Interpretation of the ISO 22923:2017 Standard, “Cranes—Load Indicators”
📌ISO 22923:2017, “Cranes—Load Indicators,” is the international standard for crane load indication devices (load and moment indicators).This standard specifies the classification, performance requirements, test methods, and calibration rules for load indicators—applicable to load indication and overload protection devices for all types of cranes.
Classification and Functions of Load Indicators
Krude Heavy Industry strictly adheres to national standards in its production processes. ISO 22923:2017 classifies crane load indicators into three categories: Load Indicator—displays the weight of the current load in real time (in metric tons or kilograms). Operators monitor the display to determine the actual load being lifted, thereby preventing overloads. Minimum requirements: accuracy of ±5% and a response time of ≤1 second. Load Limiter—automatically cuts off the hoisting motion when the load exceeds a preset value (only lowering is permitted). The trigger threshold is 110% of the rated load capacity—accuracy ±5%—response time ≤0.5 seconds. Load Moment Limiter (LMI)—Calculates the load moment in real time (moment = load × boom length)—and compares it to the rated moment for the current boom length. Issues a warning (yellow warning) when the load moment reaches 90% of the rated value—issues an alarm and automatically cuts off movement in the dangerous direction (red alarm) when it reaches 105%. Accuracy—load moment measurement accuracy ±5%. All types of load indicators shall consist of the following components: sensors (weight sensors, angle sensors, length sensors, etc.)—data processing unit (microprocessor)—display unit (LED/LCD display)—alarm output (audible and visual alarms + relay output for cutting off the control circuit). The standard specifically stipulates the self-test function of load indicators—a self-test shall be performed automatically each time the unit is powered on (to verify that all indication and alarm functions are operating normally)—and crane operation shall not be permitted if the self-test fails.
Sensor Requirements
Standard Requirements for Sensors: Load sensors—tension sensors (installed at the fixed end of the hoisting wire rope) or pressure sensors (installed at the inlet of the hydraulic cylinder in the hydraulic hoisting system) may be used. Sensor accuracy ≥ 0.51 TP3 TFS (full-scale accuracy)— —Long-term stability (annual drift ≤ 0.21 TP3 TFS). Overload capacity—The sensor must be able to withstand 2 times the rated load without damage (safety margin). Environmental adaptability—Operating temperature: -20°C to +70°C—Protection rating ≥ IP65 (dust-tight and water-jet-proof). Angle sensor (boom angle measurement)—Accuracy ≥ ±0.2°—Resolution ≤ 0.1°—Suitable for measuring the boom angle of luffing jib cranes and tower cranes. Length Sensor (Telescoping Boom Length Measurement)—Accuracy ≥ ±0.5%—Suitable for measuring the length of telescoping booms on mobile cranes. Wind speed sensor—Accuracy ≥ ±0.5 m/s—Suitable for all outdoor-operating cranes. Signal transmission—Signal transmission from the sensor to the data processing unit shall use shielded cable (to prevent electromagnetic interference) or wireless transmission (with encryption and error checking between the sensor and receiver to prevent signal loss or interference). Special Standard Requirements—Sensors must be equipped with fault diagnosis capabilities—in the event of a sensor failure or abnormal signal—the load indicator must be able to detect and display a fault code—while simultaneously disabling movement in dangerous directions (safety first—operation must not continue in the event of a fault).
Calibration and Verification
Standards for the Calibration and Verification of Load Indicators: Factory Calibration—Each load indicator shall be individually calibrated using standard weights or force transducers before leaving the factory—Calibration records shall be provided with the equipment (including the calibration date, calibration agency, and calibration data). The calibration report shall specify the deviation between the measured values at each calibration point and the standard values—all deviations shall be within the range of ±2%. On-site Calibration—After the load indicator is installed on the crane—actual load calibration should be performed on-site at each major boom length using standard weights of known mass (or by applying load via a hydraulic force gauge)—the sensor output values should be compared with the actual load and calibrated accordingly. Calibration shall use at least 3 load points (50%, 75%, and 100% rated loads) and 3 boom radius points (minimum, intermediate, and maximum boom radii). On-site calibration must be performed for each crane upon leaving the factory and after each installation (and after each relocation and reinstallation of a tower crane)—to confirm that the load indicator’s measurement accuracy is within ±5%. Periodic verification—The load indicator must undergo an accuracy verification every 12 months (verified by loading at the primary working radius using standard weights or a comparator dynamometer)—verification records must be archived for at least 6 years. After the crane has undergone major repairs or modifications (such as replacement of the boom or a change in the rated lifting capacity), the load indicator must be recalibrated. Load indicators that fail calibration must not continue to be used—they must be repaired or replaced and then recalibrated.
Display and Alarm Requirements
Standard Requirements for Display and Alarms: Display Content—The load indicator’s display screen shall show the following parameters in real time: actual load (t or kg)—current boom length (m)—current moment (kN·m)—percentage of rated moment (%). Optional display parameters—boom angle (°), boom length (m), wind speed (m/s), and number of work cycles. The display brightness should be adjustable—it must be clearly legible in both bright light (50,000 lux) and low-light conditions. Alarm modes—divided into two levels: Early warning (yellow)—when the moment reaches 90%–100% of the rated value—yellow LED flashes + intermittent beep (500 ms on/500 ms off)—to alert the operator. Alarm (red)—when torque reaches 105% of the rated value or the load reaches 110% of the rated value—red LED flashes + continuous beep— —simultaneously automatically cuts off dangerous movements such as hoist up, increasing luff angle, and extending the boom—retaining only safe movements (lowering, decreasing luff angle, and retracting the boom). Alarm reset—only occurs when the load returns to the safe range (torque<90%额定值）后——报警状态才能手动复位——危险方向动作才恢复。标准还要求载荷指示器具备数据记录功能——记录每次报警事件的时间和载荷参数——数据保存≥3个月——用于安全追溯和事故分析。
| Load Indicator | Features | Accuracy Requirements | Calibration Interval |
|---|---|---|---|
| Torque Limiter | Real-time Torque % Display | ±5% | Monthly |
| Load Indicator | Load Capacity Display: 1TP–3T | ±3% | Monthly |
| Amplitude Indicator | Real-time Amplitude Display | ±2% | Weekly |
| Operating Condition Selector | Operating Conditions Parameter Settings | Accurate | Each time the operating condition changes |
| Inspection Items | Requirements | Cycle | Methods |
|---|---|---|---|
| Display Accuracy | ≤±5% | Every year | Weights Calibration |
| Functional Testing | Audible and Visual Alarms | Monthly | Lifting Test |
| Sensor | Protection is working properly | Weekly | Visual Inspection |
| Connection Cable | No damage | Monthly | Visual Inspection |
Frequently Asked Questions
Q: What are the accuracy requirements for load indicators under ISO 22923?
Answer: The standard requires that the total accuracy error of the load indicator be ≤ ±5%. Accuracy refers to the total error of the sensor, signal processing circuit, and display instrument. An accuracy calibration should be performed once a year, using standard weights to verify each point and record the calibration curve.
Q: What is the difference between a load limiter and a load indicator?
Answer: The load indicator displays the load value in real time for the operator’s reference. The load limiter automatically cuts off the power supply and stops movement in the dangerous direction when the load reaches the set value. The two are often used together—the indicator displays the current value, and the limiter automatically cuts off the power when the load exceeds 110%. Standards require that both be calibrated separately.
Q: What is the procedure for daily calibration of a load indicator?
Answer: Perform functional tests monthly—lift standard weights of known mass to verify that the displayed values fall within the tolerance range. Test conditions include three scenarios: no load, the 50% rated load, and the 100% rated load. If any deviation exceeds the tolerance limits, immediately shut down the equipment and notify professional maintenance personnel to make adjustments.
Q: What are the sensor types and protection requirements for load indicators?
Answer: Commonly used sensors include strain gauges (mounted on the drum support or the hook sheave shaft) and pressure sensors (for hydraulic cranes). Sensors must have a protection rating of at least IP54; in high-temperature, dusty environments, the rating must be at least IP65. Sensors should be cleaned and inspected regularly.
