D-LX 100
Page
11
9.2. Infrared Flame Scanner
The IR zone of a flame is in many cases large and, relative to UV radiation, very intense. The IR zone
is easy to acquire under different angles of view, is strong in signal, and is not sensitive to absorption
by gases. Compared to a UV flame scanner, however, it is more sensitive to ambient light.
A silicon photo element with a spectral sensitivity of
λ
= 300 nm to 1100 nm is used in the D-LX 100 IS.
This flame scanner detects visible light. If the flame is red or gold in color, it is ”visible” to the scanner,
on the pre-condition, however, that there is movement in the flame, i.e., the flame is dynamic.
The D-LX 100 IG A employs a germanium photo element with a spectral sensitivity of
λ
= 780 nm to
1800 nm. The integrated flame scanner will therefore acquire the dynamic range of radiation
generated by nearly all fuels. This type of flame scanner is strong in signal, but demonstrates lower
selectivity due to the large IR zone.
Flames whose short-wave UV radiation is absorbed by dust, water vapor or other materials can be
monitored in the IR range. Applications include waste incinerators and oil-fired combustion systems.
In the case of the latter, IR monitoring in the spectral range of 300 to 1100 nm is typical.
IR flame scanners with a spectral sensitivity up to 1800 nm have proven themselves especially
effective in applications employing measures for NOx reduction, e.g., flue gas re-circulation or
systems with combination burners for gas and oil.
Note:
It can occur in practice that static emitters, like glowing boiler components, become modulated by
combustion air currents or flue gas clouds, and work like ambient light with dynamic portions of
radiation. Should this radiation lie in the range received by the scanner, i.e., in the IR spectrum, and
within the normal flicker frequency range (approx. 10 to 200 Hz), an output signal will be generated by
the flame scanner in the form of a pulse frequency corresponding to the intensity and dynamics of the
received radiation. The flame recognition threshold (pulse threshold) of the D-LX 100 may not in this
case be exceeded by the pulse frequency of the integrated flame scanner and cannot be allowed to
trigger a flame ON signal (see section 6: Setting the Flame Recognition Threshold on the Flame
Scanner).