An Installed Accuracy Assessment using Dye Dilution Testing for Seven Common Flow Metering Technologies
An accurate dye dilution testing protocol using Rhodamine WT was developed and used to quantify flow meter accuracy in the Greater Detroit Regional Sewer System. Over 150 tests were performed on 37 flow meters in conjunction with a set of good metering practice principles. A summary of the accuracy for each of the seven technologies tested before and after good metering practice is given. The seven technologies assessed are electromagnetic induction meters (magmeters); full-conduit, multiple-path, transit-time meters; full-conduit, single-path, transit-time meters; open-channel, multiple-path, transit-time meters; open-channel, ultrasonic meters; flumes; and weirs. Many meters that are typically considered to be accurate had errors of more than 30%. Some meters had errors that exceeded 70%.
Overall, the average initial system accuracy for system meters was observed to be ±15.0% of measurement with an overall bias of 6.1% (underpredicting flow). After implementing the good metering practice principles, and in particular using dye dilution testing as a diagnostic tool, the average accuracy potential observed for the system reduced to ±5.5% of measurement, with an overall bias of 0.6% (underpredicting flow). It is concluded that (i) there are observable accuracy differences between flow meter technologies, (ii) objective standards like dye dilution testing are critical to good metering, (iii) verifying installed accuracy is important, even for technologies considered to be highly accurate, and (iv) the simplest technology that can be used is often the best.
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