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AQUATRAN Model 3/40 Operator's Manual
Measuring a Water Vapor Transmission Rate
To make an accurate transmission rate measurement a known concentration Test Gas is applied to one
side of the barrier material to be tested and the other side is swept with a water vapor free Carrier Gas
(nitrogen). This process is illustrated in Figure 1-2 which depicts a package mounted in a Diffusion Cell
designed for a Cup or Tray.
As shown in the illustration the package is mounted between the parts of the Diffusion Cell. The sealing
surfaces and O-rings in the cell prevent outside moisture from affecting the measurement.
The Test Gas side of the sample is exposed to the controlled environment in the Test Chamber. The
environment in the Test Chamber is maintained at a constant relative humidity.
The Carrier Gas (Nitrogen) enters the interior of the sealed package (carrier side). As water molecule
permeates the sample barrier it mixes with the Carrier Gas. The output side (exhaust) of the diffusion cell is
routed to the water vapor sensor. The amount of water vapor in the carrier gas is measured using the
patented Modulated infrared sensor.
Seal leakage in the diffusion cell can be a significant source of error when measuring the transmission rate
of a sample. The TruSeal™ flush ring at the perimeter of the cell minimizes the effect of ambient moisture
on the measurement. During a test the TruSeal™ flush ring is purged with carrier gas minimizing the
possibility of leakage past (or permeation through) the seals.
Flush Gas In
The AQUATRAN Model 3/40 can use a generated RH for the Test Gas. The RH of the Test Gas can be
from 30% to 90% RH for a Model L. Different test cell configuration will be required for testing 100%RH
verses generated RH.
MOCON, Inc.
Test Gas (Ambient Air)
Carrier Gas In
Figure 1-2: An AQUATRAN Model 3/40 Permeation Cell
Carrier Gas Out
Revision D
Introduction
Flush Gas Out
1-3
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