Instruction Manual
IB-106-440 Rev. 1.0
October 2000
Rosemount Analytical Inc. A Division of Emerson Process Management Description and Specifications 1-3
OCX 4400
The OCX 4400 measures net oxygen con-
centration in the presence of all the prod-
ucts of combustion, including water vapor.
Therefore, it may be considered an analysis
on a “wet” basis. In comparison with older
methods, such as the portable apparatus,
which provides an analysis on a “dry” gas
basis, the “wet” analysis will, in general, in-
dicate a lower percentage of oxygen. The
difference will be proportional to the water
content of the sampled gas stream.
The OCX 4400 combustibles sensor is a
catalytic sensor consisting of two Resistant
Temperature Detectors (RTD). One RTD is
the reference element covered with an inert
coating. The other RTD element is active,
coated with a catalyst. As the sample gases
flow by the sensor, the combustible gases
oxidize on the surface of the active element.
The oxidation that occurs produces heat
and a temperature rise in the active ele-
ment. The temperature difference produces
a resistance relationship between the two
elements that is directly proportional to the
concentration of combustibles in the sample
gases.
The catalyst is specifically designed to de-
tect carbon monoxide (CO), but the sensor
responds to other combustible gases. The
sensor is calibrated using carbon monoxide
(CO), thus the output should be expressed
in terms of CO. However, since the sensor
detects other combustible gases, the output
cannot just be labeled CO. The response of
the sensor to other combustible gases gives
an output that is equivalent to the sensor
detecting CO. The term COMB is used in
this manual to describe the sensor output.
This term indicates that the sensor is cali-
brated in terms of CO, and that the sensor
output is equivalent to CO but not specific to
CO.
Dilution air is provided to the COMB sensor
to ensure there is adequate oxygen to fully
oxidize any combustible gases regardless
of the concentration of oxygen in the
process.
c. System Configuration
Transmitters are available in four length op-
tions, giving the user the flexibility to use a
penetration appropriate to the size of the
stack or duct. The length options are 18 in.
(457 mm), 3 ft (0.91 m), 6 ft (1.83 m), or 9 ft
(2.7 m). Probes are available in three mate-
rial options, 316L stainless steel, inconel
600, and ceramic to accommodate higher
temperatures.
The electronics are contained in a separate
housing from the sensors and may be inte-
grally mounted next to the sensor housing
on the probe, or split mounted up to 150
feet away from the probe.
The electronics control both sensor tem-
peratures and provide individual 4-20 mA
isolated outputs that are proportional to the
measured oxygen and combustibles con-
centrations. The power supply can accept
voltages of 100 to 240 VAC and 50 to 60
Hz. The electronics accepts millivolt signals
generated by the sensors and produces the
outputs to be used by remotely connected
devices. The outputs are isolated 4-20 mA
linearized currents. See 3-1b for specific in-
structions upon initial power up.
d. System Features
1. The O
2
cell output voltage and sensi-
tivity increase as the oxygen concen-
tration decreases.
2. HART communication is standard. To
use the HART capability, you must
have either:
(a) A HART Model 275
Communicator.
(b) Asset Management Solutions
(AMS) software for the PC.
3. Oxygen cell and heater/thermocouple
assembly are field replaceable.