The Ziegler-Nichols closed loop tuning method is a popular technique used in the field of control systems to tune the parameters of a PID (Proportional-Integral-Derivative) controller. This method involves the following steps:
1. Start with an open loop system: Initially, the system's PID controller is set to 'off' or has its parameters set to zero. This essentially creates an open loop system.
2. Identify the critical gain (Ku) and critical oscillation period (Tu): Gradually increase the proportional gain (Kp) until the system exhibits sustained oscillations, also known as the ultimate gain. Note this gain value as Ku. Measure the time it takes for one complete oscillation cycle and record it as Tu.
3. Calculate the controller parameters using the Ziegler-Nichols ultimate gain tuning rules:
Proportional Gain (Kp): Set Kp to 0.6 times Ku.
Integral Time (Ti): Set Ti to 0.5 times Tu.
Derivative Time (Td): Set Td to 0.125 times Tu.
4. Set the PID controller with the calculated parameters: Apply the newly determined values of Kp, Ti, and Td to the PID controller.
5. Verify the performance: Observe the system's response and check for any overshoot, oscillations, or settling time. If necessary, fine-tune the PID parameters manually for improved performance.
It's important to note that the Ziegler-Nichols method is a heuristic method that generally works well with most systems. However, it may not always produce optimal results for all types of control systems. Therefore, it's recommended to fine-tune the parameters further based on the specific requirements and characteristics of the system being controlled.