Peeling the Onion of Meter AccuracyTwo Steps to Evaluating Flow Meter Data

摘要

It is a natural desire and has been past practice to evaluate a meter’s accuracy byreviewing its output – a measured rate of flow (Q). Most users test a meter’s Q readingmerely by comparing it to the Q from other meters or primary devices, much the sameway drivers compare speedometers by driving next to each other and comparing outputs.The readings in such comparisons will never agree exactly, just as two watches will not.Experience shows that a traditional Q-to-Q comparison seldom results in a clearunderstanding of source of any meter inaccuracy.The technique presented in this paper offers an easy process for evaluation of meteraccuracy without a second flow measurement device. The first step in evaluatingaccuracy of any instrument is to evaluate its measurable components, not its output. Fora speedometer, measurable components are distance and time; for an open channel flowmeter, they are depth and velocity. A determination of precision and bias is then madefor each measurable component. This concept of evaluating a meter’s precision and biashas been incorporated into the EPA Environmental Technology Verification (ETV)program in the flow meter verification protocol.