Emerson Rosemount 6888A, Reference Manual

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• Loss of flame contact for powering down the heater in the event of a flame-out
condition in a furnace.
• Heaterless operation at process temperatures above 550 °C (1022 °F). This feature
will also permit operation above the heater setpoint of 736 °C (1357 °F). Sensing cell
life will be shortened by operation above 800 °C (1472 °F), however.
• Plugged diffuser diagnostic operates by measuring the return-to-process rate after
calibration gas has been stopped. This feature also includes auto gas switching when
the reading settles out versus waiting for configured gas flow time to expire.
• Stochiometer - If a furnace goes into a reducing condition (zero % O
2
), this feature
will determine how far.
• Programmable reference - Permits more accurate readings at near-ambient O
2
levels (20.95% O
2
).
• A cal check capability. New calibration values are not automatically stored after a
calibration. An accept/reject calibration feature can be enabled or disabled so that
the techniciean or operator can decice to accept or reject a potentially large change
in calibration values.
• Tolerance check that will alarm if the wrong test gases are being used or if a bottle
runs out in the middle of a calibration. Take care to ensure gas 1 and gas 2
calibration gases are properly configured if the tolerance check feature is enabled.
1.4.3 Transmitter probe and Rosemount 6888Xi with flame
safety interlock
A flame safety interlock by Emerson is available for heater power disconnect whenever
there is a loss of the process flame or a heater runaway condition (heater over-
temperature) in the O
2
probe. This input is internally powered by the Rosemount 6888Xi
and is actuated via a dry contact output from your flame scanner. A closed contact
indicates a flame is present. An open contact indicates a loss of flame. This feature is also
available with the integral autocal housing.
1.4.4 Transmitter probe with integral autocal, Rosemount
6888Xi, and HART
®
communications
This probe contains gas-switching solenoids so that the Rosemount 6888Xi electronics can
control the introduction of calibration gases. Calibrations can be initiated via a calibration
recommended diagnostic, time since last calibration, manually via external dry contact,
HART communications, or from the Rosemount 6888Xi local operator interface keypad.
The integral autocal feature can only be implemented when the probe is used with a
Rosemount 6888Xi.
1.4.5 Transmitter probe with integral autocal and
FOUNDATION
™
Fieldbus (FF) communications
This probe contains gas-switching solenoids that can control the introduction of
calibration gases for calibration. Calibrations can be initiated automatically via a calibration
recommended diagnostic, time since last calibration, manually via the optional
Description and specifications
4 Rosemount 6888A