A load moment indicator system is the safety system that determines whether a crane can safely lift a given load at a given radius. The HC4900 system covers a specific crane class, and its components are supplied as a matched set rather than as individually interchangeable items.

What the LMI system does

An LMI system measures three inputs: the load in the hook through a load cell, the boom angle through an angle sensor, and the luffing cylinder length through a length sensor. A processing unit then calculates the load moment and compares it against the rated capacity chart for the current boom length and radius. Where the calculated value approaches the limit, the system issues an audible warning and, at the threshold, an automatic cut-out of the motion that would increase the load moment.

The operator sees this as the load reading, the boom angle, the percentage of rated capacity currently used, and the warnings.

Why components must be matched

The three sensors and the processing unit are calibrated as a set. A sensor from a different system, or a processing unit of a different version, may read correctly in isolation but produce an incorrect system calculation. This is the reason a replacement sensor should be confirmed against the system variant rather than ordered as a generic part.

For a crane that has been modified, or where a sensor has previously been replaced with a non-original unit, the system variant should be established from the machine serial number before any component is ordered.

Identifying the correct variant

The system variant is usually identifiable from a label on the processing unit or from the machine parts catalogue against the machine model and serial range. A photograph of the existing system components is often sufficient for identification where the label is no longer legible.

Where the machine build year falls within a production run where the system variant changed, the change point should be established rather than assumed, since this is exactly where an incorrect component is most frequently supplied.

Supply considerations

LMI components are electronic and are sensitive to moisture and impact. Supply should be in sealed, desiccant-protected packaging. It is also worth confirming whether the processing unit can be supplied pre-programmed for the machine, since a unit supplied without vehicle-specific programming will power up but will not function.

TOP RUN supplies HC4900 LMI components and related crane safety electronics for XCMG truck cranes, with more than 12,500 SKUs held in Qingdao. Send the machine model, serial number or a photograph of the system label, and we will confirm the correct variant before dispatch.