Spectrex SharpEye 40/40I, User Manual

Page: 18 / 85

SharpEye
TM
IR3 Flame Detector User Guide
18 Principles of Operation
1.4.1 Hydrocarbon Fire Detection
The SharpEye 40/40I Detector is designed to detect flames in which carbon
dioxide (CO
2
) is produced in the combustion process. These include all
hydrocarbon flames, as well as other types of flames and burning materials
such as wood or alcohol.
The detector’s principle of operation is based on patented IR3 technology.
This technology identifies the unique spectral signature that hot CO
2
has in
the infrared (IR), i.e. a peak of intensity at wavelengths of 4.2 – 4.7µm.
The original IR3 technique (such as implemented in the SharpEye 20/20I
Flame Detector) utilizes 3 infrared sensors, each sensitive to its own
wavelength range. The first sensor is sensitive to wavelengths within the
emission peak of hot CO
2
. The other 2 sensors are sensitive to wavelengths
above and below this peak. In the event of fire, the signal measured in the
first sensor is significantly higher than those measured in the other 2
sensors. In order to trigger a fire alarm, these and other conditions must be
met (for example, radiation is flickering in frequencies typical of flames).
The detector does not react when exposed to non-fire radiation sources.
The SharpEye 40/40I also includes an additional IR sensor, sensitive to a
different band within the emission peak of hot CO
2
. Th is sensor’s signal is
compared to those of the other 3, thereby increasing sensitivity for some
types of flames, such as gas flames.
1.4.2 Heated Optics
The SharpEye 40/40 Flame Detector uses heated optics. The heater
increases the temperature of the optical surface by 5
– 8°F / ~3 – 5°C above
the ambient temperature to improve performance in ice, condensation, and
snow conditions.
The heated optics can be set to one of the following:
 Not operated.
 On continuously.
 Automatic, per temperature change (default): you can define the start
temperature below which the window is heated. (The default is
41°F/5°C.) This temperature can be defined from 32°F/0°C to
86°F/30°C. The heating stops when the temperature is 27°F/15°C above
the start temperature.
For more information, see Configuring Your Detector on page 43.
1.4.3 HART Protocol
The 40/40 Flame Detectors use the HART protocol.
HART Communication is a bi-directional industrial field communication
protocol used to communicate between intelligent field instruments and host
systems. HART is the global standard for smart process instrumentation and
the majority of smart field devices installed in plants worldwide are HART-
enabled. HART is available in wiring options 1, 2, and 3 (see Table 1, page
16).
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