Rice Lake 920i Installation Manual V2.0 - Manual (Page 110)

106 920i Installation Manual
10.9 Digital Filtering
Standard digital Þltering uses mathematical averaging
to eliminate the variant digital readings that the A/D
converter sends periodically because of external
vibration. Digital Þltering does not affect the indicator
measurement rate, but does affect the settling time.
The selections from 1 to 256 reßect the number of
readings averaged per update period. When a reading
is encountered that is outside a predetermined band,
the averaging is overridden, and the display jumps
directly to the new value.
DIGFL x Parameters
The Þrst three digital Þltering parameters, DIGFLT1,
DIGFLT2, and DIGFLT3, are conÞgurable Þlter
stages that control the effect of a single A/D reading
on the displayed weight. The value assigned to each
parameter sets the number of readings received from
the preceding Þlter stage before averaging.
The overall Þltering effect can be expressed by adding
the values assigned to the Þlter stages:
DIGFLT1 + DIGFLT2 + DIGFLT3
For example, if the Þlters are conÞgured as
DIGFLT1=16, DIGFLT2=4, and DIGFLT3=4, the
overall Þltering effect is 24 (16 + 4 + 4). With this
conÞguration, each A/D reading has a 1-in-24 effect
on the displayed weight value. Setting the Þlters to 1
effectively disables digital Þltering.
RATTLETRAP ® Filtering
RATTLETRAP digital Þltering (RATTRAP parameter
set ON) uses a vibration-dampening algorithm to
provide a combination of the best features of analog
and digital Þltering. The RATTLETRAP algorithm
evaluates the frequency of a repeating vibration then
derives a composite displayed weight equal to the
actual weight on the scale less the vibration-induced
ßaws. It is particularly effective for eliminating
vibration effects or mechanical interference from
nearby machinery. Using RATTLETRAP Þltering can
eliminate much more mechanical vibration than
standard digital Þltering, but will usually increase
settling time over standard digital Þltering.
DFSENS and DFTHRH Parameters
The digital Þlter can be used by itself to eliminate
vibration effects, but heavy Þltering also increases
settling time. The DFSENS (digital Þlter sensitivity)
and DFTHRH (digital Þlter threshold) parameters can
be used to temporarily override Þlter averaging and
improve settling time:
¥ DFSENS speciÞes the number of consecutive
scale readings that must fall outside the Þlter
threshold (DFTHRH) before digital Þltering
is suspended.
¥ DFTHRH sets a threshold value, in display
divisions. When a speciÞed number of
consecutive scale readings (DFSENS) fall
outside of this threshold, digital Þltering is
suspended. Set DFTHRH to NONE to turn off
the Þlter override.
Setting the Digital Filter Parameters
Fine-tuning the digital Þlter parameters greatly
improves indicator performance in heavy-vibration
environments. Use the following procedure to
determine vibration effects on the scale and optimize
the digital Þltering conÞguration.
1. In setup mode, set the digital Þlter parameters
(DIGFLT1ÐDIGFLT3) to 1. Set DFTHRH to
NONE. Return indicator to normal mode.
2. Remove all weight from the scale, then watch
the indicator display to determine the
magnitude of vibration effects on the scale.
Record the weight below which all but a few
readings fall. This value is used to calculate
the DFTHRH parameter value in Step 4.
For example, if a heavy-capacity scale (10000
x 5 lb) produces vibration-related readings of
up to 50 lb, with occasional spikes to 75 lb,
record 50 lb as the threshold weight value.
3. Place the indicator in setup mode and set the
D I G F LT x p a r a m e t e r s t o e l i m i n a t e t h e
v i b r a t i o n e ff e c t s o n t h e s c a l e . ( L e ave
DFTHRH set to NONE.) Find the lowest
effective value for the DIGFLTx parameters.
4. Calculate the DFTHRH parameter value by
converting the weight value recorded in Step
2 to display divisions:
threshold_weight_value / display_divisions
In the example in Step 2, with a threshold
weight value of 50 lb and a display divisions
value of 5 lb:
50 / 5 = 10. DFTHRH should be
set to 10D for this example.
5. Finally, set the DFSENS parameter high
enough to ignore transient peaks. Longer
transients (typically caused by lower vibration
frequencies) will cause more consecutive
out-of-band readings, so DFSENS should be
set higher to counter low frequency transients.
ReconÞgure as necessary to Þnd the lowest
effective value for the DFSENS parameter.