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Instruction Manual
760008-A
September 2001
Rosemount Analytical Inc. A Division of Emerson Process Management Description and Specifications 1-1
Model NGA 2000 TO2
SECTION 1
DESCRIPTION AND SPECIFICATIONS
1-1 OVERVIEW
This manual describes the Trace Oxygen
(TO2) Analyzer Module of Rosemount Ana-
lytical's NGA 2000 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
concentration 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 detec-
tion and conditioning are included in this
module.
1-2 TYPICAL APPLICATIONS
The TO2 Analyzer Module has specific appli-
cations in the following areas:
• Trace oxygen in product nitrogen
and argon streams from air
separation plants
• Trace oxygen in inerting atmos-
pheres for heat treat furnaces
• Trace oxygen in glove-box appli-
cations
1-3 METHOD OF MEASUREMENT
Coulometric Principle
The TO2 Analyzer Module uses the cou-
lometric 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 hydroxyl ions migrate to the anode
where they are oxidized to reform oxygen.
The oxidation reaction generates four elec-
trons which in turn migrate 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
-
→ O
2
+ 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.