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Feedback Control Roundup

Feedback Control Roundup. Part 2. How do controllers go out of tune? How can I recognize them? What do I do?. How do controllers go out of tune?. One of three reasons: It was not set up properly in the first place Something in the physical world has changed

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Feedback Control Roundup

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  1. Feedback Control Roundup Part 2

  2. How do controllers go out of tune? • How can I recognize them? • What do I do?

  3. How do controllers go out of tune? • One of three reasons: • It was not set up properly in the first place • Something in the physical world has changed • Worn parts - valve, motor, dampers, etc. • Change in operating conditions affected the transfer function • Flow rate affecting time constant • Pressure affecting gain • Some Mech E installed a new piece of equipment • Someone changed it because they didn’t like it • Usually decreasing Kc or increasing I to make the controller less responsive.

  4. How can I recognize them? • Controller in manual (turned off) • Sustained oscillations • Complaints from operators (users) • Occasionally, equipment damage, usually from too-aggressive a controller.

  5. What do I do? • Understand the control objective • Understand the current control configuration and why it is not meeting the objective • Figure out the process: • inputs, outputs • Rough idea of relationship(s) between input(s) and output(s) • Transfer function model(s), time permitting • Design a controller for the process to meet the objective • IMC tuning • Simulate the controller in closed loop to make sure you got it right, and to be sure it will work if the process changes • Implement the controller • If you understand the effect of Kc and I, skip steps 3 and 4 and change them directly, but carefully.

  6. Physical Examples • Vehicle control • Thickness/width control in extrusion • Engine control: fuel injection under load • Antenna position on moving vehicle

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