An Ultrasonic Flow Measurement System for Sewage and Waste Water

Abstract

A new ultrasonic flow measurement system has been developed for sewage and waste water flowing in circular conduits with or without free surface. The system is composed of three units, an ultrasonic height gauge to measure depth of water, an ultrasonic doppler velocity meter to measure velocity at a predetermined point in the water and a flow computing unit.
The flow computing unit consists of a meter coefficient generator and a multiplier to calculate the product of the meter coefficient and the velocity.
We derived the meter coefficient as a function of water depth and geometry of the conduit from theoretical investigation and some experimental work. The validity of the derived coefficient was confirmed by some field tests.
The results obtained are summerized as follows:
(1) The meter coefficient is independent of the inclination of the flow surface.
(2) When a velocity measuring point is set at 0.1D from the bottom (D is the diameter of conduit), the measuring error due to the variation of roughness coefficient may be negligible.
(3) The results of the tests show that the accuracy of the system is within ±3% of full scale.
The above results are also applied to rectangular channel, but in this case the velocity measuring point should be set at 0.1B from the bottom (B is the width of channel).