Rice Lake CLS-920i Cargo Lift Scale Installation Manual - Manual (Page 89)

CLS-920i Installation Manual 86
10.7 Digital Filtering
Standard digital filtering uses mathematical averaging to eliminate the variant digital readings that the A/D
converter sends periodically because of external vibration. Digital filtering does not affect the indicator
measurement rate, but does affect the settling time. The selections from 1 to 256 reflect 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.
DIGFLTx Parameters
The first three digital filtering parameters, DIGFLT1, DIGFLT2, and DIGFLT3, 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.
A rolling average is passed to successive filters for an overall filtering effect that is effectively a weighted average
of the product of the values assigned to the filter stages (
DIGFLT1 x DIGFLT2 x DIGFLT3) within a time frame
corresponding to the sum of the values ( DIGFLT1 + DIGFLT2 + DIGFLT3) .
Setting the filters to 1 effectively disables digital filtering.
RATTLETRAP ® Filtering
RATTLETRAP digital filtering (RATTRAP parameter set ON) uses a vibration-dampening algorithm to provide a
combination of the best features of analog and digital filtering. 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 flaws. It is particularly effective for eliminating vibration effects or mechanical
interference from nearby machinery. Using RATTLETRAP filtering can eliminate much more mechanical
vibration than standard digital filtering, but will usually increase settling time over standard digital filtering.
DFSENS and DFTHRH Parameters
The digital filter can be used by itself 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.
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 the digital filter parameters (DIGFLT1–DIGFLT3) 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 DIGFLTx parameters to eliminate the vibration effects on the
scale. (Leave 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.
Reconfigure as necessary to find the lowest effective value for the DFSENS parameter.