Kistler-Morse KM Weigh II - Manual (Page 54)

7-4
Chapter 7. Service
Filter
Vibrations in a vessel can cause changes in
the Weigh II’s weight display, even though no
material is moved, because the vibrations
affect the vessel’s structural response.
The Filter function, which is trademarked as
Kistler-Morse’s Sentry™, helps to reduce the
display changes that can result from vibra-
tion. The principle behind the filtering follows.
The ADC converter digitizes the signal
coming from a sensor. The Weigh II picks the
first signal as a reference median; this is the
value that is used in calculating the displayed
weight for vessel monitoring. As shown in
Figure 7-2, the Weigh II then compares
following signals to the reference median, and
recalculates the reference median when
either of the following happen:
• the number of successive signals above or
below the median exceeds a triggering
number
• a signal falls outside of a user-defined
window around the reference median
When the Weigh II recalculates the reference
median, the displayed weight changes to
correspond to the new reference median.
Note that the Filter function affects setpoints,
current output, and serial output as well as
the vessel monitoring display.
Filter has four submenus:
Enabe
Enabe turns the filter function on and off. The
default is Off.
Step
Step is a window of equal counts above and
below the reference median. As shown in
Figure 7-2, example 1, if a large signal
change is detected that falls outside of the
window, the Weigh II immediately moves the
location of the reference median to that point.
This allows the Weigh II to adjust quickly to
rapid material movement in the vessel.
Qlfy
Qlfy is the triggering number of successive
signals above or below the median signal
value, but within the Step window. In example
2 shown in Figure 7-2, Qlfy is 3. When the
third successive signal above the median
value (but within the Step window) is de-
tected, the Weigh II moves the location of the
median value to that point (or a percentage of
the distance from the old median as deter-
mined by DSPfact). This allows the Weigh II
to respond to definite trends in weight
changes.
Figure 7-2. Filter Function Examples
Example 1 — Qlfy=3,
DSPfact=80% (0.80)
Step
Step
Reference
Median
Time
Counts
3rd successive
signal on same
side of median
New median = last signal
Example 2 — Qlfy=3,
DSPfact=80% (0.80)
Signal falls outside of
Step envelope
Counts
Time
New median = ref median
+ 0.8 x (ref median - last signal)
Raw Counts
Corrected
Counts