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 When
choosing a CCTV system, there are a number
of points that must be taken into consideration.
Currently on the market there is a huge range
of CCTV equipment available including cameras,
lenses, pan & tilt heads, control systems,
monitors and recording equipment. As with
most systems, the higher quality the product
the more expensive the system will be. However,
Monitor recommends that you invest in the
higher-grade equipment, as the benefits will
quickly become apparent. The quality of the
image will be very clear, and the equipment,
with regular mainten-
ance checks, should outlast its rivals.
Systems are available for small one camera
to one-monitor applications for farms, small
shops or homes, to multi camera systems, to
on-site control rooms in the larger industrial
or retail applications. To help you choose
what type of system would best suit your home
or premises, ask yourself the following questions,
and then read through the list of equipment
available.
- Do
you require colour or black and white
images?
- Do
you require the image to be recorded?
- What
areas do I need to cover?
- If
the cameras are to be situated outside
the building, is there enough lighting
for the camera to see clearly during the
night?
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System
Types |
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CCTV
systems and their components fall into the following
categories and it is important to choose the
correct system category for the particular security
requirement.
- Black
& white
- Colour
- Switchable
Black & white /colour
 Black
& White: These systems tend to
be more sensitive to light than colour.
If the threat to security is during the
hours of darkness the black and white
option will therefore probably produce
the best recorded images. |
 Colour:
These systems however offer a more
lifelike reproduction of an incident and
will make the identification of a suspect
easier, i.e. the man with the ginger hair.
The traditional problem though is that
colour cameras do not work well in very
low light levels. |
 Switchable:
The Switchable black & white /colour
option offers all the lowlight advantages
of black & white during periods of
poor visibility and the lifelike reproduction
of suspects during periods of normal lighting
conditions.
The camera works in a similar way to the
human eye. When light levels are good
the camera will work in colour mode, when
the light levels drop below a certain
level the camera automatically switches
to black & white.
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 Housings:
External cameras must be housed within
an environmentally controlled housing.
The housing contains a thermostatically
controlled heater to avoid frosting and
misting. Consideration should also be
given to potential vandalism and a suitably
protected housing should be chosen if
vandalism could be a problem.
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Monitors:The
image from the camera is displayed on
a monitor which is the CCTV industry's
equivalent of a television screen. The
quality of the monitor should again
match that of the camera and lens as
the image will only be as good as the
weakest link in the system. Sizes of
monitors are similar in range to those
of televisions. It is important to choose
a monitor that will allow the person
viewing it to identify a potential crime
and identify the persons involved for
possible future criminal proceedings.
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 Time
Lapse VCR's:Time lapse VCR's are the
CCTV equivalent of the video recorder except
that they are designed for continual use
24 hours a day. They also allow a 3-hour
VHS tape to record for extended periods
from 3 hours upwards i.e. 12, 24,48,96.
This extended recording is achieved by a
system called Time Lapse. This means a short
time delay between each frame recorded producing
a playback. As with all other products there
is a wide range of VCR's available differing
largely in quality and price. Again it is
very important to match the quality of the
VCR with that of all the equipment being
used.
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Video
Processing Units
 If
a single camera and monitor is all that
is required in a CCTV system, then there
will be no need for video processing.
However, the system design may require
multiple cameras both external and internal
to be viewed from one monitor and recorded
by one VCR.
This can be achieved by the use of a
video processor. The types available
fall into the following categories.
- Switcher/Sequencer
- Quad
- Multiplexer
- Telemetry
The
switcher/sequencer simply takes
the outputs from each camera and sequences
them on to a monitor allowing the person
viewing the monitor to select which camera
is to be viewed, or to allow them to sequence
through the cameras automatically one
at a time. The problem with this type
is that a camera may be viewing an incident
which will be valuable as evidence but
every 5 seconds or so the sequencer will
move onto the next camera and the potential
evidence is lost until the sequencer moves
back to the original camera.
The quad unit on the other hand
will take the images from up to four cameras
and present them in a quad format on the
monitor simultaneously. This allows the
person viewing the cameras to see all
four images without interruptions. The
drawback with the quad system is the quality
of playback of a recorded image. This
is usually poor, due to the way a quad
processes the four camera inputs.
The alternative is a multiplexer.
This will take the inputs from multiple
cameras and present them on the monitor
simultaneously. The quality of the playback
of a recorded image will be much closer
to that of the original.
Cameras that are static have unavoidable
blind spots. A remotely controlled movable
camera will overcome this problem. This
can be achieved by the installation of
a PTZ (pan, tilt and zoom) unit and telemetry
receiver to the camera and housing. A
telemetry transmitter and other equipment
are installed adjacent to the other control
equipment. The person viewing an incident
can control the position of the camera.
This is done by a keypad or joystick controller
and will enable the camera to sweep through
(up to) 360 degrees and tilt as required.
The same controller can also control the
zoom function of the lens.
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