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Introduction
43iQHL Principle of Operation
Thermo Scientific
43iQHL Instruction Manual
1-3
The 43iQHL operates on the principle that SO
2
molecules absorb
ultraviolet (UV) light and become excited at one wavelength, then decay to
a lower energy state emitting UV light at a different wavelength.
Specifically,
2
2
2
1
2
h
SO
*
SO
h
SO
υ
υ
+
→
→
+
The sample is drawn into the 43iQHL through the SAMPLE bulkhead, as
shown in
. The sample flows through the optional heated kicker
(if installed) and then into the into the fluorescence chamber. Pulsating UV
light is focused by a condensing lens into the mirror assembly. The mirror
assembly contains four selective mirrors that reflect only the wavelengths
which excite SO
2
molecules. The UV light excites the SO
2
molecules in the
fluorescence chamber. A photodetector, located at the back of the
fluorescence chamber, continuously monitors the pulsating UV light source
and is connected to a circuit that compensates for fluctuations in the UV
light.
As the excited SO
2
molecules decay to lower energy states they emit UV
light that is proportional to the SO
2
concentration. A bandpass filter
located between the fluorescence chamber and PMT allows only the
wavelengths emitted by the decaying SO
2
molecules to reach the
photomultiplier tube (PMT). The PMT detects the UV light emission
from the decaying SO
2
molecules.
The sample exits the fluorescence chamber and flows through a capillary
and an auxiliary flow sensor. The sample then flows to the pump and is
exhausted out the EXHAUST bulkhead of the analyzer. The 43iQHL
outputs the SO
2
concentration to the front panel display and the analog
outputs, and also makes the data available over the serial or Ethernet
connection.
43iQHL Principle
of Operation
Summary of Contents for 43iQHL
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