Lecture Notes 8
Lecture 8 - Proportional-Integral-Derivative Control
For Lecture 8 we'll complete our discussion of PID controllers by adding the derivative term. The main points of this lecture for derivative action include:
- Derivative action is typically on the PV not the Error
- Derivative action helps to dampen oscillations by slowing down a controller action that is moving the PV too quickly to Setpoint (SP).
- Derivative action can create undesirable response with significant measurement noise
- Lecture 8 Class Notes
Discussion Questions
Test the lecture's ideas before or after class - commit to an answer first, then check it with a classmate or an AI tutor.
- A loop still shows steady-state offset after adding derivative action. A classmate says "increase tauD." What is wrong with that advice, and which mode actually removes offset?
- Why is derivative action usually computed on the measured process variable instead of the error? Describe exactly what happens at the moment of a setpoint change if it acts on error.
- The same PID that is smooth on a filtered temperature signal chatters the valve on a noisy flow signal. Which term is responsible, and what are two remedies that do not remove it entirely?
- In the artificial pancreas case study, insulin can only be added, never removed, and acts with a long delay. Which PID mode is most dangerous to tune aggressively here, and why is the risk asymmetric (low glucose vs high)?
"Quiz me with 5 questions, one at a time, on PID control: what each of the three modes contributes to the response, why integral action removes offset but causes windup when the actuator saturates, why derivative acts on the process variable to avoid setpoint kick, how noise interacts with derivative action, and how the artificial pancreas illustrates a reverse-acting controller with asymmetric risk. Grade my answers and list my misconceptions."
App: Run the case study yourself in the Artificial Pancreas Control Studio - dose insulin manually and then with the reverse-acting PID through meals and exercise, and watch what the long insulin delay does to an aggressive tuning.
