Making a deliberate step change to a loop and observing the response.
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
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.
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.
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.