Load Moment Indicators and Safety Devices Flashcards

What is a crane management system (CMS) and how does it integrate multiple safety devices?

Answer: A crane management system is an integrated electronic platform that combines LMI, RCL, ATB, boom angle and length sensors, anemometer, and other inputs into a single computer system that monitors all parameters simultaneously and coordinates safety interventions

Modern crane management systems integrate all sensors and safety devices into a central computer that monitors all parameters, calculates capacity, and coordinates automatic safety interventions — providing more comprehensive protection than individual standalone devices.

What is a radius derating factor in the context of LMI systems, and when would it be applied?

Answer: A radius derating factor is applied when the load chart does not provide capacity values for the actual working radius, requiring interpolation between two chart values with a conservative reduction applied

When operating at a radius between two load chart values, some LMI systems apply a derating factor to the interpolated value to ensure the conservative capacity is used. This accounts for measurement uncertainty and interpolation inaccuracy.

How does a load cell integrated into a crane's hoist line measure the actual load?

Answer: The load cell is typically installed in the headache ball, hook block, or at the dead end of the hoist wire rope and measures the tension in the wire rope using strain gauges that convert mechanical deformation to an electrical signal proportional to load

Crane load cells use strain gauge technology: the cell deforms under the rope tension, and precision strain gauges measure this deformation and output a voltage signal proportional to the applied load for the LMI system.

What is the overload protection system requirement under ASME B30.5, and how does it function on a hydraulic crane?

Answer: ASME B30.5 requires an overload protection device that automatically prevents lifting loads exceeding the rated capacity. On hydraulic cranes, this often uses a relief valve in the hoist circuit that limits maximum hydraulic pressure (and therefore maximum hoist force)

ASME B30.5 requires overload protection. On hydraulic cranes, a hydraulic relief valve in the hoist circuit limits maximum hoist pressure, preventing the crane from applying force that would exceed the structural rated capacity of the hoist system.

What does the bypass mode or override mode of an LMI system refer to, and under what controlled circumstances may it be used?

Answer: Bypass or override mode disables the LMI's automatic motion cutout, used only in specific controlled circumstances such as lowering a load that was inadvertently hoisted into an overload condition — requires authorized personnel and must be documented

Bypass or override mode disables the automatic cutout function for controlled recovery from specific situations. It is never to be used for production lifting — only for controlled load lowering in emergency situations, with authorized supervision and documentation.

What does the term two-speed hoist mean and how do safety device considerations differ between low-speed and high-speed hoist operation?

Answer: A two-speed hoist has a high-speed mode for faster load movement at lighter loads and a low-speed mode for heavier loads and precision work. The rated capacity is typically lower in high-speed mode, and the LMI and overload protection settings may differ between speeds

Two-speed hoists have different mechanical advantages at different speeds — high speed typically means reduced force capacity, so the rated capacity (and corresponding LMI settings) may be lower in high-speed mode than low-speed mode.