Scaled Variable Configuration - Emerson Rosemount 3051S Series Reference Manual

Reference Manual
00809-0100-4801, Rev FA
October 2010
Scaled Variable
Configuration
1, 4, 3, 4, 7
Traditional Fast Keys
Device Dashboard
Fast Keys
AMS v7.0
Right click on the device and select "Configure" from the menu
1. In the "Analog Output" tab, locate the "Configuration Pressure Alerts"
box, enter "Press Hi Alert Val" and "Press Lo Alert Val" to configure the
pressure alerts.
2. Configure "Press Alert Mode" to "ON" or "OFF" using the drop down
menu.
3. In the "Configuration Temperature Alerts" box, enter "Temp Hi Alert Val"
and "Temp Lo Alert Val" to configure the temperature alerts.
4. Configure "Temp Alert Mode" to "ON" or "OFF" using the drop down
menu and click Apply.
5. After carefully reading the warning provided, select yes.
The scaled variable configuration allows the user to create a
relationship/conversion between the pressure units and user-defined/custom
units. There are two use cases for scaled variable. The first use case is to
allow custom units to be displayed on the transmitter's LCD display. The
2, 2, 2
second use case is to allow custom units to drive the transmitter's 4-20 mA
output.
If the user desires custom units to drive the 4-20 mA output, scaled variable
must be re-mapped as the primary variable. Refer to "Re-mapping" on
page 3-24.
The scaled variable configuration defines the following items:
• Scaled variable units - Custom units to be displayed.
• Scaled data options - Defines the transfer function for the application
a. Linear
b. Square root
• Pressure value position 1 - Lower known value point (possible 4 mA
point) with consideration of linear offset.
• Scaled variable value position 1 - Custom unit equivalent to the lower
known value point (The lower known value point may or may not be the
4 mA point.)
• Pressure value position 2 - Upper known value point
(possible 20 mA point)
• Scaled variable value position 2 - Custom unit equivalent to the upper
known value point (possible 20 mA point)
• Linear offset - The value required to zero out pressures effecting the
desired pressure reading.
• Low flow cutoff - Point at which output is driven to zero to prevent
problems caused by process noise. It is highly recommended to use
the low flow cutoff function in order to have a stable output and avoid
problems due to process noise at a low flow or no flow condition. A low
flow cutoff value that is practical for the flow element in the application
should be entered.
NOTE
If Scaled Variable is mapped as the primary variable and square root mode is
selected, ensure transfer function is set to linear. Refer to "Set Output
(Transfer function)" on page 3-13.
Rosemount 3051S Series
.
3-21