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OX-TRAN Model 2/12 R Operator's Manual
Appendix D: Theory of Operation
How the Oxygen Sensor Works
The oxygen sensor is a fuel cell that performs in accordance with Faraday's Law. When exposed to oxygen,
the sensor generates an electrical current that is proportional to the amount of oxygen entering the sensor.
The oxygen sensor contains two electrodes, a flat PTFE tape coated with an active catalyst, the cathode
and a lead anode. The sensor enclosure is airtight except for a small capillary with allows oxygen access to
the working electrode. The cathodic and anodic reactions are respectively:
The electrons create a current which can be used to calculate the amount of oxygen entering the Oxygen
sensor.
How the Transmission Rate is measured
The OX-TRAN Model 2/12 R measures transmission rate by directly measuring the current produced by the
sensor. The vertical axis on the Permeant Sensor (Raw Counts) graph is current (1 count = ~ 10 pA).
The measured current is then corrected and scaled using the gain, barometric pressure, area and flow as is
appropriate for the Test Method and Permeant Sensor calibration specified for the measurement.
Factors that Affect the Transmission Rate of a Barrier Material
The oxygen transmission rate of barrier materials is affected by several factors:
•
Barrier test temperature
Test gas (oxygen) concentration effect on driving force
•
•
Barometric pressure effect on driving force
Relative humidity
•
Barrier Temperature
MOCON, Inc.
O
+ 2H
O +4e
-
→ 4OH
2
2
2Pb + 4OH
→ 2PbO + 2H
-
Revision L
-
O + 4e
-
2
Theory of Operation
D-1
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