Teledyne 6200E - Sulfides Analyzer - Manual (Page 212)

Theory Of Operation Model 6200E Instruction Manual
212 M6200E Rev: A1
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 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 M6200E measures light as a means of calculating the amount of SO
2
present, obviously
stray light can be a significant interfering factor. The Model 6200E 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
2
/SO
2
*.
During instrument calibration, when the analyzer is sampling zero air (calibration gas devoid of
H
2
S) a measurement of the background light that is still present in the sample chamber is
recorded and used to offset the value of the PMT output used to calculate the H
2
S concentration.
10.3. Pneumatic Operation
CAUTION
It is important that the sample airflow system is leak-tight and not pressurized over
ambient pressure. Regular leak checks should be performed on the analyzer as
described in the maintenance schedule, Table 9-1 . Procedures for correctly performing
leak checks can be found in Section 11.5.1.
NOTE
Relative Pressure versus Absolute Pressure
In this manual vacuum readings are given in inches of mercury absolute pressure (in-
Hg-A), i.e. indicate an absolute pressure referenced against zero (a perfect vacuum).