Inside this topic
By clicking the SIMULATE button, you can get simulated loop responses for FLC and PID control blocks and robustness plotting and tuning for the PID control block. Simulated responses use the identified process parameters, not the simulation modules described in the previous topic.
Fuzzy Logic Loop and Simulation
SIM_SR_FLC Fuzzy test loop with process simulation
Upon clicking SIMULATE, you will get the following responses:
If the control block is an FLC, the simulated response window will open with a simulated setpoint response.
If the control block is a PID, the recommended tuning parameters will be checked for stability and the PID structure checked for validity and normalcy.
displayed indicating an invalid configuration. You will not be able to proceed to the Simulated Response and Robustness window.
If the robustness calculations determine that the recommended tuning parameters yield an unstable result, a message will be displayed indicating unstable tuning. You can proceed to the Simulated Response and Robustness window by clicking OK in the message box.
If you do not select the integrating process check box and the structure is a P+D, then a message will be displayed indicating that this is an unusual configuration. You may proceed to the Simulated Response and Robustness window by clicking OK in the message box.
If there are no unusual or invalid conditions, then the Simulated Response and Robustness window will be opened without any warning messages.
Simulated Response and Robustness Layout
In the bottom half of the window, there is a simulated response trend plot with performance variables and simulation selection buttons on the right.
In the upper right quandrant of the window, there are entry and recommended tuning parameter display boxes with a RECOMMEND button immediately below them. If the control block is a PID, DT Margin and (if you selected the integrating process check box) % Surge are displayed just below the RECOMMEND button. If the control block is an FLC, DT Margin and % Surge are not displayed.
Simulated Response
You activate the first simulated response when you open the window using the SIMULATE button. Any new tuning parameter entries (or, for the PID, any new robustness map tuning selection) will cause a new simulated response to appear immediately. You may select whether you want a setpoint or disturbance step response simulated for the entry and/or current recommended tuning parameters. Make your selections as follows:
To select setpoint (SP) or disturbance simulated response, click either the SP or DISTURBANCE button.
To cause the current recommended tuning parameter response to be presented with the entry tuning parameter response, select the CURRENT check box.
Any change in your selections will cause the simulated response plot to be updated.
There are three (3) performance variables that are updated after every new simulated response.
Overshoot – Presented as percent of step change by which the process variable overshoots the new setpoint.
IAE – Integrated Absolute Error is presented for all SP responses. IAE will also be displayed for disturbance responses if you did not select the integrating process check box before you clicked the SIMULATE button.
Arrest – Arrest is displayed for disturbance responses if you selected the integrating process check box before clicking the
SIMULATE button. Arrest is the time it takes for the control to stop the process variable movement away from setpoint. It is also the time at which the maximum error during the response time occurs.
Entry and Recommended Tuning Parameters
You may enter the entry tuning parameters in either of the following ways:
Directly by clicking one of the parameter display boxes and entering new value(s) By clicking within the robustness plot
You may update the recommended tuning parameters with the entry tuning parameters by pushing the RECOMMEND button. The recommended parameters may be updated to the control block in the controller with the UPDATE button on the main DeltaV Tune main window.
Robustness Plot
The robustness plot presents a range of tuning parameters in the form of an area or a line. The horizontal axis is the Gain Margin
(dimensionless ratio of gain at which the loop will become unstable to the gain of the controller). The vertical axis is the Phase Margin in degrees.
The robustness plot is only displayed for the PID function block. This plot is displayed as an area whenever the PID structure is one of the P+I+D types. Otherwise, it is a line. In the unusual case where the PID structure is a P+D type and you did not select the integrating process check box, the robustness plot will be a horizontal line with an unlabelled phase margin axis.
You may select new entry tuning parameters by clicking within the presented area (or near the line if that is what is presented). This action will update entry tuning parameters and trigger a new simulated response.
Entry tuning parameters are annotated by a triangle. Recommended tuning parameters are annotated by a rectangle. Annotations are moved to the correct location on the map whenever the respective tuning parameters are adjusted. If a tuning parameter set is outside the area or off the line, the annotation will be displayed in yellow. If the robustness calculations determine that a tuning parameter set is unstable, the annotation will appear in red at the bottom left corner of the robustness plot.
DT Margin is the amount of process deadtime increase (in seconds) that causes a loop to become unstable. It applies to the entry tuning parameters, whether selected from the robustness plot or entered directly. Whenever entry tuning parameters are detected as unstable, DT Margin will be displayed as N/A.
DT Margin is only displayed for PID control blocks.
Percent (%) Surge
This variable is only displayed when the integrating process check box has been selected. It represents the percentage of tank capacity used to absorb a 100 percent difference in process input (PID output) and load.
% Surge is only displayed for PID control blocks.