Weight Calibration; Theoretical Calibration - Fisher FIELDVUE DLC3010 Instruction Manual

Configuration
October 2014
The sensor torque rate is now calibrated. Be sure to verify that there is no bias in the PV calculation and that the upper
and lower range values are correct before returning the loop to automatic control.

Weight Calibration

This procedure may be used on the bench or with a calibration jig that is capable of applying a mechanical force to the
driver rod to simulate displacer buoyancy changes. It allows the instrument and sensor to be calibrated using
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 coupling point should be marked at what is going to be the zero buoyancy weight or the zero
differential‐buoyancy weight, depending on the calibration approach. The instrument should normally be physically
coupled to the pilot shaft at that condition. (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.) The Capture Zero procedure may be
run either before or after the Weight‐based Cal. However, the PV output is expected to have a bias error until the
Reference Coupling Point is correctly marked.
Follow the prompts on the Field Communicator to calibrate the sensor.
1. For interface level or density measurements, enter the specific gravity of the upper fluid and lower fluid as
requested.
2. 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.
3. After allowing the system to stabilize, enter the actual value of the weight suspended on the displacer rod.
4. 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 highest level or the displacer is
suspended in the liquid with the higher specific gravity.
5. After allowing the system to stabilize, enter the actual value of the weight suspended on the displacer rod.
The sensor torque rate is calibrated. If the Capture Zero procedure was performed at the zero buoyancy (or zero
differential buoyancy) condition, the zero of the PV calculation will be correct also. 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 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
Level Controllers and Transmitters instruction manual supplement
sales office for information on obtaining this manual supplement.
56
Simulation of Process Conditions for Calibration of Fisher
(D103066X012). Contact your Emerson Process Management
Instruction Manual
D102748X012