PerkinElmer STA 8000, Инструкция по установке и эксплуатации оборудования

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58 . STA 8000 Installation and Hardware Guide
Sample Pans
The preferred sample pan is the self-centering, thin-walled, ceramic sample pan provided
with the instrument. The sample centers itself in the pan and the pan centers itself on the
platform of the sensor, which optimizes the sample weight data obtained by the STA 8000.
Three sample pans are provided in the spares kit.
Other sample pans can also be used. The only requirements that the pans must meet are
that they do not react or melt within the temperature range of interest, and that the sample
does not form alloys with the material of the sample pan.
Sample Atmosphere
The STA 8000 is able to operate in various gas atmospheres. There is one system purge gas
inlet and two sample purge gas inlets at the back of the analyzer.
The system purge gas should be a dry, relatively inert gas that flows through the
microbalance chamber and exits through the sample chamber. This keeps the environment of
the balance constant, prevents absorption or desorption of vapors, and protects the balance
against gaseous products evolving from the samples. The system purge gas flow rate is fixed
at 45 ml/min. To prevent delays due to equilibration of the analyzer, we strongly recommend
that the system purge gas is present at all times.
You can control the atmosphere in which the sample is run by using a sample purge gas to
augment the system purge, or to introduce reactive gases into the sample furnace.
Recommended purge gases are air, nitrogen, argon, oxygen, and helium. When changing
from one purge gas to another or changing flow rates, we recommend that you check the
temperature calibration. A sample purge flow rate of 20–40 ml/min is recommended
(controlled by the Pyris software). A purge gas inlet pressure of 2–3 bar (30–45 psi) is
suitable, with a maximum pressure of 6.2 bar (90 psi).
The sample purge gas enters the furnace/sample area directly, just below the sample, and
flows via the furnace wall to the sample. Thus, dead volume can be low, resulting in a small
gas change time constant. The time constant depends on the flow rate.
The gas atmosphere should be pure (99.9% minimum), especially if you use nitrogen. If the
analysis calls for an inert purge, there should be no trace of oxygen because this could lead
to unwanted reactions. The gas must be dry. A size 1A cylinder equipped with a suitable
regulator is recommended.
The degradation byproducts from the sample leave the instrument directly via a small hole in
the furnace cover. These byproducts could be harmful so you should use adequate protection
such as placing the instrument in a fume hood. There is some condensation of less volatile
products on the cold spots of the analyzer: the lower side of the cover and the upper inner
side of the cooling jacket. These spots can be cleaned easily with a suitable solvent.
Condensation may also occur on the top inner side of the cooling jacket.