2.5.4.1
Infrared (IR) Single Frequency Flame Detector
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NOTE: The single frequency IR flame detector has
the advantage of a fast response and is moderately
sensitive. Its disadvantages are being affected by
temperature extremes and being subject to false
alarms from a myriad of IR sources.
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The detector shall be sensitive in the range of [_____] to [_____]
micrometers only.
2.5.4.2
Infrared (IR) Dual Frequency Flame Detector
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NOTE: The IR dual frequency flame detector has the
advantages of a moderately fast response, moderate
sensitivity, and a lower false alarm rate. Its
disadvantage is being affected by temperature
extremes.
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The IR detector shall consist of two or more IR sensors, each selected for
a different IR frequency. The primary sensor shall be sensitive in the
range of [_____] to [_____] micrometers only. Secondary sensors are tuned
to different IR wavelengths to null out the effect of black body radiation
to the primary sensor.
2.5.4.3
Ultraviolet (UV) Flame Detectors
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NOTE: Ultraviolet (UV) flame detectors can be set
to respond accurately to UV wavelength light
produced by flame from both indoors and outdoors.
UV flame detectors operate on the Geiger-Muller
principle. These gas-filled vacuum tubes respond in
the UV portion of the spectrum but can ignore UV
radiation from the sun because the upper response
range of the detector falls below the range of UV
radiation that reaches the earth.
Solid-state UV detectors are available, but their
spectral response extends into the sun's UV range
and are not recommended for external use.
UV detectors have an 80 to 90 degree cone of vision.
The UV detector has a fast response time and
usually is not affected by rain, wind, snow, high
humidity, or temperature and pressure extremes. UV
units will produce false alarms if they are exposed
to arc welding or X-ray and gamma radiation. They
can also be blinded by oil film or smoke. UV flame
detectors that are used in dirty and dusty
environments should be equipped with automatic
self-test and self-cleaning devices. The cleaning
device uses a stream of clean air across the lens
surface to minimize the build-up of contaminants.
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SECTION 13851A
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