Considerations and Analysis of Non-Weight Calibration Applications for Weighing Sensors in Industrial Scales

In the field of industrial weighing, truck scales serve as critical measurement devices, and their accuracy directly impacts core processes such as trade settlement and production control. The non-weight calibration technology, which eliminates the need to handle heavy standard weights, saves time and labor costs, and has been widely applied in certain scenarios. However, potential risks must be monitored during long-term use. Additionally, subtle changes in the scale’s foundation, sensor installation position, and scale platform can have a cascading effect on measurement accuracy, necessitating a systematic analysis and strategy formulation from both positive and negative perspectives.

1. Core Considerations for Non-Weight Calibration of Truck Scales

Non-weight calibration (typically based on “simulated load calibration,” “substitution method calibration,” or relying on sensor linear parameters calculation) is convenient but essentially simulates real loads indirectly. The following key points must be strictly controlled to avoid accuracy deviations:

1. Prerequisite Condition Verification: Ensure Calibration Foundation is Valid

• Verification of Initial Equipment State Before calibration, it is essential to confirm that the truck scale has no historical faults (such as sensor drift or moisture in the junction box) and that there is valid data from weight calibration within the last three months as a baseline. If the truck scale has not undergone weight calibration for an extended period, accumulated deviations such as sensor linear errors and scale platform deformation can distort the results of non-weight calibration.
• Environmental Stability Control During calibration, it is necessary to maintain stable environmental temperature (recommended 15-25°C) and humidity (relative humidity ≤ 85%), avoiding airflow and vibration interference. Severe temperature fluctuations can cause thermal expansion and contraction of the sensor elastomer, directly affecting the accuracy of output signals. At this time, the compensation algorithm for non-weight calibration may not accurately correct the errors.
• Software and Parameter Locking Only qualified technical personnel are allowed to operate the calibration software, and original calibration parameters (such as sensor sensitivity, linear coefficients, and angle correction values) must be backed up in advance. Non-professionals are prohibited from modifying core parameters such as “calibration coefficients” and “range limits” to prevent human errors from causing measurement failures.

2. Process Compliance Control: Avoid Operational Gaps

• Step-by-Step Verification Principle After non-weight calibration, it is necessary to verify at least three different points using small-range standard weights (e.g., 5%-10% of the rated range). For example, a 30-ton truck scale should be tested with 1.5 tons, 3 tons, and 5 tons of weights. If the error exceeds ±0.1% (the allowable range according to national measurement regulations), the sensor parameters must be rechecked or weight calibration should be used instead.
• Cycle Limitation Non-weight calibration should not be used as a long-term substitute; it is recommended to use it no more than once per quarter, and a complete weight calibration must be performed once a year (covering more than 75% of the full range load) to ensure that the equipment’s accuracy meets the JJG 134-2023 “Digital Indicating Scales” measurement verification regulations.
• Record Keeping Detailed records of each calibration’s time, environmental parameters, operators, and test data before and after calibration, as well as parameter modification records, should be maintained for future traceability and fault diagnosis.

2. Impact of Foundation Changes on Truck Scales and Response Strategies

The foundation of the truck scale (concrete or steel structure) serves as the bearing reference for the scale platform and sensors. Its settlement, cracking, or horizontal deviation can directly disrupt the force balance of the weighing system, necessitating analysis from both positive and negative perspectives:

1. Positive Impact (Ideal State)

• Stable Support When the foundation’s flatness error is ≤2mm/m and there is no settlement or cracking, it ensures uniform force distribution on the scale platform, good linearity of sensor output signals, and stable weighing accuracy (error can be controlled within ±0.05%).
• Extended Equipment Lifespan Uniform load transfer can reduce local stress concentration on the sensors, avoiding fatigue damage to the sensor elastomer caused by uneven forces, thus extending the sensor’s lifespan (typically 5-8 years).

2. Negative Impact (Common Issues)

• Foundation Settlement / Tilt After long-term use, if the soil beneath the foundation is not compacted sufficiently, local settlement (settlement amount > 5mm) may occur, leading to tilting of the scale platform. At this time, the sensors experience uneven forces, resulting in smaller errors under light loads and larger errors under heavy loads, and even “jumping” phenomena may occur.
• Foundation Cracking If the concrete foundation develops cracks (width > 0.3mm) due to temperature changes, improper curing, or heavy load impacts, it will interrupt load transfer, causing parts of the scale platform to be suspended, leading to poor repeatability of weighing data (the error of weighing the same object multiple times > 0.2%).

3. Solutions

• Regular Inspections Conduct inspections of the foundation every six months, using a level to measure flatness and a tape measure to check crack widths, recording the amount of foundation settlement (settlement observation points can be set at the edges of the foundation).
• Foundation Repair If slight settlement (≤5mm) occurs, it can be adjusted by placing thin steel plates (thickness 0.5-2mm) under the sensors; if the settlement exceeds 5mm or if there are cracks, the scale must be shut down, the platform removed, and the foundation reinforced (e.g., grouting to fill soil voids, pouring concrete to repair cracks). After repairs, weight calibration must be redone.
• Preventive Measures When constructing new truck scale foundations, ensure that the concrete strength is ≥C30, the curing time is ≥28 days, the soil beneath the foundation is compacted in layers (compaction ≥95%), and a drainage system is installed to prevent rainwater from soaking and softening the soil.

3. Impact of Sensor Installation Position Changes and Response Strategies

The sensor is the “perception core” of the truck scale, and even a slight deviation (＞1mm) in its installation position can alter the force transfer path, affecting weighing accuracy, which requires special attention:

1. Positive Impact (Correct Installation)

• Uniform Force Distribution When the sensor installation position strictly follows the design drawings (usually at the four corners of the scale platform or beneath the main beam), and the sensor center aligns with the force points of the scale platform, it ensures uniform load transfer to each sensor, with output signal deviations ≤0.5mV, and after angle correction, accuracy can reach ±0.03%.
• Stable Signals When the installation gap (the gap between the sensor and the scale platform or foundation) is controlled at 0.1-0.3mm and there is no looseness, the sensor output signals are free from interference, and the weighing data response speed is fast (≤0.5 seconds).

2. Negative Impact (Position Deviation)

• Force Deviation When the sensor installation position deviates laterally by >2mm, it causes “lateral component forces” in load transfer, resulting in the actual force on the sensor being less than the real load, leading to smaller weighing results (errors can reach -0.3% to -0.5%); longitudinal deviation may cause the scale platform to jam, affecting the updating of weighing data.
• Excessive / Insufficient Gaps When the installation gap exceeds 0.5mm, the scale platform’s movement causes unstable forces on the sensors, leading to data fluctuations; when the gap is less than 0.1mm, the sensor may become “jammed,” unable to deform freely, resulting in saturated output signals, and weighing data may be excessively high and unable to zero out.

3. Solutions

• Installation Calibration After sensor installation, use specialized positioning tools (such as sensor positioning sleeves) to ensure position deviations ≤1mm, and use a torque wrench to tighten bolts to the specified torque (usually 25-35N·m, refer to the sensor manual for specifics) to avoid loosening.
• Regular Checks Open the maintenance door at the bottom of the scale platform every quarter to check if the sensor installation bolts are loose, and use feeler gauges to measure installation gaps. If deviations or abnormal gaps are found, the scale must be shut down for adjustments, and after adjustments, single-point calibration (using small-range weights to test the consistency of force on each sensor) should be performed.
• Fault Diagnosis If significant weighing errors occur, “angle difference testing” can be used to determine if the sensor position is abnormal—placing the same weight on each corner of the scale platform, if the weight value at one corner deviates from the others by >0.2%, that corner’s sensor may have a position deviation and should be checked and adjusted accordingly.

4. Impact of Scale Platform Changes and Response Strategies

The scale platform, as the core component for load bearing and transfer, can have its deformation, corrosion, or loose connections directly alter the force distribution, affecting measurement accuracy, which requires analysis from both positive and negative perspectives:

1. Positive Impact (Intact State)

• Rigid Transfer When the scale platform (usually U-shaped or box beam structure) meets rigidity standards (deflection ≤1/1000) and has no deformation, it can uniformly transfer loads to the sensors without local stress concentration, resulting in good linearity and repeatability of weighing data.
• Sealing Protection When the anti-corrosion coating on the scale platform surface (such as epoxy zinc-rich paint) is intact and the junction box is well-sealed, it prevents rainwater and dust from entering, avoiding corrosion of the sensor terminals and ensuring stable signal transmission.

2. Negative Impact (Common Issues)

• Scale Platform Deformation Long-term overload (exceeding 120% of the rated capacity) or impact loads (such as sudden braking of vehicles) can cause bending and deformation of the scale platform beams, leading to shifts in force points, non-linear output signals from the sensors, and increasing weighing errors with increasing loads (errors can exceed ±0.5% under heavy loads).
• Corrosion and Loose Connections Scale platforms used outdoors are prone to corrosion (depth >1mm) if the anti-corrosion coating is damaged, leading to a decrease in structural strength; loose bolts at the scale platform joints (insufficient torque) can increase gaps, causing discontinuous load transfer and “step-like” deviations in weighing data.
• Accessory Damage If the limit devices (longitudinal and lateral) on the scale platform are loose or damaged, excessive displacement may occur when vehicles enter and exit, impacting the sensors and leading to position deviations or damage, which also affects weighing accuracy.

3. Solutions

• Routine Maintenance Clean the scale platform surface weekly, check the integrity of the anti-corrosion coating, and promptly repaint any damage; check the scale platform joint bolts and limit devices monthly, retightening them with a torque wrench (bolt torque reference from the scale platform manual) to ensure that the limit gaps (longitudinal 5-10mm, lateral 3-5mm) meet requirements.
• Deformation Repair If the scale platform shows slight deformation (deflection ≤2/1000), it can be corrected by heating (to be performed by professionals to avoid excessive heating that could damage the material); if deformation is severe (deflection >2/1000), the scale platform must be replaced, and a complete weight calibration and angle correction must be performed after replacement.
• Overload Control Implement a truck scale management system to prohibit overloaded vehicles (exceeding 110% of the rated capacity) from weighing, and set speed limit signs (≤5km/h) at the scale platform entrance to prevent impact loads from damaging the scale platform.

5. Conclusion

Non-weight calibration of truck scales must be used under strict control of prerequisite conditions and operational specifications and cannot replace regular weight calibration. Changes in the truck scale’s foundation, sensor installation position, and scale platform fundamentally disrupt the “uniform load transfer – precise sensor perception – stable signal output” closed-loop system affecting accuracy. Enterprises must establish a “regular inspection – timely repair – standardized calibration” full-cycle management system to ensure the long-term stable operation of truck scales, meet measurement accuracy requirements, and avoid economic losses or compliance risks due to equipment errors.