ABSTRACT
The distribution of liquid media in open channels is found extensively in water irrigation schemes, sewage processing and effluent control, water treatment, and mining beneficiation.
The most commonly used method of measuring flow in an open channel is through the use of a hydraulic restriction that changes the level of the liquid. By selecting the shape and dimensions of the restriction, the rate of flow through or over it will be related to the liquid level. In this manner, a secondary measuring element may be used to measure the upstream depth and infer the flow rate in the open channel.
The two primary restrictive devices in general use are the weir and the flume.
Although in the past, several measuring methods have been used (including floats, capacitive probes, hydrostatic, and bubble injection) use is now almost universally made of ultrasonic level measurement.
Ultrasonic level measurement makes use of a transducer, located above the channel that transmits a burst of ultrasonic energy which is reflected from the surface of the water. The time delay from the transmitted pulse to the received echo is converted into distance and hence determines the liquid level.
