Det-Tronics C7052J UV/IR Flame Detector used with R7494, R7495 Controller - Manual (Page 8)

an alarm. The IR sensor can respond to IR radiation
sources that can meet the amplitude and flicker require-
ments of the detector such as vibrating hot objects.
Although the C7052J Detector is designed to reduce
false actuations, certain combinations of ambient radia-
tion must be avoided. For example, if IR radiation with
an intensity that exceeds the fire threshold of the IR sen-
sor should reach the detector as a flickering signal, and
if at the same time an electric arc welding signal also
reaches the sensors, an alarm output will be generated.
The C7052J ignores arc welding beyond 15 feet from
the detector. However, the UV sensor will respond to
the intense UV radiation generated by the arc welding,
and at distances closer than 15 feet the heated metal
from the welding can become a false alarm source for
the IR sensor.
Another important fact regarding a radiation detector of
any type is that radiation must reach the detector in
order for it to respond. Care must be taken to keep
physical obstructions out of the line of view of the detec-
tor. In addition, UV or IR absorbing gases or vapors
must not be allowed to accumulate between the detec-
tor and the protected hazard. See Table 2 for a listing
of these substances. Smoke will also absorb radiation,
therefore, the detector should not be mounted close to
the ceiling or other areas where smoke can accumulate.
It is important to keep the detector viewing windows as
free of contaminants as possible in order to maintain
maximum sensitivity and to assure proper operation of
the flame detection system. Commonly encountered
substances that can significantly attenuate UV and/or IR
radiation include, but are certainly not limited to, the fol-
lowing:
Silicones
Oils and greases
Ice buildup
Dust and dirt buildup
Paint overspray
The oi test feature is designed to register an oi fault
when the detector sensitivity is reduced to approximate-
ly 50% of its maximum detection range. For maximum
system reliability, it is recommended that the detector
viewing windows be cleaned on a regularly scheduled
basis. (Refer to the “Maintenance” section of this manu-
al for additional information regarding detector mainte-
nance.) The use of model Q1113 Air Shields can help
extend the time period between required maintenance.
The C7052J is designed to be resistant to interference
from EMI and RFI. It will not respond to a 5 watt walkie-
talkie at a distance of greater than 1 foot.
8
10 4
10 3
10 2
10 1
1
10 –1
10 –2
10 –3
10 –4
0.4 0.6 0.8 1 2 4 6 8 10 20 30
RADIANT EMITTANCE
WATTS
(CM ) (MICRON)
2
WAVELENGTH (MICRONS)
6000°K
2000°K
250°K
500°K
300°K
4000°K
1000°K
A0576
Figure 9—Blackbody Spectral Emittance
The following is a partial list of compounds that exhibit
significant UV absorption characteristics. These are also
usually hazardous vapors. While generally of little conse-
quence in small amounts, these gases can restrict UV
detection if they are in the atmosphere in heavy concen-
trations. 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, 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 compounds that have
triple bonds such as acetylene, nitriles, silane, or iso-
cyanates. Carbon dioxide concentrations higher than nor-
mally present in the atmosphere can also cause substan-
tial loss of fire detection sensitivity.
Table 2—Radiation Absorbing Gases and Vapors