Ringing (signal)

Overshoot (English overshoot ) means in electrical engineering, signal processing and control theory, that, after a sudden change in an input parameter, an output the desired value is not reached directly, but overshoots the setpoint and only then set to the desired value. The change of an output variable with sudden change in an input variable is also called the step response.

For loops, an overshoot may occur when the setpoint is changed. A thermostat in a space heating system which is often the case, for example, when the desired temperature (set value) of the thermostat of 20 ° C to 25 ° C and adjusted; The controller increases the heat output by so much that short a temperature of eg 27 ° C is reached; then the temperature drops and reaches only later the setpoint 25 ° C. Cause Delay times in the control loop, caused for example by the heat capacity of the heater and the circulating water.

Overshoot can also occur when a disturbance is suddenly changed; during heating control that would, for example, when a window is opened.

Strong overshoot of a controller indicates low stability of the control loop. At lower gain TC is reached asymptotically, there occurs no overshoot, but same end values ​​are reached later.

In electrical engineering and signal processing, the overshoot is an important characteristic of each transfer function and thus of amplifiers, filters, and other facilities for the processing and transmission of signals. The overshoot is measured in practice with square-wave signals. Overshoot occurs when higher frequencies are amplified more than low, especially when resonances in the frequency response.

The overshoot is usually given as a percentage of change in the target value; in the picture above it is about 10% (time Tm). Many oscilloscopes have a measuring function for this overshoot (positive / negative overshoot ).

Another important factor in this context is the settling time; the time after which the output is set within a given deviation. So you refers to the aperiodic component of the signal. In control engineering settling time is it usually given, ie the time after which the output variable within a range of ± 5 % of the step height remains at the value finally reached (see image above: 5 % band ).