Glossary
A
AGC Automatic Gain Control:
is circuitry in a surveillance camera which boosts the video signal (including the noise). It becomes operational when the light level is low.
Alarm interface:
is a facility which allows external alarms like PIR's, reed switches, vibration sensors etc. to be connected to the cctv (closed circuit television) switcher
so that a nominated surveillance camera is switched on when an alarm signal is received.
ALC Automatic Light Compensation:
is a setting in an auto iris lens to control the iris opening. It can be adjusted between peak and average to respond to the bright part of the scene (peak setting) or the average value of the video signal (average setting).
Algorithms:
are complex mathematical formulae or rules used to solve problems. In cctv (closed circuit television), they are used to achieve digital compression of a video picture.
Alkaline battery:
is a type of DC power source with a longer life compared to the standard battery. It cannot be recharged.
Amplitude:
refers to the strength of the video signal at a point and is measured in volts.
Angle of refraction:
is the angle of bending of light when it travels from one medium into another.
Angle of view:
represents the area of the scene (maximum horizontal and vertical angle) that can be seen through a lens. It is measured in degrees.
Aspect ratio:
is the ratio between the horizontal and the vertical lengths of the video picture. The aspect ratio for NTSC and PAL systems is 4:3.
Audible detector:
is a device which detects sound. In cctv (closed circuit television), it can be interfaced with a switcher so that a nominated surveillance camera is switched on when the detector is activated.
Audio switching:
is a device which can switch between various audio inputs either manually or sequentially. Many matrix switchers incorporate this feature.
Auto balance:
is a system of detecting and automatically correcting errors in the amplitude of color signals.
Auto iris:
is a diaphragm which is inbuilt in a lens to automatically control the amount of light falling on the chip. The tiny motors in the lens open or close the diaphragm, depending upon the amplitude of the video signal.
Automatic pan:
is a feature of a pan tilt or pan only head which allows the head to continuously move (pan) left and right between two fixed points. These fixed points can be set by adjusting the limit switches in the head.
Attenuation:
is a reduction in the strength of light or an electrical signal and is usually measured in decibels.
Average video signal:
represents the average light level of the whole picture used to open or close the automatic iris in the lens.
B
Back focus:
is a fine mechanical adjustment in the surveillance camera which moves the CCD chip or the lens mount (depending upon surveillance camera brand) to ensure the chip is placed at the exact focal point of the lens.
Backlash:
is an error present in a pan tilt head due to the play in the mechanical components like gears, pulleys etc. This results in the Pan Tilt head not stopping instantaneously. This error is critical in pre set PTZ surveillance cameras and is measured in degrees.
Balanced cable:
is a type of cable in which the signal is divided over a pair of cables and travels in opposing polarity. This reduces interference allowing transmission over longer distances.
Bandwidth:
is the range of frequencies that pass through an electrical/electronic amplifying, processing or transmission unit without attenuation or loss.
Barrel distortion:
is a distortion in the monitor due to non uniform scanning which causes the image to bulge outwards like a barrel.
Beam angle:
is the angular beam width of a conical beam of light and is measured in degrees.
Blanking pulse:
is a black pulse added during the fly back period to make the video signal invisible on the screen.
BNC connector:
is a type of connector used to interconnect two coaxial cables or connect a cable with other cctv (closed circuit television) components.
Bridging switcher:
is a type of sequential switcher which has two outputs. The sequencing output sequences all the surveillance camera inputs whereas the other output is a spot output where any surveillance camera can be called up for extended viewing.
Brightness:
represents the intensity of illumination of the reproduced picture.
Brightness Control:
is a control in the monitor which does not change the amplitude of the video signal but increases or decreases the illumination of the phosphors on the screen.
Broadcast camera:
is a high quality camera using three CCD chips. It is used extensively in the professional broadcasting industry.
C
C-mount:
is a lens mount with 17.526 mm back flange. Back flange is the distance between the lens mounting surface and the CCD chip.
Cable compensated amplifier:
High frequency video signals are attenuated when transmitted through cables. A cable compensated amplifier boosts the high frequency signals depending upon the cable distance. This ensures minimum video loss.
Cable core:
is the central part of the cable which actually carries the video , control or power signals. It can be made up of a single conductor ( solid core) or a number of electrical wires.
Cable jacket:
is the outer protective coating which covers the core of the cable.
Cable tray:
is a long tray installed in many sites which allows cables to be economically laid out.
Candela:
a new unit which replaces the candle and is a measurement of luminous intensity
Cathode ray tube (CRT):
is a tube in the monitor containing a heated cathode which emits a beam of electrons focused on a phosphor coated surface. The surface glows depending upon the intensity of the beam. The deflection circuitry in the tube controls the movement of the beam.
CCD Charge Coupled Device:
is a solid state device in a surveillance camera that converts light falling on it into an electrical signal.
CCD iris:
is a feature in modern CCD surveillance cameras by which the iris function is performed by the CCD chip itself. This eliminates the need for an auto iris lens. The CCD iris can handle minor light fluctuations only and therefore is not recommended for most outdoor applications.
CCIR International Radio Consultative Committee:
recommends a format of 625 lines per frame and a transmission speed of 25 frames per second.
Celsius:
is the metric unit for measuring temperature. In this scale, the boiling point of water is 100 deg. In the USA, the unit used to measure temperature is Fahrenheit.
Channel separation:
When signals are multiplexed at different frequencies for transmission, then the separation between these frequencies is called channel separation. Poor separation can lead to cross talk.
Chromatic aberration:
is an error in lenses which causes the focal point to be scattered. This occurs because different wavelengths of light bend differently through a lens. A combination of lenses are required to minimize this error.
Chrominance signal:
is that part of the video signal which contains the color information. In S-VHS, this signal is transmitted along a separate cable. In a composite video signal, the chrominance signal is multiplexed at a higher frequency and sent along the same cable.
Color stripe filter:
is a type of filter placed in front of a color CCD chip. It breaks up light into the basic colors - red, green and blue which are then directed to separate pixels in the CCD chip
Common sync generator:
is a device used to synchronize surveillance cameras. It generates synchronizing pulses that are sent to all surveillance cameras connected to it by coaxial cable.
Composite video:
is a standard signal format in cctv (closed circuit television) which contains the video signal, the horizontal and vertical sync pulses and the blanking pulses. The sync pulses are 0.3 volts and the video signal is 0.7 volts.
Concave:
is a type of optical lens in which the light rays passing through it are made to diverge by the inward bulge of the glass surface.
Conduit:
is a plastic or metallic tube which is used to conceal, protect or secure cables.
Connector:
a device used to interconnect cables or connect cables to various equipment.
Contrast:
is the difference in the intensity between the black parts and white parts of the picture on the monitor.
Contrast Control:
is a control in the monitor which changes the contrast by increasing or decreasing the amplitude of the video signal.
Covert:
is a mode of cctv (closed circuit television) surveillance in which the surveillance camera and lens are hidden and cannot be seen.
Convex:
is a type of optical lens in which the light rays passing through it are made to converge by the outward bulge of the glass surface.
Crimping:
is a process of connecting a cable to a connector without screwing or soldering using a special tool. In crimping a BNC connector, the centre pin of the connector is uniformly pressed against the cable core. To ensure a proper connection, a good crimping tool is needed.
Cross talk:
is the noise generated by the interference between adjacent ( in terms of signal frequency) video, audio or data channels in a multiplexed signal.
CS mount:
is a lens mount with 12.5 mm back flange. Back flange is the distance between the lens mounting surface and the CCD chip.
D
De-multiplexing:
is the process of separating the different video, audio or data channels which were multiplexed at the source.
Depth of field:
is the distance between the nearest and furthermost points of the scene which appear in sharp focus. It depends upon the F-stop and focal length of the lens.
Dielectric:
is a material which insulates the solid centre core of a coaxial cable from the shield. The thickness of the dielectric affects the impedance of the cable.
Dome:
is a type of surveillance camera housing made of smoked or tinted plastic. It is excellent for discreet surveillance and is also available with in built pan tilt heads.
DSP chip:
Digital Signal Processing chip is a solid state device which converts an analogue video signal into a digital video signal. It is used in digital surveillance cameras and also in computers to digitizes video images.
Duplex:
is a system which can handle simultaneously two channels of video, audio or data signals.
Dwell time:
is a feature in a switcher. It is the time period a picture from a given surveillance camera remains on the monitor before being replaced by a picture from the next surveillance camera. Switchers may have fixed or programmable dwell times.
E
EIA:
is a scanning method specified by the Electrical Industry Association. RS-170 is the standard for monochrome and RS-170A is the standard for color.
Electrical filter:
is a type of electrical circuitry designed to limit transmission of certain frequencies.
Electron beam:
is a concentrated flow of electrons in a nominated direction.
EMI Electro Magnetic Interference:
is a interference which is usually caused by any electrical equipment radiating electro magnetic frequencies.
Ergonomics:
is the study of man, machine and the environment to achieve maximum efficiency.
Event recorder:
is a type of recorder that is normally maintained in pause mode and starts recording only when activated by an alarm.
Extruded aluminum:
is aluminum processed through a die and shaped for use to construct housings for cctv (closed circuit television) applications.
Extruded plastic:
is a process in which smoked or tinted plastic is processed and shaped to construct dome housings.
F
F-stop:
is the ratio between the focal length of the lens and the effective diameter of the iris opening. It indicates the light gathering ability of the lens.
Fast lens:
is a lens which can gather and transmit more light to the surveillance camera. A fast lens has a larger iris opening and therefore a smaller F-stop.
Fast scan video:
is a method of sending video images over the telephone network to any part of the world. The update rate presently is not real-time but is improving continuously.
Fence disturbance sensor:
is a type of sensor installed around the perimeter fence in a site to detect any intrusion. There are many types of fence disturbance sensors available. In cctv (closed circuit television) it can be interfaced with a switcher. to switch a nominated surveillance camera for extended viewing.
Fiber optics:
is a method of modulating video, audio or data with a light beam and transmitting it along a glass core.
Field:
is one half of a frame and consists of 312.5 (PAL) and 262.5 (NTSC) lines. Odd and even fields are combined to form a single frame.
Field of view:
is the height and width of the view that can be seen through a lens.
Fixed lens:
is a lens with a fixed focal length. A wide range of fixed lens are available to suit different applications e.g. 2.6mm, 4.8mm, 8mm, 16mm, 25mm, 75mm etc.
Flexi conduit:
is a flexible PVC conduit which is used at the surveillance camera point to enclose loose cables between the surveillance camera and the junction box or wall.
Fluorescent lamp:
is a type of artificial light source in which the mercury vapor generated by a low wattage arc strikes the phosphor material to emit light. It is popularly used in indoor applications.
Fly back period:
is the time taken to move from the end of a field, frame or line to the start of the next field, frame or line. It is also called the retrace period.
Focal length:
is the distance between the optical centre of a lens and the point of focus. It is usually measured in mm or inches.
Focus ring:
is a ring on a lens which is rotated to obtain correct focus. It is available only in manual iris lenses.
Foot candle:
is a unit of luminance. 1 foot candle = 1 lumen of light incident on 1 sq. ft of surface area.
Frame interline chip:
is a type of CCD chip which is expensive to manufacture and is currently used in broadcasting video surveillance cameras. It overcomes many shortcomings of the existing CCD chips used in cctv (closed circuit television) surveillance cameras.
Frame switching:
is a process used in multiplexers or multi-recorders in which a frame is picked up from each surveillance camera in turn.
Frame store:
is an electronic device used to capture and digitally store a video image. It can be an independent unit or in built in other equipment like fast scan video transmitters or video motion detectors.
Frame transfer chip:
is a type of CCD chip in which the pixels have a dual role of sensing the light and transferring the charge. This causes picture smearing, a major shortcoming of this chip.
Frame:
is the basic unit of a moving picture. A frame contains 625 lines (PAL) or 525 lines (NTSC)
G
Gamma correction:
is a correction built into the surveillance camera to adjust for the brightness characteristic of the monitor. The gamma value ranges from 0.6 to 1.0
Geometric distortion:
is an error which causes the reproduced picture to be geometrically different from the original picture.
Graded index cable:
is a type of fiber optics cable which reduces transmission error by means of a cladding having a graded index of refraction.
Ground loop current:
is an AC current produced in a video cable when the two ends of the cable do not have the same ground potential.
Ground loop insulator:
is an isolation transformer which can eliminate ground loop currents by removing any direct connection between the inputs and outputs.
GUI Graphical User Interface:
interfaces the computer with the matrix switcher. Hot areas on the computer screen can be programmed to activate a matrix switcher, VCR etc. It helps in making the cctv (closed circuit television) system more user friendly.
H
Hertz:
is a unit of measuring frequency. 1 Hertz = 1 cycle per second.
Homing sequential switcher:
is a type of switcher used for small systems. It has only one output.
Horizontal resolution:
is the number of vertical lines which can be resolved in a picture. It depends upon the number of pixels in a chip.
Horizontal shift register:
is a part of the CCD chip to which the charge from the pixels is transferred line by line. This charge is then converted into an analogue video signal.
I
Illuminance:
is the amount of luminous flux falling on a surface area and is measured in lux or foot candle.
Image intensified surveillance camera:
is a type of surveillance camera coupled with an image intensified tube which generates additional photons. This tube allows the surveillance camera to be used in low light areas.
Image intensifier:
is a device which intensifies light by using light sensitive phosphor screens. It is used to improve surveillance camera performance under low light conditions.
Impedance:
is the input and output characteristic of any electrical system and is measured in ohms. For maximum signal transfer, the input and output impedance should be the same. cctv (closed circuit television) systems have a 75 ohm impedance.
Incandescent light:
is a type of artificial light source invented by Thomas Edison in 1862. It has a good spectral response but low life and efficiency.
Index of refraction:
is a ratio between the angle of incidence to the angle of refraction of light. It depends upon the density of a medium. A denser index of refraction and will also bend the light more.
Infrared detector:
is a type of alarm which works on the principle of infrared light to detect movement in a zone
Infrared illuminator:
is a type of light source which emits light in the infrared frequency range.
Infrared link:
is a type of transmission medium in which video, data or audio are modulated with infrared light and then transmitted into air to a receiver in a remote location.
Infrared radiation:
is electromagnetic radiation with a wavelength of more than 750 nanometers. It is not visible to the human eye.
Interference:
is external energy which interferes with an electrical signal causing picture distortions.
Interlacing:
is the process of combining even and odd fields to form a frame.
Interline transfer chip:
is a type of chip used in most of the current cctv (closed circuit television) surveillance cameras as the charge read out method is more efficient than a frame transfer CCD chip . Vertical streaking and small pixel size are some of the shortcomings.
Iris:
is a part of a lens that can be adjusted to vary the amount of light passing through the lens and falling on the CCD chip.
Iris plug:
is a type of connector which connects the surveillance camera to an auto iris lens to provide power to the iris motor and to send the video signal which controls the iris opening.
ISDN Integrated Services Digital Network:
is a type of telephone network which accepts digital signals.
J
Joystick:
is a control device in the form of a stick in a PTZ controller used to control the pan and tilt movement of a pan tilt head.
L
LAN Local Area Network:
connects different computers so that they can communicate with each other. Different connection protocols are possible.
LD Laser diode:
is a type of light source which generates a single frequency in the high end of the infrared spectrum and has a bandwidth of 1000 MHz. It is used in fiber optics and infrared links.
Lead acid battery:
is a type of DC power source which is similar to a car battery. It is generally used in temporary installations with DC surveillance cameras.
LED Light Emitting Device:
is a type of light source which generates an infrared frequency when stimulated by electricity. It is used in fibre optics , infrared links and as an infrared light source for monochrome surveillance cameras.
Lens calculator:
is a calculator provided by many lens manufacturers to help calculate the focal length of the lens that will provide the required scene.
Lens hunting:
is a field problem in which the iris opens and shuts alternatively. A correct ALC adjustment in the lens could rectify the problem.
Lens mount:
see C-mount or CS-mount.
Lens wheel:
see lens calculator.
Light:
is electromagnetic radiation between 400 nm and 750 nm which is detectable by the human eye.
Light sensor:
is a device which is activated by a pre-set amount of light falling on it. It can be used to switch infrared illuminators On / Off.
Limit switch:
is a device placed inside or outside the Pan Tilt head and used to limit the angles of pan and tilt.
Line:
is the basic unit of a frame or field containing the charge which is proportional to the light falling at various points on the scanning line.
Looping switcher:
is a type of switcher with looping outputs. These outputs allow the surveillance camera to be connected to another device without affecting the usage of the switcher.
Lumen:
is a measurement of light which indicates the amount of light radiated by a one candela light source.
Luminous flux:
is the rate of flow of light.
Luminance signal:
is that part of the video signal which contains the information on the brightness of the picture.
Lux:
is an international unit of illumination. It is the amount of uniform light falling on an area of 1 square meter and is measured in lumen per sq. meter.
M
Matrix switcher:
is a type of switcher which allows a single input to be switched to many outputs. Matrix switchers are used in large cctv (closed circuit television) systems and have many powerful features.
Mercury vapor lamp:
is a popular type of artificial light source which emits a blue-white light. Used extensive for commercial lighting.
Micron:
is a unit of measuring length. 1 micron = 10 -6 meters
Microwave detector:
is a type of alarm which uses microwaves to detect movement in a zone.
Microwave link:
is a type of transmission medium in which video, data or audio is modulated with a microwave frequency and then transmitted to a receiver in a remote location.
Mimic panel:
is a panel which shows the layout of a site with the surveillance camera positions highlighted. By interfacing it with a switcher, the operator can switch any surveillance camera to the monitors from the mimic panel itself.
Minimum scene illumination:
is a specification shown in most surveillance camera data sheets and indicates the minimum light required at the scene to provide a reasonable picture on the monitor.
Modem:
is derived from the term 'modulator -demodulator' and is used to convert a digital signal into an analogue signal so that it can be transmitted via the PSTN telephone network.
Modulate:
is a method in which a signal to be transmitted is mixed with a high frequency carrier signal .
Motorized iris:
is a type of iris control in which the iris motor is controlled from a remote location.
Multi core cable:
is a type of cable which has many cores enclosed in one outer jacket. In cctv (closed circuit television) it is normally used to transmit control signals.
Multimode cable:
is a cheaper type of fiber optics cable which allows a light beam to travel by more than one path thus causing transmission distortion.
Multiplexing:
is a process whereby many surveillance cameras are switched frame by frame. This frame switching can be used in applications like multi viewing, multi recording etc.
N
Neutral density filter:
is a type of filter used with lenses which reduces light of all wavelengths equally.
Noise:
is an unwanted signal generated by every electronic component. The noise in a video signal causes a grainy or snowy effect on the image.
NTSC National Television System Committee:
is a color television system and the standard used in the USA and Japan. NTSC has 525 horizontal scanning lines and 60 fields per sec.
O
Ohms:
is a unit for measuring resistance or impedance of any electrical device.
Omni directional transmitter:
is a transmitter which sends the signal in all directions.
Optical Filter:
is a type of filter used in optics which selectively allows light of different frequencies to pass through.
Oscilloscope:
is a device which visually displays the wave form of any electrical signal on a screen. In cctv (closed circuit television), it is used trouble shooting andmaking adjustments of various components.
P
PAL Phase Alternating Line:
is a color television system and the standard used in Western Europe, Australia, parts of Africa and Asia. PAL has 625 horizontal scanning lines and 50 fields per sec.
Persistency of vision:
The retina of the human eye retains an image for 40ms. This characteristic is called persistency of vision and is used to make a picture appear continuous by flashing images on the retina at a rate faster than 24 images per sec.
Phase adjustment:
is a surveillance camera adjustment used to synchronize all the surveillance cameras in the system by altering the phase of the power supply.
Phase angle:
is the angle at any point of the sine wave of an AC power supply and varies between 0 to 360 deg. over a cycle.
Phosphor:
is a material which is capable of emitting light. It is used in fluorescent lamps, monitors etc. The duration of the emission depends on the type of phosphor.
Photon:
is the basic unit of light.
Picture tearing:
occurs when the horizontal sync pulses are distorted or lost and the monitor is unable to latch on to them causing the horizontal lines to be displaced in a random manner. This is seen as a tearing of the picture on the monitor.
Pincushion distortion:
is a type of distortion caused due to non uniform scanning in the monitor which makes the picture to bulge inwards.
Pinhole lens:
is a small lens with a diameter of 1.5mm to 9.5mm used for covert surveillance.
Pixel ( picture element):
is the basic unit of a CCD chip which accumulates charge depending upon the amount of light falling upon it. A typical CCD chip has over 300,000 pixels.
Polarizer:
is a type of filter which reduces glare by intercepting reflected light from surfaces like water , glass. etc.
Polycarbonate glass:
is a type of toughened glass which can be used in housings for use in high vandal areas.
Polyethylene:
is a type of plastic used to make outer jackets for cables.
Potentiometer:
is an electronic component in which the resistance can be changed by a movable contact point. It is used in pan tilt heads and zoom lenses to record pre-set positions.
Power line interference:
is a type of interference caused by main power lines and usually seen as horizontal bands on the monitor.
Preamplifier:
is a type of amplifier used to increase the output of a low level source allowing the signal to be processed by other devices.
Pre set:
is a term used in cctv (closed circuit television) to define pre determined positions of a pan tilt head and zoom lens.
Pressure mat:
is a device which is activated by the application of pressure and is used to open doors, gates etc. It can also activate the switcher to bring the nominated surveillance camera up for extended viewing.
Primary Color:
is a basic color which cannot be obtained by mixing other colors. Red, green and blue are the three primary colors which can be mixed to produce other colors.
PSTN Public Switched Telephone Network:
is a type of analogue telephone network currently in use all over the world.
PTZ controller:
is a device used to control the movement of the pan tilt head and zoom lens from a remote location.
Q
Quad:
is a device which uses digital video to display pictures from 4 surveillance cameras on a single monitor.
R
Read out time:
is the time taken to read the charge from the pixels in a CCD chip.
Real time video:
is a picture with more than 24 frames per sec and therefore looks continuous.
Receiver driver:
is a part of the matrix switcher placed at the surveillance camera point and connected to the main switcher by a twisted pair cable. It is used to decode the incoming control signals for the Pan Tilt Zoom functions.
Reed switch:
is a type of alarm activated when the contact is opened or closed . It is widely used with doors, windows, roller shutters etc. and can also activate a switcher to bring the nominated surveillance camera up for extended viewing.
Regulated power supply:
is a type of DC power supply in which the ripple factor is minimal.
Remote head surveillance camera:
is a type of surveillance camera in which the CCD chip is separated from the surveillance camera body by cable. It is used in applications where the amount of space is limited.
Resolution:
is a measure of picture definition and clarity and is represented by number of lines. Greater the number of lines, higher the resolution.
RG-11:
is a type of coaxial cable with a thicker centre core and used for transmission of video signals up to 550m.
RG-59:
is a type of coaxial cable used for transmission of video signals up to 230m. It is the most popular cable used in cctv (closed circuit television).
Ripple factor:
is the amplitude variation present in a DC power supply due to insufficient filtering . A large variation can damage a DC surveillance camera.
RS-232:
is a communication protocol used for communication between microprocessor based devices.
S
S-VHS Super VHS:
is a type of video format in which the illuminance and chrominance signals are sent separately resulting in improved picture quality.
Salvo switching:
is a feature in matrix switchers. On command from the matrix switcher or an alarm event. a group of surveillance cameras can be switched simultaneously onto a group of monitors.
SECAM Sequential Coluleur A'Memorie:
a color television system used in France and a few other countries.
Sensitivity of a surveillance camera:
is the minimum light level required at the CCD chip which will generate a usable video picture. It is measured in lux.
Sequential switcher:
is a type of switcher that allows multiple surveillance cameras to be displayed or recorded one at a time.
Shield:
is a copper braid which covers the dielectric and centre core of a coaxial cable. It protects the video signal from EMI.
Signal loss:
is a reduction in signal strength expressed in decibels.
Signal to noise ratio:
It is the ratio between the signal voltage and the noise voltage generated by an electronic circuit. It is measured in decibels (dB).
Simplex:
is a system which can handle only one channel of video, audio or data signal.
Single mode cable:
is an expensive type of fiber optic cable with a narrow glass core which allows only a single path for signal transmission.
Silicon wafer:
is a semiconductor material on which the CCD chips are etched.
Snow:
is a fault in the picture, appearing as small dots on the monitor and is caused by heavy noise in the video signal.
Sodium vapor lamp:
is a type of artificial light source which is very efficient and uses sodium vapor to produce a yellow-orange light.
Spectral response:
is the sensitivity of a device to different light frequencies.
Standard angle lens:
is a type of lens which provides a view having the same proportions as seen by the human eye. It has a magnification ratio of 1.
Step down transformer:
is a transformer used in power supplies to step down or lower the main line voltage. The ratio between the number of turns of the primary coil to the secondary coil determines the step down voltage.
Stranded cable:
is a type of cable in which a number of wires enclosed in an outer jacket are used to transmit the electrical signal.
Sunshield:
is a movable accessory placed on top of outdoor housings to prevent direct light falling on the surveillance camera.
Sync generator:
is a device which generates sync pulses which are then used to synchronize surveillance cameras.
Synchronization:
is a process which ensures that the formation of frames in a multi surveillance camera system start at the same time. There are different ways to achieve surveillance camera synchronization.
T
Telephoto lens:
is a type of lens used to view far away objects. It has a magnification ratio > 1.
Terminal strip:
is a clamp used to secure the cables firmly to the housing base.
Test pattern generator:
is a device which generates a test pattern to be used to adjust and test the monitor.
Thermal paper:
is a special type of paper used in video printers.
Time based switching:
is a feature in matrix switchers which allows various programmed surveillance camera sequences to be initiated at various times.
Time lapse VCR:
is a type of video cassette recorder especially designed for cctv (closed circuit television) requirements. It allows more recording time on a single video tape by not recording all the frames.
Time/date generator:
is a device which generates time and a date superimposes it on the video signal.
Touch screen:
is a type of modern monitor screen. Action can be initiated by touching the relevant point on the monitor screen.
Trapezoidal distortion:
is a type of distortion in the monitor caused due to non uniform scanning which makes the scanning lines look wider at the top than at the bottom of the monitor.
Triaxial cable:
is a type of co axial cable which has two layers of shield to provide better protection against EMI.
Twisted pair cable:
is a type of balanced cable in which a pair of cables are twisted and the signal is divided between them.
Two speed recorder:
is a type of domestic use VCR which has two speeds of recording/playback, standard and long play. The long play mode doubles the recording time of a standard tape.
U
Ultraviolet:
is electromagnetic radiation with a wavelength of less than 400 nm and is not visible to the human eye.
Unbalanced cable:
is a type of cable in which the ends of the shields are grounded to different equipment with possibly varying ground potential. This unbalanced set up can give rise to ground loop currents and EMI induction.
UPS Uninterruptible Power Supply:
stores electricity and supplies power to a cctv (closed circuit television) system during a power failure.
Usable video:
is the minimum video signal specified in the surveillance camera data sheet to generate an acceptable picture on the monitor. It is usually measured as a percentage of the full video.
V
Varifocal lens:
is a type of manual zoom lens with a small zoom ratio (ranging between 4mm to 12mm depending on brand). It is used when the focal length of the lens needs to be fine tuned to meet the requirements of the actual scene.
Video head:
is an internal part of a VCR which rotates very rapidly and writes the video signal on to the video tape during recording while reading the video signal from the tape during playback.
Vertical resolution:
is the number of horizontal lines which can be resolved in a picture. It is limited by the television scanning method - NTSC, PAL etc.
Vertical shift register:
is a part of the interline transfer CCD chip and is placed in between every column of pixels. At the end of each frame the charge from the pixels are sent to the vertical shift register (VSR) and then row by row to the horizontal shift register.
Vertical streaking:
is a type of picture distortion that occurs due to overloading of the pixels in an interline transfer chip. It appears as vertical streaks above and below the bright part of the picture.
VHS Victor Home System:
is a type of popular recording format used in video cassette recorders. The other type of formats are betamax, 8mm, system 2000 and U-matix (professional).
Vibration sensor:
is a type of device which can be activated by vibrations in a pre determined zone and can be interfaced with a switcher to switch the nominated surveillance camera for extended viewing.
Video amplifier:
is a type of amplifier used to boost the strength of a video signal.
Video cassette recorder:
is a device which can record (or playback) video and audio signals on a magnetic tape housed in a cassette.
Video distribution amplifier:
is a type of amplifier used not only to boost the strength but also create multiple outputs of the video signal.
Video intercom:
is a door entry system which uses both audio and video to communicate and/or control movement of people.
Video monitoring:
is a new trend which uses video to monitor remote sites in any part of the world. The video images are transmitted through the telephone network.
Video motion detector:
is a device which can detect unwanted movement in the picture and then generate an alarm.
W
Wave length:
is the distance traveled by an electro magnetic wave during one cycle.
Wide angle lens:
is a type of lens which gives a wide view of the scene and has a magnification ratio of less than 1.
Z
Zoom lens:
is a type of lens with a variable focal length ranging from wide angle to telephoto.
Zoom ratio:
is the ratio between the maximum and minimum focal length of a zoom lens.
