Glossary · Automation fundamentals, platforms and components
Feedback (control engineering)
Also known as: Feedback loop
German: Rückführung
In control engineering, feedback is the return of a measured output value of a system to the controller, where it is compared with the setpoint to determine the corrective action. Feedback is what makes control closed-loop.
- Automation components
In one sentence
Feedback returns a measured output to the controller, where it is compared with the setpoint; it is what makes control closed-loop.
Example
A tachogenerator measures motor speed and feeds it back to the drive controller, which adjusts the current to keep the speed constant.
How it applies
- Engineering: Negative feedback reduces the control deviation; the design must keep the loop stable despite delays and gain changes.
- Commissioning: Wrong sign or scaling of the feedback causes the loop to run away, so polarity is checked before closing the loop.
- Documentation: Loop descriptions should name the feedback sensor and its signal. Troubleshooting guides should cover lost or implausible feedback, since the controller's reaction to it determines what the machine does.
Feedback vs. feedback signal
Feedback is the control principle. A Feedback signal is the individual signal, for example a position confirmation from a valve, that reports a state back to the controller. In the systems engineering sense, Operational feedback from the field to engineering is yet another meaning.