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SECTION 4 AIR PURGE SYSTEM
4.1 AirPurgeConnection
An air purge system is provided to purge the optical compartment with dry air to
prevent condensation on the outside of the sample cell when measuring cold
samples. This system is particularly useful when using the Flow-Thru Cell
assembly.
Note: Do not exceed 138 kPa
(20 psig).
Dry nitrogen or instrument grade air (ANSI MC 11.1, 1975) up to 138 kPa
(20 psig) can be used to air purge the optical housing compartment. The
recommended air consumption rate is between 3 and 10 SCFH (standard cubic
feet/hour). The connection is made at the Air Purge fitting on the rear panel.
When the sample temperature is expected to be near or below 2 ° C(35°F), use a
desiccant dryer and particle filter to assure the dew point of the air purge is below
the sample temperature. The air dryer contains silica gel desiccant that turns pink
when exhausted. Life expectancy of the desiccant depends on the moisture content
of the air.
If only shop air is available, use a coalescing filter with automatic drain in
conjunction with a dryer and particle filter to achieve instrument quality air. Life
expectancy of the coalescing filter should exceed 2000 hours. Change the particle
filter at the same time as the air dryer. Figure 7 illustrates methods of connecting
the two types of air supply to the instrument. The dryer and filter are not necessary
if dry nitrogen is used for the air purge.
Figure 7 Air Purge Connections
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