About Jib Length Box Tower Crane

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A Jib Length Box is a critical component in the safety and control system of a Tower Crane. It is designed to monitor, indicate, and communicate the length or position of the jib (boom) to the crane’s control panel or Load Moment Indicator (LMI) system.

Working Radius (or Jib Length Measurement)

In a tower crane, the jib length is the total horizontal distance measured from the center of the crane’s slewing axis (mast center) to the tip of the jib (where the load hook or trolley is positioned).

• When the trolley moves along the jib, the effective working radius changes.
• The maximum jib length is the fixed total length of the jib structure.
• The actual working radius at any given moment is the distance between the crane’s rotation axis and the current trolley position.

Purpose

The main purpose of the Jib Length Box is to ensure accurate measurement of the jib radius, which is essential for:

• Calculating the actual load moment,
• Maintaining safe lifting limits, and
• Preventing overload or tipping conditions during crane operations.

Working Principle

The Jib Length Box measures the extension or position of the crane’s jib (in luffing or telescopic cranes) using internal angle sensors, limit switches, or potentiometers.
The measured jib length is transmitted as an electrical signal to the crane’s indicator system or LMI, which processes it along with other parameters such as:

• Load weight,
• Boom angle, and
• Wind speed.

This allows the system to determine the safe working load for the current configuration.

Key Features

• High Accuracy Measurement of jib extension or radius
• Rugged and Weatherproof Design (IP65/IP67 rated enclosure)
• Analog or Digital Output (for easy integration with LMI or PLC)
• Compact and Durable Construction suitable for harsh site conditions
• Easy Installation and Calibration