Det-Tronics U7602B-P Unitized UV Flame Detector/Controller - Manual (Page 5)

• Designed to meet MIL-STD-810C for shock and
vibration.
• Designed for use in hazardous locations (explosion-
proof enclosure).
• Bracket mounted with swivel for ease of installation
and positioning.
• Enclosure material available in red anodized cop-
per-free aluminum or 316 stainless steel.
• Model available with 3 amp relay contact rating and
4 to 20 ma current output.
• Optional LED indicators.
GENERAL APPLICATION INFORMATION
In applying any type of sensing device as a fire
detector, it is important to know of any conditions that
can prevent the device from responding to a fire, and
also to know what other sources besides fire will
cause the device to respond. A UV detector is useful
in fire protection applications because it will provide
very fast response to the presence of ultraviolet radia-
tion emitted by a flame. In addition, it is not affected
by environmental conditions such as wind, rain or
extremes of temperature and pressure. The Det-
Tronics UV system is also insensitive to the ultraviolet
component of solar radiation.
Considering the above, it can be seen that there are
fire detection applications where only ultraviolet sen-
sors are suitable. However, success in using an ultra-
violet detector is dependent not only on knowing its
advantages, but also its limitations. It is important to
note that electric arc welding is a source of intense
ultraviolet radiation, and care must be taken to ensure
that arc welding is not performed in protected areas
without securing the fire detection system. Other
sources of UV radiation such as x-rays and radioac-
tive substances must also be considered when using
UV flame detection equipment. When x-rays or
radioactive substances are present in the area being
protected, the UV system must be disabled until those
sources are removed. For installations in which these
sources are present, systems are available from Det-
Tronics that can maintain uninterrupted protection.
Periodic lightning or sparks in the area being protect-
ed can be effectively ignored by the UV system using
the Fire Relay time delay (the factory setting of 5 sec-
onds is usually sufficient to ignore these sources).
UV detectors should not be positioned so that their
cone of vision can scan the horizon. Rather, they
should be directed down over the designated haz-
ardous area to reduce the likelihood of picking up UV
radiation from distant sources.
An important fact regarding radiation detectors of any
type is that the radiation must reach the detectors in
order for them to respond. Care must be taken to
keep obstructions out of the line of view. For an ultra-
violet detector, this means that UV absorbing gases
or vapors as well as physical obstructions must not
be allowed to come between the detector and the
protected hazard (see Table 1). Smoke will absorb
UV radiation, and if accumulations of dense smoke
can be expected to precede the presence of flame,
then ultraviolet detectors that are used in enclosed
areas should be mounted on the wall approximately 3
feet (1 meter) from the ceiling where the accumulation
of smoke is reduced. Glass and plexiglass windows
also significantly attenuate UV radiation and must not
be located between the detector and a potential
flame source. If the window cannot be eliminated or
the detector location changed, contact Detector
Electronics for recommendations regarding window
materials that will not attenuate UV radiation.
2
The following 38 substances exhibit significant UV ab-
sorption characteristics. These are also generally haz-
ardous vapors. While usually 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 can be a factor in a given appli-
cation, precautionary measures should be taken.
Detectors can be placed closer to the potential hazard
area, and/or the sensitivity of the detection system can
be increased. Contact the factory for further details.
Substances such as methane, propane, camphor, bu-
tane, hexane and octane are not UV absorbing.
Table 1—UV Absorbing Gases and Vapors