Rice Lake 420 Plus HMI Digital Weight Indicator Installation Manual - Manual (Page 53)

420 Plus Installation Manual - Appendix 49
7.7 Digital Filtering
The
420 Plus
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. Figure 7-3 shows the digital filter parameters on the CONFIG menu.
1
4
2
8
DIGFL1
32
16
64
1
4
2
8
DIGFL2
32
16
64
1
4
2
8
DIGFL3
32
16
64
8OUT
32OUT
16OUT
64OUT
DFSENS DFTHRH
2OUT
128OUT
4OUT
2DD
NONE
5DD
20DD
10DD
50DD
200DD
100DD
250DD
Figure 7-3. Digital Filtering Parameters on the Configuration (CONFIG) Menu
DIGFL1= n1 DIGFL2= n2 DIGFL3= n3
3rd Stage
Filter A verage
2nd Stage
Filter A verage
1st Stage
Filter A verage
Displayed
Value
n3
2nd Stage
Filter A verages
n2
1st Stage
Filter A verages
n1
A/D Readings
Figure 7-4. Flow Diagram for 420 Plus Digital Filters
7.7.1 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 (see
Figure 7-4).
The overall filtering effect can be expressed by adding
the values assigned to the three filter stages:
DIGFL1 + DIGFL2 + DIGFL3
For example, if the filters are configured as
DIGFL1=4, DIGFL2=8, DIGFL3=8, the overall
f i l t e r i n g e ff 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.
7.7.2 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.