Entering Theoretical Torque Tube Rates; Www.fisher.com - Fisher FIELDVUE DLC3010 Instruction Manual

Configuration
October 2014
1. Determine all the information you can about the 249 hardware: 249 type, mounting sense (controller to the right or
left of displacer), torque tube material and wall thickness, displacer volume, weight, length, and driver rod length.
(the driver rod length is not the suspension rod length, but the horizontal distance between the centerline of the
displacer and the centerline of the torque tube). Also obtain process information: fluid densities, process
temperature, and pressure. (The pressure is used as a reminder to consider the density of an upper vapor phase,
which can become significant at higher pressures.)
2. Run Instrument Setup and enter the various data that is requested as accurately as possible In Manual Setup. Set
the Range Values (LRV, URV) to the PV values where you will want to see 4 mA and 20 mA output, respectively.
These might be 0 and 14 inches on a 14 inch displacer.
3. Mount and couple at the current process condition. It is not necessary to run the Capture Zero procedure, because
it stores the current torque tube angle as the zero buoyancy condition, and will therefore not be accurate.
4. With the torque tube type and material information, find a theoretical value for the composite or effective
torque-tube rate, (Refer to the Entering Theoretical Torque Tube (TT) Rates procedure in this section), and enter it
in the instrument memory. The value can be accessed by selecting:
Configure > Manual Setup > Sensor > Torque Tube > Change Torque Rate (2-2-1-3-2)
5. If the process temperature departs significantly from room temperature, use a correction factor interpolated from
tables of theoretical normalized modulus of rigidity. Multiply the theoretical rate by the correction factor before
entering the data. You should now have the gain correct to within perhaps 10%, at least for the standard wall, short
length torque tubes. (For the longer torque tubes (249K, L, N) with thin‐wall and a heat insulator extension, the
theoretical values are much less accurate, as the mechanical path departs considerably from the linear theory.)
Note
Tables containing information on temperature effects on torque tubes can be found in the
Calibration of Fisher Level Controllers and Transmitters instruction manual supplement
Emerson Process Management sales office or at www.fisher.com.
6. Now using a sight glass or sampling ports, obtain an estimate of the current process condition. Run the Trim Zero
calibration and report the value of the actual process in the PV engineering units.
7. You should now be able to go to automatic control. If observations over time show the instrument output exhibits,
for example,1.2 times as much excursion as the sight glass input, you could divide the stored torque tube rate by
1.2 and send the new value to the instrument. Then run another Trim Zero calibration and observe results for
another extended period to see if further iteration is required.
Entering Theoretical Torque Tube (TT) Rates
The Simulation of Process Conditions for Calibration of Fisher Level Controllers and Transmitters instruction manual
supplement (D103066X012) provides the theoretical composite torque tube (TT) rate for 249 sensors with DLC3010
controllers. These numbers are nominal values. They should be within 10% of the values that the instrument would
compute when you perform a sensor calibration. They will be less accurate for the long torque tubes (249K, L, N, VS,
and P), especially with thin‐wall constructions.
If you are unable to perform a sensor calibration during installation, you may enter the values into the instrument at
the following menu item in the handheld:
Configure > Manual Setup > Sensor > Torque Tube > Change Torque Rate (2-2-1-3-2)
Then, manually set the LRV and URV to the PV values at which you desire 4 and 20 mA output, respectively:
Configure > Manual Setup > Variables > Primary Variable Range > Upper or Lower Range Value (2-2-2-3-1 or -2)
Next, perform a Trim Zero operation to align the instrument output with the sight glass reading:
Configure > Calibration > Primary > Partial Calibration > Trim Zero (2-5-1-3-3)
64
Instruction Manual
Simulation of Process Conditions for
(D103066X012), available from your
D102748X012