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Instruction Manual
IM-106-880C, OI
September 2009
Hazardous Area OCX 8800
1-4
The Hazardous Area OCX 8800 measures net oxygen concentration in the
presence of all the products 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, indicate a lower percentage
of oxygen. The difference will be proportional to the water content of the
sampled gas stream.
The Hazardous Area OCX 8800 combustibles sensor is a catalytic sensor
consisting of two Resistance Devices (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 element. 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 detect carbon monoxide (CO), but the
sensor responds to other combustible gases. The sensor is calibrated using
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 COe is used in this manual to describe the sensor output. This term
indicates that the sensor is calibrated in terms of CO, and that the sensor
output is equivalent to CO but not specific to CO.
Dilution air is provided to the COe sensor to ensure there is adequate oxygen
to fully oxidize any combustible gases regardless of the concentration of
oxygen in the process.
System Configuration
Transmitters are available in four lengths, 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 material options, 316L stainless steel, Inconel 600, and
ceramic to accommodate higher temperatures.
The electronics are contained in a separate housing from the sensors. When
the transmitter is configured with the integral electronics option the electronics
and sensor housings are mounted as a unit at the stack mounting flange.
When the transmitter is configured with the remote electronics option the
electronics are contained in a separate housing from the sensors. The
electronics housing may be mounted up to 150 feet from the sensor housing.
The electronics control both sensor temperatures and provide output signals
in one of two ways:
1. Individual 4-20 ma isolated outputs that are proportional to the
measured oxygen and combustibles concentrations. The oxygen output
also contains HART communication.
2. Single FOUNDATION fieldbus output.