Theoretical Calibration - Emerson FISHER FIELDVUE DLC3010 Instruction Manual

DLC3010 Digital Level Controller
Configuration
May 2018
equivalent weights or force inputs instead of using the actual displacer buoyancy changes. If the displacer information
has been entered prior to beginning the procedure, the instrument will be able to compute reasonable weight value
suggestions for the calibration. However, the only preliminary data essential for the correct calibration of the torque
rate is the length of the driver rod being used for the calibration.
Weight equivalent to the net displacer weight at two valid process conditions must be available. The sensor must have
been sized properly for the expected service, so that the chosen process conditions are in the free‐motion linear range
of the sensor. The instrument should normally be physically coupled to the pilot shaft at what is going to be the zero
buoyancy weight or the zero differential‐buoyancy weight, depending on the calibration approach. (However, if the
expected operational travel of the pilot is greater than 5 degrees, it is advisable to couple the transmitter to the pilot
shaft at the condition representing mid‐travel instead. This will prevent hitting a stop in the transmitter before limiting
in the sensor.) A small zero trim correction may be necessary at start-up, since the weight input may not perfectly
simulate the actual process fluid(s).
Follow the prompts on the Field Communicator to calibrate the sensor.
1. Place a weight on the displacer rod that is approximately equal to that indicated on the prompt. The suggested
weight is equivalent to the effective displacer weight when the liquid is at its lowest level or the displacer is
suspended in the liquid with the lower specific gravity. You may use a larger weight for greater separation between
data points, so long as you don't hit the lower travel limit.
2. Enter the actual value of the weight suspended on the displacer rod. Check that a travel limit has not been reached,
and allow the system to stabilize before continuing.
3. Place a weight on the displacer rod that is approximately equal to that indicated on the next prompt. The suggested
weight is equivalent to the effective displacer weight when the liquid is at its highest level or the displacer is
suspended in the liquid with the higher specific gravity. You may use a smaller weight for greater separation
between data points, so long as you don't hit the upper travel limit.
4. After allowing the system to stabilize, enter the actual value of the weight suspended on the displacer rod.
The sensor is calibrated, but a small zero trim may be required when the actual process fluid(s) are introduced. Check
the range values before putting the loop in service.

Theoretical Calibration

In cases where it is not possible to manipulate the input at all, the user may set up a nominal calibration using
information available about the hardware and the process. The theoretical torque rate for the installed torque tube
may be looked up and compensated for process temperatures. This value is then manually entered in the instrument
configuration. (The Change Torque Rate procedure under the Manual Setup > Sensor > Torque Tube menu can be used
to look up and select theoretical values for common torque tubes if you select the Need Assistance option instead of
the Edit value directly approach.) The displacer information and fluid SGs are entered. The desired range values are
entered manually. Finally,Trim Zero computes PV to the current value of the process. It should be possible to control
the loop with this rough calibration.
Note
The theoretical torque rate for the installed torque tube is available in the Simulation of Process Conditions for Calibration of Fisher
Level Controllers and Transmitters instruction manual supplement (D103066X012). Contact your
Business Partner for information on obtaining this manual supplement.
Observations of the sight glass or other independent measurements may be logged against DLC3010 outputs over
time. The ratio of the independent‐observable process changes to the DLC3010 output changes may then be used as a
scale factor to modify the theoretical torque rate stored in the instrument. After each gain adjustment, a new zero
trim will be required. When a plant‐maintenance shutdown occurs, the instrument may be isolated and calibrated in
the normal manner.
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Instruction Manual
D102748X012
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