How to tune using Ziegler Nichols Tuning Method
Source AEM forum, see link
1) Use the proportional control by itself and set the integral time constant to zero.
2) Log Map Sensor output and make a test run. Try various values and log them all 1,2,3,4,5,6,7,8,9,10... Until you find the point at which it starts to oscillate.
3) ones the oscillation starts yu have found the the ultimate proportional gain (Gu).
5) From the log, measure the period of oscillation from peak to peak, in seconds, to obtain the critical time constant or ultimate period (Pu).
6) Once the values for Gu and Pu are obtained, the P + I parameters can be calculated from the following equations.
Proportional feedback only (ki = 0)
kp = 0.5 (Gu)
Proportional and Integral feedback
kp = 0.45 (Gu)
ki = (Pu)/1.2
graphs will be added later to help demonstrate.