Det-Tronics R7495D UV/IR Flame Detection System - Manual (Page 11)

INSTALLATION
DETECTOR POSITIONING
When determining the proper number and positioning of
detectors needed for adequately protecting any given
installation, it is essential to consider the cone of vision
of the detector. The C7052J Detector has a nominal 80
degree cone of vision with the highest sensitivity along
its central axis. Refer to Figure 4. Careful observation
of this graph reveals that at 50 percent of the maximum
detection distance, the cone of vision is still 80 degrees.
As the detection distance increases beyond 50 percent,
the cone of vision gradually decreases. For example,
the C7052J will detect a 1 foot by 1 foot gasoline fire at
50 feet. Therefore, we can assume that at 25 feet (50%
maximum distance) the cone of vision will be 80
degrees. If the fire increases in size, both the maximum
detection distance and the cone of vision at longer dis-
tances will be increased.
It is also important to note that as the distance increases
between the detector and the fire source, the time need-
ed for the detector to respond to a fire of a given size
also increases (fastest response requires maximum fire
signal). The intensity of the radiation reaching the
detector decreases with distance. For fastest response
time, locate the detector as close as possible to the
anticipated fire source.
The following recommendations should be observed in
designing or installing any fire detection system:
— Use enough detectors to adequately cover the pro-
tected area with overlapping cones of vision.
— For fastest response time, position the detectors as
close as possible to the anticipated fire source.
— Aim the detector as directly as possible at the antic-
ipated fire source.
— If possible, conduct actual flame tests to verify cor-
rect detector positioning and proper system opera-
tion.
Whenever possible, the detector should be positioned
in a manner that will minimize the buildup of contami-
nants on the viewing window and oi ring. Substances
such as snow, ice, dirt, oil, paint overspray, and numer-
ous other commonly encountered materials are capable
of attenuating UV or IR radiation and adversely affecting
detector response.
For outdoor applications, the detector should be aimed
downward to minimize the buildup of water or ice on
the detector viewing window and to prevent it from
scanning the horizon. This minimizes the response to
distant radiation sources outside the protected area.
The detector should not be placed where smoke can
obscure its view of the hazardous area. For indoor
applications, if dense smoke is expected to accumulate
at the onset of a fire, mounting the detector on a side
wall a few feet (1 meter) down from the ceiling will nor-
mally allow enough time for the unit to respond before it
is affected by rising smoke. The detector should be
located where it can be easily accessed for periodic
maintenance, testing and cleaning.
95-8331
The following is a partial list of compounds that
exhibit significant UV absorption characteristics.
These are also usually hazardous vapors. While
generally of little consequence in small amounts,
these gases can restrict UV detection if they are in
the atmosphere in heavy concentrations. It should
also be determined whether or not large amounts of
these gases may be released as a result of a fire-
causing occurrence.
Acetaldehyde Methyl Methacrylate
Acetone Alpha-Methylstyrene
Acrylonitrile Naphthalene
Ethyl Acrylate Nitroethane
Methyl Acrylate Nitrobenzene
Ethanol Nitromethane
Ammonia 1-Nitropropane
Aniline 2-Nitropropane
Benzene 2-Pentanone
1,3 Butadiene Phenol
2—Butanone Phenyl Clycide Ether
Butylamine Pyridine
Chlorobenzene Hydrogen Sulfide
1-Chloro-1-Nitropropane Styrene
Chloroprene Tetrachloroethylene
Cumene Toluene
Cyclopentadiene Trichloroethylene
O-Dichlorobenzene Vinyl Toluene
P-Dichlorobenzene Xylene
If UV-absorbing gases may be a factor in a given
application, precautionary measures should be
taken. Detectors can be placed closer to the poten-
tial hazard area, and/or the sensitivity of the detec-
tion system can be increased. Contact the factory
for further details.
Substances such as methane, propane, butane,
hexane, camphor and octane are not UV absorbing.
Absorption of infrared radiation in the range of 4.2
to 4.7 microns is not a significant problem with most
organic vapors, with the exception of those com-
pounds that have triple bonds such as acetylene,
nitriles, silane, or isocyanates. Carbon dioxide con-
centrations higher than normally present in the
atmosphere can also cause substantial loss of fire
detection sensitivity.
Table 2—Radiation Absorbing Gases and Vapors
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