Notes on digital filter

The critically damped filter is preset at the factory for all GEMAC sensors with an adjustable digital filter (sensors of the Reference-, Classic- and BasicLINE). The reason for this is the universality of this filter. It has a 4 times shorter reaction time or delay than the Butterworth filter (see Fig. left). The Butterworth filter, in turn, has a higher attenuation, even at frequencies that are slightly above the set cut-off frequency.

So when is which filter to use?

Basically, users should first test with the default filter settings, since a shorter response time is usually a major requirement. If the signal response, i. e. the tilt signal, is “too noisy”, then the cut-off frequency should first be reduced until the limit of the reaction time has been reached. The response time of the filter response for the critically attenuated filter in[s] is 1/adjusted cut-off frequency[Hz]. If the response time is not relevant, a cut-off frequency of 0.1 Hz should be tested, which represents the lowest adjustable cut-off frequency.
The Butterworth filter should only be tested and used in applications where no or only slight or rare input shocks are expected and where the sensor does NOT control a loop, as the filter characteristic reacts to input jumps with overshooting in the signal response. The Butterworth filter is especially useful when there are very low-frequency, interfering vibrations in the application. In this case, the much stronger separation between passband and cutoff frequency range is used in a targeted manner.