Models FL3100/3101
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9.0 Appendix
9.1 Principle of Operation
9.1.1 UV Detector - FL3100 & FL3101
The Model FL3101 is a Flame Detector, which contains an ultraviolet phototube
that responds to Ultra-Violet (UV) radiation in the 185 to 260 nanometer region
(Figure 9-A). When radiation from a flame reaches the cathode plate within the
UV detector tube, electrons are ejected from the cathode plate. These electrons
are accelerated towards the positively charged anode of the tube. They collide
with molecules of an ionizable gas, with which the tube is filled. This emits more
electrons and produces an avalanche condition. More electrons are released
which creates a momentary electron flow from the cathode to the anode. This
momentary current (pulse) recurs at a rate proportional to the intensity of the UV
radiation.
The Model FL3101 UV Flame Detector processes these UV pulses with a
microcomputer and produces the following outputs:
• 4 to 20 Milliampere (mA) signal
• Immediate WARN relay contacts
• Time delayed ALARM relay contacts
• FAULT relay contacts
• RS-485 MODBUS RTU output
• Optional: Redundant RS-485 MODBUS RTU output
(See Sections 3, and 8.2, for more information on detector outputs.)
Figure 9-A Spectral Response of UV and IR Detectors
Relative Energy
Ultraviolet Region Visible Region Infrared Region
Sun's Radiation
Reaching the Earth
Wavelength
185nm 260nm 4.35um
IR Detector's
Spectral
SensitivitySensitivity
Spectral
UV Detector's
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