Fisher FIELDVUE DLC3010 Quick Start Manual page 26

DLC3010 Digital Level Controller
February 2016
Two point: Use any two interface levels that actually fall on the displacer. Accuracy is better if the levels are farther
apart. The result should be close if you can move the level even 10%.
Theoretical: If the level cannot be changed at all, you can enter a theoretical value for torque tube rate manually then
Trim Zero to adjust the output to the current independent observation of the process condition. Gain and bias errors
will exist with this approach, but it can provide nominal control capability. Keep records of subsequent observations of
actual process versus instrument output and different conditions and use the ratios between the process and
instrument changes to scale the torque rate value. Repeat Zero Trim after each gain change.
Density Applications - with Standard Displacer and Torque Tube
Note
When you change 'PV is' from level or interface to density, the range values will be initialized to 0.1 and 1.0 SGU. You may edit the
range values and density units after that initialization. The initialization is performed to clear out irrelevant numerical values from
length dimensions that cannot be reasonably converted to density dimensions.
Any of the full sensor calibration methods (Min/Max, Two Point, and Weight) can be used in density mode.
Min/Max: The Min/Max Calibration first asks for the SG of the minimum density test fluid (which could be zero if the
displacer is not overweight). Then, it has you set up a completely submerged displacer condition with that fluid. Next it
asks for the SG of your maximum density test fluid and directs you to completely submerge the displacer in that fluid.
If successful, the computed torque rate and zero reference angle are displayed for reference.
Two Point: The Two Point Calibration requires you to set up two different process conditions with as much difference
as possible. You could use two standard fluids with well‐known density and alternately submerge the displacer in one
or the other. If you are going to try to simulate a fluid by using a certain amount of water, remember that the amount
of displacer covered by the water is what counts, not the amount in the cage. The amount in the cage will always need
to be slightly more because of the displacer motion. If successful, the computed torque rate and zero reference angle
are displayed for reference.
Weight Based: The Weight Calibration asks you for the lowest and highest density you want to use for the calibration
points, and computes weight values for you. If you can't come up with the exact values asked for, you are allowed to
edit the values to tell it what weights you actually used. If successful, the computed torque rate and zero reference
angle are displayed for reference.
Sensor Calibration at Process Conditions (Hot Cut‐Over) when input cannot be varied
If the input to the sensor cannot be varied for calibration, you can configure the instrument gain using theoretical
information and use Trim Zero to trim the output to the current process condition. This allows you to make the
controller operational and to control a level around a setpoint. You can then use comparisons of input changes to
output changes over time to refine the gain estimate. A new trim zero will be required after each gain adjustment. This
approach is not recommended for a safety‐related application, where exact knowledge of the level is important to
prevent an overflow or dry sump condition. However, it should be more than adequate for the average level‐control
application that can tolerate large excursions from a midspan set point.
Two Point Calibration allows you to calibrate the torque tube using two input conditions that put the measured
interface anywhere on the displacer. The accuracy of the method increases as the two points are moved farther apart,
but if the level can be adjusted up or down a minimum 5% span, it is enough to make a calculation. Most level
processes can accept a small, manual adjustment of this nature. If your process cannot, then the theoretical approach
is the only method available.
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Quick Start Guide
D103214X012