Which Crane System Should I Choose?
In today’s crane market the term LMI is commonly used. However, many users may not understand the difference between the various technologies and terminologies used in the market place. To find the best solution for your needs, it is helpful to know the different system options available.
Which system type is best for your application?
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Load Moment Indicator - LMI Rated Capacity Indicator - RCI Load Indicator
Load Moment Indicator - LMI
For hydraulic cranes, the LMI reads its load value using a pair of pressure transducers, which read the cylinder pressures of the lift cylinders. An advantage of an LMI is the weight of the boom is calculated as a part of the load calculation. In doing so, the system will calculate the effects of elements such as wind and ice on available lifting capacity. The system has a digital version of the load chart programmed into it.
The down side to an LMI is that on calibration the system is calibrated using the empty boom weight of all boom configuration and loaded boom weight for all boom configurations. This can be costlier when repairs or system replacement is required. The cable reel monitors the boom length, and typically there is an angle sensor integrated into the cable reel. Length X Angle = Radius. So, the cable reel serves as the tool to calculate radius.
On lattice boom cranes, a load moment system would see load cells placed in the pendent lines, again weighing the boom as a part of the load calibration. The down side to a lattice moment system is the high cost to calibrate the empty and loaded boom configurations.
Rayco-Wylie i4500 LMI System
Rated Capacity Indicator - RCI
On a Rated Capacity Indicator, the load weight value is calculated by reading the strain on the wire rope. This is done by using a load pin in a sheave, a running line tensiometer (linerider) or a dead-end load cell installed at the becket end. A digital load chart is also available to show load capacity.
Calibration is simpler on an RCI as it removes the step of empty/loaded boom weight calibration for all boom configurations, as seen in an LMI. Calibration is done to train the load sensing device as to the strain on the wire rope. A cable reel with angle sensor is used as it is on the LMI to calculate radius.
On a lattice boom crane, the RCI installation is much simpler and less costly from a calibration perspective as compared to a load moment system. A lattice boom RCI uses a strain gauge load sensor and an angle sensor for radius calibration.
Rayco-Wylie i4301 RCI System
Load Indicator - LI
This is the simplest form of load monitoring. Here, a strain gauge device is used to read the wire rope tension producing a load value. The load sensing device can be installed in line to the crane rigging or can be placed under hook.
Users can also choose an LALR configuration. Load, Angle, Length, Radius configurations do not have the digital load chart programmed into the display. Many old school fleet managers and owners like this configuration as it forces the operator to manually read the load chart to ensure what they can safely pick.
OSHA mandates as a minimum that a load indicator be installed on new cranes over 3-ton capacity. Moreover, you see an LMI or RCI coming as standard on new factory cranes.
Rayco-Wylie i4000 Load Indicator System