Kistler-Morse KM Weigh II - Manual (Page 41)

Chapter 6. Calibration
6-3
Calibration by Adding a
Known Quantity of Material
This method provides calibration that is
accurate enough for most applications
and does not require the vessel to be com-
pletely empty. The principle behind the
calibration follows.
A value estimated to be the quantity of
material in the vessel is entered as the Lo
Span value [point (1) in Figure 6-3]. A known
quantity of material, representing at least
25% of the vessel’s total capacity, is added
to the vessel. The sum of the known quantity
plus the estimated quantity is entered as the
Hi Span value [point (2) in Figure 6-3]. The
Weigh II saves in memory the Lo and Hi Span
weights as well as the digital counts associ-
ated with each weight. These values define
the dashed straight line and the calculated
zero weight shown in Figure 6-3. The slope of
the line is called the Scale Factor, which is
calculated internally.
The slope of the line is reasonably accurate,
because it is calculated based on the known
difference between the Lo Span and Hi Span
weights and counts. However, if the estimated
Lo Span value is incorrect, the actual “loca-
tion” of the line is incorrect, resulting in errors
in vessel monitoring. The greater the error in
the estimated Lo Span, the greater the
resulting error. The “location” of the line can
be adjusted to the solid line by setting zero
[point (3) in Figure 6-3] (see Refining the
Calibration by Setting Zero in this section).
9. Add a known quantity of material, repre-
senting at least 25% of the vessel’s total
capacity, to the vessel.
10. Press the F3 Key to access HiSpan.
The display looks like this:
The unit of measure you set up in the
Units Menu shows in place of lbs.
11. Use the keypad or the Up and Down
Arrow Keys to input a value that repre-
sents the quantity of material added to the
vessel. Press the Enter Key to save the
value in memory. Hi Span is now set [point
(2) in Figure 6-2]. The display flashes a
message acknowledging your entry and
returns to:
The Weigh II is now calibrated to the
highest accuracy for the selected vessel.
12. Press the Esc Key to go up the
menu tree or press the Auto/Man Key to
return the display to vessel monitoring.
HI SPAN AUTO CAL
> X lbs
F1 F2 F3
AUTO CAL MENU
LoSpan HiSpan
F1 F2 F3
Figure 6-3. Calibration by Adding or Subtracting a Known Quantity of Material
Indicated
Weight
Weight
Signal
in Counts
Estimated
Lo Span
Weight
(3)
(1)
(2)
Estimated
Hi Span
Weight
Added or
Subtracted
Known
Quantity
Setting
Zero
Weight
Corrected Calibration
Line, Same Slope
Calculated
Zero
Weight
Scale Factor Wt = Hi Span Wt - Lo Span Wt
Scale Factor Cnts = Hi Span Cnts - Lo Span Cnts
Slope =
Scale Factor Weight
Scale Factor Counts
Lo Span
Counts Hi Span
Counts