Laurel Electronics LTA DPM SERIES ANALOG INPUT - Manual (Page 25)

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16. INPUT SIGNAL FILTERING
A moving average filter is selectable in software to process the internal digital readings, which
are taken at 60/sec with 60 Hz power and 50/sec with 50 Hz power. Eight moving average
settings are selectable with the following equivalent RC time constants: 0.08 sec, 0.15 sec, 0.3
sec, 0.6 sec, 1.2 sec, 2.4 sec, 4.8 sec, 9.6 sec. The longer time constants provide superior
noise filtering at the expense of fast response time.
Adaptive moving average filtering allows the transmitter to respond rapidly to actual changes
in signal while filtering out normal noise. An adaptive filter threshold causes the moving
average filter to be reset to the latest reading when the accumulated difference between
individual readings and the filtered reading exceeds that threshold. The accumulated difference
is also reset to zero when the latest reading has a different polarity than the filtered reading. The
adaptive filter threshold can be selected as low or high. Low is normally selected. High should
be selected if the signal has large transients.