Open channel flow monitoring is a method of determining liquid volumetric flow rates in applications that rely on moving liquids through open conduits rather than enclosed pipes. Examples of these types of applications include wastewater processing effluent flows, managing water usage in agricultural irrigation channels, and monitoring flows through storm water systems. Traditionally, this type of measurement has been performed via the use of flumes or weirs in conjunction with a liquid level sensor. In recent years, global environmental concerns and increased scarcity of freshwater resources has necessitated more accurate, reliable and cost effective methods of Open Channel Flow Measurement. Two such improved methods offered by SmartMeasurement include the advanced transit time ultrasonic Area-Velocity measurement technique and the low-cost Doppler ultrasonic method. Learn more About Coriolis Flowmeters
Environmental concerns have spawned tremendous growth in the market for open channel flow meters that make use of an Area Velocity Measurement, or AVM technique. These instruments are widely used in applications such as monitoring water management systems, storm water run-off, irrigation flows, hydroelectric generating penstocks, and industrial discharges. SmartMeasurement offers two flow meters that make use of an AVM technique; the transit-time ALSONIC-AVM and the Doppler ultrasonic ALSONIC-DAVM. Detailed descriptions of the transit time and Doppler ultrasonic measurement principles can be found on the Ultrasonic Flow Meter Page.
Volumetric flow rate is defined by the equation Q = v ● A, where Q is the volumetric flow rate, v is the fluid velocity, and A is the cross-sectional area that the liquid flows through. This equation is true for enclosed pipes as well as open channels. The ALSONIC-AVM open channel flowmeter determines flow via this equation by making use of an array of transit time ultrasonic transducers in conjunction with a user-supplied level transmitter. The area (A) portion of the equation is determined by having the user program the channel width into the instrument and then using the reading from the level sensor to determine the height of the flowing area. (The diagram below illustrates the ALSONIC-AVM’s profiling method.) The velocity (v) portion of the equation is determined by the ultrasonic transducers. Up to a total of (4) pairs of transducers are installed at predetermined depths within the channel. As the water level rises, the instrument uses the signal to turn on each individual transducer path as they become submerged. While this is happening, the instrument is constantly taking the velocity readings from the active transducer paths and using them to calculate an average velocity for the flowing area. The compelling advantage to this system is that highly accurate readings for both the area and velocity variables are obtained which results in a more accurate and reliable flow rate reading. The advanced transit time ultrasonic method used for determining the velocity allows this flow meter to be used in a wide variety of fluid conditions ranging from perfectly clean to having a solids content of up to 30%.
SmartMeasurement also offers a specialized version of the ALSONIC-AVM open channel flow meter for applications where the conduit has a cylindrical geometry, such as those seen in sewer flow applications. This product, the ALSONIC-AVM-SEWER is capable of profiling velocities in in small channels with little or no straight run. It consists of the same display module as the standard ALSONIC-AVM flow meter combined with a pre-configured cylindrical 4-path transducer array as shown in the illustrations below. This easy-to-install array is available for cylindrical channels ranging from 4” through 48” (100-1200 mm) in size and will calculate the velocity (v) portion of the flow equation in the same manner as the standard version of the product with the same high level of accuracy. Learn more information for Ultrasonic Water Flow Meter
The ALSONIC-DAVM flow meter from SmartMeasurement is an open channel measurement system that makes use of a pulsed Doppler transducer for velocity measurement. The velocity transducer also contains an integral hydrostatic level measurement transducer. The Doppler transducer tracks the fluid velocity while the hydrostatic level transmitter signal is used by the display module to determine the cross-sectional area of the flowing media. Please see our PDF for more details on straight run requirements:
Since the ALSONIC-DAVM open channel flow meter employs a Doppler technique, there must be some particles or bubbles present in the fluid – it will not work well with perfectly clean fluids. This device is best used in sewer and open channel application having sizes ranging from 3-15’ (1-5 meters) and higher solids content. This open channel flow meter provides users with a number of benefits including the low cost made possible by the single-sensor design, fast and easy installation, and the availability of either fixed-install or portable display packages.