Angle/Radius Sensor

An Angle/Radius Sensor is a critical component of Load Moment Indicator (LMI) systems used primarily in mobile and tower cranes. It precisely measures the horizontal angle of the crane's boom relative to the crane's chassis and the extension radius of the boom or jib. This data is essential for the LMI's computer to calculate the load moment (load weight multiplied by radius), ensuring the crane operates within its safe working limits and preventing dangerous overload conditions. The sensor is designed for harsh outdoor environments, featuring a stainless steel housing (grade 316L per ASTM A240) for corrosion resistance and an IP67 ingress protection rating per IEC 60529, making it dust-tight and waterproof. It operates over a temperature range of -40°C to 85°C and is powered by a 9–36 V DC supply with reverse polarity protection. The output signal is a 4–20 mA two-wire loop, which is standard for industrial process control. The measuring range for angle is 0–360° continuous rotation, with an accuracy of ±0.1°. The radius measuring range is 0–100 m, depending on boom length, with an accuracy of ±0.5% of full scale. The sensor's weight ranges from 1.5 to 2.5 kg, depending on configuration. These specifications are typical reference values; actual model-specific values must be verified with the legal manufacturer or supplier. The sensor is a component, not a standalone system, and must be integrated into an LMI system for proper operation. It is not a safety device by itself; the LMI system interprets the data and provides warnings or controls. Regular calibration and maintenance are required to ensure accuracy. The sensor's materials include stainless steel housing, potentiometer or encoder elements, PCB with electronics, and sealing polymers. It is essential to confirm compatibility with the specific crane model and LMI system before installation.

The sensor typically uses a combination of technologies. The angle measurement is often achieved via a precision rotary potentiometer, encoder, or inertial measurement unit (IMU) mounted at the boom's pivot point. The radius measurement is commonly derived from a string potentiometer, laser rangefinder, or encoder integrated into the boom extension mechanism (e.g., telescopic cylinders). These sensors output analog voltage signals or digital data proportional to the measured angle and radius, which are fed into the LMI's processing unit. The LMI then calculates the load moment and compares it to safe limits, triggering alarms or controls if necessary. The sensor's output is a 4–20 mA current loop, which is less susceptible to electrical noise and allows for long-distance transmission. The sensor is powered by a 9–36 V DC supply, and the current loop provides both power and signal transmission. The sensor's internal electronics convert the raw angle and radius measurements into the standardized output signal. The sensor is designed to operate in harsh conditions, with a sealed housing and corrosion-resistant materials. The working principle is based on the physical measurement of mechanical positions, not on load cells or force sensors. The sensor does not measure load directly; it measures the geometric parameters needed for load moment calculation.