Factors That Affect The Transmission Rate Of A Barrier Material; Barrier Temperature; Test Gas Driving Force; Barometric Pressure - Ametek mocon AQUATRAN 3/40 Operator's Manual

Theory of Operation
infrared sensor/amplifier produces a DC output proportional to the amount of water vapor. The DC output is
converted to a value and transmitted to the computer.
The computer subtracts the ReZero value from the DC output value. The result is converted to units of
Water Vapor Transmission Rate (WVTR) using a scaling factor determined by the nitrogen gas flow rate.

Factors that Affect the Transmission Rate of a Barrier Material

The water vapor transmission rate of barrier materials is affected by several factors:
Barrier test temperature
•
• Test Gas (water vapor) concentration effect on driving force
Barometric pressure effect on measured transmission rate
•
• Relative humidity

Barrier Temperature

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 Water Vapor 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 Water Vapor Transmission Rate. The driving force
of the test gas is affected by the water vapor concentration of the test gas and the cell temperature.

Barometric Pressure

Barometric pressure has an effect on the output of the water vapor sensor. The water vapor sensor vents to
the atmosphere. The pressure in the water vapor sensor is affected by changes in the barometric pressure.
The instrument automatically compensates all transmission rate data to eliminate the effect of barometric
pressure on the reported transmission rate.
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AQUATRAN Model 3/40 Operator's Manual
Revision D MOCON, Inc.