Rosemount OCX 8800, Instruction Manual

Page: 18 / 266

1-6
Instruction Manual
IM-106-880, Rev 2.1
April 2017
OCX 8800
System Operation
Figure 1-2 shows the relationship between the components of the OCX 8800.
The sensors and the electronics are contained in separate housings. The
sensor housing and probe mounts to a duct or process wall so that the probe
protrudes into the flue gas stream. An air powered eductor continuously pulls
samples of the process flue gas through the probe to a chamber in front of the
sensor housing where the sample passes the O
2
sensor and continues on to
the COe sensor. Dilution air is provided to the COe sensor and reference air
to the O
2
sensor. After the gas sample flows past the O
2
sensor and through
the COe sensor, it is drawn through the eductor where it mixes with the
eductor air and exits through exhaust back into the system. The electronics
housing contains the CPU and communication boards which convert the
sensor inputs into digital output signals. The CPU can also initiate and
perform calibrations. Three test gasses and instrument air can be turned on
and off by solenoids. Test gas flow to the sensors is regulated by a flow meter
between the electronics and sensor housings. Instrument air is separated into
eductor air, reference air, and dilution air. The instrument air solenoid does not
allow air flow until the heaters are up to temperature. This minimizes the
amount of sampled process flue gas being pulled into cold sensors causing
condensation.
Figure 1-2. System Operation Diagram
Low O
Test Gas
2
COe
Combustibles
Sensor
O
Sensor
2
Eductor
Probe
Exhaust
CPU
COMM
Board
Optional
Test Gas
Solenoids
Instrument Air
Solenoid
High O
Test Gas
2
CO
Test Gas
Instrument
Air
Dilution Air
Reference Air
Eductor Air
Flow Meter
50 cc/min.
(0.1 scfh)
SENSOR
HOUSING
ELECTRONICS
HOUSING
Flow Meter
7 scfh
39690001
Sample
Gas
Power
Supply