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29 Cards in this Set
- Front
- Back
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Feedforward block diagram
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Characteristic Equation
Feedforward Control |
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Transfer Function
Feedforward Control |
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Cascade
Requirement for Secondary Loop |
3 times as fast as Primary
ts < (1/3)tp (ISE, ITSE) Tightly Tuned |
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Cascade
Tune ___ Loop First, Controls _____ Output |
Primary
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Suppress D
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Feedforward
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Goal of Feedforward
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Compensate for the effect of disturbance before it causes an effect
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Tuning Feedforward Controller
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Field Tuning
Turn off feedback - open loop Analysis for Kff, tld, tlg, thetaff Adjust Kff to eliminate offset Adjust thetaff to minimize overshoot |
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Advantages/Disadvantages of Feedback Control
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Advantages/Disadvantages of Feedforward Control
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Inferential Control uses _____ to ______
E.g. Use ___, ___, ____ to infer _____ and ____ ____ |
Uses easily measured process variables to infer more difficult to measure quantities
Temp, Pressure, Flow to infer compositions and molecular weight |
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Inferential Control reduces
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Inferential Control reduces deadtime at a very effective price
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Inferential Control can reduce
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Can substantially reduce analyzer delay
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Inferential Control can provide
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Can provide measurements that are not available any other way
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Goal of Inferential Control is to
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Calculate y to plug in to controller, replaces measurement of y
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Conditions where inferential control needed
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An on-stream sensor is not possible
An on-stream sensor is too costly Unfavorable sensor dynamics (long dead time) or is located far downstream A inferential variable is available |
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Inputs to inferential part of controller (Logic of inferential control scheme)
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u or M(s)
d or D(s) |
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Outputs from inferential part of controller (Logic of inferential control scheme)
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y: measured output to be controlled
x: measured output that is used to estimate/infer other outputs |
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Inferential controller is physically realizable when
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Measureable in real time
Inferential measurement must correlate strongly with the CV of interest Correlation should be relatively insensitive to unmeasured disturbances Plot of y vs. x should be linear |
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Cascade
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Upstream controller to regulate deviations further down series of processes
Downstream sensitive to upstream disturbances |
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Inner loop
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High proportional gain for fast inner-loop response
Eliminate input disturbance, P or PI is sufficient |
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Outer loop
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Tuned with the inner loop in operation for overall performance
PID controller |
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