Closed
circuit TV (CCTV) is quickly becoming one of the most important and
economical security and safety tools available. A good understanding
of basic CCTV application, components and design is important when considering
a CCTV and video surveillance system.
Key steps when considering
or designing a CCTV security systems include:
- Determine the
primary application of the CCTV system.
- Define the layout and characteristics of the controlled area(s).
- Decide on camera type and features.
- Determine the best location for viewing monitors.
- Determine the best method of signal transmission.
- Decide on the type of recording/archival equipment for the system.
- You can refer to our CCTV glossary for definitions of some of the
technical terms you might encounter.
Primary
CCTV Applications
When used for video
surveillance and monitoring, the two important goals of a complete CTV
system are security and safety. The primary purposes of a CCTV system
are detection, assessment and identification. In all applications a
CCTV system must provide the ability to visually observe/monitor and
record. Observation provides real-time information for detection and
identification. Recording provides after-the-fact material for assessment,
analysis and review, usually with overlaid time/date and location information.
Layout and
Characteristics of the Controlled Areas
Before a CCTV system
can be designed, you must know specific information regarding the layout
of the controlled areas. This information will facilitate camera location
and selection. You will need to determine the height or width, and direction
of view by compass point for each camera location. Questions to consider
include:
Will a fixed mount
camera or a camera with pan/tilt/zoom capability be required?
What are the lighting characteristics of the controlled areas? Consider
the objects or area to be observed and the environment in which they
exist. Different areas contain different colors, surfaces and materials
that reflect varying levels of light. To select proper equipment, it
is necessary to determine the minimum lighting level (day and night)
that will arrive from the area to the camera. The available light will
affect picture clarity and focus. An area can be illuminated by natural
or artificial light sources. Natural sources include sunlight and moonlight.
Artificial sources include incandescent, sodium, fluorescent, infrared,
and other man-made lights. The better the light, the better the picture
quality.
What type of video signal transmission will best fit the area?
Camera Types and Features
Cameras are selected
based on sensitivity, resolution and features. A camera's sensitivity
is the amount of light that is needed by the camera to produce a quality
video image. A camera's resolution determines the quality of the video.
Some cameras can be programmed to patrol an area or respond to movement.
Factors such as distance from the scene, focal length, desired field
of view, lighting and format affect the size and clarity of the video.
Lenses - Lenses
play an important role in the design of a CCTV system. Some camera's
have powerful zoom lenses which can be focused at far distances. Choose
the proper lens for each camera by the format size of the camera, distance
from the camera to the scene and the required size of the viewing field
for adequate identification. Typically, the more light that passes through
a lens, the better the quality of the picture. Selection of a lens is
especially critical because it directly affects the size, shape, and
sharpness of the video and the camera's target viewing area. When both
wide scenes and close-up views are needed from the same camera, a zoom
lens is preferable.
Iris Control - Where the level of available light can change dramatically,
a camera equipped with automatic iris control can help provide consistent
video quality. Automatic iris control enables cameras to open or close
the lens to adjust the amount of light passing through it. In bright
light an auto iris camera will close the lens to prevent strong light
from distorting the video. In low light, the camera will open the iris
to allow a greater amount of light in and sharpen the video.
Fixed vs. Pan/Tilt/Zoom - Cameras can be fixed or have pan, tilt and
zoom capability. Fixed cameras are mounted on a fixed bracket and cannot
be automatically adjusted to different angles of the viewing area. Pan/tilt/zoom
cameras are motor driven and can pan left and right, tilt up and down
and zoom in and out for close-up or wide-angle viewing.
Color vs. Black and White - Color cameras usually require a higher level
of lighting than black & white (monochrome) cameras. Color produces
a more natural, richer image than monochrome. Color also makes it easier
to identify subjects. With a color system one could more easily distinguish
a red from a green object, while on a monochrome system both objects
would appear a similar shade of gray. However, monochrome cameras continue
to offer some advantages. Monochrome cameras are better suited for extremely
low light situations. The ability to capture good quality video images
in low light situations increases the cost of both monochrome and color
cameras. Before purchasing cameras, consider the comparison between
lighting costs and camera costs. It's possible that low-light cameras
will cost less than paying to increase the lighting in an area.
Housing - A camera's housing protects the camera and lens from the environment
and potential vandalism. It can also enhance the appearance of the camera
installation and conceal the equipment from observation. All outdoor
cameras require a housing of some type. Protection from cold, heat,
dust, and other elements is needed to ensure optimum performance and
extend the life of the camera. Where aesthetics are a concern, dome
cameras are a popular choice. Dome cameras are covered by a dark colored
Plexiglas housing that hide the camera and wires. Other advantages of
dome cameras include deterrence (one cannot tell where the camera may
be pointed) and economy (domes with no camera inside can be mounted
with the same outward appearance).
Signal Transmission
Signal transmission
is the method by which the video signal gets from the camera to the
monitor. Several video transmission technologies exist, each with its
own advantages and disadvantages. It is not uncommon to find several
video transmission technologies in use within the same CCTV system.
The choice of signal transmission depends on factors such as distance,
environment, cost and area layout. Nearly all methods of transmission
suffer from various forms of signal interference or loss. Good system
design works to minimize signal interference and loss. Examples of video
signal transmission include:
Twisted Pair Wire
- A twisted pair wire provides a physical connection or closed circuit
between the camera and the monitor. A twisted pair of wires can transmit
a video signal for distances up to one kilometer without a signal boost.
An example of a twisted pair wire is a dedicated telephone line that
connects the camera with the monitor. Specialized equipment make it
possible to use public telephone lines for video signal transmission.
Coaxial Cable - A coaxial cable provides a physical connection or closed
circuit between the camera and the monitor. The cable is shielded to
minimize interference from any other electronic devices or circuits.
Copper braided coaxial cable is recommended to maximize conductivity
and minimize potential interference. For traditional CCTV systems this
is the most common method of signal transmission over relatively short
distances.
Fiber Optic Cable - A fiber optic cable provides a physical connection
or closed circuit between the camera and the monitor. Fiber optic technology
changes an electronic signal into pulsed laser light and transmits it
through a fiber optic cable, changing the pulsed light back into an
electronic signal capable of being displayed on a monitor. Fiber optic
transmission is resistant to electrical or environmental interference.
Wireless - Wireless signal transmission uses radio frequency to transmit
video signals. It is cost effective and reliable for short distances
with line-of-sight video transmission. It is practical where hardwiring
methods are either impossible or cost prohibitive. However, wireless
transmission is susceptible to adverse environmental conditions and
other RF signals in the area.
Microwave - Microwave can be an efficient and cost-effective method
of transmitting video signals. Microwave converts the video signal into
high frequency radio signals that require no wire or cable, providing
good quality transmission over a line-of-sight path. Though microwave
technology requires line-of-sight transmission and is affected by environmental
conditions, it offers a large bandwidth to carry video and is a practical
option when a wire path between the camera and monitor locations cannot
be established or is prohibitively expensive.
Viewing Monitors
The viewing monitor
receives the video signal from the camera and displays it for viewing.
A CCTV monitor provides higher lines of resolution than a TV and accepts
only video signals. Lines of resolution is the total number of horizontal
lines the camera or monitor is able to reproduce. The more lines of
resolution, the better or sharper the video picture will appear.
Several factors
should be considered when selecting and placing a monitor. The size
of the monitor, its positioning and viewing angle, monitor resolution,
viewing station growth, and adequate ventilation. CCTV systems use both
dedicated monitors and switchable monitors. A dedicated monitor displays
the video from just one camera. A switchable monitor enables a viewer
to switch between different cameras. A multiplexed monitor gives a viewer
the ability to view multiple simultaneously cameras.
Recording
Equipment
Recording equipment
is used to record events for later review, or while you are away from
the premises. Recordings make it possible to view events that may have
gone unnoticed at the time they occurred or that may require closer
scrutiny. You can record all your cameras all of the time or some cameras
some of the time. Multiplexers make it possible to record all cameras
in the system onto a single videotape. Some Multiplexers also have a
motion detection feature that enables the system to record more video
from cameras with motion than from those without motion.
Digital video recorders
(DVRs) give you the ability to record perfect quality pictures and replay
them at the touch of a button. Digital recording also make it possible
to record video on a computer disk. DVRs are able to record much more
information in ether real-time or time-lapsed mode. Real-time mode produces
higher quality recordings that approximate the ability of the human
eye to easily distinguish moving images. Time-lapse mode records more
video over longer periods of time on less videotape. Since the number
of pictures recorded per second in time-lapse mode decreases significantly
as the recording time increases, video movement may appear jerky. Alarm
recording combines these two modes, recording in time-lapsed mode until
an event occurs (operator selected or alarm) that switches the recorder
to real-time mode.
Additional features
of a CCTV recording system include a video printer that can produce
a hard copy printout of a video scene, and a time/date generator that
can annotate the video scene with chronological information and a camera
identifier to identify the selected camera.
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