What are the key issues to note when maintaining and calibrating electronic belt scales?

Electronic belt scales are commonly used tools for weighing large quantities of bulk materials in belt conveyor systems. They offer convenience, speed, efficiency, and are suitable for various harsh industrial environments.

With high automation levels and impact resistance, they are the primary method for efficient measurement of bulk materials in industry. However, electronic belt scales also have their limitations. Since their cumulative readings are based on dynamic measurement, factors such as belt tension, vibration, structural deformation, harsh operating environments, and the timeliness and standardization of daily calibrations significantly affect their measurement accuracy. Therefore, maintaining, servicing, and regularly calibrating electronic belt scales are essential.

Key issues to consider when maintaining and calibrating electronic belt scales:

1. Calibration Interval:

   Set a reasonable calibration interval for the belt scale based on factors such as usage frequency, environmental conditions, characteristics of the conveyed material, and the equipment's condition.

Overly frequent calibrations may increase costs, while excessively long intervals may affect measurement accuracy. Generally, zero-point calibrations should be performed daily, simulated material calibrations monthly, and material calibrations every three months. If the belt scale is equipped with a physical verification device, material calibrations are recommended weekly due to their convenience, efficiency, and accuracy.

2. Zero-Point Calibration:

   Zero-point calibration is fundamental to ensuring the accuracy of electronic belt scales. The device should be accurately calibrated under zero-load conditions to avoid systematic errors during material measurement.

Any zero-point drift can affect subsequent measurement results, so regular checks and adjustments are necessary. Ensure the scale body is clear of accumulated material and impurities that could affect calibration results.

   Zero cumulative error should not exceed the following percentages of the cumulative load at maximum flow rate: 0.02% for Class 0.2 belt scales; 0.05% for Class 0.5 belt scales; 0.1% for Class 1 belt scales; and 0.2% for Class 2 belt scales.

3. Minimum Cumulative Load for Material Calibration:

   When performing material calibrations, consider the minimum cumulative load required. Different materials impose varying loads on the belt scale, and ensuring a sufficiently large minimum load during calibration can reduce errors and improve measurement accuracy.

4. Impact of Different Materials on Measurement Accuracy:

   Calibration loads should be conducted under normal operating conditions using specified or intended materials. This is because using the same control parameters for different types of materials can result in significant relative errors. When changing material types, always recalibrate using the expected material to avoid large errors.

5. Selection of Simulated vs. Actual Material Calibration:

   Choose the appropriate calibration method based on specific circumstances. Simulated material calibration is simpler but may not fully replicate actual working conditions. Actual material calibration, while more complex, provides a more accurate reflection of the device's performance in real-world operations.

Consider calibration issues during the design and installation phases of the belt scale to avoid potential space constraints during later modifications.

6. Difference in Relative Error for Repeatability:

   Repeatability testing is an integral part of the calibration process. Assessing device repeatability can be done by comparing results from multiple tests. Variations in relative error may indicate the need for adjustments or maintenance. Ensuring consistency in each measurement is key to maintenance efforts.

   For example, a Class 0.5 belt scale has a maximum allowable error of ±0.25%. If the first material test result is 0.15% and the second is -0.15%, the repeatability relative error is 0.3%. Although both results fall within the maximum allowable error of ±0.25%, the repeatability error exceeds 0.25%, indicating poor stability and the need for multiple adjustments and calibrations.

Maintaining and calibrating electronic belt scales are crucial for ensuring their long-term stable operation and measurement accuracy. Special attention should be paid to issues such as calibration intervals, zero-point calibration, minimum cumulative load for material calibration, the impact of different materials on accuracy, the selection of calibration methods, and repeatability errors during the maintenance and calibration process. Only by comprehensively considering and properly addressing these issues can electronic belt scales perform optimally and achieve the desired application results.