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Reference Manual
00809-0100-4882, Rev AB
May 2019
SYSTEM OVERVIEW
Scope
System Description
This Instruction Bulletin is designed to supply details needed to install, start
up, operate, and maintain the Rosemount Two-Wire In-Situ Oxygen Analyzer.
The analyzer consists of an oxygen probe and Rosemount 5081 transmitter.
The signal conditioning electronics of the Rosemount 5081 transmitter
outputs a 4-20 mA signal representing an O
control (IRC) allows access to setup, calibration, and diagnostics. This same
information, plus additional details, can be accessed with the HART field
communicator or Asset Management Solutions (AMS) software.
The Rosemount Two-Wire In-Situ Oxygen Analyzer is designed to measure
the net concentration of oxygen in an industrial process; i.e., the oxygen
remaining after all fuels have been oxidized. The oxygen probe is
permanently positioned within an exhaust duct or stack and performs its task
without the use of a sampling system. Rosemount 5081 transmitter is
mounted remotely and conditions the oxygen probe outputs.
The equipment measures oxygen percentage by reading the voltage
developed across a heated electrochemical cell, which consists of a small
yttria stabilized, zirconia disc. Both sides of the disc are coated with porous
metal electrodes. When operated at the proper temperature, the millivolt
output voltage of the cell is given by the following Nernst equation:
EMF = KT log10(P1/P2) + C
Where:
1. P2 is the partial pressure of the oxygen in the measured gas on one
side of the cell.
2. P1 is the partial pressure of the oxygen in the reference air on the
opposite side of the cell.
3. T is the absolute temperature.
4. C is the cell constant.
5. K is an arithmetic constant.
NOTE
For best results, use clean, dry, instrument air (20.95% oxygen) as the
reference air.
NOTE
The probe uses a Type B thermocouple to measure the cell temperature.
When the cell is at operating temperature and there are unequal oxygen
concentrations across the cell, oxygen ions will travel from the high oxygen
partial pressure side to the low oxygen partial pressure side of the cell. The
resulting logarithmic output voltage is approximately 50 mV per decade.
The output is proportional to the inverse logarithm of the oxygen
concentration. Therefore, the output signal increases as the oxygen
concentration of the sample gas decreases. This characteristic enables the
Rosemount Two-Wire In-Situ Oxygen Analyzer to provide exceptional
sensitivity at low oxygen concentrations.
Rosemount 5081FG
value. An infrared remote
2
1-3
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