Rosemount 3095 - Autotuner Operation; Alpha Adjustment for Tuning

Rosemount Model 3095 Multivariable
™
Level Controller
3-6
Autotuner Operation
The Level Controller Autotuner works without any pre-tuning of the
control loop. The Autotuner functions under any condition, and does not
require a steady-state process.
Use the Model 275 HART Communicator or Asset Management
Solutions (AMS) to simply input the required tuning setup
parameters, which are:
• Level limits around a setpoint to tune
• Level limits allowable overshoot
• Control output minimum and maximum percentage
• Number of cycles
The Autotuner automatically activates the control element to change the
vessel’s level to the minimum and maximum level limits. This activation
repeats for the number of cycles and time as specified by the user. As the
process level changes, the Level Controller learns the loop’s dynamics:
the rate of change level, dead time, and the dynamics of the control
element. The Level Controller uses Ziegler-Nichols IMC tuning rules to
calculate the optimal tuning processes (process gain, delay, and bias).
The Level Controller informs the user when tuning is completed
successfully, and asks the user to accept or reject the calculated tuning
parameters. If accepted, the new parameters must then be sent to the
Level Controller to be used.
If the Level Controller is not able to successfully calculate new tuning
parameters, the Level Controller aborts the Autotune procedure
and informs the user of a tuning failure. Common reasons for an
unsuccessful Auto-tune include a lack of sufficient time to
complete the cycles, or an insufficient allowable overshoot.
To help ensure a successful Autotune,
• Set the High and Low level limits close to the setpoint.
• Ensure that you have allowed a sufficient overshoot.
• Allow for additional cycles for extremely noisy processes; one
cycle is usually sufficient for standard applications.
• Allow enough time to complete the number of Auto-tuning
cycles selected.
Alpha Adjustment
for Tuning
The Level Controller Auto-tuning algorithm features the ability to
recalculate the tuning parameters after adjustments were made to the
controller. The “Alpha Adjustment Knob” allows users to adjust the
controller variables without having to complete a new Autotuning routine.