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How to verify the performance of multihead weigher

2022/09/08

Product testing is the best way to verify the performance of a multihead weigher. When performing product testing, the product should be weighed on a static scale with a resolution of at least 5 times the resolution of the multihead weigher, which has also been recently calibrated and checked. During the test, it is only necessary to simply take out a representative product from the production line, let the same product pass the checkweighing department at a high production speed, and then weigh it on a static scale and record the weighing result.

The same product should be run multiple times on the checkweigher to build the normal distribution curve, which will provide a mean and standard deviation σ for the basis of the performance of the multihead weigher. For daily testing during a multihead weigher run, 30 results are typically used, while for compliance assessment, 100 results are typically used. The average is the sum of all measurements divided by the average of the number of measurements.

The standard deviation is the spread of the measurements around the center point from the lowest to the highest weight value, and is calculated based on all weight measurements to determine the margin of error. By calculating the mean and standard deviation from the test data, the accuracy of the multihead weigher can be expressed in terms of ±1σ, ±2σ, or ±3σ. However, only the definition of ±2σ or ±3σ is actually used, and more manufacturers adopt the definition of ±3σ, because this definition is stricter and accepted by many users.

Accuracy testing can also use product samples from the production line. Test according to the actual operating conditions, such as passing 100 products in sequence, and record the weighing display value of these products in the multihead weigher. The theoretical weight values ​​of these products can either be weighed on a static scale first and then passed through a multihead weigher, or they can be weighed on a static scale after passing through a multihead weigher.

Then compare the difference between the theoretical weight value and the weighing display value. If the difference is less than 2g for 95 times and less than 3g for 99 times, then the accuracy according to the definition of ±2σ or ±3σ should be ±2g (±2σ) or ±2g respectively. 3g (± 3a).

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