Operational Theory; The Analyzer - Teledyne 2120XL Operating Instructions Manual

Trace Nitrogen in Argon Analyzer

Operational Theory

2.1 The Analyzer

The Model 2120XL Trace Nitrogen in Argon Gas Analyzer is a
rack mounting self-contained unit for measuring trace amounts of
nitrogen in an argon gas stream.
A customer supplied sample system directs a stream of refined
argon to the instrument at a pressure between 4 and 20 psig (14-138
kPa). The process stream enters at a constant flow rate and passes
through a flow module containing a flow control valve and a mass flow
transducer. A gas conditioning unit is installed to remove particulates
from the incoming gas sample.
The gas is then fed to a quartz analytical cell where it is ionized in a
plasma discharge. The high energy within the plasma results in constant
collisions of ions and electrons and yields a characteristic emission
spectra intimately associated with the gas comprising the plasma.
The specific line energy is identified for nitrogen and a custom
blocking filter is selectively chosen and installed at the factory which is
tuned to remove all but the narrow energy associated with the nitrogen
emission peak. The light energy passing through the filter is focused on
a photon detector also tuned to respond to that wavelength. This
instrument can only be used for analyzing nitrogen in argon.
The photodetector produces a signal which is integrated and then
amplified. The resulting signal is digitized and processed by a
microprocessor and signal processing circuit. The results are displayed
on the instrument display as parts per million (ppm). An additional
digital to analog circuit transforms the signal back to analog form and
produces an output signal, typically 4-20 mA DC that is proportional to
the nitrogen concentration on the selected range.
The microprocessor circuit accepts input from the mass flow
transducer as well as the user interface. The analyzer software interprets
operator key presses and initiates the appropriate action as well as
sending signals to the displays for prompting the user for input or data
display.
Teledyne Analytical Instruments
Operational Theory
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