Rice Lake MSI-3460 Challenger 3 - Manual (Page 35)

Calibration 31
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-3460 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-3460 in many capacities.
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-3460 is used on. For example, if the hoist
is rated for 9000 lb. you can use an MSI 10000 lb. MSI 3460 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.
The capacity of all MSI-3460 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-3460 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-3460 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 Legal-for-Trade applications.
Important
The C-Cal number must be known prior to starting this
procedure. For a
MSI-3460 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-3460 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).