Sensors for Flume & Weir Monitoring
We carry a variety of water level sensors and systems commonly used for logging and recording flow rate through a flume or weir. Most of these sensors (depending on the specific model) send a signal that is recorded by a datalogger. This data can then be retrieved later in person, or it can be transmitted live via radio or internet.
Ultrasonic Sensor
An Ultrasonic Sensor is mounted above the water at the flume inlet or upstream of a weir. It sends a sound pulse that bounces off the surface of the water and is received again by the sensor. The elapsed time between the transmission and echo is used to calculate the water level.
Ultrasonic sensors do not come into physical contact with the water, which makes them exceptionally easy to install and maintain. Their accuracy can sometimes be affected by very foamy water or a turbulent water surface. Many ultrasonic sensors can be used in a stilling well to improve accuracy by removing the turbulence. However, in many irrigation applications, the water that is running through a flume or weir, tends to be laminar and smooth.
Float and Pulley
A cable or float tape is placed over a pulley wheel with a float at one end and a counterweight at the other. The pulley is attached to either a potentiometer or a shaft encoder. (Compared to potentiometers, shaft encoders are more accurate and easier to calibrate, and do not wear out over time.)
To measure calm water, the float and pulley system is installed with a stilling well beside the flume at the point of measurement, or upstream of the weir. A float and pulley system in a stilling well is not affected by debris, turbulence, foamy water, wind, ice, or other conditions that can affect some other sensors.
Pressure Transducer
Most Pressure Transducers have a wafer to measure water pressure. When installed at the bottom of the channel, the pressure is proportional to the depth of the water, and hence flow rate through a flume can be calculated. Pressure transducers are not affected by turbulence, foam, or floating debris, but they can be damaged by ice, submerged debris, and lightning (though some models feature lightning protection). They should not be installed in channels that may freeze solid (surface ice is usually not a concern).
There are hundreds of pressure transducers (and vibrating wire piezometers) on the market, all with different features and for use in different applications. We can help you select the best sensor for your needs.
Bubbler Sensor
A Bubbler is very similar to a pressure transducer, except the sensor itself is not submerged. Instead, a tube is fed from the bubbler to the bottom of the channel, and bubbles of air are fed through the tube. The bubbler measures the pressure required to move air through the tube, which is equal to the water pressure at the bottom of the channel, and hence the depth of the water in the flume can be measured.
Bubblers have almost all of the advantages of pressure transducers, but they are not damaged by ice, and are much less susceptible to lightning. They are more expensive than pressure transducers, and very accurate.