Teledyne 6200T - Sulfides Analyzer - Manual (Page 288)

Principles of Operation Model 6200T Total Sulfur Analyzer
288 Teledyne Analytical Instruments
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.
13.1.2. The UV Light Path
The optical design of the 6200T’s sample chamber optimizes the fluorescent reaction
between SO
2
and UV Light (refer to
Figure 13-2) and assure that only UV light resulting from the decay of SO
2
* into SO
2
is
sensed by the instruments fluorescence detector.
UV radiation is generated by a lamp specifically designed to produce a maximum
amount of light of the wavelength needed to excite SO
2
into SO
2
* (214 nm) and a
special reference detector circuit constantly measures lamp intensity (refer to (Equation
13-2)). A Photo Multiplier Tube (PMT) detects the UV given off by the SO
2
* decay
(330 nm) and outputs an analog signal. Several focusing lenses and optical filters ensure
that both detectors are exposed to an optimum amount of only the right wavelengths of
UV. To further assure that the PMT only detects light given off by decaying SO
2
* the
pathway of the excitation UV and field of view of the PMT are perpendicular to each
other and the inside surfaces of the sample chamber are coated with a layer of black
Teflon
® that absorbs stray light.