Thermo Scientific 43iQ, Instruction Manual

Page: 11 / 284

Introduction
43iQ Principle of Operation
Thermo Scientific 43iQ Instruction Manual 1-3
The 43iQ 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 43iQ through the SAMPLE bulkhead, as
shown in Figure 1–2 . The sample flows through a hydrocarbon “kicker,”
which removes hydrocarbons from the sample by forcing the hydrocarbon
molecules to permeate through the tube wall. The SO
2
molecules pass
through the hydrocarbon “kicker” unaffected.
The sample then flows into the fluorescence chamber, where pulsating UV
light excites the SO
2
molecules. The condensing lens focuses the pulsating
UV light into the mirror assembly. The mirror assembly contains four
selective mirrors that reflect only the wavelengths which excite SO
2
molecules.
As the excited SO
2
molecules decay to lower energy states they emit UV
light that is proportional to the SO
2
concentration. The bandpass filter
allows only the wavelengths emitted by the excited SO
2
molecules to reach
the photomultiplier tube (PMT). The PMT detects the UV light emission
from the decaying SO
2
molecules. The 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 sample leaves the optical chamber, it passes through a flow sensor, a
capillary, and the “shell” side of the hydrocarbon kicker. The sample then
flows to the pump and is exhausted out the EXHAUST bulkhead of the
analyzer. The 43iQ 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.
43iQ Principle of
Operation