USE OF THE ADFM FLOW METERING TECHNOLOGY IN LARGE DIAMETER PIPES CONTAINING SEDIMENT

This paper describes an evaluation of the Acoustic Doppler Flow Meter (ADFM) technology mounted in standard and non-standard configurations for obtaining accurate and consistent flow measurements in large diameter pipes (greater than 10 feet) under open channel flow conditions. Furthermore, the ease of installation was evaluated for locations where it is not possible to divert flows. The ADFM meter was tested for a six month period in an eleven-foot diameter interceptor where an existing transit time meter is also installed just downstream of a pump station. The meter was tested by placing the transducer assembly at the invert as well as 18 inches and 30 inches up the side of the pipe wall.These non-standard configurations were tested primarily to avoid measurement complications caused by the presence of sediment in the invert of the pipe. The transit time meter at this location has been certified with dye dilution testing to be accurate within 10 percent. For all tests the ADFM meter showed consistent meter operation and tracked well compared to the transit time meter over the 6-month period. The difference between the transit time and ADFM meters averaged between 6 and 7 percent with the ADFM mounted at the invert of the pipe. This is within the range of discrepancies that were found using dye dilution testing on the transit time meter. The differences may partially be the result of the pipe not being perfectly round. The test results indicate that the ADFM meter operates consistently under the three setups and provides enough base data to develop site-specific algorithms. Overall, based on its relative ease of installation (less than 3-hours for each installation) and quality data collected, the ADFM meter is a promising meter that adds another cost-competitive flow metering alternative for large diameter sewers with unique geometry and sediment issues.