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Instruction Manual
748374-F
March 2003
Rosemount Analytical Inc. A Division of Emerson Process Management Description and Specifications 1-1
Model NGA2000 TO2
SECTION 1
DESCRIPTION AND SPECIFICATIONS
1-1 OVERVIEW
This manual describes the Trace Oxygen (TO2)
Analyzer Module of Rosemount Analytical's
NGA2000 Series of gas analysis components.
The TO2 Analyzer Module is designed to con-
tinuously determine the concentration of trace
oxygen in a flowing gaseous mixture. The con-
centration is expressed in parts-per-million.
The TO2 Analyzer Module is configured as a
shelf-mount module, designed to be installed
external from the platform on an associated
shelf capable of holding two modules side-by-
side, with gas connections made from the rear.
All electronics relative to sample detection and
conditioning are included in this module.
1-2 TYPICAL APPLICATIONS
The TO2 Analyzer Module has specific applica-
tions in the following areas:
• Trace oxygen in product nitrogen and argon
streams from air separation plants
• Trace oxygen in inerting atmospheres for
heat treat furnaces
• Trace oxygen in glove-box applications
1-3 THEORY OF TECHNOLOGY
The TO2 Analyzer Module uses the coulometric
principle of oxygen detection. This technology is
based on the fact that oxygen in the sample is
reduced by an electrochemical reaction. This
reduction occurs at the cathode and results in
the generation of hydroxyl ions. These hy-
droxyl ions migrate to the anode where they are
oxidized to reform oxygen. The oxidation reac-
tion generates four electrons which in turn mi-
grate to the anode to participate in the reduction
reaction:
(Cathode Reaction)
O
2
+ 2 H
2
O + 4 e
-
→ 4 OH
-
(Anode Reaction)
4 OH
-
→ O2 + 2 H
2
O + 4 e
-
A polarizing voltage of approximately 1.3 VDC
is applied between the anode and cathode to
drive the oxidation and reduction reactions. The
resulting current flow produced by the flow of
electrons is directly proportional to the oxygen
content in the sample gas.
1-4 FEATURES
Among the features included in the TO2 Ana-
lyzer Module are:
• Quick start feature
• Electrolyte level alarm
• High oxygen protection circuit with alarm
• Sample flow indication.