Emerson Rosemount 3490 Series, Reference Manual

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Note
The control unit can process mA input values in the range 3.8 to 20.5 mA.
Read-only parameters D840 and D842 are in the menu
MONITOR
→
DIAGNOSTICS .
Applying the optional percentage offset adjustment
P112 is a positive, negative, or zero offset adjustment of the converted (normalized)
percentage. This offset feature can be used to accommodate a standing level in a tank.
Note
The output from this adjustment is readable in D802 and is the Tertiary Value (TV) of the
control unit. D802 = D842 + P112
P112 is in the menu
SETUP
→
[CONTROLLER]
→
INPUT CHANNEL
→
Ch1 I/P Offset .
Applying the scaling factor to get the required units
Changing the PV display units (P200) does not automatically convert the control unit PV to
be in alternative units. A user-entered value in P114 is used to convert (scale) the offset-
adjusted percentage value (D802) to a new value (D801) that is in the required
measurement units.
If the mA input represents a liquid level, simply set P114 to the level represented by 20
mA.
Note
D801 is the Secondary Value (SV) of the control unit. D801 = (D802/100) P114
P114 is not applied if the PV display units (P200) are already configured to be “%”.
P114 is in the menu
SETUP
→
[CONTROLLER]
→
INPUT CHANNEL
→
Ch1 Pre Scale .
Read-only parameters D80* are in the menu MONITOR
→
READINGS .
Optional calculation of contents (volumetric) or flow measurement
By selecting a vessel profile or calculation using P113, a level measurement in D801 can be
used to calculate a volume measurement or open channel flow rate that is then stored in
D851. The programming (configuring) required for this is in
Volumetric contents and flow
measurement applications (advanced users) .
Applying an optional low volume or flow rate cut-off action
The channel 1 output result in D851 can be forced to zero when it falls below a positive
threshold, which is a percentage of the maximum flow. Enter the percentage in P117. 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 P117 to a positive value of 2% of maximum flow
to overcome this problem.
Note
P117 is in the menu SETUP
→
[CONTROLLER]
→
INPUT CHANNEL
→
Ch1 Low Cut-off .
Applying optional damping to the control unit PV
P210 allows the to smooth out large steps in calculated values (D851).
Reference Manual Getting started
00809-0100-4841 January 2021
Emerson.com/Rosemount 65