A traditional tuning target where each oscillation peak is a quarter the size of the one before.
Trend of a healthy PID loop: after a setpoint step the process variable overshoots slightly and settles within two peaks. One small overshoot, a second much smaller peak, then flat. The output moves decisively and then stops moving. This is what every stopping criterion in a PIDSnap session is describing.
What it means
Quarter amplitude damping means each successive peak after a disturbance is about a quarter the height of the previous one. It is the target behind several classical tuning rules.
It is more aggressive than most operating plants want. A loop tuned to quarter amplitude sits close enough to the stability boundary that a routine change in process gain — which happens whenever the load moves — can push it somewhere much less comfortable. A response settling inside two peaks is a more defensible target.
Trend of a healthy PID loop: after a setpoint step the process variable overshoots slightly and settles within two peaks. One small overshoot, a second much smaller peak, then flat. The output moves decisively and then stops moving. This is what every stopping criterion in a PIDSnap session is describing.
Two photos, thirty seconds, no signup. The pre-flight check finds the structural
problems that no amount of tuning will fix — before you touch the controller.