ClosedCircuitTelevision.pdf

8/14/2019 ClosedCircuitTelevision.pdf

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CAPTURING THE IMAGE:Capturing a good image, depends on:

a. The Light ing Conditions:

Light plays a crucial role in video surveillancebecause without it a picture cannot be

obtained. Therefore the area to be viewed

must be illuminated either naturally, by thesun, or by articial light sources. Both low

light and extremely bright conditions will

result in poor image quality as will a lack of

contrast between moving objects and the

background.

During the day the amount of illuminationreaching a scene depends on the time of

day and atmospheric conditions. Direct

sunlight produces the highest-contrastscene, allowing maximum identication of

objects. On a cloudy or overcast day, less

light is received by the objects in the scene,

resulting in less contrast.

Typically, scene illumination measured in

foot-candles (ftcd) can vary over a rangeof 10,000 to 1 (or more), which exceeds

the operating range of most cameras for

producing good quality video images.

The chart below summarizes the light levels

occurring under daylight and these low light

level conditions. The equivalent metric

measure of light level (lux) compared with

the English (ftcd) is given.

CLOSED CIRCUIT TELEVISION

CCTV is a highly effective technology which

contributes to deter and detect security

threats. A typical CCTV system consists

of the cameras, the signal transmission

medium, the monitoring station and therecording capability.

Each of these components is important

and the way in which they are integratedinuences the overall effectiveness of the

CCTV system. The purpose of this article is

to provide an overview of the components of

a CCTV system and to provide some insight

into the variables which can be manipulatedto achieve the desired outcomes for each

particular system.

Lux and low lighting chart



To produce an optimum camera picture

under the wide variation in light level (such

as when the sun is obscured by clouds), an

automatic-iris camera system is required.

b. The Lens:

The quality of the lens, conditions the amount

of light that hits the sensor.

Since conventional CCTV lenses are being

designed for the visible spectrum, once used

in the (near) infrared. This will produce an

out of focus and blurry image, even after re-

adjusting the lens. High quality IR lens has

extremely ne resolution in near infrared

because there is no offset of focus position

from visible light to near infrared. It provides

a clear image because there is no drop in its

recognition ability.

To light up a scene articially one can use:

White light Illuminators: reproducing the

wide spectrum light hence not conditioning

the camera to have a good response to

Infrared light, as not all cameras have

similar spectral sensitivity

Infra Red light Illuminators: reproducingonly Infrared light wavelength which is not

visible to the human eye – which could be

an advantage in some situations – , but

requires proper lens to have a more or

less similar refraction factor for IR light as

for white light

It is advisable to use illumination with

adaptive features so as to offer the

maximum lighting in the angle of view of

the camera/lens monitoring the scene. Not

to forget that the intensity of the light drops

with distance and is inversely proportional

to its square.

As the luminous ux travels away from the

light source the area over which it spreads

increases, therefore the illuminance (lux)

must decrease.

For instance, a light source providing a level

of 30 lux at 20 meters will provide 7.5 lux at

40 meters and only 3.3 lux at 60 meters.

Spectral sensitivity Diagram



The choice of the lens depends mainly

on the angle of view required to cover the

scene, and also on lighting condition where

the aperture of the lens is very important.

The f number of a lens is the ratio of the

focal length to the effective object lens

diameter. It does affect the amount of light

energy passed to the sensor and will playa signicant part in the resulting picture.

Traditionally camera manufacturers havespecied sensitivity with a lens having an

aperture of f 1.4. This would be ne if they

all did it the same, but they don’t. Some say

with 75% reectance some say 89% and so

on. Then again some will state the sensitivity

with AGC on but not what the AGC gain is.

Camera specmanship is too vast a subject

to expand on in this article but sufce to saythe f number of the lens is a most important

consideration.

In simple terms the smaller the f number the

more light is passed to the sensor, therefore

f1.2 is better than f1.8. The percentage of

light passed by different apertures is listed in

the table below. This shows the percentage

of light falling on the lens that is passed to

the sensor. The f stops in bold face are full

stops and each number in the scale halvesor doubles the light passed.

There are two intermediate stops shown

because they are common stops found in

CCTV lens.

Light percentage passed by f stops

Yes, it is true that with an aperture of f1.4

only 10% of the light on the lens is passed

to the sensor. Some manufacturers specify

camera sensitivity as that on the faceplate

or sensor. In these cases use these ratios

to convert to the light required on the lens.

I.e. 1 lux faceplate sensitivity requires 10 lux

with an f1.4 lens or 20 lux with an f2.0 lens.

It may seem relatively unimportant to

quibble about the difference between an

f1.2 lens and an f1.4 lens, especially whenthe latter is much cheaper than the rst. It

is signicant though because the f1.4 lens

needs 50% more light for the same energy

on the sensor, and usually cost 50% less.

The three types of common lenses arexed focal, vari-focal and zoom lenses. But

most important is to make sure that the light

variation during the day can be managed by

the cameras internal electronic shutter, other

wise it is mandatory to use auto iris lenses,

which help mechanically vary the aperture

of the lens so as to allow the exact amount

of light to the sensor. Typically all outdoor

installations require auto iris lenses.

c. The Camera Sensor:

The most important characteristics of a

sensor are its:

- Type:Both CCDs and CMOS imagers can offer

excellent imaging performance when

designed properly. CCDs have traditionally

provided the performance benchmarks in

the photographic, scientic, and industrialapplications that demand the highest image

quality (as measured in quantum efciency

and noise) at the expense of system size.CMOS imagers offer more integration (more



functions on the chip), lower power dissipation

(at the chip level), and the possibility of

smaller system size, but they have often

required trade-offs between image quality

and device cost. Today there is no clear

line dividing the types of applications each

can serve. CMOS designers have devoted

intense effort to achieving high imagequality, while CCD designers have lowered

their power requirements and pixel sizes. As a result, you can nd CCDs in low-cost

low-power cellphone cameras and CMOS

sensors in high-performance professional

and industrial cameras, directly contradicting

the early stereotypes.

Nevertheless, CMOS architectures use intra-

pixel amplication in conjunction with bothtemporal and xed-pattern noise suppression

circuitry (correlated double sampling), which

produces exceptional imagery in terms ofdynamic range and noise. CMOS sensors

also have built-in anti-blooming protection

in each pixel, eliminating artifacts, smear, or

blooming effects.

- Size:

As stated earlier, light is energy measuredin Watts per square meter. Therefore if the

area of a sensor is known then the resultant

power in watts can be easily calculated. The

nominal areas of the sensors in common

use are listed in table below.

The power produced by each individual pixelin the sensor is directly proportional to its

area. If three cameras are considered each

with the same resolution of say 500 lines

then the number of pixels on each sensor

must be the same. The result of this is that

the pixels on each smaller size of sensor

must also be smaller.

Therefore the power produced will be less

for the same aperture setting, i.e. the sameamount of light energy, unless a different Fstop is chosen for every camera. Below is

a table that shows how a lower f stop can

compensate for a smaller sensor:

- Dynamic Range:

Real environments present a very widerange of illumination levels and the human

visual system is highly effective at extracting

information in the most extreme conditions.

A camera must do the same, or better,

if its performance is not to vary strongly

depending on its location, the time of day,

and the ambient lighting conditions.

While a combination of low noise CCD or

CMOS sensors and an intelligent auto-gainalgorithm is readily able to adjust camera

sensitivity between day and night conditions,

it is scenes in which very bright and dark

areas coexist that present the most serious

challenge. These occur frequently in real

situations: at dawn and dusk; in direct sun

with deep shadows; under backlit conditions

found frequently in entrance areas; at night

under directed articial illumination.

Wide Dynamic Range CMOS sensors with arange up to 120dB, allow the sensor to adjust

the lighting on each pixel individually and

hence giving each portion of the image the

right illumination and avoid under exposed

and over exposed parts in the picture.

- Resolution:

In standard coaxial cameras the resolution,

which is directly related to the number of

pixels on the sensor, has reached 600TVL(horizontal pixels / row) in color camerasand 700TVL in B&W ones, but with Mega

Pixel IP cameras the resolution has reached



4,872TVL in 16MP cameras using 1.38”

sensor.

Remember that, for the same sensor size,

the higher the resolution the less light hits

each pixel, and hence the less the contrast

in the picture. Hence, while consideringhigher resolution for a specic camera,

always consider the sensor size, illumination

and the lens used with it, to ensure a proper

image.



- Scanning method:

There are basically two ways to display

video: interlaced scan or progressive

scan. Progressive scan, used in computer

monitors and digital televisions, displays all

the horizontal lines of a picture at one time

as a single frame . Interlaced scan, used in

standard television formats (NTSC, PAL, andSECAM), displays only half of the horizontal

lines at a time (the rst eld, containing the

odd-numbered lines, is displayed, followedby the second eld, containing the even-

numbered lines). Interlacing relies on

phosphor persistence of the TV tube toblend the elds together over a fraction of

a second into a seemingly single picture.

The advantage of interlaced video is that

a high refresh rate (50 or 60 Hz) can beachieved with only half the bandwidth.

The disadvantage is that the horizontal

resolution is essentially cut in half, and thevideo is often ltered to avoid icker (inter

eld twitter) and other artifacts.

CRTs can display interlaced video directly,

other display technologies may require

some form of de interlacing. Modern CRT-

based monitors used as computer displaysutilize progressive scanning, so they also

require de interlacing.

While the only disadvantage of progressive

scan is the high bandwidth required for the

signal transmission, its advantages are

numerous:

Higher vertical resolution than interlaced

video with the same frame rate. Absence of visual artifacts associated

with interlaced video of the same line

rate, such as interline jitter, especially

when viewing fast moving objects where

the odd lines are shown displaced with

respect to the even lines

No necessity in intentional blurring

(sometimes referred to as anti-aliasing)

of video to reduce interline jitter and eye

strain.

Offers much better results for scaling

to higher resolutions than equivalent

interlaced video, such as up converting

480p to display on a 1080p HDTV.

Scaling works well with full frames,

therefore interlaced video must be de

interlaced before it is scaled. De interlacingcan result in severe “combing” artifacts.

Frames have no interlace artifacts and

can be used as still photos.

d. The Signal Analysis:

Some cameras come with built-in signal

analysis such as motion detection that is

interesting with long distance monitoring

over limited bandwidth networks.

TRANSMITTING THE IMAGE:The most common forms of transmission for

CCTV data are ‘coaxial cable’, ‘twisted pair’

and ‘bre optics’. ‘Coaxial cable’ consists of

a central core which transmits the signal andan external shield which serves to reduce

the effect of electromagnetic interference

on the signal transmission. Coaxial can be

used for cable runs up to 300m.



Where cable runs of greater distances

are required ‘twisted pair’ provides a good

alternative to ‘coaxial cable’ and can be

used for cable runs up to 600m without any

line repeaters. ‘Twisted pair’, as the name

suggests, consists of a pair of wires twisted

around each other repeatedly which serves

to reduce the amount of electromagneticinterference, over large distances, resulting

in high quality video signal at the receiving

end. Another advantage of ‘twisted pair’

is that four pairs of wires are incorporated

into the one cable and so four cameras can

be connected on the one cable run. The

most effective form of video transmission isachieved through the use of ‘bre optic’ cable.

‘Fibre optics’ provides the best quality and

the most secure form of signal transmissionand can be used for far greater distances

than both ‘coaxial’ and ‘twisted pair’.

VIEWING THE IMAGE:With the introduction of digital storage,

analog CRT monitors are being replaced by

digital VGA LCD monitors.

CCTV LCD monitors should be favored for

surveillance purposes over a CRT for severalreasons. First, they provide better image

quality than CRTs. CCTV LCDs produce a

sharper, brighter picture because they can

process CCTV signals at a higher resolution.

These monitors are also more responsive

than CRTs, making them ideal for live video

monitoring. They are much lighter and less

bulky than CRT monitors so they take up

much less room. They also come in large

sizes for multiple camera viewing situations. A big advantage of CCTV LCDs over CRTs

is that LCDs do not suffer from magnetic

interference. Speakers, for example, do not

need to be shielded to be used in conjunction

with the monitor. Another advantage of aCCTV LCD is screen icker is not an issue.

With CRT monitors, low refresh rates leadsto screen icker, an annoying occurrence.

Despite all these advantages, there aresome disadvantages to a CCTV LCD. One

is the contrast ratio.

It is easier to produce higher contrast in

CRT monitors because the electron gun can

be turned off for true blacks. In an LCD the

backlight is always on so a certain amount

of light will always show through. Because

of this, buyers should be aware of an LCD

monitor’s contrast ratio. An effective ratio is

400:1.

Another drawback is LCD monitors

sometimes generate dead pixels, or areas

of the screen that remain black because

they no longer function. If the monitor is

under warranty, most manufacturers will

repair dead pixels, but this leads to system

downtime. Even with these drawbacks

factored in, an LCD monitor is clearly the

best choice for your surveillance needs.

Last but not least, for Mega Pixel cameras, itis recommended to use progressive scan HD

LCD monitors, since the high resolution of the

signal needs the highest resolution possibleon screen which today is 1920x1080.

Note that the HD LCDs are also progressive

– refer to the letter ‘p’ in its stands for

progressive instead of ‘I’ for interlaced.

STORING THE IMAGE:a. Methods of Storage

There are a number of recording methods

available for the storage of CCTV images

and each of them has advantages and

disadvantages over the others. The coding

formats which are commonly used include:‘Motion JPEG’, ‘Motion JPEG2000’, ‘H.26x’,

‘MPEG-1’, ‘MPEG-2’ and ‘MPEG-4’ as well

as the ‘Common Intermediate Format’ (CIF).

CIF refers to the number of horizontal andvertical lines in the video picture frame (theresolution) and the frame rate. The ofcial

CIF size is 352 x 288 lines at 25 frames per

second’, but video can also be transmitted

and displayed at 2CIF and 4CIF.

‘Motion JPEG’ records a very high quality

image because it records a full frame image

of the video stream. This is great for viewing

the video, but is not practical for storage,given the large amount of hard disk spacewhich is required. ‘Motion JPEG 2000’

enables better compression which results



in a good quality image but with a around20% less storage requirement than ‘Motion

JPEG’.

‘MPEG’ uses what is known as a key frame,

at the beginning of the video sequence,

which involves recording a full frame of the

picture and using that, as a reference, forsucceeding images. For each additional

frame only those parts of the image which

have moved are recorded which results

in a reduction in the storage requirements

and enables a longer sequence of video to

be recorded. ‘MPEG-2’ uses advances in

technology to produce a better video imagethan ‘MPEG-1’ but with the same bandwidth

and storage space requirements.

The release of the ‘MPEG-4’ (Part 2)

standard, in 2000, enabled video to be

encoded at lower bit rates while maintaining

a high quality image. It was designed to be

suitable for a wider range of video encoding

applications, from movies to mobile

phones, but it offers very little advantageover ‘MPEG-2’ for security surveillance

applications. ‘MPEG-4’ (Part 10) is also

referred to as ‘H.264’ and is currently thehighest performing video coding format

available on the market. ‘MPEG-4’ (Part 10)

can provide the same quality recordableimage as ‘MPEG-2’ but at half the bit rate.

Real-time video surveillance applications

require high performing compression

standards such as ‘MPEG-2’ (Part2), ‘MPEG-

4’(Part2) and ‘MPEG-4’ (Part10), which offer

a higher level of performance than theirpredecessors. An added advantage of these

standards is the fact that it is possible to

adjust the compression ratio. This means

that by adjusting the compression rate, and

therefore the quality and size of the image,

various qualities of video can be used.

b. What Compression Standard to Use

For real-time video surveillance applications

users should be looking for high performingcompression standards such as MPEG-2

(Part 2), MPEG-4 (Part 2) or MPEG-4 (Part

10). These are now better standards to

use than Motion JPEG, Motion JPEG2000,

H.262 and MPEG-1.

Most users will notice little difference

between the coding abilities of MPEG-2

(Part 2) and MPEG-4 (Part 2), however, a

proper implementation of MPEG-4 (Part 10)

is capable of offering the best performance

of all. Additionally, all the above standardshave the option to adjust the compressionratio (the “quality setting”) which is a measure

of the amount of compression used. This

has a direct effect on the resultant image

quality and size. As the compression ratio

is increased the smaller each frame size

becomes at the expense of image quality.

c. Determining Storage Requirements

Now that we know how different CIF sizesand compression standards can be used

together it is important to know how they

directly affect the size that each compressed

frame of video takes up when stored.

The question many people have when they

purchase recording systems is how much

hard disk drive capacity they should allow

for.



This can be a complex question to answerand one that is usually vendor specic.

Different vendors use different compression

standards and varying compression ratios.

The following step-by-step guidance is

provided to assist the end user when

determining hard disk capacity:

Determine the numbers of cameras (Nc);

Determine the frame rate (frames per

second) at which each camera will be

recorded at (Rf);

Determine the average size (in Kilobytes)

that each compressed frame of video will

take up on the hard disk (Sf) after the

compression ratio has been applied;

Approximate the activity (in percentage)time each camera will be recording at the

above frame rate (A); and

Determine the duration (in days) that video

from each camera will be retained (D).

Once these values are determined, the

following formula can be used to determine

the HDD capacity;

Among all the above factors the AverageFrame Size is the one that is directly related

to the coding format used, and as a rule of

thumb one can use the following table andgraph, which shows that for a 640 x 480

resolution with 50% activity and good lighting

conditions:at low compression: MJPEG has a ratio of

7:1 over H.264 with an average of 170KB/

frame for the MJPEG compared 25KB/

frame for the H.264

at high compression: MJPEG has

a ratio of 5:1 over H.264 with anaverage of 50KB/frame for the MJPEG

compared 10KB/frame for the H.264

Needless to say, the performance of

the server managing the storage is also

affected by the compression and gives

advantage to the H.264 format whichallows the same server conguration to

manage more cameras with the same

settings.

SYSTEM ARCHITECTURE:CCTV systems are either analogue or digitalor a combination of the two.

Analogue is the older format and more

recent developments have been in the area

of digital technology.

The digital transmission standard is Internet

Protocol (IP) which enables the video signals

to be sent over the internet. This can congest

an organization’s IT network if not managed

carefully.

The IP CCTV infrastructure is considerably

cheaper to install than a purely analogue

system.

Where analogue cameras are used instead

of IP cameras, streamers or video encoders

are used to convert the analogue signal to

digital which is then stored on a network

video recorder (NVR) or high capacity

storage array.



Nevertheless, with the Mega Pixel IP

cameras offering impressive quality, HD LCD

monitors and powerful processors and more

and more competitive TB storage systems,

the tendency today is to move directly into

the fully digital system especially for average

size to large size systems, replacing PTZ

cameras with 180° or 360° 8MP cameras,and the multitude of monitors with video

walls, giving the operator higher exibility

in viewing live and recorded cameras in

various sizes and resolution, locally or

remotely over LAN or WAN in a virtual matrix

environment.

Note that with 1 camera replacing several,

not only the license for camera connection

to the system is reduced but the cabling isalso reduced, lowering the overall system

cost.Let’s take for example 1 3MP camera

replacing 9 normal resolution cameras:

Needless to say, that if the available network

is not enough to accommodate the bandwidth

required then a separate network for the

CCTV would be recommended, knowing

that the distance is no longer limited to

100m because repeaters are now available

to extend these connections to several

hundreds of meters, that is if we do not wishto go for ber optics.

Last but not least, with the Mega Pixel

cameras, the choice of camera resolution

and zoom lens required for a scene, can

have a different approach using the conceptof PPM or Pixel/m where one starts by

dening the precision level required from the

picture, then moves up to close the sensor

that offers this resolution and the lens thatallows the proper coverage from the distance

one has.



As an example for the License plate recognition refer to the below pictures taken with different

Pixel Density:

For reference, the Pixel density adopted in the surveillance business today are:

Systems and Equipment cannot bereliable unless properly maintained by

professionals on a yearly basis



GLOSSARY OF TERMS FOR CCTV: AGC:

Automatic gain control-electronic circuitry,

to increase the video signal in low lightconditions. This usually introduces “noise”

in the picture giving a grainy appearance.Camera specications must always be

considered with AGC off.

ANGLE OF VIEW:

The maximum scene angle that can be seen

through a lens.

AUTOMATIC IRIS:

A lens that automatically adjusts to allow the

correct amount of light to fall on the imaging

device.

There is a tiny motor and amplier built in

which generally receives a control signal

from the camera to maintain a constant one-

volt peak to peak (pp) video level. There are

two manual controls on the lens to allow

compensation for varying conditions of“peak” and “average” light.

C-MOUNT:The standard screw

mounting for 2/3”,

and 1”camera lenses.

The distance fromthe ange surface

to the focal point is

17.526 mm.

A C-mount lens can

be used on a camera with a CS-mount

by adding an adaptor ring to reduce thisdistance to 12.5mm (see CS-mount).

CCD:

Charge coupled device, a at thin wafer

that is light sensitive and forms the imaging

device of most modern cameras. Size ismeasured diagonally and can be 1/4”-1/3”-

1/2” or 2/3”. There are two types, frame

transfer and interline transfer.

CCIR:

The European 625 line standard for the

video signal.

CCTV:

The common abbreviation for closed circuit

television. A private or closed television

system.

CAMERA:

A device that translates light into a video

image and, transmits that image to a monitor

for viewing. It contains the image sensor and

other electronic circuitry to create a video

signal.

CONTRAST:

The range of light and dark values in apicture or the ratio between the maximum

and the minimum brightness values.CS MOUNT:



A new generation of lenses designed for2/3”,1/2” and 1/3” cameras incorporating

CS-mount. The distance from the ange

surface to the focal point is 12.5 mm.

CS-mount lenses cannot be used oncameras with C-mount conguration. These

lenses are more compact and cheaper than

the C-mount equivalents.

DEPTH OF FIELD:

The proportion of the eld of view that isin correct focus. The depth of eld in focus

DECREASES when: the focal length is

longer, the f-number is smaller, or the object

distance is shorter.

DIGITAL SIGNAL:

An analogue signal that has been converted

to a digital form so that it can be processed

by a microprocessor.

DSP:

Digital Signal Processing, a method of

adjusting various parametera of the video

signal to obtain improved performance.

DVR:

Digital Video Recorder, a method of storing

video information in digital form as opposed

to analog recording.

DWELL TIME:

The length of time a switcher display one

camera before sequencing to the next.

Usually a variable setting.

EIA:

The American 525 line standard for the video

signal.

F STOP:

This is the ratio of the focal length to the

effective diameter of the lens (f/A). It is not ameasure of the efciency or the transmission

value of the lens. The smaller the f–number

the more light is passed.

FOCAL LENGTH:

The distance between the secondary

principal point in the lens and the plane of

the imaging device. The longer the focal

length, the narrower is the angle of view.

FOCUS:

The focal point. An adjustment to the lensoptics to improve the clarity of the picture.



FORMAT:

The size of the camera’s pickup device

(imager).

GAMMA CORRECTION:

An electronic correction carried out in the

camera circuitry to balance the brightness

seen by the camera to that of the monitor.

GEN LOCK:

Also called external sync. A separate coaxial

cable is run to each camera and carries sync

pulse information to ensure that

All cameras are producing elds at exactly

the same time. This eliminates picture

bounce during switching and can improve

quality and update time in multiplexers.

GHOST:

A shadowy or weak image in the received

picture, offset to either the right or to the left

of the primary image.

GRAY SCALE:

The number of variations from white to gray

to black.

HERTZ:

The number of variations per seconds.

HORIZONTAL RESOLUTION:

The number of horizontal lines on a video

monitor.

IMAGE DEVICE (IMAGER):

The detector in the camera, either a tube or

a CCD solid state device.

INFRARED LIGHT:

The wavelength of light produced above the

visible part of the spectrum.

INFRARED TRANSMISSION:

A method of transmitting video and telemetry

signals across free space along an infrared

beam.

This opens possibilities for using CCTV

where it had been previously impossible to

run cables. Distance can be limited and the

signal can be degraded in adverse weather

conditions.

INTERLINE TRANSFER:

Another type of CCD imaging device in which

the rows of charge are stepped down one at

a time and processed straight away.



IP RATING:

Index of protection, a number combination that denes the protection from outside inuences

offered by an enclosure.

Protection of persons and protection of equipment indicated by the IP code j61 RATING CHART



NEMA RATING

The National Electrical Manufacturers

Association (NEMA) in the United States also

publishes protection ratings for enclosures

similar to the IP rating system published by the

International Electrotechnical Commission

(IEC). NEMA however also dictates other

product features not addressed by IP codes,such as corrosion resistance, gasket aging,

and construction practices. For this reason

while it is possible to map IP Codes toNEMA ratings that satisfy or exceed the IP

Code criteria, it is not possible to map NEMA

ratings to IP codes, as the IP Code does not

mandate the additional requirements. The

table to the right indicates the minimum

NEMA rating that satises a given IP code,

but can only be used in that way, not to mapIP to NEMA

IR SHIFT:

The difference in the eld of view in focus

between daylight and infrared light.

IRIS:

The mechanism that can be adjusted to vary

the amount of light falling on the imaging

device.

ISIT:

‘Intensied silicon intensied target’, a

camera for use in exceptionally low light

conditions. These require great care if

needed for use in daylight. Some cameras

have an internal sensor that automatically

cuts out the rst level of intensication.

LENS: A transparent optical component that

converges light rays to form a two dimensional

image of that object.

LIGHT:

Portion of the spectrum visible to the human

eye.

LIGHT SCATTERING:

The action of light being reected and/

or refracted off particles of combustion

for detection by a photoelectric smoke

detector. The action of light being refracted

or reected.

LINE LOCKED:

The sync pulses of cameras are locked to

the AC mains frequency.

LINE POWERED:

A camera in which the power is supplied

along the same coaxial cable that carries the

video signal. Makes for ease of installation,but cabling distances can be restricted and

connections to other equipment can cause

problems.

IP Code Min NEMA Enclosure rating

to satisfy IP Code

IP20 1

IP54 3

IP65 4.4X

IP67 6

IP68 6P



MATRIX SWITCHING:

This is an advanced method of switching

video signals where there can be any

number of inputs directed to any number of

outputs. These are generally associated withlarger systems where it is necessary to have

several control positions, each of which can

be programmed to control different groups

of cameras.

MICROWAVE TRANSMISSION:

Another method of transmitting video and

telemetry signals over free space. This is

less affected by weather conditions and

transmits over longer distance. The need for

a license should be checked for the system

being considered.

LISTED:

Equipment or materials include in a list

published by an organization acceptable

to the “authority having jurisdiction” and

concerned with product evaluation, that

maintains periodic inspection of production

of listed equipment or materials and whose

listing states either that the equipment ormaterial meets appropriate standards or

has been tested and found suitable for usein a specied manner. NOTE: the means

for identifying listed equipment may vary for

each organization concerned with product

evaluation, some of which do not recognize

equipment as listed unless it is also labeled.“The authority having jurisdiction” should

utilize the system employed by the listing

organization to identify a listed product.

LOCAL AREA NETWORK (LAN):

A private communications network for

transferring data among computers and

peripheral devices.

LOOP FRAME STORE:

There is a variety of proprietary names

for this latest advance in video storage

technology. The principle is that a series ofvideo frames is compressed and stored in

digital form in what is likened to a continuous

loop. This records, for instance, 200 frames

and then records over the top again and

carries on doing this until an alarm signal

is received. When this happens it carries

on recording for (say) 150 frames and then

stops. This means that 50 frames BEFORE

the event causing the alarm and 150 frames

after the event are captured. It eliminates thetedious searching through hours of dubious

quality video recording and concentrates the

reviewing on the period of real activity. There

are currently systems that can record four or

eight cameras using this technique.

LUMEN:

Amount of light emitted by a 1 candela sourcepassing through a specied area space.

LUX:

Density of light measured in lumens/sqmeter. This is used to dene the sensitivity

of camera imaging devices.



PIC IN PIC (PIP):

An electronic device to superimpose the

view from one camera over that of another.

PIXEL:

Picture element. The smallest cell or area for

a CCD chips capable of displaying detail on

a screen. The greater the number of pixels,the higher the resolution.

REMOTE SWITCHER:

A video switcher to which the cables from

the cameras are connected and which

contains the switching electronics. This unitmay be remotely located and connected to a

desktop controller by a single cable for each

monitor.

RESOLUTION:

A measure of the ability of a camera, or,

television system to reproduce detail.

Typically refers to the number of picture

MONITOR:

A device that converts electronic signals

into video images that was generated by the

camera and lens. The picture end of a CCTV

system.

MULTIPLEXER (MUX):

Electronic systems that can accept a number

of cameras inputs and record them virtually

simultaneously. Most also provide many

other features such as multi screen displayswith four, nine, sixteen, etc. Cameras on the

screen at once. Most have alarm inputs that

trigger several pre programmed functions.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.

PAN TILT:

A device that can be remotely controlled

to provide both vertical and horizontal

movement for a camera.



elements that can be reproduced with gooddenition.

RS-232-C:

Designation for a communications interface

used to communicate with devices such as

printers.

S/N RATIO:

Signal to noise ratio, a measurement ofthe noise level in a signal expressed in DB

(decibels). In a video signals values from 45DB to 60 DB produce an acceptable picture.

Less than 40 DB is likely to produce a “noisy”

picture.

SCREEN SPLITTER: A term usually used for a device that can

combine the views from two cameras on

a single screen. The split can be arranged

horizontally vertically or one picture inserted

in another.

SENSITIVITY:

Of a camera – usually specied in LUX and

should be the amount of light falling on the

imaging device to produce a video signal of

1 volt pp (peak to peak). However, it is moreoften given as the amount of light at the

lens. This can be confusing unless the lensspecication is provided in detail, including

its light transmission value.

SLOW SCAN:

A term usually applied to a method of

transmitting video signals through the public

telephone network.

The speed of transmission is dependent

on the type of network the transmitter

and receiver. The quality of picture is

proportional to the speed of transmission.Modern systems using digital compression

techniques can transmit good quality pictures

in a few seconds.

SWITCHER:

A device used to switch the video signalsfrom two or more cameras to a monitor.

TELEMETRY:

The system by which a signal is transmitted to

a remote location in order to control operation

of equipment. In CCTV systems to control pan

and tilt and zoom functions, switch on light,

move to preset positions, etc. the controller

at the operating position is the transmitter

and there is a receiver at the remote location.The signal can be transmitted along a simple“twisted pair” cable or along the same coaxial

cable that carries the video signal.

TERMINATION:

The video cable requires an impedance of 75

ohms at normal video signal bandwidth. This isoften called “low Z”. There is a switch on the back

of the monitors to select either 75 ohm or “high

Z” (sometimes “high/low”). If a signal is looped

through more than one monitor all should beset to “high” except at last, which should be to

“low” or 75 ohm.


http://slidepdf.com/reader/full/closedcircuittelevisionpdf 20/20

TILT:

The up and down movement of a camera.

To elevate or depress the vertical angle of

view.

VMD OR VIDEO MOTION DETECTION:

A method of detecting movement in the view

of the camera by electronic analysis of thechange in picture contrast.

ZOOM RATIO:

The ratio of the starting focal length (wide

position) to the ending focal length (telephoto

position) of a zoom lens. Typically 10x.

ZOOM LENS:

A lens with a variable focal length. This lens

may be effectively used as a wide angle,standard, or telephoto lens by varying the

focal length of the lens. A varifocal lens, they

exist in manual or motorized form.

ZOOM LENS

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