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Principles Of Operation Model T101 Instruction Manual
246
*SOkF
2
Where:
F = the amount of fluorescent light given off.
k = The rate at which the SO
2
* decays into SO
2.
SO
2
*
= Amount of excited state SO
2
in the sample chamber.
Therefore:
nm3302
kF
2
hvSO*SO
Furthermore, the function (k) is affected by the temperature of the gas. The warmer the
gas, the faster the individual molecules decay back into their ground state and the more
photons of UV light are given off per unit of time.
Given that the absorption rate (a) of SO
2
is constant, the amount of fluorescence (F) is a
result of:
The amount of SO
2
* created which is affected by the variable factors
from equation 10-2 above: concentration of SO
2
; intensity of UV light
(
I
0
); path length of the UV light (x) and;
The amount of fluorescent light created which is affected by the variable
factors from equation 10-5: the amount of SO
2
* present and the rate of
decay (k) which changes based on the temperature of the gas.
The amount of fluorescent light emitted (F) is directly related to the concentration of the
SO
2
in the Sample Chamber, when:
the intensity of the light (I
0
) is known
the path length of excitation light is short (
x)
the temperature of the gas is known and compensated for so that the
rate of SO
2
*decay is constant (k)
there are no interfering conditions present (such as interfering gases or
stray light)
The Model T101 UV Fluorescence SO
2
Analyzer is specifically designed to create these
circumstances.
The light path is very short.
The optical design reduces the effects of stray light geometrically and
spectrally.
A special hydrocarbon scrubber removes the most common interfering
gases from the sample gas.
A reference detector measures the intensity of the available excitation UV
light and is used to remove effects of lamp drift.
Finally, the temperature of the sample gas is measured and controlled
via heaters attached to the sample chamber.
The net result is that any variation in UV fluorescence can be directly attributed to
changes in the concentration of SO
2
in the sample gas.
07266B DCN6485