Crane Warning Systems
Crane Safety Systems FAQ
What is the difference between a load indicator and an LMI (Load Moment Indicator)?
These are the three most misused and confused terms in the crane indicator business. A crane load indicator is a cab mounted display connected to various types of load sensors that show the crane operator the weight they are lifting. The load indicator can have other options to monitor more additional information such and anti-two-block, boom angle, length, and radius, but it does not monitor the crane's capacity. So it does not have the crane's load chart programmed into memory and does not calculate the safe working load or warn of an overload unless the operator has manually set a load limit.
What is the difference between an RCI and LMI?
The difference is in how the force/weight is measured. An RCI or rated capacity indicator uses load sensors that measure the force directly on the hoist line. For example, a dynamometer, also known as a "line rider" uses a load pin in a sheave that the hoist line exerts a force on. The pin then outputs an electronic signal, which can be translated into the weight reading.
The LMI or load moment indicator uses sensors that measure the force on the boom, not directly on the hoist line to calculate the weight being lifted. An LMI can use load pins that measure the force on the pendant line on a lattice boom crane or pressure transducers that measure the rod and bore side pressure of a boom lift cylinder.
What crane indicator do I need for my crane?
A crane load indicator will be less expensive than a load moment indicator (LMI) or rated capacity indicator (RCI), but it also provides much less information. Knowing the weight, you are lifting is critical for working safely and keeping your crane from being overloaded, so a load indicator is helpful for that. However, a load indicator still leaves it up to the crane operator to know how much they can lift at each change in their boom angle or radius. The LMI and RCI calculate all that for the operator and show it to them in real-time with the actual numbers and easy to read bar graphic that is green when you are under capacity, yellow as you get near the limit, then red at overload.
What is an anti two block warning system?
The anti-two-block warning system or indicator is also known as an A2B or ATB indicator for short. This is the minimum crane safety indicator all cranes should have. It warns the operator when the hook block is getting too close to the boom tip. A2B warning systems come in wireless and wired versions. The only difference is one requires a cable to connect from the display to the A2B switch at the boom tip and the other uses a wireless transmission for the connection.