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Abstract

A sonic-type fluid flow measuring system wherein reflections or echoes of an ultrasonic acoustic emitter are sensed and typically comprise a number of frequencies representative of a number of discrete velocities of flow in a volume of fluid. As a sample, they simply appear as a voltage plot as a function of time and wherein the time width of a given signal excursion relates to the frequency of a given signal. Thereafter, this time domain signal sample is converted to a frequency domain sample whereby the presence and magnitude of each frequency component, or velocity component, is isolated, this being typically done by what is known as a Fast Fourier Transform. The highest frequency, velocity, signal from each of a rapid succession of samples is then obtained and stored in a memory. The highest and lowest of these are then discarded, and the remaining are averaged to obtain more likely representations of velocity. As the goal is to determine an average fluid velocity for a whole cross section of fluid flow, the measured peak velocity is a detected reference from which a lesser velocity, for example, 0.9, of it is chosen. To achieve a value for volume of flow, the average velocity is then multiplied by the cross-sectional area of the containment through which flow occurs.

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