Dilution; Third Body Quenching; Light Pollution - Teledyne 100E Instruction Manual

Model 100E Instruction Manual
Because the light path is so short, the amount of O
would be much higher than could be reasonably expected in any application for which
this instrument is intended.

10.2.6.3. Dilution

Certain gases with higher viscosities can lower the flow rate though the critical flow
orifice that controls the movement of sample gas though the analyzer reducing the
amount of sample gas in the sample chamber and thus the amount of SO
react with the to the UV light. While this can be a significant problem for some analyzers,
the design of the Model 100E is very tolerant of variations in sample gas flow rate and
therefore does not suffer from this type of interference.

10.2.6.4. Third Body Quenching

While the decay of SO
instantaneous it is possible for the extra energy possessed by the excited electron of the
SO * molecule to be given off as kinetic energy during a collision with another molecule.
2
This in effect heats the other molecule slightly and allows the excited electron to move
into a lower energy orbit without emitting a photon.
The most significant interferents in this regard are nitrogen oxide (NO), carbon dioxide
(CO ), water vapor (H
2
quenching effect of these gasses is negligible. For stack applications where the
concentrations of some or all of these may be very high, specific steps MUST be taken to
remove them from the sample gas before it enters the analyzer.

10.2.6.5. Light Pollution

Because M100E measures light as a means of calculating the amount of SO
obviously stray light can be a significant interfering factor. The Model 100E removes this
interference source in several ways.
• The sample chamber is designed to be completely light tight to light from sources
other than the excitation UV source lamp.
• All pneumatic tubing leading into the sample chamber is completely opaque in
order to prevent light from being piped into the chamber by the tubing walls.
• The optical filters discussed in section 10.2.4;remove UV with wavelengths
extraneous to the excitation and decay of SO
• During instrument calibration, when the analyzer is sampling zero air (calibration
gas devoid of SO
the sample chamber is recorded and used to offset the value of the PMT output
used to calculate the SO
045150102 Rev XB1
* to SO happens quickly, it is not instantaneous. Because it is not
2 2
O) and molecular oxygen (O
2
) a measurement of the background light that is still present in
2
concentration.
2
Theory Of Operation
needed to cause a noticeable effect
3
). In ambient applications the
2
/SO *.
2 2
available to
2
present,
2
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