Glossary · Control theory and process control
Settling time
Also known as: Response settling time
German: Einschwingzeit
In control engineering, settling time is the time after a step change until the controlled variable enters and stays within a specified tolerance band around its final value, for example ±2 percent.
- Control theory
In one sentence
Settling time is how long after a step the controlled variable takes to enter and stay within a tolerance band around its final value.
Example
A filling scale's weight loop settles within ±0.5 percent of the target 350 ms after the dosing valve closes, which determines the cycle time of the filler.
How it applies
- Engineering: Settling time depends on damping and bandwidth; a loop with large Overshoot or poor damping settles slowly even if it rises fast. In machines, settling time often limits throughput directly, for example in positioning before a process step.
- Commissioning: Always state the tolerance band used. A loop that settles in 1 s to ±5 percent may take several seconds to reach ±1 percent.
- Documentation: When settling time is an Acceptance criterion, specify the step size, the tolerance band, the load and how the measurement is taken. Put the same definition into the test procedure.
Settling time vs. rise time
Rise time describes how fast the response gets close to its final value; settling time describes when it has calmed down there. Both appear in specifications because each can be good while the other is poor.