Ziegler-Nichols tuning method

Ever got frustrated by trying to tune your boost control or idle control?

This is a method published by 2 dudes back in the 1940s, producing parameters resulting in quarter wave decay for closed loop control. While it may not be optimal for all instances, it serves as a good basis to start.

Step 1:
Make sure the process is lined out.

Step 2:
Increase the gain in 1/2 steps of the previous gain. After each increase, if there's no oscillation change the setpoint slightly to trigger an oscillation.

Step 3:
Adjust the gain so oscillation is sustained. i.e. same amplitude. If the oscillation is increasing, decrease gain. Conversely, increase gain if the oscillation is decreasing.

Step 4:
Note the gain causing the sustained oscillation, and the period.

Use one of the following tuning equations as appropriate.

Proportional control only: Gain=0.5
PI: Gain=0.45, reset=PU/1.2
PID: Gain=0.6, reset=PU/2, derivative=PU/8