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Theory Of Operation Teledyne API M100E Analyzer Operation Manual
228
11.2.7.5. LIGHT POLLUTION
Because M100E measures light as a means of calculating the amount of SO
2
present, obviously stray light can
be a significant interfering factor. The M100E 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 11.2.5; remove UV with wavelengths extraneous to the excitation
and de
cay of SO
2
/SO
2
*.
Most importantly, during instrument calibration the difference between the value of the most recently
recorded PMT offset (refer to Section 11.2.4) and the PMT output while measuring zero gas (calibration
gas d
e
void of SO
2
) is recorded as the test function OFFSET. This OFFSET value is used during the
calculation of the SO
2
concentration.
Since this offset is assumed to be due to stray light present in the sample chamber is also multiplied by
the SLOPE and recorded as the function STR. LGT. Both OFFSET & STR. LGT are viewable via the
front panel (refer to Section 6.2.1).
11.3. 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 10-1. Procedures for correctly performing leak checks can be found in Section 10.3.6.
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).
04515F DCN6048