Quarter amplitude damping

Quarter amplitude damping: each peak a quarter of the one before. Classical Ziegler-Nichols aims at it; most operating plants want a loop that settles inside two peaks instead.

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.

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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.

Questions that come up

Is quarter amplitude damping a good target?

It is a traditional one and 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 can push it somewhere much less comfortable. Aim for a response that settles inside two peaks.

Glossary

Where this comes up

Written by PIDSnap control engineering. Published 2026-08-01, last reviewed 2026-10-22.