your letters: Readers Respond by ProQuest

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[...] the flow errors associated with positive and negative measurement errors of 1 "WC at 10% flow with a 200"WC full scale are 2.25 and 2.93 percent of full scale flow, respectively. [...] the graph is incomplete and should depict the worst case error, or both positive and negative errors. 4. Using the assumption immediately above, the article implies that a 1"WC measurement error with a 200"WC full scale will perform within a (satisfactory) criteria of 2 percent of full scale (common of orifice plates) over a 10:1 turndown. a. At 10 percent of full scale flow, the positive and negative flow errors are 2.25 and 2.93 percent of full scale respectively - neither of which meets the 2 percent of full scale (satisfactory) criteria. b. The article incorrectly characterizes orifice plate measurement systems as 2 percent of full scale systems when they are actually 2 percent of flow rate systems. c. The 2.25 and 2.93 full scale flow errors correspond to 22.5 and 29.3 percent of flow rate respectively - both of which are over 10 times higher than the 2 percent of flow rate criteria. d. The actual turndown is approximately 2:1 in order to stay within a 2 percent of flow rate error.

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