Rice Lake 880 Performance Series Indicator/Controller Technical/Service Manual - Manual (Page 113)

Appendix 107
10.10 Digital Filtering
Digital filtering can be used to create a stable scale reading in challenging environments. The 880 has two filtering
methods that can be set; Sample rate and Digital filter.
10.10.1 Sample Rate:
The Sample rate should be set first. Better stability is achieved with a lower sample rate setting, so 7.5 Hz is more
stable than 960 Hz.
10.10.2 Digital Filter:
The digital filter is an adaptive filter that has two parameters to set the filter settling and response times: sensitivity
and threshold.
With the digital zero threshold set at zero, determine the amount of instability that is present. Convert this
instability to display divisions. The number of display divisions of instability will be used to set the threshold of the
digital filter. The digital filter can be set to
OFF
by entering 0 in the
DFTHRH
parameter.
Digital Filtering Sensitivity
Digital filtering sensitivity (
DFSENS
) controls the stability and settling time of the scale. The sensitivity parameter
can be set to heavy, medium, or light. A heavy setting will result in an output that is more stable and will settle
more slowly than that of light. However, small changes in weight data (a few grads) on the scale base will not be
seen as quickly.
If the difference in typical subsequent weight values on the scale will be only a few grads, use a light setting. If
using a truck scale where the changes in subsequent weight values will be 100s of grads, a heavy setting will be
more appropriate.
Digital Filtering Threshold
Digital filtering threshold (
DFTHRH
) should be set for the amount of observed noise in the system. This parameter
can be set in the range of 0 to 99999 display divisions. When a new sampled weight value is acquired, the adaptive
filter compares the new value to the previous (filtered) output value. If the difference between the new value and
the previous output value is greater than the
DFTHRH
parameter (displayed division) the adaptive filter output is
reset. The newly acquired sample value replaces the filtered output. If the difference between the new value and the
previous output value is less than the
DFTHRH
parameter, the two values are averaged together using a weighted
average. The weighed average is based on the amount of the difference, time the system has been stable, and
selected
DFSENS
value.