Control Systems and PID Controllers

Closed Loop Control

• Closed-loop control systems use feedback to control system states. The output is fed back into the system to achieve a desired performance.
• Open-loop control systems don't use feedback, so the output depends solely on the input.

PID Controller

• PID controllers are used to regulate process variables like temperature, flow, pressure, and speed.
• The input signal is an error signal, the difference between the measured value and the actual value.
• PID controller components:
  • Proportional: Responds to changes in input by scaling the output proportionally. Higher gain (PG) leads to faster response but potential instability.
  • Integral: Responds to accumulated error over time. Gradually eliminates error.
  • Derivative: Responds to the rate of change of input. Predicts future error and adjusts output accordingly.

Measuring a System's Response

• Overshoot: The maximum amount the response exceeds the final steady-state value.
• Steady-state error: The difference between the process variable and the set point after the system settles.
• Rise time: The time it takes for the response to reach 90% of its final steady-state value.
• Settling time: The time it takes for the response to reach a specified tolerance around the final steady-state value.
• Periodic time/period: Duration of one cycle of oscillation. The interval between peaks or troughs.
• Frequency: The reciprocal of the period. Measured in Hertz.
• Transport delay: The time it takes for the process variable to start changing after a step change in the set point.

Experiment Procedure:

• Close Loop (PID):
  • The experiment uses a PCT-100 system to simulate flow control in a closed-loop system.
  • By adjusting the proportional (PG), integral (I), and derivative (D) parameters, students can analyze the effects on system performance.
  • The experiment compares the results of using only a proportional controller to using PID control.
• Investigating the affect of changing PG and SP on system response:
  • Changes in PG affect the steady-state error, overshooting, and oscillation.
  • Increasing PG leads to faster response but can also lead to more overshooting.
  • Changes in SP affect the steady-state error as the system adjusts to achieve a new target value.
• Investigating the effect of changing the I parameter:
  • Increasing I value reduces steady-state error but can lead to oscillations.
  • The I parameter influences the settling time.
• Investigating the effect of the D parameter:
  • The D parameter plays a role in predicting future errors and adjusting output accordingly.
  • It can help the system anticipate changes and stabilize the response.
  • The D parameter is often used to minimize overshoot and improve settling time.

Key Takeaways

• The experiment aims to help students understand the impact of different control parameters (PG, I, D) on the performance of a closed-loop control system.
• Students use the experimental data to analyze the relationship between the control parameters and the behaviors like steady-state error, overshoot, oscillation, and settling time.
• This knowledge is critical for tuning and optimizing control systems in real-world applications.

Explore the concepts of closed-loop and open-loop control systems, including the functionality of PID controllers. Understand how each component—Proportional, Integral, and Derivative—contributes to system regulation by responding to various input changes. This quiz will test your knowledge on feedback mechanisms and system responses.