1939. Techniques for Calculating and Minimizing Cumulative Error in Multiple Instrument CG Measurements


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G A Jones: 1939. Techniques for Calculating and Minimizing Cumulative Error in Multiple Instrument CG Measurements. 1990, (L. R. ‘Mike’ Hackney Award).



The process of measuring the CG of large test items often involves the use of several different instruments. These may include three or more load cells, length scales, calipers, micrometers, calibrated weights, machined test fixtures, vernier inclinometers, optical measurement systems and so on. In any mass properties lab, some of the instruments will be of the highest precision, whereas other equipment items may suffer somewhat from cost compromise. When using several instruments together, the measurement uncertainty of each instrument contributes in a definite way to the uncertainty of the overall measurement. The mass properties engineer must know how the uncertainty tolerances of each instrument ”stack up,” so that he can estimate the uncertainty tolerance of his final answer. Herein the author proposes a method for tolerance stacking which requires the investigator to Derive, Differentiate, and Substitute (DDS). After developing the DDS method, the author suggests techniques for using the DDS function to not just find the uncertainty, but also to minimize the cumulative uncertainty. DDS is a measurement optimization technique, which allows the mass properties engineer to get the greatest advantage out of his finest instruments and to arrange his less precise instruments in such a way as to minimize the effect of the larger uncertainty they introduce.


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