My settings are;
Proportional band = 5 Integral time = 3600 Derivative time = 1800 Initial integral = 0 Max sample interval = 600 Derivative smoothing factor = 4
The PID is monitoring soil humidity, and it's output is scaled & operates a water pump which proportionally hydrates the soil. The aim is to keep it near to 62%, and I've attached a screenshot below, which shows the setpoint of 62% (yellow), the soil humidity (red) and the scaled PID output is the bottom (orange).
The PID output is scaled 1:266, so the maximum output is 266ml.
What I've noticed is that even when the setpoint has been reached, a drop in the humidity can produce a disproportionate effect. For example, see about 5.30am, where the humidity sensor recorded a drop of about 1.5% and responded with over 220mls of water, despite the humidity still being in excess of 1% above the setpoint.
This resulted in the humidity rising even further away from the setpoint.
It's unfortunate that the sensor readings deviate as they do, but to date I've used a smooth node, to smooth out the deviations, and it worked pretty good - except that there was a delay in response.
I did start tuning using your tuning blog post, but I've probably made umpteen changes since...
Any comments appreciated.