Function Block Properties dialog box - Autotune tab (IMC)

The Internal Model Control (IMC) instruction controls a single process variable by manipulating a single control-variable output. This function block performs an algorithm where the actual error signal is compared against that of an internal first-order lag plus deadtime model of the process. The IMC function block calculates the control variable output (CV) in the Auto mode based on the PV - SP deviation, internal model, and tuning.
Use the
Autotune
 tab to configure autotuning for the selected IMC function block.
The following table describes the parameters available on the
Autotune
 tab:
Parameter
Description
Autotune Input
Process Type
Select the process type as
Integrating
 or
Non-integrating.
The default value is Non-integrating.
PV Change Limit
Enter a value for the PV tuning limit scaled in the PV units.
When Autotune is running and predicting PV exceeds this limit, the tuning aborts.
The default value is 0.
Autotune Timeout Limit
Enter a value in minutes for the maximum time for autotune to complete.
When autotune exceeds this time, tuning aborts.
The default value is 60.0 minutes.
Noise Level
Select an estimate of the noise level expected on the PV to compensate for it during tuning.
Valid values include:
  • Low
  • Medium
  • High
The default value is Medium.
Perform Autotune
CV Step Size
Enter a percentage for the CV step size for the tuning step test.
Step size is directly added to the applicable CV subject to high or low limiting.
The valid range is -100...100%.
The default value is 10%.
Start
Click this button to start the autotune request.
The request is ignored when the IMC is not in Manual mode.
The Start button is enabled when:
  • Online, and
  • AtuneOn is FALSE.
Otherwise, the Start button appears dimmed.
If you have made changes to any of the property dialog boxes, a dialog box displays that prompts you to save all changes before you start auto tuning.
If you click:
  • Cancel
     - no changes are applied to the tag and the auto tuning operation is not performed.
  • No
     -  no changes are applied to the tag and the auto tuning operation starts.
  • OK
     - all modified parameters are applied to the tag and the auto tuning operation starts.
Abort
Click this button to abort the autotune request.
The
Abort
 button is only enabled while auto tuning is being performed.
Autotune State
Displays one of the following statuses:
  • In Progress
     - auto tuning has been initiated.
  • Complete
     - auto tuning has completed successfully.
  • User Abort
     or
    Error Abort
     - auto tuning has been aborted by you or due to errors that occurred during the auto tuning operation.
  • Ready
     - no auto tune has been done since this instruction was created.
Current Model Values
Displays the current model values from the IMC tag.
These values are refreshed to match the corresponding tag parameter values when you click the Set Tuned Values button.
  • Gain
     - displays the internal model positive or negative gain parameter.
  • Time Constant
     - display the internal model time constant in seconds.
  • Deadtime
     - displays the internal model deadtime in seconds.
  • Response Time Constant
     - display the tuning parameter that determines the speed in seconds of the controller action.
Autotuned Model Values
Displays the tuned model values for the applicable CV1, CV2, or CV3.
When the dialog box is opened without a tune being in process, displays the current tuned values from the tag.
These values are updated when:
  • You click the
    Start
     button.
  • You click the
    Abort
     button.
  • Auto tuning is complete or aborted with errors.
The following values are displayed:
  • Gains
     - displays the calculated value of the internal model gain after tuning is completed.
  • Time Constant
     - displays the calculated value in seconds of the internal model time constant after tuning is completed.
  • Deadtime
     - displays the calculated value in seconds of the internal model deadtime after tuning is completed.
  • Response Time Constant
     - After a tune is completed select the desired speed of closed loop responses, either:
    Slow
    - the desired speed of the closed loop response and the calculated value in seconds of the controller time constant in a slow response speed.
    Medium
    - the desired speed of the closed loop response and the calculated value in seconds of the controller time constant in a medium response speed.
    Fast
    - the desired speed of the closed loop response and the calculated value in seconds of the controller time constant in a fast response speed.
Set Tuned Values
Click this button to accept the Autotuned Module Values and Response Time Constant speed .
At this time, the Autotuned Model Values and selected Response Time Constant values are copied to Current Model Values.
This button is only enabled in online mode.
Status
Indicates the block tuning status.
  • Ready
     - a tag was created; no autotune has been performed
  • In Progress
     - autotune is in progress.
  • Complete
     - autotune is complete.
  • Error Abort
     - the autotune has been aborted for an AtuneStatus status other than tuning in progress.
  • User Abort
     -the autotune has been aborted.
  • Status
     - Displays status information for blocks containing status bits. If none of the status bits are set, an OK message appears in this field. Otherwise, a list of the status bits that are set appears here. This list is comprised of the parameter names associated with the status bits, and typically explain which parameters were configured with invalid values.
Execution Order
Displays the block's execution number if the routine is in a verified state. If the routine is not yet verified, a Routine not verified message appears. Note that this item is read-only.
Never display description in a routine
Select this check box if you do not want the description to display in the routine.
OK
Click this button to add the selected item in the instruction list to the routine and close the
Function Block Properties
 dialog box.
Cancel
Click this button to cancel any edits you have made and close the
Function Block Properties
 dialog box.
Apply
Click this button to accept your changes and continue editing in the
Function Block Properties
 dialog box.
Note that the
Apply
 button is not used to set autotune values. You must use the
Set Tuned Values
 button instead.
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