry. This transfer of signals occurs sixty times per second. The CCD camera's electronic shutter is not really a moving shutter, but a clever piece of signal processing. Under low light conditions, the CCD is allowed to gather signal for the full 1/60th of a second. Under brighter lighting conditions, the video processing chip automatically responds by reading the CCD and then immediately "early purging" it, resulting in precise control over the video level. Even at a shutter speed of 1/100,000 of a second, the CCD camera is still delivering 60 images per second, but each image is gathered over a much shorter period of time. It doesn't end with the CCD...the image is constantly monitored and optimised by advanced on board signal processing circuitry. The end result is a fantastic picture, with no fiddling, no adjustments, and best of all, unbelievable reliability. |
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CCIR
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Committee Consultative International Radiocommunications. Monochrome Video Signal for most of Europe, Australia and the Middle East 625 lines, 50Hz.
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CCTV
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Closed Circuit Television A television system used for private purposes and not for public or general broadcast.
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CHROMA BURST
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A reference signal (4.43Mhz) included in the video signal after the horizontal synchronisation line pulse.
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CHROMINANCE
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The part of a video signal that contains all of the colour information.
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CLADDING
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In Fibre Optics the outermost region of an optical cable, less dense than the central core, it acts as an optical barrier to prevent transmitted light leaking away from the core.
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CLOCK
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A name commonly used for any of the sources of timing signals used in synchronous data transmission.
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CMOS
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Complimentary Metal Oxide Semiconductor Solid state switching device, also used as a camera pick up device MOS chip.
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C-MOUNT
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Industry standard thread mounting portion on the rear of a lens. Note a C mount lens can be used on a CS mount camera with a 5mm adaptor ring, however a CS mount lens cannot be used on a C mount format camera.
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| 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 C-mount configuration. These lenses are smaller and cheaper than the C-mount equivalents. |
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COAXIAL CABLE
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A shielded cable containing a central conductor.
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COMET TAILS
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A condition that appears on a VDU that is caused by near burn combined with image movement.
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COMPOSITE SYNC
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A signal containing Line and Field pulses, but one which has no video information.
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COMPOSITE VIDEO
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The combination of all electronic information required to produce a video signal. Comprising 0.7 volts video and 0.3 volts sync., hence the term one volt peak to peak.
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COMPRESSED PICTURE
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A compressed picture is a full size picture that has been reduced in size while still displaying all of the original screen information.
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COMPRESSION
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Taking standard video signals and reducing them into compact digital data.
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CONDITIONAL REFRESHMENT
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A technique used by some video transmission systems. Once the first image has been constructed only the part of the image that changes is subsequently transmitted, allowing high speed updates when little movement is seen. However, the speed of update decreases with more movement.
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CORE
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Central region of a cable.
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CPU
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Central Processing Unit the main device that contains the processing logic.
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CROSS TALK
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Electrical interference caused by electromagnetic or electrostatic coupling by nearby conductors or external sources. Interference between two or more signals in close proximity within a bandpass.
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CRT
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Cathode Ray Tube a device that is used to display information on a TV or Monitor.
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CS to C MOUNT ADAPTOR
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A spacer ring of 5mm that allows the use of C mount lenses on CS mount cameras.
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CS-MOUNT
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Uses the same thread as C mount but requires the lens to be 5mm closer to the image sensor, new industry standard for lens mounting.
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 adapter ring to reduce this distance to 12.5mm.
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20mA CURRENT LOOP
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Electronic signaling method for CCTV, used for controlling remote camera functions. Data is sent via a pair of wires, offers greater distance capability and is less susceptible to interference than similar 2 wire data transmission systems.
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DARK CURRENT
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The thermally induced current that exists in a photo diode in the absence of incident optical power.
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DAT
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Digital Audio Tape, a technology for storing massive amounts of digital information in a small package.
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DB
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Decibel a logarithmic ratio between two signals.
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DC
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Direct Current.
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DD
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Direct Drive a new form of auto iris drive for lenses, whereby the lenses requires a DC reference from the camera opposed to a video level required by AI lenses.
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DECODE
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Seen in multiplexer terminology referring to the playback of images from tape.
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DECOMPRESSION
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Taking digitally compressed DVST information and restoring this to normal video images.
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DEFINITION
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The ability of a camera or monitor to resolve fine detail, measured in lines.
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DEPTH OF FIELD
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Area of view that is in focus, the depth of field decreases as the aperture increases.
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DESKTOP SWITCHER
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A device to select incoming signals from a number of cameras for display onto one or more monitors.
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DIGITAL SIGNAL
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A signal that comprises binary information i.e.. 1 or 0, to allow processing by micro processor based equipment.
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DISTRIBUTION AMPLIFIER
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A device that separates and amplifies input signals for multiple outputs.
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DROPOUT
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The loss of video signal from a magnetic tape playback head or worn or damaged tapes.
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DTMF
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Dial Tone Multi Frequency used by some manufacturers for telemetry signaling over twisted pair cables.
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DUPLEX
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Seen in multiplexer terminology where two simplex units have been assembled as one unit, allowing the equipment to perform two functions simultaneously, i.e.. record pictures to tape whilst displaying multiscreen images of cameras at the same time.
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DVST
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Digital Video Storage & Transmission name given to equipment that can compress video pictures to a fraction of their former size for transmission over communication networks or for digital storage. Note, this equipment transmits the total image every time.
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DWELL TIME
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The time duration a video switcher will stay on a camera before moving onto the next camera.
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EI
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Electronic Iris a feature of modern CCD cameras where the camera electronics automatically varies the shutter to mimic an AI lens, allowing the use of fixed or manual iris lenses in a wider range of areas.
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EIA
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Electrical Industries Association. Monochrome video signal for North America and Japan TV standard 525 lines 60Hz,
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EMI
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Electro Magnetic Interference electrical or electromagnetic energy that may cause unwanted responses, degradation or failure in electronic equipment.
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ENCODE
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Seen in multiplexer terminology as the recording of images to tape.
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ERROR CORRECTION
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Method employed by modems to ensure that data is transmitted or received error free.
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EXTERNAL SYNC
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The ability of electronic equipment (normally seen in cameras) to accept a synchronisation signal from an external source and synchronise itself to it.
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'f' STOP
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The ratio of the focal length to the effective diameter of the lens. The smaller the 'f' stop, the more light is passed. The 'f' stop directly affects the depth of field.
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FC
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Foot Candle American measurement of light, 10fc equals 1 lux.
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FI
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Fixed Iris.
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FIBRE OPTIC
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More efficient method of sending signals than the more conventional method of copper cable.
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FIELD
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One half of a frame comprising 312.5 lines, there are 50 fields per second.
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FIELD OF VIEW
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The image area produced by any camera/lens combination.
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FLANGE LENGTHS
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Referring to lenses C mount = 15.5mm, CS mount = 12.5mm.
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FM
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Frequency Modulation.
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FOCAL LENGTH
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The focal length of a lens measured in millimetres, has a direct relationship to the angle of view that is obtained. A short focal length provides a wide angle of view and a large focal length provides a narrower angle of view.
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FOCAL POINT
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The point at which light passing through a lens is concentrated.
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FRAME
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One complete TV picture, one frame is made up of two fields, TV pictures are made up of 25 frames per second.
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FRAME STORE
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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 dialed up. When the link is confirmed, the picture is transmitted.
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FRAME TRANSFER
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Type of CCD imager used by some cameras.
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FREQUENCY RESPONSE
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The capability of a device to transmit or receive a given range of frequencies.
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FRONT PORCH
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A portion of a composite video signal that is located between the start of the horizontal blanking pulse and the start of the corresponding sync. pulse.
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FSK
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Frequency Shifted Keying a form of signaling employed by some coaxial born telemetry equipment.
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FULL PICTURE UPDATE
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Used to describe video transmission products that send the total image on each update.
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GALVANOMETRIC
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A method of converting the minute electric currents produced by AI circuits, used by both AI & DD lenses.
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GAMMA CORRECTION
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Balances the light seen by the camera to that of the monitor.
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GEN LOCK
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As per external sync, allows cameras to synchronise to a common signal, providing bounce free switching of images.
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GHOSTING
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Multiple images caused by video signal transmission echoes, not to be confused with burn in.
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GIGA
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Order of magnitude 10 9.
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GIP
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Graded Index Profile a measurement shown in the form of a diagram which illustrates how the quality of glass used in fibre optics alters gradually from the densest at the core to the optically less dense cladding.
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GLT
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Ground Loop Transformer an isolation transformer with no direct contact between input and output.
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GROUND LOOP
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Caused by different earth potentials clearly seen as interference or humbars on a video signal.
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