Measurement
6.1.3.4 Overall Bandwidth
To get the overall bandwidth we must consider the bandwidth of the analogue filter and the ADC which is 70kHz.
Illustration 187: Overall Bandwidth
6.1.3.5 Anti-Aliasing Filter
Illustration 188 below shows an overview of the different filters and sampling rates in the frequency domain:
The sample rate of Sirius is set to 2kS/s
The analogue aliasing filter is automatically set to 5kHz (since the sampling rate is 2kS/s) and guarantees
aliasing free acquisition
The oversampling factor is automatically set to 256 (because the sampling rate is < 50kS/s) so that the internal
sampling frequency of the Sigma-Delta ADC is 512 kS/s
Finally the digital FIR filter of the ADC is set to 1kHz (half of the sampling rate)
Illustration 188: Sirius® Anti-Aliasing Filter
6.1.4 DEWESoft®: Custom Low Pass Filter Settings
The filtering described in the previous chapters is done in the Sirius® measurement hardware: it assures that the data
that Sirius® passes to the DEWESoft® software is aliasing free. But you must be careful not to introduce aliasing again
in software.
Doc-Version: 1.4.2 www.dewesoft.com Page 135/166
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