What AspenWatch parameters can help to understand dynamic disturbance rejection in the controller.
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Products:
Aspen DMC3 Builder, Aspen Watch Performance Monitor
Last Updated:
03-Jan-2022
Last Updated:
03-Jan-2022
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Article ID:
000096705
Article ID:
000096705
Primary Subject:
Problem Statement
Is there anything in AspenWatch to help understand the dynamic disturbance rejection rather than the steady state solution.
Solution
Two useful KPIs in the AW history are LSTRBI (TRI) for MVs and LSTRBD (TRD) for CVs. These are the contributions to the dynamic move plan. High values of LSTRBI tells you which MVs are contributing least to the dynamic move plan and high values of LSTRBD tells you which CVs are being controlled most with the dynamic move plan. As an example ramp variables often have high LSTRBDs. Looking at the values and what the controller is doing can provide insight into why the controller is moving dynamically in a certain way.
Both values can be positive or negative and are typically in the range of -5% to 105%. An LSTRBD of zero indicates the CV has zero weighting in the dynamic move calculation – an effective ECE of 10^6. The LSTRBI can be changed by tuning move suppression and LSTRBD can be changed by tuning dynamic ECEs and transition zones.
Below is a general description of what values LSTRBD and LSTRBI roughly mean.
LSTRBI for MVs
From 20% to 100%
Move suppression is an important priority for this MV, controller is attempting to minimize movement of this MV
The controller is sacrificing dynamic control of CVs or moving other MVs to minimize the movement of this MV
From -3% to 3%
The dynamic response of this variable is not an important priority
The controller will move this MV as needed to control the CVs
LSTRBD is negative
The move plan for this MV involves at least one change of direction as it moves from its current value to steady state
The MV is moving aggressively to improve the response of a higher priority variable
LSTRBD for CVs
From 20% to 100%
The dynamic response of this variable is important
From -3% to 3%
The dynamic response of this variable is not important
Is negative
The dynamic response of this variable is made worse to improve the response and get tighter control of a higher priority CV
Below is a screen shot of the PCWS where to find these parameters and they can be plotted in the PCWS by setting the attribute to Contribution.