Glossary · Automation fundamentals, platforms and components
Disturbance variable
Also known as: Disturbance, Load variable
German: Störgröße
In control engineering, a disturbance variable is an external quantity that acts on the controlled system and changes the controlled variable in an unwanted way, and that the controller does not set.
- Automation components
- Standards
In one sentence
A disturbance variable is an external influence that changes the controlled variable in an unwanted way, such as load or ambient temperature.
Example
Opening the oven door lets cold air in; this disturbance lowers the temperature until the controller increases heater power.
How it applies
- Engineering: Feedback control corrects disturbances after they appear. When a disturbance can be measured, Feedforward (control) can counteract it earlier.
- Commissioning: Tuning is checked against typical disturbances, not only setpoint changes.
- Documentation: Control descriptions can list the main disturbances and how the system handles them. Operating instructions should describe operator actions that act as disturbances, such as opening doors or changing material.
- Operation: Trend displays that show disturbance signals next to the controlled variable help operators understand why values change.
Disturbance vs. noise
A disturbance changes the real process. Measurement noise changes only the measured signal, not the process itself. Filtering helps against noise but hides real disturbances if overdone; see Noise suppression.