Emerson Process Management 3000 - Manual (Page 102)

Instruction Manual
Appendix A Rev. 3.8
July 2002
A-4 Appendices Rosemount Analytical Inc. A Division of Emerson Process Management
World Class 3000
d. Cell - General
The components which make up the cell are
machined to close tolerances and
assembled with care to provide accurate
oxygen measurements. Any replacement
requires attention to detail and care in
assembly to provide good results.
Failure to follow the instructions in
this manual could cause danger to
personnel and equipment. Read and
follow instructions in this manual
carefully.
The oxygen probe includes an inner
electrode for the cell assembly. It consists of
a platinum pad and a platinum/inconel
composite wire which produces the cell
constant offset voltage described in the
Nernst equation.
With this pad and wire, the constant will be
between -10 and +15 mV. The cell constant
is noted in the calibration data sheet
supplied with each probe.
Every probe should be calibrated and
checked after repair or replacement of cell,
pad and wire, heater, and thermocouple, or
after disassembly of the probe.
A-3 INNER PROBE ASSEMBLY
The inner probe assembly, Figure A-5, consists
of six main parts:
a. Ceramic support rod with four holes running
through the length. The holes serve as
insulated paths for the cell signal wire and
thermocouple wires.
b. A heater that is helically wrapped on a
quartz support cylinder and insulated.
c. A chromel-alumel thermocouple which acts
as the sensing element for the temperature
controller. (Not visible in Figure A-5; located
within ceramic support rod.)
d. A platinum screen pad which forms
electrical contact with the inner electrode of
the electrochemical cell. (Not visible in
Figure A-5; located at end of ceramic
support rod.) The pad is attached to an
inconel wire which carries the signal to the
terminal strip.
e. A V-strut assembly to give support to the
inner probe assembly.
f. A tube to carry reference air to the cell.
Turn to Service and Normal Maintenance, for
repair procedures for probe components.
HEATER
V-STRUT
CERAMIC
SUPPORT
ROD
INSULATING
GASKET
27270015
REFERENCE
AIR TUBE
Figure A-5. Inner Probe Assembly