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Configuration, Startup and Operation 35
6
888Xi Advanced Electronics Instruction Manual Section 3: Configuration, Startup and Operation
PN 51-6888Xi December 2012
3.3.1 Extended Temperature
The Oxygen Analyzer employs a heater and thermocouple to maintain a temperature normal set
point at 736°C (1357°F). Temperature control is maintained within ±1°C to process temperatures
of about 705°C (1300°F). This is satisfactory for most applications, but excursions to higher tem-
peratures can occur in some processes.
The extended temperature function allows the heater to be turned off and the process tempera-
ture used to heat the sensing cell. The function also provided for configuring the heater to oper-
ate at either 736°C (1357°F) or 550°C (1022°F). A lower temperature may be desirable by turn-
ing off the heater at a lower temperature to reduce the instance of an ignition source in the
process. Furthermore, the user has the ability to choose whether or not the heater will turn back
on if the process temperature falls below the set point. Again, this reduces the instance of an
ignition source in the process if a flameout condition should occur.
When the extended temperature function is disabled the heater normal set point is at 736°C. An
alarm will occur if the heater falls below 726°C or rises above 750°C. Either of these alarms will
also force the analog output signal to a critical alarm level of either 3.5 mA or 21.5 mA as config-
ured. When the extended temperature function is enabled, an alarm will occur if the heater falls
10°C below the set point of either 550°C or 736°C and will force the analog output signal level to
either 3.5 mA or 21.5 mA. With either set point, the high temperature alarm defaults to 750°C
but can be configured to any temperature between 750°C and 850°C. However, a heater tem-
perature above this level will cause an alarm but will not force the analog output signal level to
either 3.5 mA or 21.5 mA.
When the heater turns off, the oxygen reading is adjusted continuously to compensate for the
varying process temperatures. It should be noted that cell life will be reduced by continuous
operation at temperatures above 736°C (1357°F). If process temperatures are expected to be
continuously above 705°C, the use of an optional bypass or probe mounting jacket accessory is
recommended.
3.3.2 Stoichiometer
Process upsets can sometimes cause a combustion process to go into sub-stoichiometric or
reducing conditions. The oxygen readings from one or more probes may decline all the way to
zero. The stoichiometer cell will measure the amount of oxygen deficiency during these reduc-
ing conditions. The trends in your DCS can be set up for a lower range limit of -1 or -2% oxygen
to depict the level of oxygen deficiency.
NOTE
For enhanced software feature option upgrades or to enable the feature to duplicate the existing
configuration, contact Emerson Process Management at 1-800-433-6076. Reference the following:
6A00269G01 Enhanced Software Option Upgrade, Stoichiometric Function
6A00269G02 Enhanced Software Option Upgrade, Programmable Reference Function
6A00269G03 Enhanced Software Option Upgrade, Extended Temperature Function
6A00269G04 Enhanced Software Option Upgrade, Diffuser Warning Function