Velocity Distribution and Its Effect on the Accuracy of the Gibson Method of Water Measurement

Abstract

The author demonstrates that significant basic errors are introduced into the Gibson method of measuring water flow rates, even in uniform straight pipes, by failure to take account of velocity distribution in calculating results. Dr. Thoma’s 1926 analysis of the method is quoted extensively, including his conclusion that long straight lengths of pipe upstream and downstream from straight differential-diagram test sections would eliminate the effects of accessory motions and his recommendations for establishing an experimental installation to determine the effects of various disturbed flow conditions. The need for these correction factors or “meter coefficients” in order to avoid consistent errors of approximately 2 percent is emphasized.