greater the intensity emitted radiation. The U7652
ignores steady state IR sources that do not flicker.
However, it should be noted that if these steady state
IR sources are hot enough to emit adequate amounts
of IR radiation in the response range of the detector
and if this radiation becomes interrupted from the
view of the detector in a pattern characteristic of a
flickering flame, the IR sensor can respond. The clos-
er the IR source is to the detector, the greater the
potential for the IR sensor to respond.
AMBIENT RADIATION
The U7652 is designed to reduce false actuations,
however, combinations of ambient radiation that
could activate both the UV and IR sensor must be
avoided. For example, if IR radiation with an intensity
that exceeds the fire threshold of the IR sensor should
reach the detector as a flickering signal (activating
the IR sensor), and if at the same time an electric arc
welding signal also reaches the detector (activating
the UV sensor), an alarm output will be generated.
NON-CARBON FIRES
The U7652 uses a single frequency IR sensing device
with detection limited to the hot CO
2
emission peak,
therefore, it should not be used to detect fires that do
not contain carbon, such as hydrogen, sulfur and
burning metals without thorough verification testing.
Exceptions to this are when the U7652C is used. The
U7652C with auxiliary relay can be set to activate to
UV only radiation. The U7652C with 4 to 20 ma out-
put has a discrete milliampere output for UV only,
allowing it to monitor for UV only radiation.
GASES, VAPORS, SMOKE AND OTHER OBSTRUC-
TIONS
Radiation must reach the detector in order for it to
respond. Keep physical obstructions out of the line of
view of the detector. UV or IR absorbing gases or
vapors must not be allowed to accumulate between
the detector and protected hazard (see Table 4 for a
list of these substances). Do not mount the detector
close to the ceiling or in other areas where smoke can
accumulate.
EMI/RFI INTERFERENCE
The U7652 is resistant to interference by EMI and RFI.
It will not respond to a 5 watt walkie-talkie at a dis-
tance of greater than 1 foot.
VIEWING WINDOWS
Keep the detector viewing windows as free of con-
taminants as possible in order to maintain maximum
sensitivity and assure proper operation of the flame
detection system (refer to the “Maintenance” section
for cleaning instructions). Commonly encountered
attenuating substances include, but are not limited
to, the following:
— silicones
— oils and greases
— ice buildup
— dust and dirt buildup
— paint overspray.
4
Table 4—UV Absorbing Gases and Vapors
The following 38 substances exhibit significant UV
absorption 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 may be a factor in a given applica-
tion, 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, butane, cam-
phor, hexane 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 compounds that have
triple bonds such as acetylene, nitriles, silane, or iso-
cyanates. Carbon dioxide concentrations higher than
normally present in the atmosphere can also cause sub-
stantial loss of fire detection sensitivity.
