|
What
is Closed Circuit Television (CCTV)
CCTV is a system in which all the elements are directly
connected, i.e.: Systems linked by radio waves, Internet connections, or
hardwires. In this website you will find all the components that can go to
make up Closed Circuit TV systems of varying complexity.
The
Applications of CCTV
The most common
use of CCTV is in security systems and such applications as
retail shops, banks, casinos, malls, condos, government establishments, home
security, etc. The true scope for applications is almost unlimited. Some
examples are listed below.
-
Home Security
Cameras for monitoring babies
-
Recording how
their caretakers treat your elders at homes or nursing homes
-
A Television
Security Camera System to check the surroundings of a block or a building
-
Television
Cameras for Quality Control in factories or laboratories
-
Security
Television Cameras for checking parts storage in an auto repair shop
-
Covert Cameras
hidden in buses to control vandalism
-
Cameras for
aerial photography from a small airplane or helicopter
-
Mini cameras or
other Television Cameras for production control in a factory
-
Closed Circuit Television has many more applications, and they are limited
only by your imagination and creativity.
In addition you
will find a great array of cameras, either for security or many other
possibilities. Hidden cameras, also known as spy cameras or covert cameras
are hot items. We have cameras for a variety of purposes and needs, both
outdoors and indoors, such as Pan Tilt Zoom Cameras, Bullet Cameras,
Professional Cameras, Monitors, Quads, Multiplexers, Digital Video Recorders
(DVR’s) Video Transmitters & Receivers.
Buy your home
security cameras with confidence. We provide the best available high quality
CCTV and home security television, at affordable prices.
THE
CAMERA
The starting point for any CCTV system must be the camera. The camera
creates the picture that will be transmitted to the control position. Apart
from special designs, CCTV cameras are not iitted with a lens. The lens must
be provided separately and screwed onto the front of the camera. There is a
standard screw thread for CCTV cameras, although there are different types
of lens mounts.
Diagram 1.1 Camera and Lens
THE MONITOR
The picture created by the camera needs to be reproduced at the control
position. A CCTV monitor is virtually the same as a television receiver
except that it does not have the tuning circuits.
Diagram 1. 2 CCTV Monitor
SIMPLE CCTV SYSTEMS
The simplest system is a camera connected directly to a monitor by a coaxial
cable, with the power for the camera being provided from the monitor. 'This
is known as a line powered camera. Diagram 1.3 shows such a system. Probably
the earliest well known version of this was the Pye Observation System that
popularised the concept of CCTV mainly in retail establishments. It was an
affordable, do-it-yourself, self contained system.
Diagram 1. 3 A Basic Line Powered CCTV System
The next
development was to incorporate the outputs from four cameras into thc
monitor. These could be set to sequence automatically through the cameras or
any camera could be held selectively. Diagram 1.4 shows a typical
arrangement of such a system. There was even a microphone built into the
camera to carry sound, and a speaker in the monitor
Diagram 1. 4 A Four Camera Line Powered CCTV System
The speaker,
of course, only puts out the sound of the selected camera. There were
however a few disadvantages with the system, although this is not to
disparage it. The microphone, being in the camera, tended to pick up sound
close to it and not in the area at which it was aimed. There was a
noticeable, and sometimes annoying; pause between pictures when switching.
This was because the camera was powered down when not selected and it took
time for the tube to heat up again.
The system was, though, cheap to buy and simple to install. It came complete
in a box with camera, l6mm lens, bracket, switching monitor and 12 metres of
coaxial cable with fitted plugs. An outlet socket for a video recorder was
provided, although reviewing could be a little tedious when the cameras had
been set to sequence. There are now many systems of line powered cameras on
the market that are more sophisticated than this basic system. Most of the
drawbacks mentioned have been overcome. Cameras had been around for a long
time, of course, before this development. The example is given to show the
simplest, practical application. The use of some line powered cameras can
impose limitations on system design. They do though, offer the advantage of
ease of installation.
MAINS POWERED CCTV SYSTEMS
The basic CCTV installation is shown in diagram 1.5 where the camera is
mains powered, as is the monitor. A coaxial cable carnes the video signal
from the camera to the monitor. Although simple to install it should be
borne in mind that the installation must comply with the relevant
regulations such as British Standard BS 7671. Failure to do so could be
dangerous and create problems with the validity of insurance.
Diagram 1. 5 A Basic Mains Powered CCTV System
This
arrangement allows for a great deal more flexibility in designing complex
systems. When more than one camera is required, then a video switcher must
be included as shown in diagram 1.6. Using this switcher, any camera may be
selected to be held on the screen or it can be set to sequence in turn
through all the cameras. Usually the time that each camera is shown may be
adjusted by a control knob or by a screwdriver.
SYSTEMS
WITH VIDEO RECORDING
The next development of a basic system is to add a video recorder. The
arrangement would be as shown in diagram 1.7.
Diagram 1. 6 A Multi Camera System With Video Recorder
With this
arrangement, the pictures shown during playback will be according to the way
in which the switcher was set up when recording. That is, if it was set to
sequence then the sequenced views will be displayed on the monitor. There is
no control over what can be displayed.
MOVABLE
CAMERAS
So far, all the cameras shown have been fixed with fixed focal length
lenses. In many applications the area to be covered would need many fixed
cameras. The solution to this is to use cameras iixed to a movable platform.
This platform can then be controlled from a remote location. The platform
may simply rotate in a horizontal plane and this is generally known as a
scanner. Alternatively, the platform may be controllable in both horizontal
and vertical planes and is generally known as a pan, tilt unit. A basic
system is illustrated in diagram 1.8.
This Chapter does not deal with how cameras are controlled or wired; it is
just showing the facilities that may be incorporated into a CCTV system.
Therefore, the diagrams that follow are simply descriptive block diagrams
and not connection drawings.
Diagram 1. 7 Basic Movable Camera System
Diagram 1. 8 Multiple Camera System
Cameras may
be used indoors or outdoors. When used outdoors they will always require a
protective housing. For indoor use, the environment or aesthetic constraints
will dictate whether a housing is needed. Systems may contain a combination
of both fixed and movable cameras.
OTHER
CONSIDERATIONS
This has been an introduction to some of the fundamentals of CCTV. Recent
developments have made some very sophisticated systems possible. These
include concepts such as multiple recording of many cameras; almost real
time pictures over telephone lines; true real time colour pictures over the
ISDN telephone lines; switching of hundreds, even thousands, of cameras from
many separate control positions to dozens of monitors; reliable detection of
movement by electronic evaluation of the video signal; immediate full colour
prints in seconds from a camera or recording; and the replacement of manual
controls by simply touching a screen. |
