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Preparing for a Test
OX-TRAN Model 2/28 Operator's Manual
Simultaneously testing barriers with widely divergent transmission rates is not recommended. The data for
the samples may not be accurate when there is a large difference in the transmission rates. If during a test
there is a large difference in the transmission rates, set the divergent cell (or cells) to Idle and continue
testing the remaining cell (or cells). You may want to determine which samples will condition more rapidly
and test those samples first.
Developing Test Methods for your Films
Choosing the appropriate test conditions and methodology is one of the most important preparatory tasks.
Inaccurate test results and "Failed" tests are commonly caused by inappropriate methodology. A good
understanding of the characteristics of the barrier sample will be very helpful in choosing an appropriate
methodology. For specific information on how to set or adjust the Test Method parameters discussed in this
section please refer to the Instrument Help System.
The Examination Time
The Exam Time specifies how long (in minutes) the Test Cell (containing the sample) will be examined to
determine the oxygen transmission rate. During this examination time the carrier gas (along with any
oxygen that has permeated the sample) is routed to the sensor. For some barriers you may need to
increase the examination time. This is because the sensor approaches its final value at an exponential rate.
For some barriers, the sensor may not properly stabilize within the default examination time. For most
barriers, the small increase in oxygen transmission rate caused by increasing the examination time is
insignificant.
The ReZero Frequency
The baseline of the instrument can shift slightly during testing due to such changes as ambient temperature.
The ReZero process adjusts for these small shifts in the instrument baseline.
The ReZero function can be turned on and off. The default is on with a new zero taken every two cell
examination periods (equivalent) to one pass for each cell. The default values were chosen to provide a
new baseline (the ReZero value) within a reasonable time interval.
The Sample Conditioning Time
When you condition a sample in the test cell, carrier gas and test gases are routed to the test cell as they
are during testing. However, the carrier gas is not routed to the Permeant sensor. This conditioning period
allows a sample barrier to acclimate to the conditions within the test cell.
3-2
Revision J
MOCON, Inc.
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