|
|
|
|
ACTIVITY DETECTION
|
Activity detection produces
an alarm indication when the light levels change. Generally used
with video multiplexers to update the cameras where activity has
occurred.
|
|
AFC
|
Automatic Frequency Control
- automatic tracking of an oscillator within specific narrow range
of frequencies.
|
|
AGC
|
Automatic
gain control - electronic circuitry component designed to increase
the video signal in low light conditions. Because this generally
introduces 'noise' on the picture producing a grainy appearance
the AGC should be set to 'off'.
|
|
AI
|
Automatic Iris - Allows varying
light levels to automatically adjust to the correct light level
i.e. dirct sun light, torches and other lighting etc.
|
|
ALARM ACTIVATED VCR
|
Video Recorder set to begin
recording from the idle position. Warning - Alarm Activated VCR
can take up 20 seconds to start recording . If evidence is required
of activity during spooling - it will not be recorded. However,
If the VCR is set to time lapse mode the trigger can take
considerably less time for a recording.
|
|
ALARMING
|
Alarming allows the CCTV equipment
to respond to an alarm situation, this provides a number of functions
such as alarm activated VCR.
|
|
ALC
|
Automatic Level Control a facility
to make the lens adjust and respond to the highlights, or to the
darker scenes . Highlights can
be known as 'peak' and darker scenes can be known as 'average'.
|
|
AM
|
Amplitude Modulation.
|
|
AMBIENT LIGHT
|
Ambient light is the generally
accepted level of light in any given scene.
|
|
ANALOGUE
|
Analogue is an electrical voltage
directly proportional to the given input, i.e.. giving a correspondingly
variable output.
|
|
ANGLE OF VIEW
|
Angle of View restricts the
viewing area of a camera/lens.
|
|
APD
|
Avalanche Photo Diode.
|
|
APERTURE
|
Aperture is the opening in the
lens and measure of the light gathering capability. The maximum
aperture is the minimum 'f' stop of a lens, and the lower the 'f'
stop the better.
|
|
APERTURE CORRECTION
|
Aperture Correction - Switchable
circuit that electronically sharpens the image of a picture.
|
|
ARMOUR CABLE
|
Armour Cable is protected cable
providing resistance to damage that may occurr from being cut or
crushed.
|
|
ASPECT RATIO
|
Aspect Ratio - the ratio between
the vertical and horizontal image size of a camera sensor, the normal
ratio is 4:3.
|
|
ATTENUATION
|
Attenuation - The decrease in
magnitude of a wave or signal when it travels through a medium
or an electric system. It is usually
measured in decibels (dB).
|
| AUTOMATIC
IRIS |
Automatic Iris - 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. |
|
BACK
FOCUS |
Back Focus - A procedure of
adjusting the physical position of the CCD-chip/lens to achieve
the correct focus for all focal length settings (especially critical
with zoom lenses).
|
|
BALANCED SIGNAL
|
Balanced Signal is a 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.
|
|
BANDWIDTH
|
Bandwidth is a value expressing
the difference between the upper and lower limits through a range
of allowable frequencies. The complete range of frequencies over
which a circuit or electronic system can function with minimal signal
loss, usually measured between the 3 dB points (half power) at each
end of the frequency spectrum. In PAL systems the bandwidth is generally
accepted as 5.5MHz.
|
|
BAUD
|
Baud is the speed at which data
is transmitted, i.e.. 1 baud = 1 Bit per second.
|
|
BIT
|
A binary digit, the smallest element
of information in a binary system.
|
|
BLACK LEVEL
|
A measure of picture signal level,
that matches to a specified maximum limit for black peaks.
|
|
BLANKING PERIOD
|
The period of the composite video signal
at black level (0.3V) and below when the retrace occurs.
|
|
BLC
|
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.
|
|
BNC
|
The most common form of video connector
used in CCTV.
|
|
BPS
|
Bits per second.
|
|
BROADBAND
|
Communications transmission where the
signal is impressed on a higher frequency carrier.
|
|
BRIDGING
|
The connection of more than 1 electrical
circuit or component in parallel.
|
|
BURN
|
An image that has become permanently
frozen onto the sensitive region of a camera or monitor tube.
|
|
BUS NETWORK
|
A topology network where all terminals
are attached to a transmission medium serving as a bus.
|
|
BYTE
|
A unit of 8 Bits.
|
|
CABLE EQUALISER
|
Increases the video signal level by
amplification, used on long cable runs to compensate for the loss
in video signal level.
|
|
CAD
|
Computer Aided Design.
|
|
CAMEO
|
Term seen in video multiplexer terminology,
represents one sixteenth of the area of a full screen.
|
|
CATV
|
Communal Aerial Television.
|
|
CCD
|
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.
|
| 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. |
|
CCIR
|
Committee Consultative International
Radiocommunications. Monochrome Video Signal for most of Europe,
Australia and the Middle East 625 lines, 50Hz.
|
|
CCTV
|
Closed Circuit Television A television
system used for private purposes and not for public or general broadcast.
|
|
CHROMA BURST
|
A reference signal (4.43Mhz) included
in the video signal after the horizontal synchronisation line pulse.
|
|
CHROMINANCE
|
The part of a video signal that contains
all of the colour information.
|
|
CLADDING
|
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.
|
|
CLOCK
|
A name commonly used for any of the
sources of timing signals used in synchronous data transmission.
|
|
CMOS
|
Complimentary Metal Oxide Semiconductor
Solid state switching device, also used as a camera pick up device
MOS chip.
|
|
C-MOUNT
|
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.
|
| 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. |
|
COAXIAL CABLE
|
A shielded cable containing a central
conductor.
|
|
COMET TAILS
|
A condition that appears on a VDU that
is caused by near burn combined with image movement.
|
|
COMPOSITE SYNC
|
A signal containing Line and Field
pulses, but one which has no video information.
|
|
COMPOSITE VIDEO
|
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.
|
|
COMPRESSED PICTURE
|
A compressed picture is a full size
picture that has been reduced in size while still displaying all
of the original screen information.
|
|
COMPRESSION
|
Taking standard video signals and reducing
them into compact digital data.
|
|
CONDITIONAL REFRESHMENT
|
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.
|
|
CORE
|
Central region of a cable.
|
|
CPU
|
Central Processing Unit the main device
that contains the processing logic.
|
|
CROSS TALK
|
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.
|
|
CRT
|
Cathode Ray Tube a device that is used
to display information on a TV or Monitor.
|
|
CS to C MOUNT ADAPTOR
|
A spacer ring of 5mm that allows the
use of C mount lenses on CS mount cameras.
|
|
CS-MOUNT
|
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.
|
|
20mA CURRENT LOOP
|
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.
|
|
DARK CURRENT
|
The thermally induced current that
exists in a photo diode in the absence of incident optical power.
|
|
DAT
|
Digital Audio Tape, a technology for
storing massive amounts of digital information in a small package.
|
|
DB
|
Decibel a logarithmic ratio between
two signals.
|
|
DC
|
Direct Current.
|
|
DD
|
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.
|
|
DECODE
|
Seen in multiplexer terminology referring
to the playback of images from tape.
|
|
DECOMPRESSION
|
Taking digitally compressed DVST information
and restoring this to normal video images.
|
|
DEFINITION
|
The ability of a camera or monitor
to resolve fine detail, measured in lines.
|
|
DEPTH OF FIELD
|
Area of view that is in focus, the
depth of field decreases as the aperture increases.
|
|
DESKTOP SWITCHER
|
A device to select incoming signals
from a number of cameras for display onto one or more monitors.
|
|
DIGITAL SIGNAL
|
A signal that comprises binary information
i.e.. 1 or 0, to allow processing by micro processor based equipment.
|
|
DISTRIBUTION AMPLIFIER
|
A device that separates and amplifies
input signals for multiple outputs.
|
|
DROPOUT
|
The loss of video signal from a magnetic
tape playback head or worn or damaged tapes.
|
|
DTMF
|
Dial Tone Multi Frequency used by some
manufacturers for telemetry signaling over twisted pair cables.
|
|
DUPLEX
|
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.
|
|
DVST
|
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.
|
|
DWELL TIME
|
The time duration a video switcher
will stay on a camera before moving onto the next camera.
|
|
EI
|
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.
|
|
EIA
|
Electrical Industries Association.
Monochrome video signal for North America and Japan TV standard
525 lines 60Hz,
|
|
EMI
|
Electro Magnetic Interference electrical
or electromagnetic energy that may cause unwanted responses, degradation
or failure in electronic equipment.
|
|
ENCODE
|
Seen in multiplexer terminology as
the recording of images to tape.
|
|
ERROR CORRECTION
|
Method employed by modems to ensure
that data is transmitted or received error free.
|
|
EXTERNAL SYNC
|
The ability of electronic equipment
(normally seen in cameras) to accept a synchronisation signal from
an external source and synchronise itself to it.
|
|
'f' STOP
|
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.
|
|
FC
|
Foot Candle American measurement of
light, 10fc equals 1 lux.
|
|
FI
|
Fixed Iris.
|
|
FIBRE OPTIC
|
More efficient method of sending signals
than the more conventional method of copper cable.
|
|
FIELD
|
One half of a frame comprising 312.5
lines, there are 50 fields per second.
|
|
FIELD OF VIEW
|
The image area produced by any camera/lens
combination.
|
|
FLANGE LENGTHS
|
Referring to lenses C mount = 15.5mm,
CS mount = 12.5mm.
|
|
FM
|
Frequency Modulation.
|
|
FOCAL LENGTH
|
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.
|
|
FOCAL POINT
|
The point at which light passing through
a lens is concentrated.
|
|
FRAME
|
One complete TV picture, one frame
is made up of two fields, TV pictures are made up of 25 frames per
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 dialed up. When the link is confirmed,
the picture is transmitted.
|
|
FRAME TRANSFER
|
Type of CCD imager used by some cameras.
|
|
FREQUENCY RESPONSE
|
The capability of a device to transmit
or receive a given range of frequencies.
|
|
FRONT PORCH
|
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.
|
|
FSK
|
Frequency Shifted Keying a form of
signaling employed by some coaxial born telemetry equipment.
|
|
FULL PICTURE UPDATE
|
Used to describe video transmission
products that send the total image on each update.
|
|
GALVANOMETRIC
|
A method of converting the minute electric
currents produced by AI circuits, used by both AI & DD lenses.
|
|
GAMMA CORRECTION
|
Balances the light seen by the camera
to that of the monitor.
|
|
GEN LOCK
|
As per external sync, allows cameras
to synchronise to a common signal, providing bounce free switching
of images.
|
|
GHOSTING
|
Multiple images caused by video signal
transmission echoes, not to be confused with burn in.
|
|
GIGA
|
Order of magnitude 10 9.
|
|
GIP
|
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.
|
|
GLT
|
Ground Loop Transformer an isolation
transformer with no direct contact between input and output.
|
|
GROUND LOOP
|
Caused by different earth potentials
clearly seen as interference or humbars on a video signal.
|
|
HARDWARE COMPRESSION
|
Video data compression taking place
in specialised purpose built microchips.
|
|
HARD WIRED
|
Direct cable connection between one
product to another, used for control of equipment in simple systems.
|
|
HAYES COMPATIBILITY
|
When a modem complies with the Hayes
AT command language used by most communication software packages.
|
|
HELICAL SCAN
|
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.
|
|
HORIZONTAL RESOLUTION
|
The amount of information that can
be displayed upon any VDU (measured in lines).
|
|
HZ
|
Hertz Cycles per second. The measure
of frequency.
|
|
IDENT
|
Camera caption or number displayed
on a video signal.
|
|
ILLUMINANCE
|
Measurement of light in lumens per
square metre, the unit of which is lux.
|
|
IMAGE INTENSIFIER
|
A device that uses fibre optics to
increase the sensitivity of a pick-up tube.
|
|
IMAGE PLANE
|
The surface upon which an image is
formed in a camera.
|
|
IMAGE SENSOR FORMAT
|
Refers to the size of the image plane
within a camera.
|
|
IMPEDANCE
|
Measured in ohms, refers to the combined
resistance and reactance in an electrical circuit.
|
|
INTERLACE (2:1)
|
Refers to the combination of two fields,
one odd, one even to produce a single frame.
|
|
INTERLEAVING
|
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.
|
|
INTERLINE TRANSFER
|
Type of CCD imager used by some cameras.
|
|
INTERNAL SYNC
|
The internal generation of sync pulses
in a camera using a crystal controlled oscillator. This is needed
on non-mains powered cameras.
|
|
IP RATING
|
A rating used to provide an index of
protection from elements such as water and dust ingress. (see page
34)
|
|
IR LIGHTING
|
Lighting that is above the visible
wavelength, used for discrete illumination in CCTV systems.
|
|
IR SHIFT
|
Difference in focus of a camera's field
of view between white and IR lighting.
|
|
IR TRANSMISSION
|
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.
|
|
IRIS
|
Mechanism within a lens to regulate
the amount of light that passes through, and falls upon, the image
sensor.
|
|
ISDN
|
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).
|
|
ISIT
|
Intensified Silicon Intensified Target
usually used for extreme low light CCTV or X-Ray machines.
|
|
ISO
|
International Standards Organization.
|
|
I/O
|
Input/Output.
|
|
I/P
|
Input.
|
|
KILO
|
Order of magnitude 10 -3.
|
|
LAG
|
Retention that occurs in a video image
when rapid motion of the camera or viewed object leaves a trail.
|
|
LAN
|
Local Area Network Communications network
for electronic equipment, limited to usually a single building or
site.
|
|
LASER
|
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.
|
|
LEASED LINE
|
A telephone connection giving a permanent
point to point link.
|
|
LED
|
Light Emitting Diode.
|
| Lens
calculator |
|
|
LINE AMPLIFIER
|
Device that prepares a signal for transmission
over extended cable runs by amplifying the signal strength.
|
|
LINE FED
|
A camera that is powered down the same
cable which it uses to send the video information back to the monitor.
|
|
LINE LOCKED
|
A camera that is synchronised to the
frequency of its AC power supply.
|
|
LINE POWERED
|
See line fed.
|
|
LOOPING
|
A piece of video equipment that allows
video signals to pass through without being terminated.
|
| 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. |
|
LUMINANCE
|
Y the monochrome element of a video
signal.
|
|
LUX
|
Unit of light measurement.
|
|
MATRIX SWITCHING
|
A video switcher that allows any input
to be switched to any monitor output.
|
|
MCL
|
Maximum camera length.
|
|
MEGA
|
Order of magnitude 10 -6.
|
|
MEGASTREAM
|
Communications network comprising many
hundreds of individual communication channels.
|
|
MFD
|
Mode field diameter fibre optics.
|
|
MI
|
Manual Iris.
|
|
MICRO
|
Order of magnitude 10 -6 (one millionth).
|
|
MICROWAVE TRANSMISSION
|
Method of sending video signals and/or
data over free space, longer distances than IR transmission can
be achieved. Licencing is usually required.
|
|
MILLI
|
Order of magnitude 10 -3 (one thousandth).
|
|
MODE
|
Path taken by light rays along fibre
optic cable.
|
|
MODEM
|
Modulator / Demodulator device used
for sending digital signals over an analogue network, i.e.. video
transmission over the PSTN network.
|
|
MODULATION
MODULATOR
|
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.
|
|
MONITOR
|
A video display unit used to display
images from a camera or computer.
|
|
MONOCRHOME
|
A black and white picture.
|
|
MOS
|
Metal Oxide Semiconductor a form of
CCD imager used in some CCD cameras.
|
|
MTBF
|
Mean Time Between Failure the average
time between equipment or component failure.
|
|
MTTR
|
Mean Time To Repair the average time
it takes to repair a piece of equipment.
|
|
MULTIMODE
|
An optical fibre that supports more
than one propagation mode.
|
|
MULTIPLEXER
|
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.
|
|
MULTIPLEXING
|
Process in which multiple cameras are
transmitted or recorded.
|
|
MUX
MULTIPLEXER
|
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.
|
|
NANO
|
Order of magnitude 10 -9.
|
|
ND
|
Neutral Density.
|
|
ND FILTER
|
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.
|
|
ND SPOT FILTER
|
A graduated filter fitted to the centre
of a lens, restricting the amount of light that can effectively
pass through to the image sensor.
|
|
NEUTRAL COMPUTING
|
Powerful software used in motion detection
to teach the computer to learn object sizes and shapes.
|
|
NOISE
|
Appears on screen as graininess or
'snow' effects on a video image.
|
|
NON-COMPOSITE VIDEO
|
A video signal that is complete, except
for the synchronisation information.
|
|
NTSC
|
National Television Standards Committee.
Colour Video Signal, North American and Japanese television standard
- 525 Lines, 60Hz.
|
|
N/C
|
Normally Closed.
|
|
N/O
|
Normally Open.
|
|
O/P
|
Output.
|
