Sistema ultrassônico para medição de velocidade de escoamento de fluidos por efeito Doppler

Abstract

The present work proposes the development of an ultrasonic system to measure the flow velocity of fiuids using the Doppler eflect. The system transmits an ultrasonic signal wilh a frequency of 1 MHz through the fluid and receives an echo signai. The frequency of which deviates from the transmitted frequency, called the Doppler shift, is proportional to the flow velocity. The developed system has a double element ultrasound transducer, with a central operating frequency of 1 MHz, one element intended for transmission and another for the reception of signals. The excitation of the transmitting element is made by a circuit that converts a reference signal, supplied by a function generator. of low amplitude to a high amplitude signal. To ensure maximum power transfer, an LC impedance matching circuit is employed between the transmitting element and the excitation circuit. The signals received by the receiving element are amplified by an amplifier circuit with approximately 40 dB of gain. The amplified signai is applied to an AM demodulator circuit, where mixing and envelope detection processes allow the Doppler shift component to be recovered. The developed measurement system was subjected to a series of tests for a flow in a rotating cylinder for 4 different speeds of rotation. The results achieved, given the digital processing of the Doppler shift signal, allowed to validate and analyze the accuracy of the system. in comparison to the value obtained through a theoretical model. In this sense, the measurement system developed showed a maximum relative error of 3.37%, for a rotation of 25 RPM.