The Acoustic Flowmeter Using Electroric Switching

Abstract

The flowmeter described in this paper measures the velocity of a fluid by measuring the difference in times of transmission of an acoustic wave in the upstream and downstream directions. The acoustic wave is propagated in the fluid by pressing a barium titanate transducer against the outside wall of the tubing carrying the fluid. The wave is then picked up by a similar transducer acting as a receiver and mounted on the tubing a short distance away from the first transducer The reversal in direction of propagation is effected by interchanging the functions of the two transducers, i.e., making the transmitter the receiver and vice versa. The time measurement is made in terms of the phase difference between transmitted and received waves. The phase difference measured for propagation in one direction is compared with the phase difference measured for propagation in the reverse direction and the difference between these is an indication of the fluid velocity. This difference is measured with a synchronous rectifier. The transducer functions are switched rapidly enough so that, by means of electrical differencing of the two phase measurements, a continuous velocity indication is obtained. Two methods of switching the transducer functions and performing the synchronous rectification have been employed. The first method utilizes a mechanically driven switch and has been described previously.1 The second method uses an entirely electronic system to perform both functions. It is this electronic system that is described in this paper.