Flow velocity measurement by coherently modulated ultrasound

Abstract

The opportunities for measurement of flow velocity by the continues wave frequency- modulated acoustic signals are investigated. It is shown that the transducers should have the highest possible carrier frequency adjusted to the path length of the measuring bases which will give a received signal of the order of a few microvolts. Block diagram of the ultrasonic flow velocity meter with the frequency manipulation of carrier frequency is described. With the purpose to achieve the coherency of signals the radiated signals like as the manipulating signals are obtained from one reference signal by dividing of its frequency. The duration of the period of manipulating frequency is chosen so that between the transmitter and receiver one period of these oscillations is always located. With the purpose to increase the accuracy of measurements the frequency of reference signal it is proposed to adjust not only to the minimal difference of phases of the transmitted and received manipulating signals but also to the minimal difference of phases of the transmitted and received carrier frequencies. It enables to increase the accuracy and reliability of measurement of flow parameter especially when the flow rate is small.