Glossary · Data, timing and communication
Feedback signal
In control engineering, a feedback signal is a signal that represents measured system behavior and is used for monitoring or control, for example a position, speed, pressure or contact state.
- Functional safety
- Data and interfaces
In one sentence
A feedback signal reports what a system actually does; control loops, monitoring and safety diagnostics depend on it being correct and timely.
Example
The mirror contact of a safety contactor feeds back to the safety relay whether the contactor has really dropped out before the machine may restart.
How it applies
- Functional safety: Feedback is how a control system detects that an output did not do what was commanded, for example a welded contactor. Monitoring feedback is a common way to achieve diagnostic coverage in safety-related control systems.
- Integrated systems: Document what the signal measures, its unit, range, update rate and quality status. A feedback value without timestamp or quality information can be outdated without anyone noticing.
- Maintenance: Wear, misalignment and sensor drift degrade feedback gradually. Inspection and calibration intervals must cover the feedback sensors.
Feedback signal vs. command signal
A command signal says what should happen; a feedback signal reports what did happen. Only the comparison of both reveals that an actuator or a process did not follow.