The Hierarchy Of Accuracy, Resolution, And Capacity For Scales

By Author: Karl Nowosielski
Total Articles: 4762
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Analytical scales set the accuracy standards for scales produced in commercial quantities. However, they are capacity limited and usually have capacities between 50 and 200 grams.

These scales all require a wind screen because of their sensitivity. The capacity limitation is partly because the force restoration load cell is difficult to produces in higher capacities while maintaining the phenomenal linearity, computer corrections not withstanding. But, equally important, is the reduced demand for the extreme accuracy at higher capacity (and at higher prices). However, we can go down in capacity into the semi-microbalance arena where the capacity is approximately 10 to 50 grams, and the accuracy and resolution (1:1,000,000) remains comparable to the analytical scale.

We can go yet further, into the microbalance, where capacity drops to about 1 gram with a resolution of 1 microgram. Weighing in these ultra light areas requires special knowledge and skills. The displacement of air and the atmospheric pressure start to become real factors effecting accuracy. Dust particles become very undesirable on the weigh pan. ...
... Gloves become a necessity. A hair seems to be a tree.

Laboratory scales are still a high accuracy device. Here, we see a much wider range of capacities from 50 grams to approximately 20,000 grams. These scales are generally executed using the force restoration load cell. At the lower capacities a wind screen may be required depending upon the environment.

There are still mechanical scales manufactured that meet these standards. These scales require special skills and controlled environments for their manufacture and are expensive by comparison with their strain gauge counterparts. The next step down the hierarchy ladder is the industrial scale.

These are generally thought of as having a resolution of one part in ten thousand (1:10,000) with a linearity of /- 3 parts per ten thousand ( /-0.03%). These scales are usually based upon strain gauge technology which has made great strides through the use on computer technology for error correction. There are also some very refined strain gauge scales that have specifications very close to those of lab scales.

Industrial scales have the widest range of capacities because the strain gauge technology allows it to expand up to tremendous capacities. The range goes from 100 grams to hundreds of tons. These scales can be portable (battery operated), used to weigh vehicles (truck weighing stations), used to weigh packages (platform scales), used to weigh I beams (crane scales), and just about everything else.

The hierarchy loses form after this as we get into bathroom scales, baby scales, any many other special purpose scales that varied, but generally lower accuracy and resolution requirements.
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