Lastgröße

Lastgröße is a term used in German engineering and physics to denote a quantity that represents the external influence or load acting on a system. In modeling and control theory, it describes the input or forcing function that drives the dynamic behavior of a plant. The concept is closely related to other variables such as the Regelgröße (controlled variable or setpoint), Messgröße (measured value), and Störgröße (disturbance). While terminology can vary, Lastgröße generally refers to the external input that must be considered when predicting or regulating system response.

In control engineering, the Lastgröße is the quantity that directly excites the system dynamics. Examples include the voltage applied to an electric motor, the force acting on a mechanical spring-damper, or the heat input to a thermal process. It can be a commanded signal (known input) or an external influence that is not fully controllable (disturbance). In state-space models, the Lastgröße often appears as part of the input vector that governs state evolution.

Modeling approaches treat the Lastgröße as a time-dependent function, u(t), which can be deterministic or stochastic. Depending on the application, engineers may seek to estimate, constrain, or compensate for the Lastgröße to achieve desired performance, robustness, or energy efficiency.

Contexts vary by discipline, and some authors may prefer terms like input or disturbance for similar concepts. Understanding the Lastgröße helps in designing controllers, performing system identification, and analyzing how external loading shapes system behavior. See also: input, disturbance, Regelgröße, Messgröße, state-space model.