MSI-4260M Port-A-Weigh Crane Scale
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5.4 Guidelines for Capacity and Resolution
Crane scales are subject to forces that other scales are not subject. Many bridge cranes, hoist cranes and mobile cranes lack
rigidity and tend to bounce or swing when loads are lifted. Rice Lake Weighing Systems recommends the resolution is within
the 1:2000 to 1:3000 range. Stability improvements can be achieved by increasing the filtering. Do not program the resolution to
a value that is greater than needed. If the MSI-4260M display is not stable, it is recommended that the resolution is reduced or
the filtering increased.
Due to Legal for Trade requirements and general scale design criteria, the weight must be stable for certain features to work:
• ZERO – the weight must be stable to be zeroed
• TARE – the weight must be stable to be tared
• TOTAL – the 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-4260M defaults to
±1 d as a motion window. It can be changed at Rice Lake Weighing Systems to a higher value if desired. Often ±3 d 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. Rice Lake Weighing Systems supplies the MSI-4260M in
many capacities.
Never set the capacity of the scale higher than the rating of the load cell. Capacity should always be set to the
capacity listed on the front of the scale. Setting capacity below this may reduce scale accuracy and setting capacity
above this value could expose the scale to loads beyond its design limits.
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-4260M is used on. For example, if the hoist is rated for 3000 lb, use an MSI-4260M and reset the capacity to 3000 lb so
that the scale indicates overload at 3000 lb instead of 5000 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-4260M systems are rated approximately 20% higher than the rated capacity
in pounds. This allows the kg capacity to be exactly one-half the number of the lb capacity.
Note
