Emerson Rosemount 3490 Series, Справочное руководство

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Selection of a HART variable as source for further processing
Parameter P121 selects one of the four HART variables (PV, SV, TV, or FV) on the
transmitter to be the source for further processing to get a result from Input Channel 2.
The unselected HART variables are mapped to control unit D80x parameters.
Note
In Figure 4-13 , the selected source is the HART Primary Variable (PV). Alternatively, Tx2:
SV, Tx2: TV, or Tx2: FV could have been selected.
Read-only parameters D80* are in the menu
MONITOR
→
READINGS .
Applying the optional offset adjustment to the selected source
P122 is a positive, negative, or zero offset for adjustment of the selected HART variable.
As an example, this feature may be used to accommodate a standing value of level in a
tank. P122 is at
SETUP
→
CONTROLLER
→
PV CALCULATION
→
CHANNEL 2
→
Ch2 I/P
Offset .
Applying the optional scaling and profiling to the selected source
If volumetric or flow values are in the selected HART variable, set parameter P123 to
Scaled. Use parameter P124 to convert (scale) the value into units that match the selected
display units (P200, P201, P202, or P203, as applicable in
SETUP → CONTROLLER →
DISPLAY ).
If level values are in the selected HART variable, parameter P123 can be set to Scaled if
wanting just level measurement, and then use parameter P124 as described in the
paragraph above. By selecting profile calculation using P123, a level value can be used to
calculate a volumetric or open channel flow rate. The programming (configuring) required
for this can be found in
Volumetric contents and flow measurement applications
(advanced users) .
Note
P123 and P124 are in the sub-menus
Ch2 Profile
and
Ch2 Pre scale
at:
SETUP
→
CONTROLLER
→
PV CALCULATION
→
CHANNEL 2
Applying an optional low-cut-off action
The channel 2 output result in D852 can be forced to zero when it falls below a positive
threshold, which is a percentage of the maximum flow. Enter the percentage in P127.
By default, the setting is “None” to switch off this optional check.
This feature is particularly useful in an open channel flow application where a small
standing or remaining liquid level in the channel would cause continued totalizing of flow
when no actual flow exists. As a guide, set P127 to a positive value of 2% of maximum flow
to overcome this problem.
Note
P127 is in this menu SETUP
→
CONTROLLER
→
PV CALCULATION
→
CHANNEL 2
→
Ch2
Low Cut-off .
Applying optional damping to the control unit PV
P210 is used to apply damping to smooth out big steps in calculated values in D852.
Getting started Reference Manual
January 2021 00809-0100-4841
70 Emerson.com/Rosemount