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7.6
Adaptive Filtering
The CCD100 includes an adaptive averaging filter on the display and comms readings
output to aid in ‘smoothing out’ unwanted ‘noise’ on the displayed readings.
(a)
Operational band
The filter can be configured to only operate within a certain band, meaning that
excursions between subsequent readings that fall outside that band are shown as
real (and not filtered) readings. The band is configurable between 0.01% and 1.00%
of the full scale range of the input channel. It can also be set to OFF, which means
that no filtering is performed (i.e. every reading is a ‘real’ one) and can also be set to
ON which means that filtering is always shown no matter how big of an excursion
occurs.
(b)
Filter size
The size of the filter is currently configurable between 0 and 6 seconds and simply
indicates the amount of readings that are taken and buffered to calculate and show
the averaged reading. A filter size of 0 will naturally turn of the filtering, irrespective
of the band setting.
It should be noted that this type of adaptive filtering can cause readings to be displayed
abnormally, particularly if the buffer size is one of the larger available settings, where the
displayed readings seem to ‘jump about’ as the filter is disabled and then re-enabled when
the data excursions fall into the pre-set band. This is because outside of the band, the
display will show the ‘real’ unfiltered readings (whilst constantly taking an average in the
background). When the excursions fall into the band then the display will switch to
showing the filtered data. If this data is quite significantly slugged (due to a large buffer
size) then the display will appear to nearly reach the new data value (due to ‘real’ values
being shown) and then jump back to the filtered data which could be several seconds
behind. Because of this, the setting of a buffer size greater than 5 seconds will
automatically change the band to ON, meaning that filtered data will always be shown.
Selecting different filter band/size combinations will reduce these anomalies, turning the
band OFF and ON will stop this anomaly.
