Table of Contents
Advertisement
Manual
00809-0500-4881
1.2
System overview
1.2.1
Scope
This Reference Manual supplies details needed to install, start up, operate, and
maintain the Rosemount OCX8800.
Signal conditioning electronics outputs separate 4-20 mA signals representing
oxygen (O
additional details, with the HART
The local operator interface (LOI) also provides a communications interface with
the electronics.
1.2.2
System description
Emerson has designed the Rosemount OCX8800 to measure oxygen and
combustible concentrations in flue gas temperatures up to 2600 °F (1427 °C).
Electrical connections, power, and communications are made through two ¾
national pipe thread (NPT) ports in the flameproof electronics enclosure using
fittings and cables provided by the customer. Cable installation must meet NEC,
IEC, and/or other applicable national or local codes for Class I, Zone 1, Group IIB
+H2 T3/T6 permanently mounted equipment. The transmitter is close coupled to
the process and requires minimum sample conditioning requirements.
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 operating at the proper temperature, the following Nernst equation gives
the millivolt output of the cell.
EMF = KT log10 (P
where:
1. P
2. P
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 percent oxygen) as the
reference air.
When the cell is at operating temperature and there are unequal oxygen
concentrations across the cell, oxygen ions 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
Rosemount OCX8800C
) and combustibles (COe) values. You can access this information, plus
2
/P
) + C
1
2
is the partial pressure of the oxygen in the measured gas on one side of
2
the cell.
is the partial pressure of the oxygen in the reference air on the opposite
1
side of the cell.
Description and specifications
Field Communicator or Emerson AMS software.
®
December 2022
11
Advertisement
Table of Contents
