Rice Lake MSI-7300 Dyna-Link 2 - Manual (Page 35)

Calibration 31
5.3 Guidelines for Capacity and Resolution
Dyna-Links are subject to forces that static scales do not experience. Many bridge
cranes, hoist cranes, and mobile cranes lack rigidity and tend to bounce or swing
when loads are lifted. For this reason, MSI recommends that resolution is kept in the
1:2000 to 1:3000 range. Some improvement in stability can be achieved by increasing
the filtering. However, you should never program resolution that is far greater than
you need. If the MSI-7300 Dyna-Link 2 display is never stable, it is recommended that
the resolution is reduced as well as filtering increased. In any circumstance, the
resolution should never be set higher than 1:15000 due to temperature and noise
considerations common to all strain gage based load cells.
The tension must be stable for certain features to work: ZERO tension must be stable
to be zeroed. TARE tension must be stable to be tared. TOTAL tension 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-7300 Dyna-
Link 2 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 Dyna-Link if the zero or tare operation happens to capture the tension in a
valley or peak.
Setting capacity is dictated primarily by the capability of the load cell. MSI supplies
the MSI-7300 Dyna-Link 2 in many capacities. Never set the capacity of the Dyna-
Link higher than the rating of the load cell. Due to the excellent linearity of the
MSI Link load cell, it is acceptable to set lower capacities to better match the crane
the MSI-7300 Dyna-Link 2 is used on. For example, if the hoist is rated for 9000lb,
you can use a 10000 lb capacity Dyna-Link and reset the capacity to 9000 lb so that
the Dyna-Link will indicate overload at 9000 lb instead of 100000 lb. Derating as
much as 50% of the capacity is usually acceptable, but the Dyna-Link may be less
stable if the ‘d’ is decreased (resolution increased).
Note
The capacity of all the MSI-7300 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.