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Teledyne API M100E Analyzer Operation Manual Theory Of Operation
221
The amount of detectable UV given off by the decay of the SO
2
* is affected the rate at which this reaction occurs (k).
*SO
k
F
2
(Equation 11-4)
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
(Equation 11-5)
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 11-2) 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 11-5): the
amount of SO
2
* present and the rate of decay (k) which changes based on the temperature of the gas.
When and 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.
04515F DCN6048