6 | Configuration and function
D-LX 201/721
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6 Configuration and function
This section explains the working method of the compact flame monitor and the inter-
play between the various involved components.
6.1 Functional description
The compact flame monitor consists of an optical flame sensor and a control unit
within a housing. The flame sensor converts the light signal from the flame into an
electrical signal, while the control unit ensures self-monitoring, evaluates the flame
signal [}115] and communicates the results.
The operator must provide the supply voltage and the purge air required in order to
protect the optics from hot and/or aggressive gases.
Modbus
0/4 ... 20 mA
Opt. Output
Contact
Purge air
supply
Supply
24V 5W
Boiler
Sighting
tube
Fig.6.1: System overview - D-LX 201
Boiler
Purge air
supply
Supply
24V 5W
Opt. Output
Contact
Fibre-optic system
Fig.6.2: System overview - D-LX 721
The flame monitor can be delivered with semi-conductor photodiodes for the radiation
range in ultraviolet (UV) or infra-red (IR).
Depending on the design, the photodiodes used in the flame sensor evaluate different
spectral ranges of the flame. On a dual-channel basis (channel 1 and channel 2), the
signal from the photodiodes passes through an amplification process with filtering
stages controlled by the microcontroller. The dynamic section of the flame radiation
[}115] is available for evaluation at the output. The range selection function enables
the flame monitor settings to be changed to a different parameter set (intensity and
frequency switching threshold, gain characteristic curve, FFDT).
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