Glossary · Control theory and process control
Rise time
Also known as: Response rise time
German: Anstiegszeit
In control engineering, rise time is the time a step response takes to go from a lower to an upper percentage of its final value, commonly from 10 to 90 percent.
- Control theory
In one sentence
Rise time is how long a step response takes to rise between two percentages of its final value, commonly 10 and 90 percent.
Example
The speed loop of the conveyor drive reaches 90 percent of the new speed setpoint 40 ms after the step, with a 10–90 rise time of 30 ms.
How it applies
- Engineering: Rise time relates to the loop bandwidth: a wider bandwidth means a shorter rise time. Definitions differ (10–90 percent, 0–100 percent, 5–95 percent), so always state which one is used.
- Commissioning: Measure rise time with a step small enough to avoid actuator saturation; otherwise the result reflects the actuator limit, not the loop tuning.
- Documentation: In data sheets and specifications, give rise time with its definition, the step size and the load. Values without conditions cannot be compared between products or verified in acceptance tests.
Rise time vs. latency
Latency is the delay before a response starts; rise time describes how fast the response develops once it has started. For communication-based loops, both add up in the observed reaction.