Digital Filtering; Digflx Parameters; Dfsens And Dfthrh Parameters - Rice Lake CW-90 Technical Manual

CW-90/90X Checkweigher
9.5

Digital Filtering

The CW-90/90X 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.
DFLTR1
4
8
16
32
64
128
256
1
2
DIGFL1= n1
A/D Readings
1st Stage
Filter Average
9.5.1

DIGFLx Parameters

The first three digital filtering parameters, DFLTR1, DFLTRL2, and DFLTR3, 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:
DFLTR1 + DFLTR2 + DFLTR3
Example: if the filters are configured as DFLTR1=4, DFLTR2=8, DFLTR3=8, the overall filtering effect is
20 (4 + 8 + 8). With this 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.
9.5.2

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
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DFLTR2
4
8
16
32
64
128
256
1
2
Figure 9-2. Digital Filtering Parameters on the Configuration (CONFIG) Menu
DIGFL2= n2
n2
n1
1st Stage
Filter Averages
2nd Stage
Filter Average
Figure 9-3. Flow Diagram for CW-90/90X Digital Filters
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DFLTR3 DFSENS
2OUT
4
8 4OUT
8OUT
16
32 16OUT
32OUT
64
64OUT
128
128OUT
256
1
2
DIGFL3= n3
n3
2nd Stage
Filter Averages
3rd Stage
Filter Average
DFTHRH
NONE
2D
5D
10D
20D
50D
100D
200D
250D
Displayed
Value