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Instruction Manual
IM-106-880C, OI
September 2009
Hazardous Area OCX 8800
3-10
COe PURGE / ZERO
FEATURE
This feature provides a way to periodically flood the COe sensor with air to
perform two functions; a) provide additional oxygen to help burn off any
combustible residue from the COe sensor, and b) allow for optional
adjustment of the COe calibration constant. If the OCX8800 is configured to
update the COe calibration constant, only the constant is updated. The COe
calibration slope is not affected. To update both the constant and slope a full
calibration must take place.
The feature uses the calibration solenoid that is also used for high O2 test gas
and COe zero gas. For the feature to work properly, instrument air is used as
the high O2 test gas. This also requires the high O2 test gas value to be set
at 20.95%.
As an option, a two way valve may be installed to switch the high O2 test gas
between the normal calibration gas and instrument air. This allows the
Hazardous Area OCX 8800 to use a specified calibration gas for calibration,
then instrument air for the COe zero feature. Switching between the two
gases must be manually coordinated between scheduled calibrations and
COe zero events.
When the COe zero feature is used, special pneumatic connections are
required. See Section 2, Pneumatic Installation, for details.
The COe zero feature is only valid if the Hazardous Area OCX 8800 is
supplied with calibration solenoids and the solenoids have been activated.
A Hazardous Area OCX 8800 shipped from the factory must be configured
before the COe zero feature can be implemented. This same process must
be performed any time a replacement card stack is installed.
Configuring the COe Zero Feature with the Field Communicator - HART
1. Use the 375 Field Communicator or AMS software to access the HART
menu.
2. From the DETAILED SETUP menu, select INPUT/OUTPUT.
3. From the INPUT/OUTPUT menu, select COE ZERO.
4. From the COE ZERO menu, select the functions as follows:
Zero Enabled - Select "Yes" or "No" to enable or disable this feature.
Zero Intrvl - Length of time between COe zero events. Range is 60 to
480 minutes. Default is 60 minutes.
During the COe Zero Function the analog output signals may track the oxygen and
combustibles readings if configured to do so. To avoid a potentially dangerous operating
condition, the Hazardous Area OCX 8800 must be removed from the automatic combustion
control loop before performing the COe Zero Function procedure.
At the completion of the COe Zero Function, the COe analog output signal will change if the
Zero Update parameter is set to "Yes".