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M102E/M501 TRS THEORY OF OPERATION
(Addendum to M101E Manual - P/N 04740 Rev A)
The amount of detectable UV given off by the decay of the SO
2
* is affected by the rate at which this
reaction occurs (k).
(
)
*SO
k
F
2
=
(Equation 9-5)
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 SO
2
in the sample chamber.
So:
()
nm3302
F
2
hvSO*SOk +⎯⎯→⎯
(Equation9-6)
Finally, 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.
In summary, given that the absorption rate of SO
2
(a) is constant, the amount of fluorescence (F)
is a result of:
• The amount of exited 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.
So, when the intensity of the light (
I
0
) is known; path length of excited 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).
and; no interfering conditions are present (such as interfering gases or stray light); the amount of
fluorescent light emitted (
F) is directly related to the concentration of the SO
2
in the Sample
Chamber.
The Model 100 E UV Fluorescence SO
2
Analyzer is specifically designed to create these
circumstances.
• The light path is very short (
x).
• A reference detector measures the intensity of the available excitation UV light and is used
to remove effects of lamp drift(
I
0
).
• The temperature of the sample gas is measured and controlled via heaters attached to the
sample chamber so that the rate of decay (
k) is constant.
• A special hydrocarbon scrubber removes the most common interfering gases from the
sample gas.
• And finally, the design of the sample chamber reduces the effects of stray light via its
optical geometry and spectral filtering.
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.
05514 Rev A1 45