Glossary · Data, timing and communication
Open-loop control
German: Steuerung ohne Rückführung
In control engineering, open-loop control is control that does not use feedback to confirm the effect of its output. The controller issues a command and assumes that the process follows it.
- Systems engineering
- Integrated systems
In one sentence
Open-loop control acts without measuring the result; it is simple and predictable but cannot detect that its output had no effect.
Example
A timer-controlled lubrication pump on a CNC machine runs for 5 seconds every hour without checking whether lubricant actually reaches the guideways.
How it applies
- Integrated systems: Open-loop control suits processes that are well known and have small disturbances, such as stepper motors without encoders or timed sequences. Document what the control relies on as operating assumptions.
- Functional safety: Without a feedback signal, actuator failures go undetected. Where such a failure matters for safety, additional monitoring is needed to detect it.
- Maintenance: Because the controller cannot notice a blocked nozzle or a stalled motor, periodic checks in the maintenance documentation take over the role of feedback.
Open-loop vs. closed-loop control
Closed-loop control measures the result and corrects the output. Open-loop control only commands, which makes it simpler and free of feedback faults, but blind to disturbances.