New sewer flow monitor accurate to within 2%

Conventional sewer flow monitors measure the velocity at only one position, and can be highly inaccurate especially in turbulent conditions or large diameter pipelines: OnSite has the answer

Conventional sewer flow monitors measure the velocity at only one position, and can be highly inaccurate especially in turbulent conditions or large diameter pipelines.

They are generally unsuitable for use near bends, weirs, or other discontinuities, and even then do not take account of boundary layer effects and variations in velocity throughout the cross-section.

The Acoustic Doppler Flow Monitor (ADFM) Velocity Profiler, recently introduced into the UK by OnSite, overcomes these limitations by profiling the distribution of velocities throughout the entire flow area.

It can produce accurate results in almost any location, including in conditions of high turbulence such as near flumes, weirs and overflows, and also in large diameter pipelines or channels where there is often a significant variation in flow velocities throughout the cross section.

The OnSite ADFM Velocity Profiler comprises an array of four velocity transducers plus and ultrasonic depth measuring transducer, incorporated within a low-profile housing which causes minimal interference to the flow pattern.

The ADFM transducers emit a very short pulse along each of four narrow acoustic beams, which are at an angle to each other.

The return signals are divided into discrete intervals known as 'bins', and an independent velocity measurement is recorded for each of these bins.

This produces a linear distribution of velocity values at different levels along the length of each beam, allowing the velocity profile throughout the entire flow area to be established.

Integration of all the velocity and depth data allows the overall flowrate within the pipeline or channel to be determined with a high degree of accuracy.

Tests carried out at the University of Utah, at flow depths up to 24" (610mm) and velocities from zero to 12 ft/s (3.66m/s), produced accuracies between 98.42 and 99.93 percent.

The tests were carried out in a 48" diameter pipe and in rectangular channels 36" and 84" wide, with data being collected at five minute intervals for a minimum of two hours.

The OnSite ADFM Velocity Profilers can be used as very accurate short or medium term monitors to establish sewer flows in conjunction with modelling and simulation studies.

Alternatively they can be permanently installed to provide continuous data on network flows via telemetry.

They are especially suited to measuring flows in trunk sewers, and for installation at waste water treatment works as a basis for trade effluent treatment charges calculated from actual flows.

The equipment operates either from a mains or street lighting supply, or on batteries for up to a month without recharging.

ADFM Velocity Profilers are available for sale or hire, and OnSite provides an installation service together with full technical support.

The system has been used successfully in the UK by major clients including Thames Water.

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