Glossary · Data, timing and communication
Closed-loop control
Also known as: feedback control
German: Regelung mit Rückführung
In control engineering, closed-loop control is control that uses feedback to compare the actual behavior of a process with the intended result and corrects its output based on the difference.
- Systems engineering
- Integrated systems
In one sentence
Closed-loop control corrects its output from measured feedback; the loop is only as reliable as its feedback signal, timing and fault handling.
Example
The servo drive of a CNC machine compares the encoder position with the commanded position and adjusts the motor current until the axis reaches its target.
How it applies
- Integrated systems: Document the setpoint, the measured variable, the feedback signal, the sampling rate and the permitted control deviation. Latency and jitter in the loop affect its stability.
- Functional safety: A loop that controls a process is not automatically a safety function. If feedback is lost or implausible, the controller must detect it and react in a defined way, for example by stopping the drive. Monitoring functions such as SLS also rely on feedback, but they monitor limits rather than control the process.
- Maintenance: Sensor faults and sensor drift corrupt the loop without an obvious alarm. Calibration intervals for feedback sensors belong in the maintenance documentation.
Closed-loop vs. open-loop control
Open-loop control issues an output and assumes the effect. Closed-loop control measures the effect and corrects the output, so it can compensate for disturbances, but it depends on correct feedback.