User Manual SERVOPRO Plasma Trace N
2
Analyzer
8.0 START-UP
8.1 Routine and operational verification
From time to time, it is a good idea to go in the "DIAGNOSTIC MENU",
check cell counts with
a reference gas and record this value for comparison with a later value. This gives an indication
of the degree of cell offset.
Also, check the flow count stability. Too much variation is an indication of line clogging.
The frequency of calibration is normally once a week.
8.2 Hints and tips
When the analyzer is used to verify gas cylinders, there are no special considerations. But, when
you use it for argon in the liquid phase, or for trucks in loading stations, you must be aware of a
few facts.
Analysis is made with a gaseous sample of the cryogenic liquid. For trucks, a common procedure
is to use a quick connector. Then, the liquid vaporizes inside the line in the direction of the flow.
Other installations use a flash vaporizer for tanks, and a distillation column.
A special difficulty arises in obtaining a gas sample which has the same molar concentration of
trace contaminants as the liquid being sampled.
For example, liquid argon may typically contain traces of oxygen, nitrogen, hydrogen, methane
and water. When the temperature of liquid argon is raised, the vaporization of argon and its
different contaminating gases take place at different temperatures and thus at different points in
time.
This way, fractionation of the sample occurs: the analytical composition of the gas sample
obtained varies continuously and does not accurately represent the analytical composition of the
cryogenic liquid. For example, this phenomenon is very apparent when analyzing hydrocarbons
in pure oxygen.
If your reading varies a lot on the liquid sample, you must think of a way to present a true sample
of the liquid to the analyzer. Normally, this is not a problem for the customer in the electronics
industries, foundries or specialty gas laboratories.
When mounting a quick connector on a truck, moisture and air get into the sample line. Allow
some time, depending of line length, to purge the sample line.
Often (very often) quick connectors can leak, when the lines attached to them are moving. Be
aware of this.
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