Kistler-Morse KM Weigh II - Manual (Page 55)

Chapter 7. Service
7-5
DSPfact
DSPfact determines the magnitude of change
from the old reference median to the new
reference median, for change triggered by the
Qlfy parameter. In example 2 in Figure 7-2,
the Weigh II moves the reference median
80% of the distance from the old median to
the last signal (which triggered the change),
based on a DSPfact of 80%. A value of 100%
sets the new median to the last signal value;
a value of 50% sets the new median halfway
between the old median and the last signal
value. Note that DSPfact does not affect the
change caused by a signal falling outside of
the Step window, as shown in example 1 in
Figure 7-2.
Trk
Tracking provides the ability to reject sensor
drift and other related long-term errors while
preserving the displayed weight’s stability and
accuracy. Discrimination between material
movement and sensor drift is accomplished
by calculating the rate of change of the
sensor input signal every ten seconds, and
comparing this rate to a user-defined
threshhold rate. The Weigh II stops tracking
when the rate of change exceeds the
threshhold rate, indicating that material is
actually moving. Additionally, discrimination
between slow material loss (such as from a
leak in the vessel) or gain and sensor drift is
accomplished by comparing the total drift to a
user-defined limit. The Weigh II limits the
maximum correction to this user-defined limit,
so that the tracking function does not mask
real material losses or gains. There are two
aspects to the Weigh II’s tracking function:
zero tracking and material tracking.
Zero tracking establishes a user-defined
window around the voltage associated with
zero live load, as shown in Figure 7-3. When
the raw voltage falls inside of the window
(usually indicating a negligible amount of
material in the vessel) and the rate of change
is below the threshhold rate, the corrected
voltage and counts remain constant as those
associated with zero live load, and the
displayed weight remains at zero. The
correction is done by the algebraic addition of
a correction offset value to the output of the
A/D converter. If the raw voltage falls outside
the window on the negative side, the Weigh II
resets the zero calibration point to that raw
voltage, and sets the window around the new
zero calibration point. Unlike the Zclmp
function (see Chapter 4, Display), zero
tracking affects setpoints, current output, and
serial output as well as the vessel monitoring
display.
Figure 7-3. Zero Tracking Function Example — Rate of Change Less than Rate Threshhold, and
Material Tracking Off
Zero
live load
voltage
Win
Win
Time
mV
Corrected Voltage
Raw Voltage
New zero live
load voltage
Win
Win