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Operational Theory
Figure 2-1 Block Diagram for the Model 2120 Analyzer
2.2 Overrange Protection
If nitrogen content approaches 1000 ppm, the overall content of
light from the plasma discharge decreases considerably. At about 2
percent nitrogen, the ionization is completely extinguished. This
effect causes the PMT output to decrease; resulting in a signal
that looks like no nitrogen is present in the argon sample, when in
fact the content is greater than 1000 ppm.
At the heart of the Overrange Protection Circuit in the Model 2120
is a photodiode that detects the ionization glow and generates a
warning when the intensity of the emission signal is low. It is set to
trip the warning alarm when the nitrogen concentration reaches the
1000 ppm level. The overrange alarm LED on the front panel turns on
when this alarm is generated.
2.3 Sample System
A suitable external sample system must be provided by the
customer. The external sample system delivers calibration or sample gas
to the analyzer at a suitable pressure. Internally the Model 2120 employs
a flow control orifice which provides proper flow through the analyzer
when the inlet pressure is maintained between 2 to 7 psig (14-48 kPa).
The proper flow rate should be maintained around 2 cfh (940 ccpm).
Teledyne Analytical Instruments
16
Model 2120
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