Precautions for Using Crane Load Moment Indicator

Load moment indicator serve as the “life-saving devices” for cranes, yet their effectiveness critically depends on proper usage and maintenance. Any negligence may cause failure, potentially leading to catastrophic accidents. The following detailed precautions cover four key phases: pre-operation, during operation, post-operation management, and maintenance.

Core Principle: Always Remember

The moment limiter is an auxiliary safety device and must never replace the operator's professional judgment or standardized procedures. It serves as the “last line of defense,” not the “first line of defense.”

I. Pre-Operation Inspection and Verification

This is the first critical step to ensure the moment limiter functions properly and must be executed as a mandatory procedure.

1. Power-On Self-Test Verification:

After activating the crane's power supply, the moment display will perform a system self-test. Wait for the self-test to complete and confirm no fault codes or alarm prompts appear on the screen.

Verify all data displayed (e.g., length, angle, pressure values) are normal, with no garbled characters or flickering.

2. Parameter Verification:

Carefully verify and select the correct operating mode based on the task at hand. For example: Full outriggers, half outriggers, or tire mode? Using the main boom or with a jib?

Ensure all input parameters precisely match the actual configuration, including boom length, jib installation angle, counterweight status, and leg deployment. Incorrect operating mode selection is a common cause of accidents.

3. Empty Load Test Run Verification:

Perform simple hook lifting, hook lowering, minor slewing, and rotation maneuvers under no-load conditions.

Observe whether data changes on the display (reach, angle, weight) are continuous, smooth, and reasonable. For example: As boom elevation increases, working radius should decrease; with an empty hook, the displayed weight should be the lifting device weight (or close to zero).

Attempt to trigger warnings: Slowly perform hook lifting or boom extension operations. Observe whether audible and visual warnings activate normally when reaching 90% of rated load (or manufacturer-set threshold). This is a critical step to verify system effectiveness.

4. Sensor Inspection:

Visually inspect primary sensors (length, angle sensors) for obvious physical damage, loosening, or buildup of dirt/ice that could impair data collection.

II. Operational Precautions

1. Maintain constant awareness of display information:

Develop the habit of frequently glancing at the display, similar to monitoring a car's dashboard. Focus particularly on actual weight/rated weight and the percentage of rated load.

When torque percentage exceeds 90%, the system issues a warning. At this point, operation must be performed with extreme caution and at a slow pace.

2. Prioritize Warnings and Alarms:

Upon hearing/seeing a warning (e.g., 90% alarm), immediately cease operations in the hazardous direction (e.g., stop hooking up, extending the boom) and assess the current status. Consider reducing torque by operating in a safe direction (e.g., retracting the boom, lowering the hook).

When overload limits (100% alarm) trigger automatic shutdown, FORCEFUL OPERATION IS STRICTLY PROHIBITED! Under no circumstances bypass the system to continue operation (e.g., disconnecting sensors or pressing override switches). This constitutes an extremely dangerous and severe violation.

3. Understanding System Limitations:

The load moment indicator does not prevent collisions: It only prevents overturning, not collisions between the load and surrounding equipment, structures, or personnel.

It does not sense external conditions: It is unaware of sudden wind increases, ground subsidence, or load impacts on outriggers. Operators must proactively account for these factors, maintain a safety margin, and never attempt to operate at the absolute limit (“pushing the 100% threshold”).

Dynamic Loads: Rapid lifting, slewing, or emergency stops generate dynamic loads. Instantaneous impact forces may far exceed rated values, yet system response may lag. Therefore, smooth operation is essential; avoid abrupt movements.

4. Vigilance in Special Conditions:

Multiple Crane Operations: When multiple cranes lift together, load distribution per crane is complex. The moment limiter displays only the load on the current crane. Close communication with the signalman and other cranes is required.

Long-Radius Operations: At maximum outreach, even light loads can generate significant torque due to the boom's own weight—never underestimate this.

Soft Ground or Slope Operations: Always use base plates to ensure stable outrigger support. The  load moment indicator cannot monitor ground bearing capacity.

III. Post-Operation Procedures

1. Proper Shutdown: Follow procedures to power down the crane, allowing the load moment indicator system to shut off normally.

2. Cleaning and Maintenance: Clean dust, oil, rainwater, etc., from the display screen and sensor exteriors.

IV. Management and Maintenance

This section falls under the responsibility of equipment managers and maintenance personnel but is critical to operator safety.

1. Strictly Prohibit Unauthorized Adjustments or Bypassing:

Absolutely prohibit any non-professional personnel from adjusting, calibrating, disassembling the  load moment indicator, or modifying its internal parameters.

Absolutely prohibit disabling system functions through any means, including using “forced switches” or disconnecting sensors.

2. Regular Professional Calibration and Testing:

Periodically calibrate and verify the  load moment indicator using standard weights or certified force measurement devices (typically at least once annually).

3. Prompt Maintenance:

Immediately cease equipment operation and report for repair upon detecting any malfunction, display anomaly, or inaccurate data.

“Operating with faults” constitutes a major accident hazard. Equipment may only be reused after thorough fault resolution and successful recalibration.

4. Personnel Training:

All operators, supervisors, and equipment administrators must undergo specialized training on the load moment indicator's principles, functions, limitations, and precautions.