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SCAIME Manual : NU-eNod4B-ETH-E-236708-D.docx
7
FILTERS
There are four available filtering levels which can be associated:
Filtering
related to the A/D conversion rate
including rejection of the mains frequency (50 or 60 Hz) harmonics.
Low-pass Bessel filter
Notch filter
Moving average filter
7.1
Filtering related to the A/D conversion rate
The signal resolution is related to the conversion rate. The conversion rate might be chosen as low as possible, particularly
for static applications. For dynamic applications, a compromise must be found between the measurement rate and the low-
pass filter cut-off frequency. The
eNodView
software can be used to determine appropriate filter values. Choose a
measurement rate that rejects the mains frequency harmonics according to the place of use, 50 or 60Hz.
7.2
Bessel low pass filter
A low-pass digital filter can be applied as an output of the A/D converter. The filter orders (available values are 2 or 3) and
cut-off frequency are adjustable.
eNodView
software can be used to determine appropriate filter values.
7.3
Notch filter
A notch filter might be applied as an output of the low-pass filter (if used) or the A/D converter. It allows attenuating the
frequencies within a band defined by high and low cut-off frequencies. The
eNodView
software can be used to determine
appropriate filter values.
7.4
Moving average filter
This filter can be set in cascade after the previous filters. The Moving average filter is used to smooth the weight value in case
of random interferences. This sliding average computes the mean of the ‘n’ last measures from the results of the previous
activated filters. A high filter depth gives a better stability, with a longer response time.
