Emerson Rosemount 6888A, Reference Manual

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Rosemount 6888 probe with integral autocal housing
This probe contains the autocal solenoids within the blue electronics housing, eliminating
the need and cost for an SPS or IMPS solenoid enclosure. Both calibration gases are
permanently piped into two ports on the probe. It's important to confirm that there are no
piping leaks or the calibration bottles will leak down prematurely.
Note
The calibration sequence from the Rosemount 6888Xi electronics will be identical to that for
manual/semiautomatic calibration, but with the integral auto cal version of this probe it is not
possible to conduct a manual calibration. The factory offers a probe rebuild capacity if solenoid or
other failures occur.
Note
Calibration gas bottles are piped and under pressure at all times, so be sure to leak-check all fittings,
tubings, and connections. Always use dual-stage pressure regulators.
3.6.3 Other features associated with calibration
1. Cal check capability: You can choose to look at new calibration values prior to having
them load in and become active. If this feature is selected, a
calibration
changed
alarm comes up after the calibration is complete. Push the Diagnostics
button on the Rosemount 6888Xi to require an Accept Cal step so that the
technician or operator can decide if they are ready to accept a potentially large
change in calibration values.
2. Plugged diffuser diagnostic: This feature measures the return-to-process rate after
calibration gases are removed and will alarm when this tiem exceeds 75% of the
purge time configured. A
purge time too short
alarm indicates that the
diagnostic could not work because of a short purge time and is another indication
that the diffuser is plugged. Increase purge time in this case.
Another feature that comes with the plugged diffuser diagnostic is auto gas
switching. This feature switches cal gases and also ends the purge sequence when
the readings settle out, vs. waiting for a configured flow time. This saves time and
gas.
3. Tolerance check: Alarms if the cell MV signal is significantly different from the
expected signal of the bottles noted in the setup. This indicates if the wrong bottles
are being used or if a bottle runs out in the middle of a calibration.
Calibration setup is under the Detailed Setup menu.
Calibration setup can be found in the Rosemount 6888Xi menu.
For the factory default menu, see Figure 3-1 .
Configuration, startup, and operation
52 Rosemount 6888A