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The Key Principles and Applications of Crane Load Moment Indicators (LMI)

Crane Load Moment Indicators

A crane load moment indicator (LMI) is a safety device that measures and displays the load moment on a crane. The load moment is a measure of the force that the load is exerting on the crane. The LMI uses sensors to measure the weight of the load, the length of the boom, and the angle of the boom. The LMI then calculates the load moment and displays it on a display unit.

In this blog post, we will elaborate on the key principles and applications of crane load moment indicators (LMIs).

Key Principles of Load Moment Indicators (LMIs)

The LMI is an important safety device because it helps to prevent the overloading of the crane. If the load moment exceeds the crane's rated capacity, the LMI will sound an alarm to warn the operator and/or shut down the crane.

A Load Moment Indicator (LMI) is a device used on a crane to monitor the lift and alert the operator if the lift exceeds the safe operating capacity of the crane. The LMI achieves this by using various sensors to monitor the load and boom angle and a computer to calculate the crane's load moment, which is the product of the load's weight and its distance from the crane's center of rotation.

The load moment is then compared to the crane's rated capacity, which is typically determined by the maximum load the crane can lift in a given configuration (including boom angle and length) without tipping over.

Applications of Load Moment Indicators (LMIs)

Load Moment Indicators (LMIs) are used in various applications in the crane industry to improve safety and prevent accidents. Some of the common applications of LMI systems include:

  • Monitoring the load on a crane to ensure it stays within its rated capacity limits

  • Preventing overloading of the crane and avoiding the risk of the crane tipping over

  • Providing real-time feedback to the crane operator about the crane's load status

  • Alerting the operator when the crane is operating outside of safe parameters

  • Recording crane usage data for analysis and maintenance purposes

  • Providing visual and audio pre-operational checks to ensure the safe operation of the crane

Here are some tips regarding the application of crane load moment indicators (LMIs).

  • Inspect the LMI before use. Make sure that the LMI is in good condition and that all of the sensors are working properly.

  • Enter the correct load information. The LMI needs to know the weight of the load, the length of the boom, and the angle of the boom. This information can be found in the crane's load chart.

  • Monitor the LMI display. The LMI display will show the current load moment. If the load moment exceeds the crane's rated capacity, the LMI will sound an alarm and/or shut down the crane.

  • Do not overload the crane. If the LMI indicates that the load moment is approaching the crane's rated capacity, reduce the load or reposition the crane.

  • Never lift a load that is too large or too heavy. The crane's rated capacity is based on the weight of the load and the length of the boom. If you are lifting a load that is too large or too heavy, the crane may overload and tip over.

By following these tips, you can help to ensure the safe use of crane load moment indicators. Now that you know the workings of key principles and applications of crane LMIs, let's find out how to select the right device for different applications.

Selecting the Right LMI for Crane Load Measurement

When buying a crane load moment indicator (LMI), it's important to consider several factors to ensure that you select the right system for your crane and application. Here are some key factors to consider:

  1. Crane type and capacity: The LMI system you choose must be compatible with the crane type and capacity. Different types of cranes have different load capacities and operating characteristics, and the LMI system must be able to account for these factors.

  2. Load measuring sensors: The sensors used by the LMI system to measure load must be appropriate for the application and load capacity. The sensors must be able to withstand the harsh operating environment and provide accurate readings.

  3. Display and controls: The LMI system should have a clear and easy-to-read display that provides real-time load information and warnings. The controls should be intuitive and easy to operate.

  4. Safety features: The LMI system should have built-in safety features that prevent overloading and provide warnings when the crane is operating outside safe limits.

  5. Compatibility with other crane systems: The LMI system should be compatible with other systems on the crane, such as the boom angle sensor, anti-two block system, and other safety devices.

  6. Certification and compliance: The LMI system should meet all relevant safety and certification standards, such as OSHA and ANSI requirements.

  7. Maintenance and support: Consider the maintenance requirements and support options for the LMI system. The system should be easy to maintain and repair, and the manufacturer should provide adequate support and service.

Selecting the right LMI system requires careful consideration of the crane type and capacity, load measuring sensors, display and controls, safety features, compatibility, certification, and maintenance and support. It's important to consult with a qualified LMI system provider to ensure that you get a system that meets your specific needs and requirements.


LMI systems play a critical role in maintaining the safety, efficiency, and productivity of crane operations in a wide range of applications and environments. LMIs are required by many safety regulations. For example, OSHA 1910.179, Overhead and Gantry Cranes, requires that all overhead and gantry cranes be equipped with an LMI.

Crane Load Moment Indicators

Using LMIs such as i4500 Load Moment Indicator pictured above helps to prevent overloading, which can lead to accidents and injuries. The use of crane safety devices is necessary to ensure compliance with many safety regulations regarding crane load.

Crane Warning Systems Atlanta is the official distributor of LMI and RCI systems crane warning indicators.

We have over 20 years of experience in the RaycoWylie crane safety industry, and we are committed to providing our customers with the best possible products and services. We offer a wide range of crane warning indicators, including wind speed indicators, crane scales, LMI, and ATB indicators. We also offer free product manuals, troubleshooting guides, and support tools to help our customers get the most out of their products.

We are proud to offer our products and services to customers in Texas, Georgia, Washington, Ohio, California, Florida, and all other states. We are confident that we can provide you with the crane safety products and services you need to keep your workers safe. Call 770-888-8083



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