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Theory of Operation
OX-TRAN Model 2/12 R Operator's Manual
The temperature at which the barrier is tested has a great effect (usually logarithmic) on transmission rate.
This makes temperature one of the most important test conditions for most barrier materials. Many barriers
exhibit a 6% to 15% rise in oxygen transmission rate for each degree C rise in temperature.
Test Gas Driving Force
The driving force of the test gas has a direct effect on the oxygen transmission rate. The driving force of the
test gas is affected by the oxygen concentration of the test gas and the ambient Barometric pressure.
Barometric Pressure
Barometric pressure has a proportional effect on the oxygen transmission rate of a specimen due to the
increase/decrease in the density of the test gas.
The instrument automatically compensates all transmission rate data to sea-level pressure (760 mmHg).
Due to the wide potential variation in altitudes, reproducibility between laboratories may not be possible
unless the transmission rate data is compensated to sea-level pressure. The instrument compensates all
transmission rate data to sea-level pressure using the following ratio:
Standard
barometric
pressure
(760mmHg)
Ambient
barometric
pressure
Relative Humidity
The amount of water vapor some materials (such as nylon, cellophane and ethyl vinyl alcohol) are exposed
to significantly affects the oxygen 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 OX-TRAN Model 2/12 R provides the capability to test these types of materials in a controlled "wet" test
environment. A Relative Humidity for the Test and Carrier gases between 0% and 90% RH can be
specified.
How a Humidified Test Gas is Generated
Humidified Carrier and Test Gases are created by moving pressurized gas through a humidifier filled with
HPLC-grade water and mixing the wet gas with a dry gas in the appropriate ratios.
D-2
Revision L
MOCON, Inc.
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