Sensors for Flume & Weir Monitoring

We carry a variety of sensor systems commonly used for logging and reporting 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 sensor do not come in contact with the water, which makes them exceptionally easy to install and maintain. Their accuracy can sometimes by affected by very foamy water or high winds.

SR50A Brochure
SD100 Brochure

Float and Pulley

H3311 Shaft Encoder

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.

H-3311 Shaft Encoder Brochure

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.

CS451 Brochure
Acculevel Brochure

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.

OTT-CBS Bubbler Brochure

Radar Level Sensor

Radar Level Sensors function like ultrasonic sensors, but use radar waves instead of sound. Radar sensors have a number of advantages over ultrasonic sensors. They are a little more accurate and can measure distances up to 200 feet. They are also less sensitive to obstructions. The primary drawback of radar sensors is the higher cost compared to ultrasonic sensors.

CS475 Radar Sensor Brochure