AN EXPERIMENTAL FEASIBILITY INVESTIGATION OF A LOW COST ULTRASONIC FLOW MEASUREMENT TECHNIQUE

Abstract

Currently conventional paddle wheel flowmeters are used to measure the flow rate in prairie grain farm sprayers. These flowmeters experience relatively short operating life due to failure of the paddle bearing. Wear on the paddle bearing and the bushing is caused by grit in the water used for spraying. One way to avoid this problem is to measure the flow with a meter that has no moving parts. There are a variety of techniques that can be used to measure flow. Ultrasonic flow measurement is one of the promising techniques. It has advantages of being nonobstructive and no moving parts. But it is relatively expensive compared with other flowmetering devices. In this thesis, an ultrasonic flow measurement system is proposed as a relatively simple scheme which could be implemented with low cost. It makes use of the different phase delays experienced by ultrasonic waves travelling with and against the flow in a pipe. The differential phase is proportional to the flow rate. To investigate the feasibility of the proposed scheme in a practical situation, an ultrasonic flow system was constructed and its reciprocity and triple transit were tested to ensure the setup system was working properly. An electronic measuring system consisting of a transmitter, a receiver and a switch array was designed and developed in printed circuit boards to implement the technique. The measuring system was then briefly calibrated by a standard flowmeter. It was proved that the system had fairly good linearity between its differential phase output and the flow rate. The system repeatability was found to be influenced by fluid temperature and the flow system setup. The experimental test results clearly demonstrated the proposed scheme was feasible and could be exploited practically for the prairie grain sprayer applications.