Glossary · Control theory and process control
Frequency response
Also known as: Frequency characteristic
German: Frequenzgang
In control engineering, the frequency response of a linear system describes how the amplitude and phase of a sinusoidal output relate to a sinusoidal input across frequencies, in steady state.
- Control theory
In one sentence
Frequency response describes how a linear system changes amplitude and phase of sinusoidal signals across frequencies.
Example
A frequency response measurement of a servo axis reveals a mechanical resonance at 380 Hz, so the engineer adds a notch filter to the speed loop.
How it applies
- Engineering: Frequency response analysis reveals bandwidth, resonances and stability margins. It is measured with sine sweeps or noise excitation, or computed from a model of the Controlled system.
- Commissioning: Drive and motion controllers often include a measurement function that records the frequency response of the mechanics. Save these measurements with the machine's commissioning record.
- Documentation: Specify the operating point, excitation amplitude and whether the curve shows open or closed loop. For customers, a bandwidth figure without these conditions is not comparable between products.
Frequency response vs. step response
The step response shows behavior in the time domain (Rise time, Overshoot, Settling time). The frequency response shows the same system in the frequency domain. Both describe one linear system; each makes different properties easier to see.