Truck Scale Fault Diagnosis And Rapid Maintenance Guide

01 Common faults and solutions

The display number jumps

Symptom: The instrument display is unstable, the value jumps frequently, and the number increases by dozens of kilograms or more in a short time, and the display number keeps changing.

Solution: First, check if the junction box is damp or waterlogged, while confirming the instrument remains intact. Additionally, troubleshoot power supply issues and inspect sensors, junction boxes, and cables for potential malfunctions causing signal abnormalities. Also, verify whether there are obstructions between the weighing platform and foundation, and ensure proper clearance between limit bolts and the base.

Inaccurate weighing

Symptom: Significant measurement discrepancies occur, with identical items displaying inconsistent weights on the scale platform.

Solution: First, inspect the scale platform and foundation for structural issues such as unevenness or subsidence, requiring corrective leveling if present. Verify the instrument's linear error remains within acceptable limits – recalibration is necessary if deviations exceed specifications. Additionally, troubleshoot sensor and junction box components for malfunctions, while checking four-corner balance consistency. Address any detected issues through recalibration or component replacement.

Displaying an error message

Phenomenon: For example, the Yaohua XK3190 series instrument often displays [Err03] to indicate positive overload, or [Err02] to indicate negative overload and other error codes.

Solution: First, rule out potential instrument damage. Next, verify the stability of the bridge power supply. Additionally, confirm that components including sensors, junction boxes, and DB-9 connectors are functioning properly, and check for faults causing significant signal fluctuations. For uncommissioned scales, faults typically resolve automatically after calibration. If issues persist, the weighbridge sensor itself may be faulty, requiring further inspection or replacement.

No self-test when booting

Phenomenon: After the power is turned on and the instrument is turned on, there is no display of any instrument, or only a part of the stroke section is displayed, sometimes accompanied by the sound of the buzzer.

Solution: First, check whether the external 220V power supply is functioning properly and verify if there are any faults in the power supply circuit (including wiring, fuses, internal transformer, and three-terminal voltage regulator). Additionally, confirm whether the instrument PCB board is damaged, and ensure that the LED display tube is intact with no loose connections.

The instrument does not return to zero

Phenomenon: After power-on self-test or uninstallation, the instrument display is not zero, with error prompt or a stable value displayed. In addition, during weighing process, when the vehicle is removed from the weighing platform, the instrument still displays positive or negative value and cannot return to zero.

Solution: First, check whether there is a fault in the instrument discharge part, and check whether the performance of the sensor has changed, such as lag or drift. In addition, it is necessary to confirm whether there is any debris blocking between the scale body and the foundation. If there is any debris, clean it and restart the machine.

02 Maintenance method

Visual observation

Upon arriving at the site, we first conducted a visual inspection of the weighing platform's surroundings and base surface to check for obstructions, verify limit clearance compliance, inspect cable damage, examine junction boxes for moisture, and identify any visible wear on instrument components. For instance, when detecting significant measurement inaccuracies, our observation revealed that a bridge plate had collapsed from prolonged use, compressing the platform and causing complete blockage. Additionally, dust accumulation from years of operation had clogged both lower ends of the platform. After implementing targeted solutions, the instruments resumed normal functionality.

Multimeter measurement comparison method

Using the voltage range of a multimeter, we first test the bridge power supply. For instance, check the +8V power supply of the XK3190-A9 instrument and its operating power supply at +5V to confirm normal operation. If it's an analog signal, measure the sensor output for stability and compare outputs from multiple sensors to detect significant deviations. For digital weighbridges, consult error codes or directly use the multimeter to check for cable short circuits or open circuits, while verifying the sensor resistance values are within normal ranges.

Counterweight simulator replacement method

When basic diagnostic methods fail to pinpoint faulty components, we can replace questionable parts with reliable alternatives and verify their removal through observation. This approach helps identify specific component locations. For example, when diagnosing sensor-related issues, simulators can substitute actual sensor signals. By monitoring instrument readings, technicians can determine whether the problem originates from the instrument itself or the sensor. This method demonstrates remarkable flexibility, allowing engineers to effectively utilize readily available substitutes for suspected components.

Sensor troubleshooting methodSensor troubleshooting method

Without affecting the working conditions of the whole system, we can try to disconnect from the system to check whether the suspected faulty sensor can cause the system to return to normal operation. This method helps us further determine whether the sensor is indeed faulty.

Counterweight calibration alternative method

When maintaining weighbridges, calibration challenges such as inaccurate range or linear errors may occur. For large-scale equipment lacking standard weights, alternative calibration methods prove effective. The procedure involves transporting a heavy-duty vehicle (recommended to carry 60% of its rated load) to the certified facility for initial weighing, followed by returning to the original weighbridge for final calibration. Smaller models can be calibrated through repeated measurements using smaller weights, progressively increasing the range until achieving accurate final readings. Notably, modern industrial scales and digital measurement systems now feature automatic weight-free calibration capabilities.