Troubleshooting Common Weighing Errors in Concrete Mixing Equipment: A Guide to Moisture-Proof Maintenance, Calibration, and Drop Compensation Adjustment of Weighing Sensors
A precise weighing system is crucial for ensuring stable concrete quality and controlling production costs. The proportions of aggregates, cement, fly ash, water, and admixtures all rely on the weighing accuracy of the weighing sensors to ensure consistency with the design mix proportions.
For global construction contractors and ready-mixed concrete plant operators, unstable weighing drift and recurring over- or under-mixing can lead to two major losses: firstly, excessive raw material consumption increases operating costs; secondly, mismatched material proportions can result in substandard concrete strength, leading to rework and compensation risks.
Most weighing deviations stem from two fundamental causes: moisture-induced damage to the weighing sensors and improper calibration, and inappropriate drop compensation parameter settings. This article outlines the system's inspection logic, moisture-proofing modification solutions, standardized calibration procedures, and practical drop compensation adjustment techniques for all HZS stationary concrete mixing plants and YHZS mobile concrete mixing plants.
Before troubleshooting, typical fault symptoms should be identified to quickly pinpoint the source of the problem:
- Severe Zero Drift: After emptying the weighing hopper, the weight value fails to automatically return to zero, fluctuating randomly.
- Excessive or Insufficient Material Quantity: Consistent positive or negative deviations occur between batches with the same formula.
- Significant Deviation Differences in Dry and Rainy Weather: Measurement errors increase significantly in high humidity environments.
- Unstable Readings in a Single Hopper While Other Weighing Scales Work Normally: The fault only occurs in the aggregate scale, cement scale, or admixture scale.
- Deviance Changes with Feed Speed: Rapid feeding leads to larger errors, while slow feeding yields relatively accurate readings.
Signal value fluctuates under no load, and cannot lock at zero after zeroing.
The measuring resistance of the signal cable deviates from the standard 350Ω range.
Condensation on the inner wall of the junction box, and oxidation and rust on the terminals.
Aging of the cable inlet sealing rubber ring, allowing mud and rainwater to seep into the internal strain gauge.
Immediately disconnect the power supply to the control cabinet to prevent short circuit and burnout of the PLC module;
- Remove the junction box and wipe the condensation and rust on the terminals with a dry, lint-free cloth; purge the internal cavity with low-pressure dry compressed air.
- Place a desiccant bag inside the junction box and seal all wire outlets with silicone rubber.
- Remove the damp load cell and place it in a constant temperature drying oven (≤60℃) for 3-4 hours to remove internal moisture.
- Reinstall and recalibrate after complete drying; if the signal still fluctuates drastically, replace the load cell directly.
Default configuration includes standard IP67/IP68 stainless steel load cells; avoid using low-grade ordinary sensors with poor sealing.
All signal cables are double-shielded waterproof cables, with cable joints hanging downwards to prevent rainwater backflow.
Install an independent rain and dust cover above each set of load cells to isolate splashed mortar and rainwater.
Place a desiccant inside the weighing junction box and replace it every 30 days during the rainy season.
Keep all flexible connecting sleeves between the hopper outlet and the weighing hopper loose to prevent water vapor from entering the weighing system through rigid connections.
Remove residual concrete, sand, and stones from the bottom and side walls of the weighing hopper to eliminate additional load interference.
Check that all support points of the load cell are on the same horizontal plane and that there are no foreign objects obstructing the hopper and support frame.
Relax the tension of the flexible connection rubber sleeve to ensure that the weighing hopper can independently bear the weight without external tension.
Prepare standard calibration weights with a total weight of 60%–80% of the weighing hopper's capacity.
Empty the weighing hopper, access the PLC weighing parameter page, perform zero-point reset, and confirm that the displayed value returns to ±0 kg.
Evenly place standard weights on each weighing sensor support position sequentially for calibration, recording the display reading for each sensor group.
If a single sensor shows significant deviation, adjust the height of the support bolts to balance the stress of the multi-sensor group.
Gradually stack weights from light to heavy, calibrating the linearity of the entire measurement range, and modify the gain coefficient of the control system according to the weight difference.
Completely remove the weights and verify the zero point again; repeat the calibration twice until the error is controlled within ±0.5%.
Dry inland construction sites: Perform a comprehensive calibration monthly;
Coastal, rainy, and high-humidity areas: Perform static calibration every 15 days and a dynamic feeding test weekly;
Before large-scale continuous concrete production (bridges, dams, wind power projects): Complete the full set of weighing calibrations in advance.
Drop compensation is a core software parameter used to correct the falling of residual material after the unloading gate closes. Inappropriate drop value settings are the most common cause of persistent batch deviations.
When the system reaches the target weight, the feed gate immediately closes, but the material suspended in the air continues to fall into the weighing hopper, forming additional "drop weight." The control system pre-deducts a preset drop value to compensate for this material.
Set the initial drop value parameter to zero, run one automatic batching cycle, and record the actual total weight after feeding stops;
Calculate the difference between the actual weight and the target weight:
Actual weight > Target weight → Increase the drop value compensation;
Actual weight < Target weight → Decrease the drop value compensation;
Adjust the feeding speed matching parameters: For coarse aggregates with larger particle sizes, appropriately extend the gate closing delay time; for fine powder cement and admixtures, use a smaller drop value and a slower secondary feeding speed;
Two optional compensation modes in the PLC system:
- Fixed drop compensation: Suitable for situations where the raw material moisture content is stable and the particle size is uniform;
- Automatic dynamic drop compensation: The system automatically corrects the drop value based on historical batch data to adapt to changes in material moisture content during rainy weather.
After calibrating the load cells and adjusting the drop compensation, inspect for potential mechanical issues to prevent recurrence of errors:
- Remove foreign objects and hardened concrete around the weighing hopper limit positions;
- Inspect the weighing frame for deformation after long-term heavy-load impacts, and correct or replace bent support beams;
- Regularly tighten all load cell fixing bolts to prevent stress imbalance caused by loose supports;
- Replace aged and hardened flexible connection sleeves, as rigid tension will generate continuous additional weighing loads;
- Regularly clean the silo arched crusher to avoid random weighing deviations caused by intermittent and unstable feeding.
Raw Material Cost Savings: For medium to large-sized concrete batching plants, accurate weighing can reduce excessive cement consumption by 3%–7% annually.
Avoiding Environmental Penalties and Project Losses: Qualified concrete mix proportions meet international construction acceptance standards, avoiding the risk of rework or substandard strength.
Reduced Equipment Maintenance Frequency: Stable weighing sensor operation avoids frequent replacements due to long-term moisture exposure and overload drift.
Complete Production Data Traceability: Accurate weighing records can be exported as inspection documents for overseas project supervision audits.
Most weighing error faults in concrete batching plants are predictable and repairable. Plant management should establish standardized maintenance procedures, focusing on three core aspects: daily moisture protection checks of weighing sensors, monthly full-range calibration, and real-time optimization of drop compensation parameters.