Teledyne 6200T - Sulfides Analyzer - Manual (Page 287)

6200T Total Sulfur Analyzer Principles of Operation
Teledyen Analytical Instruments 287
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 13-4)
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.
Therefore:
 
nm 330 2
F
2
hv SO * SO k     
(Equation 13-5)
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 13-2) 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 13-5): 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.