Teledyne Camera Accessories T100 Manual Do Utilizador

It should be noted that the fluorescence method for detecting SO

2

 is subject to 

interference from a number of sources. The T100 has been successfully tested for its 
ability to reject interference from most of these sources.  

13.1.9.1. DIRECT INTERFERENCE 

The most common source of interference is from other gases that fluoresce in a similar 
fashion to SO

2

 when exposed to UV Light. The most significant of these is a class of 

hydrocarbons called poly-nuclear aromatics (PNA) of which xylene and naphthalene are 
two prominent examples. Nitrogen oxide fluoresces in a spectral range near to SO

2

.  For 

critical applications where high levels of NO are expected an optional optical filter is 
available that improves the rejection of NO (contact Technical Support for more 
information). 

  The T100 Analyzer has several methods for rejecting interference from these gases: 
  A special scrubber (kicker) mechanism removes any PNA chemicals present in the 

sample gas before it the reach the sample chamber. 

  The exact wavelength of light needed to excite a specific non-SO

2

 fluorescing gas is 

removed by the source UV optical filter. 

  The light given off by Nitrogen Oxide and many of the other fluorescing gases is 

outside of the bandwidth passed by the PMT optical filter. 

13.1.9.2. UV ABSORPTION BY OZONE 

Because ozone absorbs UV Light over a relatively broad spectrum it could cause a 
measurement offset by absorbing some of the UV given off by the decaying SO

2

* in the 

sample chamber. The T100 prevents this from occurring by having a very short light 
path between the area where the SO

2

* fluorescence occurs and the PMT detector. 

Because the light path is so short, the amount of O

3

 needed to cause a noticeable effect 

would be much higher than could be reasonably expected in any application for which 
this instrument is intended. 

13.1.9.3. 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

2

 available to 

react with the to the UV light. While this can be a significant problem for some 
analyzers, the design of the T100 is very tolerant of variations in sample gas flow rate 
and therefore does not suffer from this type of interference. 

13.1.9.4. THIRD BODY QUENCHING 

While the decay of SO

2

* to SO

2

 happens quickly, it is not instantaneous. Because it is 

not instantaneous it is possible for the extra energy possessed by the excited electron of 
the SO

2

* molecule to be given off as kinetic energy during a collision with another 

molecule. 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

2

), water vapor (H

2

O) and molecular oxygen (O

2

). In ambient applications the 

quenching effect of these gases is negligible. For stack applications where the 

06807C DCN6650