PIDSnap

Bump test

A bump test is a deliberate step in manual (or a small setpoint change in automatic) so you can see how the loop actually responds. Without it, a quiet trend tells you almost nothing.

A healthy control loop response Trend of a healthy PID loop: after a setpoint step the process variable overshoots slightly and settles within two peaks. high low PV SP Output PIDSnap time
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

A bump test means putting a known change into the loop — usually a step in controller output with the loop in manual, or a small setpoint change in automatic — and watching what comes back.

It is the foundation of everything else. Without a deliberate disturbance there is nothing to analyse: a steady trend of a loop sitting quietly tells you almost nothing about how it will behave when something happens. This is why PIDSnap's first instruction in any session is to capture a baseline response rather than to change anything.

A healthy control loop response Trend of a healthy PID loop: after a setpoint step the process variable overshoots slightly and settles within two peaks. high low PV SP Output PIDSnap time
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.

Also called

On a plant you will hear this called step test. They mean the same thing.

Related

Glossary

Where this comes up

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

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