Spectrex 40/40I Triple IR (IR3) Flame Detector - Manual (Page 17)

TM 40/40I, Rev (6) July 2013
Principles of Operation 5
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), namely a peak of the intensity at wavelengths 4.2 to 4.7µ.
The original IR3 technique (such as implemented in the SharpEye 20/20I
flame detector) utilizes three 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 two 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 two sensors. In order to issue a fire alarm, the detector requires
that this occurs, as well as other conditions (for example, radiation is
flickering in frequencies typical of flames). If exposed to non-fire radiation
sources, the specific conditions required does not occur, and the detector
does not react.
The SharpEye 40/40I further includes an additional IR sensor, sensitive to a
different band within the emission peak of hot CO
2
. The signal of this sensor
is compared to those of the other three. This increases sensitivity for some
types of flames. (For example, gas flames).
1.4.2 Heated Optics
The SharpEye 40/40 Flame Detectors use 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 icing, 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 between 32°F (0°C) to 122°F
(50°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 29.
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 2 and 3, see Table 1, page 3.
HART technology is easy to use and very reliable.