Infinite Impulse Response Filter
The digital filter is a so-called infinite impulse response filter (IIR) of fourth order.
Four different filter types can be set:
1. Low pass filter: Sensor signals at low frequency (including DC size with f=0) pass
through the filter, signals at a higher frequency are attenuated.
2. High pass filter: Sensor signals at low frequency (including DC size with f=0) are
attenuated, signals at a higher frequency pass through the filter. Note: Frequencies above
half of the measured data rate cannot be processed. The measuring amplifier includes an
Analog-to-digital sampling system, which in itself acts as a low pass.
3. Band pass filter: Signals are allowed to pass through within a frequency range, signals
which are above or below this range are attenuated.
4. Band stop filter (‘Notch filter’): Signals are attenuated within a frequency range, signals
which are above or below this range are allowed to pass through.
The cutoff frequency can be configured for low and high pass filters. The cutoff frequency
is the frequency at which the signal is already attenuated by -3 dB. This corresponds to a
factor of approx. 0.7. Frequencies lying above for low pass and lying below for high pass
will continue to be attenuated.
Two cutoff frequencies can be configured for band pass and band stop filters; the upper
and the lower. Attenuation by -3 dB also occurs here. The two cutoff frequencies may not
be the same. Signal frequencies lying between these are allowed to pass through for the
band pass filter, and are attenuated for the band stop filter.
The maximum (and also the minimum if need be) of each cutoff frequency is dependent on
the measured data rate. Cutoff frequencies can be set to (0.49 * measured data rate), i.e.
almost to half.
The filters can be individually configured for each channel and also switched on and off.
The configuration also remains the same for filters that have been switched off.
