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CCTV
Systems
By John W. Colley
Grill
The CCTV Expert
January,
2004 Issue
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The Grill The CCTV Expert Archives
Our customer is experiencing various results when they transmit
video from point "a" to "b" using standard telephone lines.
They want to know if there is formula for this transfer procedure.
Yes you may use a formula to figure out the speed from point
"a" to point "b". Unfortunately, it is a variable formula.
Video data is converted to an image file. Determining the
size of each file requires knowing the type of compression,
the level of compression, image resolution, color or black
and white, does the image have movement and the detail of
the image will all have an impact on the file size.
Using
a standard public telephone circuit (POTS) we assume one frame
of video equals 12KB file and if we download over a dial up
POTS line connection and the connection is 28.8Kps the most
we can expect is one image every three (3) seconds. Please
remember a byte is a unit of data that is eight binary digits,
or bits, long. In the example of 12 KB that works out to be
9600 bits divided 28800 bits per second, which would be 3.3
seconds to download.
Our local school district is interested in a video recording
system for the area school buses. Do you have any recommendations
on the features they should include in their bid specifications?
Mobile surveillance is growing segment of the CCTV market.
Due high insurance and legal costs involved with providing
municipal services to the public video is a deterrent to frivolous
law suits and documenting a potential problem before in gets
out of hand.
You
should look for products with features that have been develop
for this vehicular application. Digital recorders are available
with removable disc's. The removable disc size should be the
largest available with a minimum of 120 GB. Power consumption
may vary from 9-36 VDC depending on how the power is configured
for the vehicle. A very important consideration is the provisions
for shock absorption. Carefully consider third party verification
of the data. The unit should operate in real time. Most digital
recorders allow a connection to the Internet and Ethernet
and this application should offer this option. The programming
and memory should be backed up by an uninterruptible power
supply (UPS). Each ensemble should be lightweight and not
exceed fifteen (15lbs). The camera input should except 75
ohm, 1-volt peak-to-peak composite analog video inputs in
NTSC or Pal. Color or black white cameras or a combination
or either should be acceptable to the DVR. The manufacture
should provide a list of camera manufactures that the DVR
will accept. Each unit should have on board capability to
program the unit in the field or from a laptop or workstation.
Security provisions should a feature in case of theft to annunciate
the unit is being tampered with be someone. Optional secure
cabinets for the unit should be made available.
The
unit must have a recording buffer up to ten (10) minutes prior
to the incident.
What is your recommendation on perimeter exterior camera placement?
The first step should be to review a site plan for the property.
Camera placement and views partially will be determined by
the physical size of the area to be viewed. Your selection
of lens, lighting and local obstructions will be the next
consideration. An important issue is to keep the intruder
in view. If the intruder can easily hide behind objects and
obstructions, the system will be less reliable. Avoid windows,
moving objects, steep ground grades and select camera views
that give an accurate view of the people.
Recently we installed an auto iris lenses. The picture appears
to be dark and grainy. Are we doing something wrong with the
install?
First you need to check on the type of auto iris you installed.
There are two types of lenses. The first being DC driven and
the second lens is video driven. Reexamine what type you have
purchased. Usually most cameras have a switch, located on
the rear of the camera body or in concealed location to choose
the type of lens, video or DC. Adjust the level on the lens
following the supplied instructions for the type of lens you
are using.
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John
W. Colley is president of Integrated Security Systems, Ltd.
and has been in the security industry for over 25 years, beginning
his experience in the CCTV segment of security and gaining
knowledge through field experience, manufacturer training
and designing systems to meet customer needs. Colley started
his security integration firm 18 years ago, providing design,
engineering, installation and service to commercial accounts
using integrated systems. Send your CCTV/Surveillance questions
to jwc@securityiss.com.
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