What ASFM can do   Early measurements   ASFM Advantage   ASFM Monitor   Recent measurements    Code acceptance

What the ASFM can do for you

ASFM Advantage: One-time measurements of absolute or relative turbine discharge to:

  • determine optimum settings for maximizing operating efficiency of individual units and/or entire plants,
  • facilitate field performance testing and/or acceptance testing,
  • check measurements obtained with other technologies,
  • calibrate Winter-Kennedy taps,
  • review effects of fish diversion screens on turbine efficiency.

ASFM Monitor: Continuous long-term flow measurement in near-real time to:

  • monitor unit/plant performance,
  • document compliance with regulatory/environmental requirements,
  • monitor trashrack blockage,
  • detect penstock rupture.

ASFM frame

ASFM frame installation at Kootenay Canal
(Click image to enlarge)

ASL Environmental Sciences Inc. (ASL), of which ASL AQFlow is a wholly-owned subsidiary, has been carrying out successful flow velocity measurement programs in difficult ocean environments from the Arctic to the tropics with acoustic scintillation methods since 1977. ASL has been working in hydroelectric applications for over 20 years, since October 2000 as the ASL AQFlow subsidiary.

Early measurements at low-head plants

A prototype of the Acoustic Scintillation Flow Meter (ASFM) was introduced at Rocky Reach dam, Chelan PUD, in 1992.

The first model of the ASFM was used for flow studies at Fort Patrick Henry and Wheeler Dams, Tennessee Valley Authority, in 1997 and 1999.

The first production ASFM system was produced for the US Army Corps of Engineers (USACE), Portland District in 1998. Between 1998 and 2001, measurements with this system were conducted successfully at McNary, Bonneville, Lower Granite and The Dalles Dams.

ASFM Advantage

In 2001, the second generation instrument, ASFM Advantage was released. It incorporated significant refinements, and has since been used effectively by:

Initially the instrument was used for relatively short duration, one-time flow measurements. But because all ASFM Advantage instruments are located away from the flow, protected from debris impact, it was recognized that the technology is ideally suited for long-term, continuous flow monitoring.  

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ASFM Monitor

Thus, in 2005, ASFM Monitor was introduced. This non-intrusive system, installed permanently in the intake, provides continuous, repeatable and reliable real-time monitoring of turbine discharge. Examples of its use may be found at:

Recent measurements at higher-head plants

Although the ASFM was initially developed for and used at low-head plants with no penstocks, its features make it an accurate, repeatable and cost-effective flow measurement method for higher head plants as well. Recent examples:

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ASFM 3 bay

Example of three bay ASFM Advantage installation




ASFM Advantage

ASFM Advantage



ASFM Monitor

ASFM Monitor

International Code acceptance

The process of obtaining code recognition is progressing. Both the ASME PTC-18 Hydraulic turbine and pump turbines and the international IEC 60041 Test code for field acceptance tests to determine the performance of hydraulic turbines committees, are currently working on the inclusion of the acoustic scintillation technology in the next issue of their respective codes. The acoustic scintillation method for measuring turbine discharge, used by ASL AQFlow’s Acoustic Scintillation Flow Meter (ASFM) has been mentioned in the latest American Society of Mechanical Engineers Performance Test Code (ASME PTC 18-2020) for Hydraulic Turbines and Pump-Turbines. A detailed explanation of how the method works and guidance on its use appears in the nonmandatory appendix C section of this code document. See press release here

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