Overshoot
Overshoot (engl. Overshoot in) represents electrical , signal processing and control engineering that, after an abrupt change in an input, an output is not directly reaches the desired value, but overshoots the setpoint and only then is adjusted to the desired value. The change in an output variable when there is a sudden change in an input variable is also referred to as a step response .
In control loops , overshoot can occur if the setpoint is changed. This occurs, for example, with room heating, when the desired temperature (setpoint) on the radiator thermostat is increased from 20 ° C to 25 ° C; the controller increases the heating output so much that a temperature of, for example, 27 ° C is briefly reached; then the temperature drops again and only later reaches the setpoint 25 ° C. The cause is delay times in the control loop, which are caused, for example, by the heat capacity of the radiator and the circulating water.
Overshoot can also occur if a disturbance variable is suddenly changed; In the case of heating control , for example, this would be when a window is opened.
Strong overshoot of a controller indicates poor stability of the control loop. If the gain is lower, the end value is reached asymptotically, there is no overshoot, but the same end values are reached later.
In electrical engineering and signal processing, overshoot is an important characteristic of every transfer function and thus of amplifiers , filters and other devices for processing and transferring signals . The overshoot is measured in practice with square-wave signals. Overshoot occurs when higher frequencies are amplified more than lower ones, especially when there are resonances in the frequency response .
The overshoot is usually given as a percentage of the change in the setpoint; in the picture above it is about 10% (time T m ).
Many oscilloscopes have a measurement function for this overshoot ( positive / negative overshoot ).
Another important variable in this context is the settling time - the time from which the output variable has set itself within a certain deviation. It therefore relates to the aperiodic component of the signal. In control engineering, settling time is usually specified for this , i.e. the time after which the output variable remains within a range of ± 5% of the jump height around the final value (see figure above: 5% band).
literature
- Holger Lutz, Wolfgang Wendt: Pocket book of control engineering with MATLAB and Simulink. 11th edition. Verlag Europa-Lehrmittel, 2019, ISBN = 978-3-8085-5869-0.
- Otto Föllinger : Control engineering. Hüthig Verlag, ISBN 3-778-52336-8 .