Rice Lake 120 Digital Weight Indicator - Manual (Page 38)

34 120 Installation Manual
7.6 Digital Filtering
The 120 uses averaged digital filtering to reduce the
effect of vibration on weight readings. Adjustable
threshold and sensitivity functions allow quick
settling by suspending filter averaging, allowing the
weight reading to jump to the new value. Digital
filtering parameters are set using the CONFIG menu.
7.6.1 DIGFLx Parameters
The first three digital filtering parameters, DIGFL1,
DIGFL2, and DIGFL3, are configurable filter 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 filter stage before averaging.
The overall filtering effect can be expressed by adding
the values assigned to the three filter stages:
DIGFL1 + DIGFL2 + DIGFL3
F o r e x a m p l e , i f t h e f i l te r s a r e c o n f i g u r e d a s
DIGFL1=4, DIGFL2=8, DIGFL3=8, the overall
f i l t e r i n g e f f e c t i s 2 0 ( 4 + 8 + 8 ) . Wi t h t h i s
configuration, each A/D reading has a 1-in-20 effect
on the displayed weight value. Setting the filters to 1
effectively disables digital filtering.
7.6.2 DFSENS and DFTHRH Parameters
The three digital filters can be used by themselves to
eliminate vibration effects, but heavy filtering also
increases settling time. The DFSENS (digital filter
sensitivity) and DFTHRH (digital filter threshold)
parameters can be used to temporarily override filter
averaging and improve settling time:
• DFSENS specifies the number of consecutive
scale readings that must fall outside the filter
threshold (DFTHRH) before digital filtering
is suspended.
• DFTHRH sets a threshold value, in display
divisions. When a specified number of
consecutive scale readings (DFSENS) fall
outside of this threshold, digital filtering is
suspended. Set DFTHRH to NONE to turn off
the filter override.
7.6.3 Setting the Digital Filter Parameters
Fine-tuning the digital filter parameters greatly
improves indicator performance in heavy-vibration
environments. Use the following procedure to
determine vibration effects on the scale and optimize
the digital filtering configuration.
1. In setup mode, set all three digital filters
(DIGFL1, DIGFL2, DIGFL3) to 1. Set
DFTHRH to NONE. Return indicator to
normal mode.
2. Remove all weight from the scale, then watch
t h e i n d i c a t o r d i s p l a y t o d e t e r m i n e t h e
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
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
digital filters (DIGFLx) to eliminate the
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 a v e
DFTHRH set to NONE.) Reconfigure as
necessary to find the lowest effective values
for the DIGFLx parameters.
4. With optimum values assigned to the DIGFLx
parameters, calculate the DFTHRH parameter
value by converting the weight value recorded
in Step 2 to display divisions:
threshold_weight_value / DSPDIV
In the example in Step 2, with a threshold
weight value of 50 lb and a display division
value of 5lb:
50 / 5lb = 10DD. DFTHRH
should be set to 10DD 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.
Reconfigure as necessary to find the lowest
effective value for the DFSENS parameter.