STX Signal Transmitter Installation and Operation ... - Kistler-Morse

Chapter 7. MVS-STX Calibration Menu
10. Press the F3 Key to access HiSpan. The
display looks like this:
HI SPAN AUTO CAL
> 9999 lbs
F1 F2 F3
(Units are consistent with Units Menu.)
11. Use the keypad or Arrow Keys to input a
value that represents the quantity of
material added to the vessel. Press the
Enter Key. The display acknowledges the
entry and returns to:
AUTO CAL MENU
LoSpan
HiSpan
F1 F2 F3
12. Press the Esc Key to scroll up the menu
tree or press the Auto/Man Key to return
to channel monitoring.
Calibration by Adding a
Known Quantity of Material
This calibration method does not require the
vessel to be empty. The principle behind the
calibration follows.
A weight estimated to be the quantity of
material in the vessel is entered as the
Lo Span weight [point (1) in Figure 7-3].
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 weight [point (2) in
Figure 7-3]. The MVS saves in memory the
Lo Span and Hi Span weights as well as the
digital counts associated with each weight.
These values define the dashed straight line
and the calculated zero counts shown in
Figure 7-3. 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 weight is incorrect, the actual
‘location’ of the line is incorrect, resulting in
errors in channel 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 7-3] (see Refining the
Calibration by Setting Zero in this section).
The greater the known quantity of material
added during the calibration procedure, the
greater the accuracy of the calibration.
Adding 50% of the total capacity results in
greater accuracy than adding 25% of the
total capacity.
Follow this procedure to calibrate by adding a
known quantity of material:
1. If in Auto Mode (Auto LED illuminated),
press the Auto/Man Key to put the MVS
in Manual Mode. The Auto LED turns off.
2. Use the Arrow Keys to scroll to the
desired channel.
Indicated
Weight
Added or
Subtracted
Known
Quantity
Estimated
Hi Span Weight
(1)
(2)
Scale Factor Weight
Slope =
Scale Factor Counts
Scale Factor Wt = Hi Span Wt - Lo Span Wt
Scale Factor Cnts = Hi Span Cnts - Lo Span Cnts
Estimated
Lo Span
Weight
Corrected Calibration Line,
Same Slope
Calculated
Zero Counts
(3)
Setting
Zero
Lo Span
Counts
Hi Span
Counts
Figure 7-3. Calibration by Adding or Subtracting a Known Quantity of Material
7-3
Weight
Signal
in Counts