Systematic Errors in Shirley Analyzer Measurements

Abstract

Lint in the ASTM Shirley analyzer method of testing for visible waste results in a positive bias when measuring the trash content of cotton and a negative bias in the lint cleaning efficiency calculation. An experimental protocol was designed and demonstrated on major grades of ginned cotton to isolate the "true" trash content from Shirley analyzer visible waste. Due to the lint in the visible waste, trash contents were too high by 44.9% for Good Ordinary cotton to 429% for Strict Middling cotton. An equation was derived to predict the cleaning efficiency (E) systematic error, E(%) = (n/m - 1)10²/( W_b/W_a- 1), where m and W_b are the trash coefficient and visible waste content, respectively, before lint cleaning and n and W_a are the corresponding values after lint cleaning. The error in E(%) is always negatively biased because the operational limit of n/m is < 1 and that of W_b/W_a is > 1. E(%) increases with a decrease in the efficiency and the n/m value. The magnitude of E(%) is greater for successive stages of cleaning than for the cumulative efficiency over several cleaning operations.

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References

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