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| Cameras |
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CCD Camera |
B/W CCD Camera
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CCTV | Digital
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| CCTV
Cameras are the most important part of a CCTV installation.
In most of the cases the quality and performance of a
CCTV installation is assessed only on the basis of the
Camera. There are numerous cameras utilizing many different
technologies available in market. |
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- Picture Tube Cameras:
The picture tube cameras have long been obsolete.
They used to take a little time to warm up their system.
They are highly temperature dependent and a slight
temperature variation may alter their performance.
After continuous usage the picture tube got defected
and starts giving faded images in the video. Another
important drawback with picture tube cameras is that
they are unable to work in low lights and have very
low resolution.
- CMOS Cameras:
On the other front CMOS Cameras are quite cost effective,
but they also lack in many fronts. They have a low
shutter speed which results in flickering, especially
under artificial light conditions. They also lack
in resolution and low light usage. They are also not
made for continuous usage and usually lack in performance
in most of the industrial applications.
- CCD Cameras: CCD
(Charged Coupled Devices) are currently the best available
in this field. Invented in late 80's and early 90's
in Germany, they have proved to be the best. The cost
of picture tube cameras was reduced many times by
the use of CCD Image Sensors. They have high resolution,
low operating light, less temperature dependence and
high durability in long operating cycles. The image
of the object is formed on the CCD Image Sensor. For
the sake of understanding it is considered as an array
of photo sensitive diodes that picks up this image
and converts it into electronic pulses, which are
saved in an array of CCD Memory. From materials science
point of view CCD Sensor is a combination of semi-conductor
and electro magnetic technology, in which magnetic
wells are produced by electrodes etched on the CCD
Chip, these wells resemble an individual pixel and
after image formation, they are moved in linear fashion
towards an output electrode, from where it is given
to CCD Video Processor. However, it is usually considered
as photo diode array and CCD memory for the sake of
understanding and simplicity. The CCD Video Processor
chips picks us the signal from this CCD Memory and
converts it into useful signal, i.e. Video Composite
or S-Video. In colored cameras DSP (Digital Signal
Processing) circuitry can be further employed to pick
the data from CCD array more effectively and enhance
it in terms of resolution and colors. Sony's CCD Chips
have the most effective range of CCD Sensors, which
are high in resolution, have low light requirements,
provides excellent shutter speeds and highly efficient
in long duration operating. But Sony sensors are bit
expensive and usually 60% of the total cost of the
camera is only of the Sony's Image Sensor. Sony Sensors
are employed in AVC-371A and AVC-377 in B/W Cameras
and AVC-571 in Colored Digital Cameras. Sharp CCD
Sensors are second to Sony, but have very little difference
in price from Sony Sensors. Samsung's CCD Sensors
provides a low cost alternative for B/W Cameras and
are employed in Mondial's AVC-306 and AVC-201. In
Colored Cameras the low cost alternative is Toshiba's
CCD Sensors and are employed in AVC-551A and AVC-556
Colored Cameras. But very special care is required
in selecting a Colored Camera with the Toshiba Sensor
as there are low quality and low resolution Toshiba
sensors in the market, which are delivered with Video
Conferencing Kits as in Zoltrix Face to Face Video
Capture Cards.
- Super CCD Cameras:
In ordinary CCD Image Sensors the photo diodes (actually
magnetic wells) are arranged in rectangular array.
Recently, it has been found that if these photo diodes
(magnetic wells) are doped in the form of Honey Comb
structure, then more photo diodes (magnetic wells)
can be doped on the same sensing area. In ordinary
Sony's Image Sensor around 1.3 million photo diodes
(magnetic wells) are doped on 1/3" Image Pickup
area, while using this technology around 2 million
photo diodes can be placed, which increases the resolution
of the sensor many times.
- Cool CCD Camera:
In advanced application, especially in Infra Red CCD
Detection the temperature of the CCD Sensor plays
an important role. Infra Red rays are evolved from
heated objects as black body radiations and in Infra
Red imaging the black body radiation produced by CCD
Sensors temperature are quite harmful. To keep the
temperature of the CCD Sensor stable, it is enclosed
in a special sealed container with a built-in cooling
arrangement and temperature sensor, which keeps its
temperature within the required range. Such CCD Cameras
are quite expensive and are used in medical, fire
fighting, military and other high end applications.
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| Camera
Selection Guide: |
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| Selection
of a CCTV Camera can sometimes be very difficult and in
most of the cases the final result of the camera is only
observed when the full project has been installed, which
is too late to make any decisions. So to simplify this
we have prepared a few tips for both the technical and
non-technical people which one should observe in specifications
during making a decision to select a camera: |
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- Image Sensor:
Image Sensor is the most important aspect of the specifications
of the camera. As already discussed Sony Sensors are
most preferred and in B/W Samsung and in Colored Toshiba
provides a low cost alternative. 1/3" Image Sensing
Area is most preferred for CCTV Cameras as now a days
lenses are mostly available in 1/3" Format. In
old days 1/2" Sensing Area was preferred for
picture tubes. 1/4" is also used in CCD Sensors
for CCTV Application.
- Number of Pixels:
A pixel is the smallest unit of the image sensor device
which can detect light and convert it into useful
image. It is directly related with the resolution
of the camera, but cameras resolution cannot be assessed
only on its basis, due to the involvement of Video
Processing Circuitry and DSP. It may be possible that
a CCD Sensor have high pixel number but resolution
is low due to poor Video Processing Circuitry or it
may also be possible that a low pixel CCD Sensor may
yield a high resolution image by employing latest
image processing and enhancement algorithms.
- Resolution: Resolution
is the second most important factor of the camera.
It should be more than 380TV Lines for B/W Cameras
and 350TV Lines for Colored Cameras.
- Minimum Illumination:
Minimum Illumination is the minimum light that is
required by the camera to make a viewable image. It
is expressed in Candela or Lux, in current CCTV field
Lux is more commonly used. It should be less than
1 Lux. In B/W Cameras normally minimum illumination
less than 0.1 Lux is preferred and can be as low as
0.05 Lux in normal CCTV Cameras. While in Colored
Cameras which require more light to operate in, 1
Lux is most suitable. But colored cameras greater
than 5 Lux minimum illumination must be avoided as
they fail to operate properly indoors.
- S/N Ratio: Most
of the time Signal to Noise Ratio is ignored while
selecting a camera, but I personally believe that
it is of vital importance especially to the installer,
as lower S/N Ratios might prevent Video from camera
to reach the monitor properly. Cameras with S/N Ratio
less than 45dB must not be used at all. S/N Ratio's
ranging from 46-48dB is most commonly suitable for
use with Coaxial Cable (RG-59).
- Electronic Shutter Speed:
Electronic Shutter speed also plays a very important
role in the ultimate performance of the camera. Usually
a range of shutter speeds is provided like 1/60~1/100,000
sec., which means that the camera's electronic shutter
opens and closes 60 to 100,000 times a second. The
minimum side should not be less than 1/60 and maximum
side should not be greater than 1/100,000 of a second.
Unsuitable shutter speed results in the flickering
of the Video Image on the monitor, especially under
artificial light as in tube light or diffused light
environments.
Synchronization method: In picture tube cameras, an
external sync generator was employed to operate all
the cameras with same rate, but after the modernization
of CCD Technology it is no longer required, so an
internal synchronization method is the most suitable
and simple for CCTV installations.
- Video Signal:
In Pakistan and other countries CCIR System for B/W
and PAL System for Colored cameras is employed to
get a Video Composite Signal. So for a typical application
PAL / CCIR cameras giving Video Composite output should
be employed. While the impedance of the Video signal
must not be different from 75 ohms as it is the impedance
of the Coaxial Cable used for the wiring. However,
for advanced applications other standards like Progressive
Scan, RGB, RGBA, Y/C, S-Video, etc. Progressive Scan
System or Non-Interlace Scanning is of special importance
as it is employed is high resolution CCD applications
like Angiography Equipment. But progressive scan technology
is an extremely expensive one.
- White Balance, Backlight
Compensation and AGC: In colored cameras, color
adjustment used to be a tough job, but thanks to the
new technologies colors and brightness of the camera
is automatically adjusted by functions like Automatic
White Balance, Back light compensation, etc. AGC (Automatic
Gain Control) controls the contrast and video gain
of the built-in video amplifier of the camera. Thus
these functions make cameras to install easily without
any toil.
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Carpet Chambers,
Ground Floor,
10 Abbot Road Lahore - Pakisatn. |
| Tel: 92-42-631
6543, Fax: 92-42-636 6543 |
| E-mail: mondial@lahorebiz.com |
| ©2003 Mondial
All rights reserved. |
| Developed By:
eTechsol.net |
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