What is the error standard for electronic belt scales? What qualifies as acceptable?

Electronic belt scales are continuous cumulative dynamic weighing instruments installed on belt conveyors. As weighing instruments, they inherently have a certain degree of error in practical use. However, accuracy is a crucial performance indicator. For weighing instruments, there are specific error standards, and different grades must fall within prescribed ranges to be considered qualified measuring instruments. The error standard for electronic belt scales is also specifically regulated, with GBT7721-2017 outlining the standards, including characteristics, configuration, verification, and measurement errors of electronic belt scales.

Guonuo Technology has summarized the content of the error standards for electronic belt scales to help users better understand them and select the appropriate measurement grade based on their actual needs.

1. Accuracy Grades of Electronic Belt Scales

   Electronic belt scales are classified into four accuracy grades: 0.2, 0.5, 1, and 2. Each grade has its specified error standard.

2. Maximum Permissible Errors for Automatic Weighing

   Different accuracy grades have different maximum permissible errors for automatic weighing:

   - Grade 0.2: Type test ±0.10%, In-use ±0.20%

   - Grade 0.5: Type test ±0.25%, In-use ±0.50%

   - Grade 1: Type test ±0.50%, In-use ±1.0%

   - Grade 2: Type test ±1.0%, In-use ±2.0%

3. Maximum Permissible Errors for Influence Factor Tests

   For different accuracy grades, the maximum permissible errors under influence factor tests (e.g., temperature, humidity, voltage fluctuations) are:

   - Grade 0.2: ±0.07%

   - Grade 0.5: ±0.175%

   - Grade 1: ±0.35%

   - Grade 2: ±0.7%

   Note: The maximum permissible errors for separate evaluations of different modules (e.g., weight sensors, speed sensors) differ from overall evaluations.

4. Consistency Among Multiple Indicating Devices

   For the same load, the difference in weighing results provided by any two devices with the same division value should be zero on digital displays and printing devices. Simply put, the displayed and printed weighing results of electronic belt scales should be consistent.

5. Zero Stability

   Zero stability is divided into short-term and long-term stability:

   - Short-term Zero Stability: After simulating operation for 15 minutes at the maximum belt speed without load, the difference between the initial and final indications should not exceed the percentage of the cumulative load during the period for:

     - Grade 0.2: 0.0005%

     - Grade 0.5: 0.00125%

     - Grade 1: 0.0025%

     - Grade 2: 0.005%

   - Long-term Zero Stability: After simulating operation for 3.5 hours at the maximum belt speed without load, the absolute value of the difference between the initial and final zero indications should not exceed the percentage of the cumulative load during the period for:

     - Grade 0.2: 0.0007%

     - Grade 0.5: 0.00175%

     - Grade 1: 0.0035%

     - Grade 2: 0.007%

6. Maximum Permissible Error for Zero Cumulative Value

   After the belt completes one full rotation lasting as close to but not less than 3 minutes, the absolute value of the change in zero indication should not exceed the percentage of the cumulative load at maximum flow for:

   - Grade 0.2: 0.02%

   - Grade 0.5: 0.05%

   - Grade 1: 0.1%

   - Grade 2: 0.2%

The above are the main aspects of the error standards for electronic belt scales. Other requirements, such as durability and the zero discrimination of displays, also exist. When selecting an electronic belt scale, determine the required accuracy grade and choose based on the error standards within that grade. Only products that meet the error standards for electronic belt scales qualify as acceptable cumulative dynamic weighing instruments.