Glossary · Control theory and process control
Control error
Also known as: Control deviation, Error signal
German: Regeldifferenz
In control engineering, the control error is the difference between the setpoint (reference variable) and the measured value of the controlled variable, which the controller uses to compute its output.
- Control theory
In one sentence
The control error is the difference between setpoint and measured value that a controller acts on to bring the process back on target.
Example
With a setpoint of 80 °C and a measured tank temperature of 76 °C, the control error is 4 K and the heating controller increases its output.
How it applies
- Engineering: Sign conventions matter. Some controllers compute setpoint minus measurement, others the reverse, combined with a direct or reverse action setting. A wrong sign turns negative feedback into positive feedback.
- Operation: A persistent control error is a symptom: an undersized actuator, a saturated output, a sensor fault or wrong tuning. Deviation alarms on large or long-lasting errors help operators spot it.
- Documentation: Define the term once and use it consistently; German sources distinguish Regeldifferenz (error) from Regelabweichung (deviation, with opposite sign in older DIN usage), which can confuse translations. State the sign convention in the control description.
Control error vs. control deviation
In many English texts the two are used as synonyms. Where a standard or company style distinguishes them by sign, follow that definition and note it in the terminology database.