Emerson NGA 2000 TO2 Section Description and Specifications, Overview, Typical Applications

Model NGA 2000 TO2

Instruction Manual

760008-A September 2001

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)

O2 + 2 H2O + 4 e- → 4 OH- (Anode Reaction)

4 OH- → O2 + 2 H2O + 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.

Rosemount Analytical Inc. A Division of Emerson Process Management Description and Specifications 1-1