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AQUATRAN Model 3/40 Operator's Manual
Theory of Operation
Relative Humidity
The amount of water vapor that some materials (such as nylon, cellophane and ethyl vinyl alcohol) are
exposed to significantly affects the water vapor transmission rate of the barrier. The barrier properties of
some of these materials can be permanently affected by prolonged exposures to significant amounts of
water vapor.
The PERMATRAN-W Model 3/34 provides the capability to test these types of materials in a controlled
"wet" test environment. A Relative Humidity for the Test Gas between 0% and 90% RH can be specified.
How a Humidified Test Gas is Generated
Humidified Test Gas is created using a steam generator to add water vapor to dry compressed air. An RH
sensor is used to measure the actual RH delivered. The instrument uses the measured RH value to control
the water and compressed air usage to maintain the RH in the Test Chamber at the specified value.
The RH that the sample will be tested at can be changed by simply changing the RH set point. The
"Sequential Test" feature can be used to automatically perform a sequence of tests at different RH levels.
How the ReZero Cell Works
The transmission rate measured for samples mounted in the Test Cells is the sum of the transmission rate
due to permeation through the barrier material and all other sources of water vapor ingress. This includes
the system baseline. If the system baseline can be measured, subtracting it from the apparent transmission
rate of the Test Cells will give a more accurate representation for the transmission rate of the barrier
material.
During a ReZero State the instrument routes carrier gas (which is at the same temperature and RH as used
in the Test Cells) to the water vapor sensor. The instrument components used to perform this function are
referred to as the ReZero Cell. The ReZero Cell is different from the Test Cells in that it does not contain a
barrier material that is exposed to a Test Gas. This means that any residual water vapor in the carrier gas is
not due to permeation through the barrier materials mounted in the Test Cells. The residual water vapor
measured in the ReZero State is therefore considered to be a good representation of the system baseline.
Periodically the instrument baseline is measured using the ReZero Cell. The ReZero Interval and
Examination Time is determined the by currently active Test Method. The resulting data is used to correct
the transmission rate data for any active tests. This ensures that changes in the baseline do not affect the
accuracy of the transmission rate data.
MOCON, Inc.
Revision D
D-3
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