MSI 4260B, Operator'S Manual, Page: 40 / 64

36 MSI-4260 Port-A-Weigh Operator’s Manual
Due to LFT requirements and general scale design criteria, the weight must be stable
for certain features to work: ZERO – Weight must be stable to be Zeroed. TARE –
Weight must be stable to be Tared. TOTAL – Weight must be stable to be added to the
total registers. One way to improve the stability is to increase the filtering, at the risk
of increasing settling time. The other is to increase the ‘d’ (reduce resolution). The
third way is to increase the “Motion Window”. The
MSI-4260
defaults to ±1d as a
motion window. It can be changed at MSI to a higher value if desired. Often ±3d is
chosen for bridge cranes as these tend to have a lot of bounce to them. This of course
carries an accuracy penalty adding ±3 d to the total accuracy of the scale if the zero or
tare operation happens to capture the weight in a valley or peak.
Setting capacity is dictated primarily by the capability of the load cell. MSI supplies
the
MSI-4260
in many capacities.
Note
Never set the capacity of the scale higher than the rating of the load cell.
Due to excellent linearity of the MSI S-Beam load cell, it is acceptable to set lower
capacities to better match the crane the
MSI-4260
is used on. For example, if the hoist
is rated for 9000 lb, you can use an MSI 10000 lb
MSI 4260
and reset the capacity to
9000 lb so that the Scale will indicate overload at 9000 lb instead of 10000 lb.
Derating as much as 50% of the capacity is usually acceptable, but the scale may be
less stable if the ‘d’ is decreased.
Due to kg to lb conversions, the capacity of all
MSI-4260
systems is rated
approximately 20% higher than the rated capacity in pounds. This is to allow the kg
capacity to be exactly 1/2 the number of the pounds capacity.
5.3 C-Cal Calibration
When adequate test weights are not available, the
MSI-4260
can be calibrated using a
programmed constant calibration which is referred to as C-Cal. To use C-Cal, a C-Cal
number must be known from a previous calibration. MSI supplies replacement load
cells for the
MSI-4260
with the C-Cal value stamped on the serial number label.
When a calibration is performed with test weights, a new C-Cal is generated. C-Cal
can be used when the electronics are replaced to get an approximate calibration that
may be suitable for non L-F-T applications.
Important
The C-Cal number must be known prior to starting this
procedure. For a
MSI-4260
with its original Load Cell, MSI prints
this number on the Calibration Record, the Serial number tag,
and on the calibration log found inside the battery compartment.
C-Calibration reduces slightly the absolute accuracy of the system if the electronics
are replaced or a new load cell is installed, and is intended for non-critical use only.
Legal-for-Trade installations require that the
MSI-4260
is calibrated using test
weights. If a system was originally multi-point calibrated, the C-CAL calibration will
erase the additional span points, as C-Cal is only a two point calibration (Zero and
Span at 10% of capacity).